High School Science Part II

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Air and Water : 21 :

18

Air and Water
You have already studied that air is a mixture of gases, which we cannot see. It is the main abiotic component of the environment. Air is an extremely important natural resource. Air is also necessary for all the living organisms, because they breathe in air. A human being breathes about 22,000 times in a day and takes about 16 kg of air into the body during this process. Further, the air envelope, which surrounds the surface of the earth, presses the earth’s surface and creates a pressure on it. This air pressure, also called atmospheric pressure, is found to be useful. It would be interesting to know about air in this context also. Like air, water is another abiotic component of the environment, which is also essential for all living beings. Water is the most abundant and renewable natural resource. It covers about three quarters of earth crust. Water occurs in nature in the free state as well as in the combined state. The different properties of water make it useful, important and essential in our daily life. We will also learn about water and its properties in this lesson. OBJECTIVES After completing this lesson, you will be able to: • tabulate various component of air according to their amount; • explain the importance and utility of various components (O2, N2, CO2) of air; • measure atmospheric pressure and its variation with height; • discuss the various atmospheric phenomena; • list different sources of water; • list simple methods for making water potable; • describe various properties of water; • recognise the utility of water for various purposes; • argue in favour of rainwater harvesting. 18.1 COMPOSITION OF AIR Ancient philosophers considered air as one of the most vital element. Mayow in 1674 proved that air is not an element but the mixture of two substances, one of which is active and the other is non-active. Lavoiser in 1789 named the active element as oxygen and said that it is 1/5 of the total volume of air. The non-active

: 22 : Air and Water

element is nitrogen and it is about 4/5th of the total volume of air. The ratio of oxygen and nitrogen in the air is about 1:4 by volume. The major components of air are nitrogen (N2) and oxygen (O2), while the minor components are argon (Ar), carbon dioxide (CO2) and some are trace gases like neon (Ne), helium (He), krypton (Kr) and xenon (Xe). The composition of dry air at sea level is given in table 18.1. Table 18.1 : Composition of air Gas N2 O2 Ar CO2 Composition (% by volume) 78.03 20.09 0.94 0.033 Gas Ne He Kr Xe Composition (% by volume) 0.0015 0.000524 0.000014 0.000006

Water is excluded from this table because its concentration in air varies drastically from location to location. Let us perform a simple activity to study the presence of oxygen and nitrogen in the air. ACTIVITY 18.1 Aim : To show the presence of oxygen and nitrogen in air What is required? About 5cm long test tube, a beaker, water, graph paper, cotton wool and a small piece of yellow phosphorus. What to do? • Take the small piece of phosphorus on cotton wool. • Insert the cotton wool inside a test tube. • Now place the tube in inverted position in the beaker. • Pour the water in beaker in such a way that 5 cm length of tube should be above the water. • With the help of stand, hold the test tube in this position for one hour (Fig 18.1).
5 Phosphorus 4 3 2 1 0 Water Cotton wool plug 5 4 3 2 1 0 Water Phosphorus

Fig. 18.1 Experimental set-up to show that air contains oxygen and nitrogen

Air and Water : 23 :

What to observe? After one hour you will see that water level in the test tube rises up by 1 cm. Why is it so? The oxygen present in air within the test tube slowly reacts with phosphorus and forms the oxide of phosphorus. The oxide dissolves in water to form phosphoric acid, which can be shown as follows: P4 (s)
phosphorus

+ +

5O2 (g)
oxygen

P4O10 (s)
oxide of phosphorus

P4O10 (s)
oxide of phosphorus

6H2O (l)
water

4H3PO4 (l)
phosphoric acid

The pressure of air within the tube falls, because the oxygen completely reacts with phosphorus. To make up this loss in pressure, the air from outside exerts pressure and hence, forces the water to rise upward within the tube. From this activity it is clear that air consist 1 part oxygen and 4 parts nitrogen because the level of water rises by 1 cm out of the initial volume of 5 cm. Let us perform another activity that shows the presence of carbon dioxide in air. ACTIVITY 18.2 Aim : To show the presence of carbon dioxide in air What is required? A test tube, freshly prepared lime water, a cork with two holes, two glass tubes bent at right angles.
Suction by mouth

Lime water turns milky

Fig. 18.2 To show that air contains carbon dioxide

What to do? • Take about 4 mL freshly prepared lime water in a test tube. • Fix a cork (having two holes) in the mouth of the test tube. • Fix the two glass tubes in two holes in such a way that only one tube should be dipped in lime water but the other one should be above the lime water as shown in Fig. 18.2.



Suck the air from the tube, which is not dipping in limewater. Due to suction the pressure of the air within the test tube falls.

What to observe? To make for this loss in pressure, the air from outside enters into the tube through the tube dipping in limewater and air bubbles are liberated in limewater. You will see that after a minute the limewater turns milky. We know that only carbon dioxide can turn limewater milky. So this activity clearly shows the presence of carbon dioxide in the air.

: 24 : Air and Water

CHECK YOUR PROGRESS 18.1 1. Is air an element or a mixture? 2. What are the major constituents of air? 3. What is the ratio of major constituents of air? 4. Does the percentage of CO2 remain constant in air or it vary from place to place? 5. Does the percentage of water remain constant in air or it vary from place to place? 18.2 IMPORTANCE OF VARIOUS COMPONENTS OF AIR Oxygen, nitrogen and carbon dioxide are useful for human beings and plants. Without oxygen and nitrogen it is impossible to survive. 18.2.1 Importance and utility of oxygen Since we live on the surface of the earth, we are surrounded by air, which contains oxygen. Oxygen is the main part of the air i.e. about 21%. We know that the life is not possible without oxygen. Therefore, oxygen is very much essential for life. The importance and utility of oxygen are as follows: (a) General uses • Oxygen is absolutely necessary for respiration. • It is the supporter of combustion. • Liquid O2 is used as oxidant in rocket fuel called as LOX (Liquid oxidant). • In nature it dissolves in water. The dissolved oxygen keeps the water fresh and is a source of respiration for aquatic life. • In some situations it is used for artificial respiration such as: – in the submarines and by deep sea divers. – climbers, during high altitude climbing and also aviaters during high altitude flying. – firemen during fire fighting. • Corrosion is the term usually applied to the deterioration of metals by an electrochemical process. The most common example of corrosion is the formation of rust on iron. Oxygen gas and water must be present for iron to rust. It clearly indicates that oxygen is necessary for corrosion. • Oxygen combines with almost all elements to form oxides. (b) Medical uses • Carbogen: It is a mixture of 95% oxygen and 5% carbon dioxide. It stimulates natural breathing. It is given to the patients suffering from asthma or for reviving patients from drowning or gas poisoning. • Anaesthesia: It is a mixture of oxygen and nitrous oxide, which is used in surgical operations. (c) Industrial uses • In steel industry: Since oxygen produces more heat as compared to air (because air contains some non reactive substances); it is used in place of air for the purification of iron.

Air and Water : 25 :





For cutting and welding purposes: Oxygen is mixed with hydrogen (hydrogen torch) or acetylene known as oxyacetylene torch. These are used for cutting and welding purposes. It is also used for the manufacture of sulphuric acid from sulphur and nitric acid from ammonia (NH3).

18.2.2 Importance and utility of nitrogen Nitrogen is the main constituent of proteins. A number of amino acids containing nitrogen join together to form protein. It is essential for the life of living beings. Its main uses are: • It dilutes the activity of oxygen: If the amount of oxygen is increased in the air then the process like metabolism, combustion and corrosion will became very fast and becomes harmful. The presence of nitrogen dilutes the concentration of oxygen and thus, the combustion of fuel during burning and combustion of food during respiration takes place at moderate rate. • The compounds of nitrogen are of vital importance to plants as they help them to manufacture proteins. Living beings obtain protein from plants. 18.2.3 Importance and utility of carbon dioxide The percentage of carbon dioxide in air varies from place to place. The areas where more fuel containing carbon is burnt have more carbon dioxide. It is necessary for the production of food i.e. photosynthesis in plants. Its main uses are: • During photosynthesis plants absorb carbon dioxide and water vapour from air. In the presence of chlorophyll and sunlight, they are converted to carbohydrates. • It also provides Ca2+ and Mg2+ ions in the soil, which are necessary for the growth of plants. It dissolves in water and can also dissolve rocks containing calcium carbonate (CaCO3) or magnesium carbonate (MgCO3). The salts formed are Ca (HCO3)2 and Mg(HCO3)2. These salts give taste of natural water and also supply these ions to the plants. • It is also used in food preservation. In the presence of CO2 the grains are prevented from being destroyed by insects. • CO2 is a green house gas. It traps infrared radiations . • Solid CO2 is also known as dry ice which is used as refrigerant. • As it can be dissolve in water, it is used for the preparation of soft drinks. • CO2 is used in fire extinguishers to put off fire. CHECK YOUR PROGRESS 18.2 1. Oxygen is essential for life, why? Give one example. 2. Carbon dioxide acts as food for plants. Name the process in which it happens. 3. What is dry ice? 4. Name the element which is the main constituent of proteins.

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18.3 THE AIR AND ITS PRESSURE We know that the air is a mixture of gases and particles of these gases have weight due to gravity. It shows that the air has weight. Anything that has weight pushes and presses against things. The air presses down on the earth’s surface and creates a pressure on it. So there is a force exerted by gas particles of air, which act downwards on the surface of the earth. The force of air column acting per unit area of a surface results in a pressure exerted by atmosphere. This pressure is called atmospheric pressure. The atmospheric pressure is about 1kg wt cm-2 or 10 ton wt m-2 Let us perform an activity to show that air exerts pressure ACTIVITY 18.3 Aim : To show that air exerts pressure What is required? A glass tumbler, a piece of cardboard and water. What to do? • Fill the glass tumbler with water. • Put the piece of cardboard on the top of the glass tumbler. • Hold the glass tumbler firmly with the palm of your hand. • Grip the base of glass tumbler with your other hand. Turn the glass tumbler quickly upside downs as shown in figure 18.3. • Remove the palm of your hand carefully below the cardboard. What do you observe? You will find that the cardboard and the water remain in their place. Can you think of the reason behind this? The water in the glass tumbler stays because air is exerting a pressure on the cardboard. The pressure of air against the cardboard is greater than pressure of water against the card board. If you turn the glass side ways and in any other position, the water still remains in the glass showing that air exerts pressure in all directions.

(b) (a) Fig. 18.3 Air exerts pressure

In our everyday life, atmospheric pressure plays an important role in the working of many things, for example, working of a straw, working of a syringe or ink dropper, working of a lift pump etc. Think and try to explain how atmospheric pressure helps in the working of these above mentioned things?

Air and Water : 27 :

18.3.1 Normal or standard pressure and its units By international agreements, the normal or standard pressure is the pressure exerted by 76cm of mercury column. It is shown that, Normal pressure = hDg Where h = height of mercury column= 76 cm of Hg D = density of mercury = 13.6 x 103 kg m-3 g = acceleration due to gravity = 9.8 m s-2 Therefore, the pressure exerted by a column of mercury at a height of 76 cm = 0.76 x (13.6 x 103) x 9.8 N m-2 = 1.014 x 105N m-2 Thus,

1 atmosphere = 1.014 x 105N m-2
The unit of pressure used in meteorology is known as 1 bar where by definition

1 bar = 105N m-2 Thus, 1 atmosphere = 1.014 bar
Another unit used for atmospheric pressure is known as torr Where, 1 torr = 1mm of mercury = 133.3 N m-2 Thus,

1 atmosphere = 760 torr
1 torr =1mm Hg 1 atmosphere = 760 mm Hg =760 torr The SI unit of pressure is the Pascal (Pa), defined as one Newton per square metre. 1Pa = 1N/m2. The relationship between atmosphere and Pascal is, 1 atmosphere = 101.325 kPa or 1.01325 x 105 Pa Since 1000 Pa = 1kPa 1 atmosphere = 1.01325 x102 kPa 18.3.2 Measurement of atmospheric pressure The instrument used to measure atmospheric pressure is called barometer. There are different types of barometers such as, Simple barometer, Fortin barometer, Aneroid barometer etc. Simple barometer consists of long glass tube, closed at one end and filled with mercury. If the tube is carefully inverted in a dish of mercury in such a way that no air enters the tube, then some mercury will flow out of the tube into the dish, creating a vacuum at the top as shown in fig 18.4. The weight of the mercury remaining in the tube is supported by atmospheric pressure acting on the surface of the mercury in the dish.

: 28 : Air and Water

Fortin’s barometer consists of a long vertical glass tube about 80 cm long. It is completely filled with mercury and inverted over a cistern containing mercury. A small ivory peg is fitted into the lid of the cistern. While reading the atmospheric pressure, the tip of ivory peg should touch the level of mercury on which the atmospheric pressure acts (Fig 18.5). An Aneroid barometer is more portable and cheaper than mercury type. No liquid is used here. The main features are as shown in the figure 18.6.

S

V S2

Change
in Ra
Fa

S
ir

p
76cm
Brass tube

yd Ver

Stor my

ry

PIVOT C L
Ivory pointer

B

S1

PARTIAL VACUUM

Fig. 18.4 Simple barometer

Fig. 18.5 Fortin’s barometer

Fig. 18.6 Aneroid barometer

B : Sealed metal box of corrugated sheet which is partially evacuated and sealed. Increase in atmospheric pressure causes the top to cave in while decrease allows it to expand. L : A lever which magnifies the movement of the metal box. C : A chain wrapped round the spindle of the pointer. P : It is pulled by lever. This moves the pointer over a scale S. 18.3.3 Variation of air pressure with height The atoms and molecules of the gases in the atmosphere like those of all other matter, are subject to earth’s gravitational pull. As a consequence, the atmosphere is much denser near the surface of earth than at higher altitudes. In fact, the density of air decreases very rapidly with increasing distance from earth. Thus, atmospheric pressure decreases with altitude. Often at higher altitudes, people find their nose bleeding because blood pressure is much more than the pressure outside (i.e. atmospheric pressure). CHECK YOUR PROGRESS 18.3 1. What is the unit of pressure? 2. At high altitude the people find their nose bleeding. Why?

Air and Water : 29 :

18.4 ATMOSPHERE The region of air around earth is called atmosphere. The atmosphere protects us and all living things from harmful radiations like ultraviolet rays etc. We can divide the atmosphere into different layers according to temperature, pressure variation and composition. The main layers of the atmosphere (Fig. 18.7) from the surface of earth upward are troposphere (0-10km), stratosphere (10-50km), mesosphere (50-85 km) and thermosphere (85-500 km). The most active region is the troposphere, the layer of the atmosphere, which contains about 18% of the total mass of air and practically all the atmosphere’s water vapours. It is the thinnest layer of atmosphere and here all the dramatic events of the weather (such as rain) occur.
500 km Principal chemical species

Thermosphere

N2, O2, N, O + + + + N2 , O2 , NO , O

Altitude

85 km Mesosphere Mesosphere 50 km Stratosphere 15 km Troposphere 150 Stratosphere

Temperature
+ +

100 nm and more N2 , O2 , NO
+

220 nm and more N2, O2, O3 330 nm and more

Troposphere

N2, O2, H2O Ar, CO2 300

200 250 Temperature/Kelvin
–2

1× 10

1× 10

0

1× 10

2

1× 10

4

1× 10

6

Fig. 18.7 Layers of the atmosphere

18.4.1 Evaporation We know that air contains water vapour. Their amount in the air is not the same everywhere. It is the maximum in the low latitudes and over oceans. The atmosphere over polar regions and land has less amount of water vapour. It is also more in summer than in winter. Though water vapour comprises a very small part of the atmosphere, it plays an important role in heating and cooling of the atmosphere and in the day to day change in weather. In fact clouds, rain, snow, fog, frost and dew that we experience, result from water vapour in the atmosphere.

: 30 : Air and Water

But how does water vapours come in the atmosphere? It comes in the atmosphere through a process called evaporation due to solar heat. In fact evaporation is a process in which water from any source change into vapour state due to heat. 18.4.2 Cloud formation Condensation of water vapour in the atmosphere leads to the formation of clouds. Clouds are formed when moist air rises upwards and is cooled as it rises. When the dew point i.e. the temperature at which the water begins to change into water drops, is reached, condensation of water vapour and the formation of very tiny droplets of water or ice crystal occurs. They cling to the dust particles in the air. These millions of minute water droplets or tiny ice crystals almost hang in the air rather than fall. They are blown as clouds by the wind. Clouds are of different types according to their shapes and height. If you watch the sky carefully you will be able to see that clouds are of different types. 18.4.3 Rain When clouds are cooled owing to rising up or when they are blown into cooler region of the atmosphere, the small droplets of water in them become still cooler and they come closer to each other. A number of droplets combine to form big drop of water. These drops are so big that they can no longer float in the air, they fall downwards on the earth. As they fall, they pickup more and more small drops of water on their way down. The falling of these big drops of water from the clouds is known as rain. This process is called as precipitation. The instrument used to measure rainfall is called rain gauge. Rainfall is measured in centimeters. The maximum rainfall occurs in the countries near equatorial regions and South-East Asia. In these regions, annual rainfall is 200 cm or more. The lowest rainfall occurs in Tundra Pradesh, central Asia and hot deserts, where it is less than 25cm. The medium rainfall (between 25cm to 200cm) occurs in west European countries, Tega regions and China. 18.4.4 Relative humidity The existence of water vapour in the atmosphere, is known as humidity. Humidity of the air is related to its temperature. For example, during summer, you must have experienced days when both the temperature and humidity are high. Relative humidity is the ratio of the mass of water vapour actually present in a certain volume of air at room temperature to the mass of water vapour required to saturate the same volume of air at that temperature. The instrument used to measure relative humidity is called hygrometer.
F 120 110 100 90 80 70 60 50 40 30 20 10
o

F 120 110 100 90 80 70 60 50 40 30 20 10

o

Fig. 18.8 Hygrometer

Air and Water : 31 :

CHECK YOUR PROGRESS 18.4 1. Name the instrument used to measure: i) atmospheric pressure. ii) relative humidity. iii) rainfall. 2. Name the process through which water vapours come in air. 18.5 WATER - ITS SOURCES AND PROPERTIES 18.5.1 Sources of water Other than air, water is the most important substance needed by living beings. Living beings cannot live long without water. The water is available in plenty on earth. It fills the seas, rivers and lakes, which cover more than three-fourth of the earth surface. It is also find inside the crust of the earth. Most of the water that we get from the wells comes from this source. The natural sources of water are rain, spring, well, river and sea. (a) Rain water: The rain water is considered to be the purest form of natural water (distilled water) free from impurities. Why do we say so? We know that water from sea and rivers get evaporated into water vapour by the heat of sun. During this process of evaporation, impurities are left behind. When the water vapours go high up in the air they condense to form clouds. The water drops come down as rain. (b) Spring water: Springs are formed by percolation of rain water into soil. Spring supply water to wells and lakes. (c) Well water: The rain water seeps through the soil and goes down. On digging the well this underground water is available to us. This is known as well water. This water is not pure and contains impurities such as suspended particles, bacteria and other microorganisms. (d) River water: Rivers form by melting of snow on the mountains and also 1.3×10 kg sometimes from the rain water. It is Evaporation also not pure and not fit for drinking. 3.86×10 kg y 6×10 kg (e) Sea water: Out of these sources, sea water is the largest natural source of water. However, it is the source of common salt and is the most impure Evaporation form of water. All the impurities 4.23×10 Uptake and kg y photosynthesis dissolved in river water are carried into Pore and ground water the sea. As such, sea water can not be 4.2×10 kg Shallow plus soil moisture 5.3×10 kg deep used for drinking purpose. There is a 1.37×10 kg constant cyclic movement of water Lakes and rivers throughout the globe, which is called Ice 1.27×10 Kg 2.9×10 Kg water cycle. Fig 18.9 shows the diagram of water cycle in biosphere. Fig. 18.9 Water cycle in nature
16 21 –1 14 17 –1
18 18

21

17

19

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18.5.2 Purification of water for drinking Water from different sources contains different substances in different amounts. In addition to salts found in sea water, water from other natural sources may contain foreign materials like suspended solids, minerals, certain compounds viruses, bacteria, eggs of insects and other animals, algae, protozoa and other aquatic plants. Such water is not safe for drinking and causes many harmful effects in the body. There are different ways of purifying water for drinking. These are: • By boiling during which bacteria and other germs die. When boiled water is allowed to cool, heavy impurities collect at the bottom and dissolved salts form a thin layer on the surface called scum. Now if we filter the water, the filtered water is safe for drinking. • By decantation and filtration. • By chlorine treatment in which small living organisms and bacteria are killed. 18.5.3 Properties of water Water, which seems to us to be a common ordinary material, is really a highly unusual substance with many unique properties which makes its use important and essential in our daily life. 18. 5.3a Water acts as universal solvent Water is certainly one of the best and most useful solvents that we have. It has a unique property to dissolve many substances starting from solids such as common salts, sugar, to gases like oxygen, carbon dioxide etc. Indeed, so many substances dissolve in water that is why it is called as a universal solvent. This property is useful for plants to take in their food materials and minerals from the soil. It helps us to absorb food that we eat, in the form of water solution. Many chemical reactions also take place only in solution form in water i.e. aqueous solution. 18.5.3b Lather formation Water forms lather with soap which is used for cleaning purpose. But sometimes water from some sources like rivers or hand pumps does not produce any lather with soap. Why? This is because of the presence of dissolved salts in water. Water, which we get from taps, contains lesser amounts of dissolved salts in it than water that we get from hand pumps. The dissolved salts are usually bicarbonates, sulphates and chlorides of calcium and magnesium. These salts prevent lathering but how? The soap is a sodium salt called sodium stearate. This is soluble in water. However the calcium and magnesium stearates are insoluble and so when soap is added to hard water, which contains calcium and magnesium ions, a precipitate of Ca or Mg stearate is formed. This appears as a greasy scum. The formation of scum wastes soap (does not forms lather) and makes it more difficult to clean things. Sodium stearate + Calcium sulphate Calcium stearate + Sodium sulphate (Soap) (Scum) Hence we can say that, • Water which forms lather with soap is called soft water.

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• •

Water which does not form lather is called hard water. The hardness of water is due to the presence of salts of magnesium and calcium in water.

18.5.3c Conversion of hard water into soft water Hard water does not form lather with soap –can this hard water be converted into soft water? Yes, hard water can be converted into soft water. Let us see how ? The removal of Ca and Mg ions which are responsible for hardness is called the softening of water. Hardness of water is of two types namely, • Temporary hardness • Permanent hardness a) Temporary hardness Temporary hardness of water is due to the presence of soluble bicarbonates of calcium and magnesium. It is also called carbonate hardness. It can be removed by boiling and by soda lime process. (i) By boiling: On boiling hard water, the calcium or magnesium bicarbonate present is decomposed and give magnesium or calcium carbonate. These carbonate salts are insoluble in water. They settle down easily and water can be decanted. Decantation is the process of separation of solid from the liquid by allowing the former to settle down and pouring off the latter. Heat Ca (HCO3)2
calcium bicarbonate (Soluble)

CaCO3
calcium carbonate (Insoluble)

+

H2O

+ CO2

Heat Mg (HCO3)2
magnesium bicarbonate (Soluble)

MgCO3
magnesium carbonate (Insoluble)

+

H2O

+ CO2

(ii) By soda lime (Clark’s method):When a calculated amount of lime is added to hard water, then the soluble bicarbonates are converted to insoluble carbonates as follows: Ca(HCO3)2 + Mg(HCO3)2 + Ca(OH)2
lime

2CaCO3 + 2H2O 2MgCO3 + 2H2O

Ca(OH)2

b) Permanent hardness Permanent hardness of water is due the presence of soluble chlorides and sulphates of calcium and magnesium. It is also known as non-carbonate hardness. It can be removed by addition of washing soda and by the ion exchange method. A brief description of removal of permanent hardness of water is given below: (i) By addition of washing soda: The hard water is treated with the calculated quantity of washing soda (Sodium carbonate). Washing soda reacts with chloride

: 34 : Air and Water

and sulphate of calcium and magnesium to form precipitate of calcium and magnesium carbonate. The reactions are as follows:
CaCl2
calcium chloride

+ +

Na2CO3
sodium carbonate

CaCO3
calcium carbonate

+ +

NaCl
sodium chloride

MgSO4
magnesium sulphate

Na2CO3
sodium carbonate

MgCO3
magnesium carbonate

Na2SO4
sodium sulphate

The precipitate settles down and the water can be removed by decantation. (ii) By ion exchange method: Two types of ion exchangers can be used, namely, inorganic ion exchanger and organic ion exchanger. In inorganic ion exchange process, complex compounds known as Zeolite are used to soften the hard water. The salts causing the hardness of water are precipitated as insoluble zeolite of calcium and magnesium.On the large scale, this process is carried out in tanks as shown in figure 18.10

Inlet for hard water

Tap to take out soft water

Zeolite or permutt

Coarse sand

By using organic ion exchanger the water obtained is free from cations and anions and is known as deionized water or demineralized water. 18.5.3d Polar nature of water Water is very effective solvent for ionic compounds. Although water is an electrically neutral molecule, it has a small positive charge (on the H atoms) and a negative charge (on the O atoms), Therefore, it is a polar solvent. Oδ Hδ+ Hδ+

Fig. 18.10 Obtaining soft water on a large scale using tanks

Let us perform an activity, which proves the polar nature of water ACTIVITY 18.4 Aim: To study the polar nature of water What is required? Burette, water, ebonite rod (negatively charged), glass rod (positively charge) and burette stand. What to do? • Take a burette and fill it with water. • Fix the burette vertically in a burette stand.

Air and Water : 35 :

• Open the stopcock of the burette and allow the water to flow. • Take a ebonite rod (negatively charged by rubbing one end with fur) near the water What to observe? You will see that the stream of water is attracted towards negatively charged rod (Fig. 18.11a). Why? Because the water molecules have positive charge. Similarly, now we take a glass rod near water, which is positively charged. You will see the rod again attracts the stream of water. This indicates that water molecule also has negative charge (Fig. 18.11b). This proves the polar nature of water.

Burette

Water

Negatively charged Thermocol or Ebonite rod

Positively charged glass rod



– – – – – – Stream of water

+

+ + + + + +

(a)

(b)

Fig. 18.11 To show that water is polar in nature

18.5.3e Surface tension Surface tension is the property of all the liquids. Due to this tension water drops try to occupy a minimum surface area. Hence, the water droplets always tend to take the shape of a sphere. The tension exerted by molecules of water present on the surface layer is called as surface tension. To understand this let us perform an activity. ACTIVITY 18.5 Aim: To study surface tension What is required? Glass and razor blade. What to do? Take a glass full of water. Put a safety razor blade (having a coating of very thin layer of wax) gently on the surface of water. What to observe? You will find that it remains there although it is heavier than water. Have a close look at the surface of water. You will find a thin film of water on the lower surface of the blade. Why is it so? The upper layer of water is acting like a tight sheet. Why is the sheet tight? Due to intermolecular forces i.e. forces between the molecules of the liquid surface and the blade, there is a tension or force acting on the surface of the thin film of the liquid. 18.5.3f Capillarity – Rise of water When a capillary tube with a fine bore is dipped in water, water rises in the capillary. The extent to which the water rises depends on the diameter of the capillary. The smaller the diameter of the capillary the higher will be the rise of water in the capillary tube.

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This property of rise of water inside a capillary is called capillarity. This is the property, by which water from the soil enters the leaves and branches of the plants through its stems. When a piece of cloth or bloating paper is placed on water, it soaks the water by this process of capillary action. The thread strands in the cloth and cellulose of the bloating paper serves like very fine bore tubes for the water to rise. 18.5.4 Density of water Water behaves in an unusual way when it is heated from 0 oC. As the temperature rises from 0 oC to 4 oC it actually contracts. However, at 4 oC upwards it expands like any other liquid. This means that water takes up least space at 4 oC. It has the greatest density at this temperature and will sink through warmer or colder water around it. Density of a substance is defined as its mass per unit volume. Measurements on different volume of water at 4 oC show that, 1 m3 of water has a mass of 1000 kg. 2 m3 of water has a mass of 2000 kg. And so on. Thus, the density of water at 4 oC is found to be, Density = = Mass of water ————— = Volume of water 1000 kg m-3 or 1g cm-3 1000 kg of water —————— 1m3

Because of this property of water, we can explain why it takes months for a lake to freeze while a small bucket of water can freeze over night on a bitterly cold day. 18.5.5 Specific gravity or relative density The relative density of a substance is the ratio between density of a substance and density of water at 4 oC. It tells us that how many times more dense is the substance than water i.e. Relative density (RD) = Density of a substance ————————————— Density of water at 4 oC

As Relative Density is a ratio, it has no unit. For a particular substance its numerical value is always constant irrespective of whatever system of units are used. It is known as specific gravity. Another formula for calculating relative density or specific gravity is, RD = Mass of substance ————————————— Mass of the same volume of water at 4 oC

Air and Water : 37 :

CHECK YOUR PROGRESS 18.5 1. How much earth surface is covered by water? 2. Name any two sources of water. 3. Is rainwater pure or impure? 4. 5. 6. 7. What is the role of chlorination during purification of water? If water does not form lather, which type of water is it? Name the type of hardness due to presence of bicarbonate of Ca2+ or Mg2+. Name the type of hardness due to presence of chloride or sulphate of Ca2+ or Mg2+. 8. Which type of hardness is removed by the following (i) boiling (ii) ion exchange method 9. Is water a polar or nonpolar solvent? 10. What is the unit of density? 18.6 UTILITY OF WATER Water is used for many purposes, including growing crops, metallurgical operations to obtain metals such as copper, generating electricity, watering lawns, cleaning drinking and recreation. We can say that water is essential for life of living organisms. Without water, plants and animal cells cannot function and they ultimately die. Let us discuss the role of water for domestic use, agricultural use, industrial use and for the generation of electricity. 18.6.1 Domestic uses of water Water plays an important role in domestic purposes, for example, it is used for cooking food, to wash utensils, clothes and clean the floor of houses. It is also used for whitewashing. It is used to take bath. Water dissolves the waste material of body such as stool, urine etc. and hence provides a good medium for extracting the body waste. The salts and the nutrients of the food dissolve in water. Therefore, these nutrients are easily absorbed by our body. 18.6.2 Agricultural uses of water Water plays a similar important role in the plants life as in the human body. In agriculture sector water is used for the irrigation of crops, it helps in the germination of seeds and growth of plants. The nutrients provided by fertilizers to the soil are soluble in water. These dissolved nutrients are easily absorbed by the plants. Water is required for the preparation of food by plants (photosynthesis). It also acts as medium for the transport of nutrients and minerals from one part of the plant to other parts. It helps in maintaining firmness and structure of plant parts by providing appropriate pressure to the plant tissue. It is required for respiration by aquatic plants.

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18.6.3 Industrial uses of water Water is used as a coolant in industries, for example the production of NH3 in Haber’s process. It is also used in production of ice and as coolant in vehicles. It is used for the production of steam in industrial boilers and in steam engines. It is used as solvent in many industrial processes. Water is used to prepare many chemical compounds, for example H2SO4 is prepared by dissolving SO3 in water and HNO3 by dissolving NO2 in water. Water is also used to prepare fuels like hydrogen gas and water gas. 18.6.4 Uses of water to generate electricity There are many different ways to harness the energy from water. The most common way of capturing this energy is hydroelectric power. Electricity is generated by falling water. Water is used in thermal power stations or nuclear power station to produce steam for the generation of the electricity. 18.6.5 Rain water harvesting Over the years rising population, growth in industrialization and expending agriculture have pushed up the demand for water. Efforts have been made to collect water by building dams and reservoirs and creating ground water structures such as wells. Some countries have also tried to recycle and desalinate water. Wise conversion of water has become the need of the day. The idea of ground water recharging is gaining its importance in many of the cities. This is being done through rain water harvesting. Rainwater harvesting essentially means collecting rain water on the roofs of building and storing it underground for latter use. Not only does this recharging arrest underground depletion of water but also raises the declining water level and can help augment water supply. While many people may not realize it, but those few centimeters of annual rainfall are a valuable resource. Harvesting rainwater not only helps reduce the possibility of flooding, but it also decreases the community’s dependence for ground water for demestic uses. Rain water is perfectly suited for landscape irrigation, use in room coolers, washing and many other home applications. When rain water is used in room coolers and for washing needs, hardness deposits do no accumulate and there is no problem with soap scum. Harvested water may also be used for personal consumption, but it must be filtered and treated prior to use. By reducing runoff and rain water that falls on your house or field, you can put a valuable water resource to work around your house. • • • • • Thus, the benefits of harvesting rain water can be summarized as follows. Conserves valuable ground water. Reduces local flooding and drainage problems. Decreases landscaping and property maintenance needs. Provides excellent quality water for many household uses. It can be used for domestic purposes such as for vegetables, flowers, trees and shrubs and seedling in a green house etc.

Air and Water : 39 :

CHECK YOUR PROGRESS 18.6 1. What are the uses of harvesting rain water? LET US REVISE The major components of air are nitrogen and oxygen. The air also contains argon, carbon dioxide and some trace gases like neon, helium, krypton and xenon. It also contains water vapour. The weight i.e. the force of air column acting per unit area results in a pressure exerted by atmosphere called the atmospheric pressure. Atmospheric pressure plays an important role in our every day life in the working of common things like ink dropper, to straw, to lift pumps. The state of atmosphere in relation to the amount of water vapour is known as humidity. Mass per unit volume of a substance is known as its density. Next to air, water is the most abundant substance available to us. The natural source of water is rain, spring, wells, rivers and sea. The following properties of water make it suitable for use in our everyday life: ability to dissolve many things i.e. to behave as a universal solvent. lather formation. surface tension. capillarity. density of water at 4oC being 1 g cm-3. Relative density is the ratio between the density of a substance to the density of water at 4oC. Water resources in a country is managed for proper and judicial use by constructing dams, canals, reservoir, wells and tube wells. Water collected in dams is not only used for irrigation but also to generate electricity. Rain water can be conserved by recharging it to ground or using it for various other purposes. This is known as rainwater harvesting. TERMINAL EXERCISES A. Multiple choice type questions. 1. Air is a) compound b) element c) mixture d) non of these 2. Major components of air are a) CO2 + H2O b) N2 + O2 c) CO2 + He d) H2O + Xe



• • • • • • • • • • • • •



: 40 : Air and Water

3. Carbogen is the mixture of a) O2 + CO2 b) O2 + N2 c) O2 + CO d) CO2 + CO 4. The instrument used to measure humidity is a) barometer b) hygrometer c) lactometer d) none of these 5. Water has maximum density at b) 10 oC a) 0 oC B. Descriptive type questions. 1. 2. 3. 4. 5. 6. Name the various components of air. Air is considered a mixture, why? Prove by an activity that air is a mixture of different gases. List the utility of oxygen and nitrogen in our lives. What is atmospheric pressure? How is it measured using simple barometer? How does the atmospheric pressure depend on altitude? Write down the units of atmospheric pressure. 7. Name the different types of barometers. Explain the working of Aneroid barometer with diagram. 8. Give an activity, which proves that air exerts pressure. 9. What is relative humidity? How is it measured? 10. What is evaporation? How does it help in the formation of clouds? 11. What are the different source of water? Explain any two. 12. Why is water called as universal solvent? On what basis the following components dissolve in water: NaCl, Sugar and NH3? 13. Explain water cycle with the help of a suitable diagram. 14. What are the different ways to purify drinking water? What is the role of chlorination? 15. Water is a polar solvent. Give an activity to prove it. 16. What do you mean by hard and soft water? Explain the types of hardness in water. 17. How are the temporary and permanent hardness removed from water? 18. Explain the following properties of water (i) Surface tension (ii) Density 19. What is rainwater harvesting? How is it beneficial for everyday life? 20. List the utility of water for, domestic purpose, agriculture, industry and generation of electricity. 21. What do you mean by conservation of water? How is it useful? c) 5 oC d) 4 oC

Air and Water : 41 :

ANSWERS TO CHECK YOUR PROGRESS 18.1 1. 2. 3. 4. 5. 18.2 1. 2. 3. 4. Mixture Nitrogen and oxygen 4:1 It varies from place to place. It varies from place to place. Needed for respiration by plants and animals Photosynthesis Solid CO2 Nitrogen

18.3 1. Pascal 2. Low pressure. 18.4 1. (i) (ii) (iii) Barometer Hygrometer Rain gauge

2. Evaporation. 18.5 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 18.6 1. 2. 3. 4. 5.

Three fourth Rain and sea Pure To kill microorganism Hard water Temporary Permanent (i) Temporary, (ii) permanent Polar g cm-3 It conserves valuable ground water. It reduces local flooding and drainage problems It decreases landscaping and property maintenance needs It provides quality water for many household needs It can be used for domestic purposes

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GLOSSARY Atmospheric pressure: The force of air column acting per unit area results in a pressure exerted by atmosphere. Barometer: Instrument used to measure atmospheric pressure. Cloud: Condensation of water vapour in the atmosphere. Dew point: The temperature at which the water begins to change into water drops. Density: Mass per unit volume of any substance. Evaporation: Vaporization of water due to solar heat. Greenhouse effect: Trapping of infrared radiations, increased concentration of CO2. Humidity: The state of atmosphere in relation to the amount of water vapour it contains is known as humidity. Hard water: Water that do not form lather with soap. Hygrometer: Instrument used to measure relative humidity. Pascal (Pa): The SI unit of pressure. One Pascal in one Newton per square meter. One atmosphere is equal to 1.01325 x 105Pa. Relative humidity: It is ratio of the mass of water vapour actually present in a certain volume of air at room temperature to the mass of water vapour required to saturate the same volume of air at the same temperature. Rain: The falling of big drops of water from the clouds is known as rain. Soft water: water that form lather with soap. Surface tension: Tension exerted by the molecules of water present in the upper layer is called surface tension.

Mineral Resources–Metals and Non-metals : 43 :

19

Mineral Resources– Metals and Non-metals
We use large number of materials but very few of them occur naturally. Most of these are obtained by transforming a relatively small number of naturally occurring raw materials chemically into more useful substances. You have learnt in earlier lessons that environment provides all the necessary support for the existence of mankind through its various components and resources both biotic and abiotic. In this lesson you will learn about some abiotic resources and how they are used to obtain useful substances and materials. OBJECTIVES After completing this lesson, you will be able to: • differentiate between metals and non-metals on the basis of their properties; • distinguish between minerals and ores; • recognize various metallurgical processes in the extraction of common metals– Fe, Al and Cu; • explain the corrosion of metals; • list various uses of metals and their alloys; • explain the preparation, properties and uses of various non-metals–H, Si and P; • describe the allotropes of P and S and state the use of sulphuric acid. 19.1 MINERAL RESOURCES 19.1.1 Minerals and ores There are 83 naturally occurring elements. The remaining ones can be produced in the laboratory only by nuclear reactions about which you learned in lesson 14. Out of all the naturally occurring elements oxygen (O), silicon (Si), aluminium (Al) and iron (Fe) are four most abundant elements ( arranged in the decreasing order) and account for more than 87% of earth’s crust (lesson 2, fig. 2.2). Only few elements are found in the free or native state i.e. in the uncombined state. Cu, Ag, Au and Platinum are some of them. The remaining elements are found only in chemically combined state, that is, in combination with one or more other elements as minerals. A mineral is a

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naturally occurring homogeneous inorganic substance having a definite chemical composition and characterstic crystalline structure, colour and hardness. Although all minerals are sources of metals, it is not always possible to recover metals from them economically. A mineral from which it can be done is called an ore. Thus, ore is a mineral from which a metal can be extracted profitably. For example, copper pyrite (CuFeS2) is a mineral of copper. Copper can be profitably extracted from it only if its copper content is 4% or more. If so, it is called the ore of copper otherwise a mineral. 19.1.2 Metals and non-metals There are 83 naturally occurring elements. They can be broadly divided into two categories namely, metals and non-metals. The two differ widely in their physical and chemical properties. The properties which distinguish metals from non-metals are given in the tabular form below. Table 19.1(A): Differences in physical properties of metals and non-metals
Property State Metals They are solids at ordinary temperature and usually non-volatile (exception: mercury which is a liquid). Non-metals They exist in all the three states, i.e. solid, liquid and gas. They are either gases or volatile liquids at low temperatures (exception: diamond and boron which are hard solids). Their density is generally low. Generally they do not possess metallic lustre (exception: graphite and iodine). They are neither malleable nor ductile.

Density

Their density is generally high. They possess metallic lustre and take a high polish. They are malleable and ductile. They can be beaten into thin sheets and drawn into wires (exception: Bi) They form alloys with other metals and some non-metals. They are good conductors of heat and electricity (exception: lead which is a poor conductor of electricity).

Metallic lustre

Malleability and ductility

Alloy formation

They do not form alloys (except carbon, silicon and phosphorus). They are poor conductors of heat and electricity (exception: graphite and gas carbon).

Thermal and electrical conductivity

Mineral Resources–Metals and Non-metals : 45 :

Table 19.1(B): Differences in chemical properties of metals and non-metals Property Metals Non-metals
Nature of oxides They generally form basic oxides which form alkalis with water For example: 4Na + O2 → 2Na2O sodium sodium oxide Na2O + H2O → 2NaOH sodium hydroxide (alkali) They either form no compound with hydrogen or form unstable hydrides. They are electropositive elements and form cations. They are liberated at cathode during electrolysis. Some metals like chromium and manganese form some anions also with other elements like oxygen. They generally dissolve in mineral acids forming a salt with the evolution of a gas. For example: Zn + H2SO4→ZnSO4 + H2 zinc sulphuric zinc hydrogen acid sulphate They generally dissolve by a chemical reaction. They form acidic oxides only.

Hydrides

They form stable hydrides with hydrogen.

Electrochemical nature

They are electronegative elements and form anions. They are liberated at the anode during electrolysis (exception: hydrogen).

Action of acids

P4+20HNO3 → 4H3PO4+ 20NO2+4H2O

They either do not dissolve in mineral acids or form the corresponding oxacids*. For example:

Solubility

Many non-metals dissolve without any chemical changetaking place. For example: chlorine, bromine or iodine dissolves in water.

* Acids which contain oxygen are called oxoacids or oxyacids. 19.1.3 Activity series of metals In the last section you learned that metals are electropositive in nature. In all their chemical reactions metals give off their electrons i.e. they act as reducing agents and themselves get oxidized. This process may be written as: M Mn+ + neMetals can give off their electron to the atoms of non-metals, hydrogen ions and even to ions of other metals. Electropositive character varies in different metals. A metal that can lose electrons more easily is more electropositive and would be more active in nature. Such a metal when dipped in a solution of salt of a less

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active metal would displace it (less active metal). Thus if a zinc rod is dipped in a solution of copper sulphate it would displace copper which is precipitated. Zn(s) + Cu2+ (aq) Cu(s) + Zn2+(aq) zinc cupric ion copper zinc ion This happens because zinc is more electropositive in nature than copper. The arrangement of metals in the decreasing order of their activities is known as activity series or electrochemical series. It is also known as reactivity series. A portion of this series is given below: Ca, Na, Mg, Al, Zn, Cr, Fe, Pb, (H), Cu, Hg, Ag Hydrogen is the only non-metal that stands in this series. It is because hydrogen also shows electropositive character like metals. Any metal can displace all the metals that are on its right-side and which follow it. In other words, a metal can be displaced by only those metals which precede it and are on its left-hand side. Thus, Zn can displace any of Cr, Fe, Pb, H, Cu, Hg and Ag, metals which follow it and are placed on its right-hand side. But zinc can be displaced only by those metals which precede it and are on its left-hand side i.e. Ca, Na, Mg and Al. 19.1.4 Mineral resources in India India is very fortunate to have been gifted by nature with rich mineral resources. It is the chief producer of mica and has monopoly for monazite, a mineral of thorium and has vast reserves of many important minerals. You will learn more about our mineral wealth in the discussion of various metals later in this lesson. CHECK YOUR PROGRESS 19.1 1. Name two most abundant elements in earth’s crust. 2. Which two of the following metals occur in native state? Na, Cu, Zn, Ag, Fe 3. An element A forms basic oxide whereas another element B forms an acidic oxide. Which of them is expected to be malleable and ductile? 4. A non-metallic element forms a cation and is liberated at cathode during electrolysis. Which element could it be? 5. Which of the following metals can displace hydrogen from solutions of acids? Ag, Zn, Cu 19.2 METALS We see a large variety of machines around us. Today man cannot live without machines. Some of them perform simple mechanical operations and substitute for the weak muscles of man like bulldozers, diggers, machine tools, and agricultural equipments. Others do very precise jobs that man can never do himself like high precision machine tools. Yet others substitute in many cases for human brain like computers. The pace of progress in any field- industry, transport or agriculture, is controlled by the number of machines that are produced and are usefully employed. But all machines are made of metals. Indirectly, the rate of development of a nation can be measured by the rate at which it produces and

Mineral Resources–Metals and Non-metals : 47 :

consumes various metals. In this section we will learn about various metallurgical operations which are used for extraction of metals from their ores and also about extraction, purification and properties of three important metals namely iron, aluminium and copper. 19.2.1 Basic metallurgical processes Metallurgy is the branch of science dealing with extraction of metals from their ores.The three main steps in extraction of a metal from its ores are (i) concentration of ore, (ii) production of the metal and (iii) purification of metals. Now we will learn about these steps. 19.2.1a Concentration of ore The preliminary treatment of an ore to separate the waste materials from it is called its concentration. The waste materials usually associated with the ore are clay and silicates. They are collectively called the gangue. The method used for concentration of ore depends on the nature of gangue associated with it as well as its own nature. Various methods used are: (a) Magnetic separation This method is used when a mineral is magnetic in nature and is attracted towards a magnetic field whereas the gangue is not. A schematic diagram of the process is shown in Figure 19.1 For example, separation of magnetite (Fe3O4) and pyrolusite (MnO2) from gangue can be done using strong electromagnets. (b) Hydraulic washing This method is used due to a large difference in densities of ore which is heavy and of the gangue which is light. The lighter gangue particles are washed away in a stream of water while heavier minerals stay back. (c) Froth floatation This method is used for the concentration of sulphide ores. The powdered ore is mixed with water and oil and air is bubbled through it as shown in Figure 19.2. This produces froth which floats on the surface. The oil preferentially wets the sulphide mineral particles which are carried by air bubbles to the surface of the mixture and are skimmed off. The froth is allowed to collapse and dried to recover the mineral.
Air Agitator

ELECTRO-MAGNETS

Magnetic partciles

Non-magnetic particles

Fig. 19.1 Schematic diagram of magnetic separation

Gangue

Fig. 19.2 Froth floatation process

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(d) Calcination It is used to remove volatile matter like moisture or water of crystallization from the ore by simple heating. (e) Roasting It is used to remove volatile impurities and to convert a sulphide or carbonate ore into oxide by heating it in a stream of air. For example Cu2S(s) + O2(g) 2Cu2O(l) + 2SO2(g) 2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g) 19.2.16 Production of metal After enriching the ore, it is converted into free metal. Metals in their combined state are always present as cation in their minerals. Therefore, production of a free metal is always a reduction process. The method of reduction depends upon the activity of the metal. Different methods employed are shown in the following table in which metals have been arranged in the decreasing order of their activity. Highly reactive metals are reduced by carrying out electrolysis of their molten salts like chlorides or oxide. The less reactive metals are produced by reduction of the metal oxide with a more reactive metal, or reduction with coke (carbon) and carbon monoxide. Table 19.2 lists the reduction processes which are employed for extraction of some metals. Table19.2: Reduction processes employed to obtain some metals from their ores Reduction process Metals Lithium, sodium, magnesium, calcium Aluminium Chromium, iron, manganese, zinc Copper, gold, silver Electrolytic reduction of their chlorides Electrolytic reduction of its oxide Al2O3 Reduction of the metal oxide with a more reactive metal, or reduction with coke (carbon) and carbon monoxide Roasting of their sulphide ores

Removal of impurities associated with ores Some impurities are also associated with most of the ores which are called gangue. They are usually infusible in nature and are removed with the help of a flux. Flux is a material that is added during its reduction in a furnace to convert infusible impurities (gangue) into a fusible substance that is called slag which is separated from the molten metal and removed. The nature of flux depends upon the nature of impurity to be removed. An acidic flux (like sand) is added to remove basic impurities like FeO: FeSiO3 FeO + SiO2 →
basic gangue acidic flux fusible slag

A basic flux (e.g. CaO) is added to remove acidic impurities (e.g. sand): SiO2 + CaO CaSiO3 →
acidic gangue acidic flux fusible slag

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19.2.1c Refining of metals The metals obtained by the metallurgical processes described in the preceding sections usually need further treatment to remove the impurities. The refining process removes undesirable impurities from the metal. The following are the most commonly used methods of refining. (a) Distillation or sublimation This removes nonvolatile impurities from volatile metals like zinc and mercury which are obtained in the pure state. (b) Liquation Readily fusible metals like lead, tin and bismuth are refined by this method. Impure metal is melted on the sloping surface (called hearth). Pure metal melts and flows down and is collected separately while impurities are left behind. (c) Electrolytic refining It is the most commonly used method of refining of metals and produces highly pure metals. Impure metal is made the anode (positive electrode) and a piece of pure metal the cathode (negative electrode). These electrodes are dipped in a solution of a soluble salt of the metal. When electric current is passed, impure metal from the anode gradually passes into the solution and pure metal from the solution gets deposited on the cathode. Thus, effectively pure metal from anode passes to cathode gradually. Impurities either collect below the anode as anode mud or dissolve in the solution. Copper, aluminium etc. are purified in this way. (d) Oxidation Impurities like carbon, phosphorus, silicon etc. are removed as oxides by passing air through molten impure metal. Iron is purified by this method. (e) Zone refining This method is used for obtaining extremely pure metals and silicon. The metal (or silicon) rod which has already been purified extensively is placed in a quartz tube filled with a noble gas. It is moved slowly through a heating coil that melts only a small portion of the metal rod. Pure metal Metal rod Heating coil crystallizes from the melt. The impurities are more soluble in the molten metal and are carried to the end of the rod. The metal rod is moved repeatedly through the heating coil. Impurities collect at the end of the metal rod (Figure 19.3). This end of the metal rod is cut off and discarded. The remaining metal is Fig. 19.3 Zone refining extremely pure.

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After learning about steps involved in extraction of metals from their ores we will now learn how three important metals, iron, aluminium and copper are extracted from their ores. 19.2.2 Iron Iron is the chief metal used for making machinery and therefore plays very important role in growth of industry. It has been in use since long time. In India the art of making iron had reached an advanced state. This is testified by Ashok’s Iron Pillar in Delhi and iron joints used in the temple of Puri which remained rustfree even centuries after they were made. Aristotle in 340 B.C. provided a description of the manufacture of a type of steel called wootz steel which was first produced in India but later on became famous as Damascus steel. It was renowned for its suppleness (bending easily), its ability to maintain a cutting edge and its use in making swords. 19.2.2a Ores of iron Haematite (Fe2O3) is the most abundant ore of iron which is a reddish brown ore. Some other ores of iron are magnetite (Fe2O4), lemonite (2Fe2O3.3H2O), siderite (FeCO3) and pyrite (FeS3). Out of these, haematite and magnetite are more suitable for the extraction of iron. Huge deposits of haematite are available in India in Mayurbhanj, Singhbhum and Mysore. Iron and steel are manufactured at Asansol, Jamshedpur, Durgapur, Bhilai and other places. 19.9.2b Extraction of iron The following are the main steps in the extraction of iron from its ores:. a. Concentration of ore Ore is first broken into small pieces and if necessary it is washed with water. Usually the ore is rich enough and does not need any concentration. In case the carbonate (siderite) or sulphide (pyrites) ores are used, they are roasted to convert to oxide and in case hydrated oxide (limonite) is used it is calcinated to remove the water of crystallization. In case of oxide ore (haematite or magnetite) these treatments are not required. b. Reduction to iron The oxide ore is reduced chemically by carbon monoxide which is formed in a blast furnace by reaction of coke with air (shown in the box). A mixture of iron ore, limestone, CaCO3, and coke, called charge is fed into the furnace. The main reactions that occur are given below. 2C (s) Fe2O3(s) FeO(s) + + + O2(g) CO(g) CO(g) 2CO(g) 2FeO(s) + CO2(g) Fe(l) + CO2(g)

Mineral Resources–Metals and Non-metals : 51 :

Blast Furnace Blast furnace is a chimney-like structure made of steel plates and lined inside with firebricks. A mixture of iron Charge (ore, limestone,coke) ore, limestone, CaCO 3 , and coke, CO, CO called charge is 200°C introduced into the 3Fe O + CO → 2Fe O +CO furnace from the top. CaCO → CaO + CO A blast of hot air, fed Fe O + CO → 3FeO +CO from near the bottom 700°C into it. The oxygen in C + CO → 2CO the air reacts with FeO + CO → Fe +CO coke to form mainly 1200°C Iron melts Molten slag forms carbon monoxide and 1500°C 2C + O → CO some carbon dioxide. 2000°C These reactions are Hot air blast highly exothermic in nature and a lot of Slag heat is generated. The Molten iron hot gases rise in the Fig. 19.4 Manufacture of iron in a blast furnace furnace and react with iron oxide ore. Before the iron ore falls to the bottom of the furnace most of it is reduced to iron. At the bottom of the furnace the temperature is high enough to keep it in the molten state. It is taken out from the outlet near the bottom of the furnace. Lime stone decomposes into calcium oxide which then reacts with impurities (SiO2 and Al2O3)
2 2 3 3 4 2 3 2

Solid charge descends

3

4

2

Hot gases rise

2

2

2

CaCO3(s) CaO(s) + SiO2 (s) CaO(s) + Al2O3(s)

CaO(s) + CO2(g) CaSiO3(l) Ca(AlO2)2(l)

The mixture of calcium silicate and calcium aluminate, known as slag, remains in molten state and being lighter than molten iron floats on it and is removed from time to time from a separate outlet. The iron obtained from blast furnace is called cast iron. It is also called pig iron. It contains about 95% iron and about 5% carbon along with many other impurities in small amounts like silicon, phosphorus, manganese and sulphur. It has a relatively low melting point and can be cast into desired shapes. 19.2.2c Properties of iron (A) Physical properties (i) Pure iron is a silver white metal. (ii) It is strongly attracted by magnets.

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Commercially it is obtained in three forms: cast iron, wrought iron and steel. (B) Chemical properties (i) When exposed to atmosphere, iron gets rusted. Rust is hydrated ferric oxide in which the amount of water associated varies. It is therefore represented as Fe2O3.xH2O. For the rusting process oxygen (air) and water are required. It is accelerated by acidic substances like CO2, SO2 and retarded by alkalis. Presence of NaCl and other salts also increases the rusting rate. Completely homogeneous iron does not rust. ACTIVITY 19.1 Aim: To study the rusting process What is required? A few test tubes, corks, common salt, sodium hydroxide or washing soda, iron nails, small piece of zinc from used cells and a small piece of copper wire. How to do? Take 7 test tubes. Paste labels on each of them and mark them as 1,2 and so on. Prepare the test tubes as given below. (Fill about half the test tube with the liquid/solution mentioned. Test tube no. 1 2 Liquid solution Boiled water + iron nail and cork the test tube Tap water + iron nail What to observe? Practically no rust is formed A small amount of rust is formed. A reddish brown coloured solid is formed on and around the nail. A little more amount of rust is formed than in test tube 2. A reddish brown coloured solid is formed on and around the nail. Amount of rust formed is much more. A reddish brown coloured solid is formed on and around the nail. Practically no rusting occurs.

3

Solution of common salt in tap water + iron nail

4

Solution of common salt and vinegar in tap water + iron nail

5

6

7

Solution of common salt and sodium hydroxide or washing soda in tap water + iron nail Solution of common selt + iron nail with a small piece of zinc attached to it. Solution of common salt + iron nail with a small piece of copper wire around it.

White coloured precipitate is formed. A large amount of rust is formed. A reddish brown coloured solid is formed on and around the nail.

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What do we conclude? • In test tube 1 practically no rusting occurs although iron nail was in contact with water. The nail was not in contact with oxygen of air. Boiling of water had expelled the air from test tube and cork prevented the contact later. • In test tube 2 the nail was in contact with air and water and it rusted. • In test tube 3 the addition of sodium chloride increases the rusting process. • In test tube 4 the addition of an acid (vinegar) further increases the rusting process • In test tube 5 the addition of an alkali (sodium hydroxide or washing soda) retards the rusting process. • In test tube 6 corrosion occurs but not of iron but that of zinc which is indicated by the white coloured solid that is formed rather than the reddish brown rust. Contact of iron with a more active metal protects it against rusting. The more active metal zinc gets corroded instead. • In test tube 7 the corrosion of iron increases when it is in contact with a less active metal. (ii) When steam is passed over red hot iron, hydrogen is liberated 3Fe(s) + 2H2O(g) Fe3O4(s) + 4H2(g)

(iii) It reacts with dilute hydrochloric and sulphuric acids and displaces hydrogen from them. Fe(s) + 2H+(aq) Fe2+(aq) + H2(g) (iv) Iron does not react with alkalis. When hot, it combines with halogens and sulphur to give halides and sulphide respectively. 2Fe(s) + 3Cl2(g) 2FeCl3(s) Fe(s) + S(s) FeS(s) (v) Iron displaces less active metals from solutions of their salts. Fe(s)+ Cu2+(aq) Fe2+(aq) + Cu(s) 19.2.2d Commercial forms of iron There are three commercial varieties of iron, namely cast iron, wrought iron and steel. These varieties differ from each other mainly in their carbon content. • Cast iron contains from 2.5-4.5% carbon together with traces of sulphur, phosphorus, manganese and silicon. It is hard and brittle and cannot be welded. It has a low melting point and expands on solidification. Therefore it is good for casting. It does not easily rust and is used for making parts exposed to weather such as lamp posts. It is used for making engine blocks, brake drums etc. in automobiles . • Wrought iron is the purest form of iron. It is obtained from cast iron by heating it with ferric oxide in a furnace. Its melting point is higher than that of cast iron. It is malleable and can be forged, hammered, machined and welded. It is used to make iron nails, sheets and machine parts. • Steel is an iron-carbon alloy and contains 0.05–1.5% carbon. It is manufactured from pig iron. While production of iron is basically a reduction process

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converting iron oxide into iron, the conversion of iron to steel is an oxidation process in which excess of carbon is oxidized to carbon monoxide. Then, the required amount of carbon is added to it. Its hardness depends upon the amount of carbon in it. If the carbon content in steel is between cast iron and wrought iron it is called mild steel. It is used for manufacture of rails, wheels and building material. 19.2.2e Alloy steels Some very useful properties may be imparted to steel by alloying it with other metals. Composition and properties of some alloy steels are given below. (i) Stainless steel: It is prepared by mixing 11.5% chromium to steel. It is called stainless steel because it is resistant to rust formation. It is used for making utensils, cycles and automobile parts. (ii) Nickel steel: It is prepared by mixing 3.5% nickel to steel. It is very strong material. It is used for making cables, propeller shafts, armour plates, automobile and aeroplane parts. (iii) Chrome steel: It is prepared by mixing 1.5 to 2.0% chromium to steel. It is extremely hard and strong. It is used for making armour piercing projectiles, crushing machinery and cutlery etc. 19.2.3 Aluminium You have learnt in the beginning of this lesson (section 19.1) that aluminium is the third most abundant element. It does not occur free in nature. Therefore it remained unknown until the nineteenth century. 19.2.3a Ores of aluminium Main ores of aluminium are bauxite, (Al2O3.2H2O), corundum, (Al2O3), cryolite, (Na3AlF6) and silicates like feldspar (KAlSi3O8). Bauxite is the chief ore of aluminium. In India it is found in Bihar, Kashmir, Madhya Pradesh, Maharashtra and Tamil Nadu. It is manufactured in Muri (Bihar), Belur and Jaykay Nagar (West Bengal), Kalna (Maharashtra), Alwaye (Kerala), etc. 19.2.3b Extraction of aluminium Aluminium is extracted from bauxite by electrolysis. The ore contains oxides of silicon, iron and titanium as main impurities. The ore is first treated with a strong solution of sodium hydroxide (caustic soda) which converts aluminium oxide (Al2O3) into soluble sodium meta aluminate (Na AlO2). Al2O3(s) + 2NaOH(aq) 2NaAlO2 (aq) + H2O(l) Other impurities, oxides of iron and titanium remain unaffected and are filtered off. The solution is then treated with an acid which precipitates insoluble aluminium hydroxide Al(OH)3 which is then heated to obtain pure aluminium oxide. AlO2-(aq) + H3O+(aq) 2Al(OH)3(s) Al(OH)3(s) Al2O3(s) + 3H2O(l)

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Fused anhydrous aluminium oxide or alumina is then reduced by Hall process electrolytically. Aluminium oxide obtained by heating Al(OH)3 has an extremely high melting point (2045 oC) and its direct electrolysis Carbon anodes is not practicable. Instead a few per cent Al2O3 is dissolved in fused cryolite, Na3AlF6 which acts as Carbon solvent for it. The cell is operated at about 950 oC. cathode Further, molten cryolite is a much better electrical conductor than Al2O3. The schematic diagram of the Molten aluminium electrolytic cell used in Hall process is shown in Figure 19.5. This cell consists of an iron tank which is lined Al O in molten cryolite inside with gas carbon which acts as cathode. A Fig. 19.5 The schematic diagram of number of carbon rods are used as anode. Electrolysis electrolytic cell used in Hall’s process of this molten mixture produces aluminium and oxygen gas according to the following net processes:
2 3

Anodic process (oxidation): Cathodic process (reduction): Net process:

[2O2[Al3+ + 3e2Al2O3(l)

O2(g) + 4e-]×3 Al(l)] ×4 4Al(l) + 3O2(g)

The liquid aluminium metal (m.p. 660.2 oC) collects at the bottom of the cell and is drained out from time to time. The metal obtained has the purity of 99.6 – 99.8 %. 19.2.3a Properties of aluminium (A) Physical properties (i) Aluminium is a bluish white metal and can take high polish. (ii) It has extremely low density (2.7 g cm-3) and high tensile strength i.e. it can be stretched. It is malleable and ductile. It is drawn into wires. It is used for making thin foils used for packing of food articles because it is not involved in living systems and is considered to be non-toxic. (iii) It is an excellent electrical conductor. Its conductivity is about 65 % of that of copper and only silver, copper and gold surpass it in this regard. Being cheaper and lighter than copper, it is increasingly taking the place of copper for making electrical wires for domestic use as well as for making high voltage transmission lines. (B) Chemical properties (i) It is a trivalent electropositive element. (ii) In air its surface gets coated with a protective layer of aluminium oxide. This oxide film protects aluminium from corrosion and also accounts for the unexpected inertness of aluminium. It is thus a self protective metal. (iii) If heated to redness, it burns with a brilliant white light with evolution of much heat. 4Al + 3O2 2Al2O3 (iv) Although it is considered as an active metal, it does not react with water as do metals like sodium and magnesium.

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21

Materials in Our Daily Life
The basic aim of science is not only to study and understand natural phenomena but also to use this knowledge to make our lives more comfortable. Science and technology have enabled us to develop more economical and convenient methods to recover useful materials from nature and to put them to various uses. Chemistry has enabled us to synthesize new materials which have desired properties, thus, making them even better than natural materials. We need different types of materials to meet our daily needs. Some of them are obtained from nature while others are prepared by man. The materials that we get from nature are called natural materials. Wood, silk, cotton, leather, rubber, coal, etc. are natural materials. However, some materials that we use are manmade. Synthetic textiles like terylene and nylon, cement, glass, plastics, dyes, soap, detergents, fertilizers, insecticides and pesticides are some man-made materials which are commonly used. In this lesson, you will learn about the ways in which various materials are used in making common household items, in construction of houses and other buildings. You will learn about different polymers and their uses in our daily life. In addition, you will learn about the various medicines that help to cure different diseases and keep us healthy. OBJECTIVES After completing this lesson, you will be able to: • differentiate between natural and man-made materials; • name the materials used for making some common household items and for housing purposes; • state the principles involved in preparation and properties of some man-made materials in our daily life; • list various medicines used in some common diseases; • explain harmful effects of man-made materials on the environment. 21.1 COMMON HOUSEHOLD ITEMS We use many things in our house like candles in case of emergency lighting, ink to write, soaps and detergents to wash our clothes, matchbox to light gas stove or candles and many more. Let us now learn about these items of daily use.

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21.1.1 Candles We use candles as emergency light source and for decorative and ceremonial purposes. Usually they are made from a mixture of paraffin wax or some other slow-burning substance like tallow (stearic acid). They are commonly made in cylindrical form but are also made in fanciful designs. They contain a wick at their centre. When lighted with a matchstick heat from its flame liquefies the wax of the candle. This liquefied wax rises up along the wick where it is converted into vapour form, which then catches fire. Now a days, candles are made in a variety of colours, shapes and sizes. Some candles are scented and their aroma spreads in the air when lighted while some others can float on water. Nainital (in Uttaranchal) is famous for the variety of beautiful and decorative candles manufactured here. 21.1.2 Inks We all use inks in various writing instruments like fountain pens, ball pens, gel pens, roller pens, soft tip pens, etc. Have you ever thought what ink is? Ink is a coloured fluid or a paste that is used for writing or printing. Earlier, black ink, also called India ink, was most widely used. It was made by mixing lamp black or carbon black in water or oil to which some gum was added which stabilized the mixture and also gave it better sticking property. This ink is used even these days but more commonly used inks are solutions of water or alcohol soluble dyes. Inks used in printing are similar in nature but are in the form of thick paste, which has a better sticking property. This is an essential quality as it causes the ink to stick to the typefaces and to paper when it is pressed against it. 21.1.3 Soap and detergents We use soap and detergents to wash our clothes. We wash our hands and take bath with soap. Soap and detergents help in removing dirt, oil and grease. How do soap and detergents remove the dirt and grease? What are the chemicals present in them? What is the difference in soaps and detergents? 21.1.3a Soap Soap has been in use for at least last three thousand years. Soaps are sodium or potassium salts of long chain organic acids (called fatty acids) like stearic acid and palmitic acid. How is soap manufactured? Soap is made by heating oil with sodium hydroxide. The oil and sodium hydroxide solution are fed into an enclosed reaction vessel under high pressure and heated at high temperature. At this temperature, the reaction is completed in a few minutes. The mixture of soap and glycerol is cooled and a concentrated solution of sodium chloride is added. Glycerol dissolves readily in salt solution but soap does not. So, solid soap separates out from the mixture. It is then removed by centrifugation. While still hot it is sprayed into a hot vacuum chamber to dry it. Perfume is added and the particles are compressed into soap cake.

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The basic materials used to manufacture soap are animal fats (lard) or vegetable oils (olive oil, neem oil, etc.) and an alkali, usually sodium hydroxide. Fats and oils are compounds of organic acids (containing 12–14 carbon atoms) and glycerol (commonly called glycerine). When the fat or oil is heated with sodium hydroxide solution, the acids are broken away from glycerol and are neutralized by the alkali to form soap. Soaps produce lather (foam) with soft water. With hard water, which contains calcium and magnesium salts in it, they do not produce lather. Instead they themselves are precipitated as insoluble salts of calcium and magnesium. 21.1.3b Detergents Animal fats and vegetable oils are important foodstuffs and ideally should not be used for making something even as important as soap. In their place, long chain sulphonic acids (usually C8 to C22) are used. Sodium or potassium salts of these sulphonic acids are known as detergents. Detergents can be manufactured in solid form (for washing powders) or in liquid form (for shampoos and liquid soaps). Unlike soaps detergents can be used with soft as well as hard water. This is because their calcium and magnesium salts are water soluble. ACTIVITY 21.1 Aim : To compare the lather forming ability of soap and detergent in soft and hard water. What is required? Four test tubes, two small pieces of soap and detergent cakes. What to do? Take four test tubes. In two of them take some amount of ordinary tap water which is soft water. In one of them add a small piece of soap while in the other add a small amount of some detergent (a small piece or a small amount of powder). Shake both the test tubes. What do you observe? • Lather is formed in both the test tubes. • Now repeat the above procedure with hard water from a hand pump or a well. • You will find that soap does not form lather but detergent does form lather even with hard water. 21.1.3c Cleansing action of soap and detergent Soaps and detergents form lather or foam with water. Lather removes grease and dirt particles from clothes. Water by itself cannot do it as it does not wet oily or greasy dirt. Addition of soap or detergents improves the wetting property of water and thus helps in removing oily or greasy dirt. 21.1.4 Matchboxes In every house you will find a matchbox. Can you imagine life without it? How would you light up a candle or gas stove without it?

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Do you know how a matchstick catches fire? The head of matchstick consists of a mixture of potassium chlorate and antimony trisulphide bound together by glue. The striking surface on the matchbox is a mixture of red phosphorus and powdered glass held by glue. When a matchstick is struck against the coated surface of the matchbox, some heat is produced that makes the chemicals in the match head react. The heat of this reaction ignites the wood. Be careful Matches must be used carefully. While lighting, it should not be struck so hard on the side of the matchbox that it’s burning head breaks and flies away. This can result in an accident. After using a matchstick, we should not throw it anywhere carelessly. Even when its flame is blown off, the tip of the stick continues to burn slowly as can be seen by the dull red glow at the tip. This is known as after glow. Many accidental fires may occur by this after glow. Therefore, while throwing away a matchstick you should always check that it is completely extinguished and there is no after glow. Sometimes matchsticks are dipped in a solution of borax or sodium carbonate (karborized matches) and dried as a first step in the manufacture of matches. Matchsticks thus treated are completely extinguished when blown away and are safer to use. CHECK YOUR PROGRESS 21.1 1. Give two examples each of natural and man-made materials? 2. Name the substances used for making candles. 3. What are soaps? 4. Can soap be used with hard water to wash clothes? 5. Which type of matches do we use today? 21.2 HOUSING MATERIALS In the last section, we learned about some common household items. In this section, we will learn about two important housing materials – cement and glass. 21.2.1 Cement Do you know what cement is made of and how is it manufactured? a) Raw materials required: Three main raw materials required for manufacture of cement are as follows: • Limestone which is calcium carbonate, CaCO3 • Clay which is mainly a mixture of aluminium silicates containing alumina, Al2O3 and silica, SiO2 • Gypsum which is CaSO4.2H2O b) Manufacture: Limestone and clay are mixed in definite proportion and ground to a fine powdery state. This dry powder is used as such or mixed with water to form a paste and heated in a rotary kiln (a type of furnace). It is slowly made to pass through the kiln wherein limestone and clay combine chemically and form a mixture of calcium silicate, CaSiO3 and calcium aluminate, CaAl2O3. This mixture is in the form of small greenish black or grey-coloured

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hard balls known as clinkers. These clinkers are allowed to cool down and then ground to very fine powder. To this powder, 2-3% gypsum is added and the mixture is again ground to obtain a grayish coloured powder, which is cement. It is then packed in airtight bags to exclude the moisture. Gypsum is added to decrease the setting time of cement. c) Uses: Cement is one of the most important building materials. It is employed in the construction of buildings, roads, bridges, dams, etc. For general uses like plastering or laying of bricks, this powder is mixed with sand and water and the resulting thick paste is used for construction purposes. As a result of chemical reactions between water and cement this mixture sets into a hard mass. Concrete is a mixture of cement, sand, gravel or small pieces of stone and water. It sets to an extremely hard structure. It is used for making floors and roads. Concrete may be further strengthened by filling it around or over a network of steel rods and allowing it to set. It is known as reinforced concrete cement or R.C.C. Such structures are very strong and are used in construction of pillars, roofs of buildings, roads, bridges and dams. 21.2.2 Glass Glass is used for various purposes. You must have seen glasses fitted in windows and doors, looking mirrors, windscreens of vehicles, reading glasses, sunglasses, etc. Have you ever wondered how is glass prepared? What are the raw materials required for manufacturing of different types of glasses? a) Raw materials required: The basic raw materials needed for making glass are: • Washing soda which is sodium carbonate, Na2 CO3. • Limestone which is calcium carbonate, CaCO3. • Sand which is silica, SiO2. b) Manufacture: The raw materials are mixed in a definite proportion. These are then ground and the mixture is heated in a furnace. Sometimes scrap glass is also mixed with other raw materials. By doing so glass can be recycled and it also helps in melting of the mixture. The fused mixture is then allowed to cool. The glass so produced is transparent, non-crystalline and brittle. c) Types of glass and their uses: There are various types of glasses depending upon their composition and the purpose of their use. • Soda-lime glass: The glass produced as given above is called sodalime glass or soft glass. It is used for manufacture of bottles ordinary crockery, ordinary laboratory glass apparatus like soda glass test tubes etc. • Hard glass: If instead of sodium carbonate, potassium carbonate is used for making glass another variety of glass known as hard glass is produced. It can withstand very high temperatures. It is used for making hard glass laboratory apparatus like hard glass test tubes, beakers, conical flasks etc.

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Borosilicate glass: It is sodium aluminium borosilicate. It can withstand rapid heating and cooling without breaking. It is used for making kitchenware and laboratory apparatus. It is sold under the trade names Borosil and Pyrex. Flint or optical glass: It is used for making lenses, prisms, spectacles, etc. because of its excellent optical properties. It is composed of alkalis, lead oxide and silica. It is also known as flint glass. A superior variety of optical glasses is made by adding cerium oxide. It cuts harmful ultra violet rays that are harmful to eyes. It is known as Crooke’s glass. Coloured glass: It is made by adding small quantities of oxides of different metals to basic ingredients. Blue glass contains traces of cobalt or copper oxide, green glass contains chromium ferrous oxide, red glass contains selenium oxide. Fibre glass: It is produced by passing molten glass through rotating spinners when it gets converted into fine threads. It is used as an insulating material for heat, electricity and sound in different equipment like electric ovens, geysers, refrigerators, etc. It is also used for reinforcing plastics and rubber to make bodies of cars and scooters and safety helmets.

CHECK YOUR PROGRESS 21.2 1. What is mixed with cement before using it for construction purposes? 2. Which type of glass can withstand rapid heating and cooling without breaking? 3. What is the role of small pieces of stone that are added to cement when it is used to make floor or roads? 4. How is coloured glass made? 21.3 SOME IMPORTANT CHEMICALS A large number of chemicals are used in industry and in our homes for various purposes. In this section we would learn about some such useful chemicals. 21.3.1 Washing soda Washing soda is used for washing of clothes. It is because of this chemical used that the clothes washed by a washerman appear so white. Chemically, washing soda is sodium carbonate decahydrate (Na2CO3.10H2O). It is an important chemical required as basic raw material in hundreds of industries. Now let us learn about the raw materials used in its manufacture and how is it manufactured. a) Raw materials required: The raw materials required to manufacture washing soda are • Lime stone is calcium carbonate (CaCO3) • Sodium chloride (NaCl) in the form of brine • Ammonia (NH3) b) Manufacture: Washing soda is manufactured by Solvay process. In this process, firstly, carbon dioxide is obtained by heating limestone strongly. CaCO3 CaO + CO2
lime stone quick lime carbon dioxide

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It is then passed through cold brine (a solution of concentrated NaCl in water), which has previously been saturated with ammonia. NaCl(aq) + CO2(g) + NH3(g) + H2O(l) NaHCO3(s) + NH4Cl(aq)
Sodium chloride ammonia sodium hydrogen carbonate ammonium chloride

NaHCO3 being sparingly soluble in water, crystallizes out. It is calcinated (heated strongly in a furnace) to get sodium carbonate. 2NaHCO3 Na2CO3 + CO2 + H2O Ammonia used in this process is regenerated by first converting the quicklime obtained earlier with water and then reacting it with ammonium chloride obtained from carbonating tower. CaO + H2O Ca(OH)2
quick lime slaked lime

Ca(OH)2 + 2NH4Cl ammonium chloride

CaCl2

+ 2NH3 + 2H2O

calcium chloride

c) Uses: Washing soda is used in the manufacture of glass, water glass, caustic soda, borax and soap powders. It is also used for the softening of water, as laboratory reagent and as a starting material for the preparation of a number of other sodium compounds. Of course, its most common use in laundry is for washing of fabrics and clothes from which it gets its name. 21.3.2 Baking soda You must have seen your mother using baking soda while cooking some dals. If you ask her why she uses it, she would tell that it helps in cooking some items faster which otherwise would take much longer time. Chemically, baking soda is sodium hydrogen carbonate or sodium bicarbonate and its formula is NaHCO3. a) Manufacture: You have already learned in the previous section that it is the primary product of the Solvay process used to manufacture washing soda. It gives small white crystals sparingly soluble in water. Its solution in water is alkaline in nature. b) Uses: Baking soda is mainly used in the baking industry. When sodium hydrogen carbonate or its solution is heated, it gives off carbon dioxide. It is this carbon dioxide which raises the dough during baking. The sodium carbonate produced during the heating of sodium hydrogen carbonate gives bitter taste. Therefore, usually baking powder is used, which is a mixture of baking soda, NaHCO3 and an acid like tartaric acid. The latter is added to neutralize the sodium carbonate formed in the reaction given above, to avoid its bitter taste. You must have eaten cakes. They are made so soft and fluffy by using baking powder. Baking soda is also used in medicines to neutralize the excessive acidity in the stomach. Mixed with a solid acid such as citric or tartaric acid, it finds use in effervescent drinks used to cure indigestion. Another important use of baking soda is in certain types of fire extinguishers about which you have already learned in lesson 14.

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21.3.3 Bleaching powder Have you ever wondered at the whiteness of a new white cloth? How is it made so white? It is done by bleaching the cloth at the time of its manufacture. Bleaching is a process of removing colour from a cloth to make it whiter. Bleaching powder has been used for this purpose since long. Chemically, it is calcium oxychloride and its formula is CaOCl2. Now we shall learn about the raw materials required for its manufacture and how it is manufactured from them. a) Raw materials required: The raw materials required for manufacture of bleaching powder are • Slaked lime, Ca(OH)2 • Chlorine gas, Cl2 b) Manufacture: It is prepared in a vertical tower made of cast iron with inlets for chlorine and hot air near the base. The dry slaked lime, calcium hydroxide, is fed into the chlorinating tower from the top. It moves downward slowly and meets the upcoming current of chlorine. As a result of the reaction between them it is converted into bleaching powder which collects at the bottom. CaOCl2 + H2O Ca(OH)2 + Cl2 c) Uses: It is used mainly for bleaching cotton, linen and wood pulp in textile and paper factories. Apart from this, it is used as a disinfectant and germicide for the sterilization of water, in rendering wool unshrinkable and for the manufacture of chloroform. It also finds use as an oxidizing agent in many chemical industries. 21.3.4 Plaster of Paris You must have seen beautiful designs made on the ceiling and walls of rooms in many houses. They are made with Plaster of Paris, also called POP. a) Manufacture: It is manufactured from gypsum which is hydrated calcium sulphate (CaSO4.2H2O) found in nature. When gypsum is heated at about 325 K, it loses part of its water of crystallization to form CaSO4. ½H2O or 2CaSO4.H2O which is plaster of Paris. When made into a paste with a little water, Plaster of Paris sets to a hard mass, which expand with hardening. b) Uses: Plaster of Paris finds use in making casts and patterns. It is used for making plaster casts to hold fractured bones in position while they set. It is also used for making chalks for writing on blackboard. Now a days it is increasingly being used for plastering the walls, pillars and ceilings and to make ornamental patterns on them. CHECK YOUR PROGRESS 21.3 1. What is the common name of NaHCO3? 2. Name the process used for manufacture of washing soda? 3. Which chemical can be used for removing stains of ink from clothes? 4. What is the chemical formula of Plaster of Paris?

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21.4 FIBRES: NATURAL AND SYNTHETIC Fibre is a fine thread like material, like cotton, which is woven or knitted into a cloth. We need different types of clothes, such as cotton, silk, nylon, polyester, etc. to suit different weather conditions. Fibres are made of polymers. Cotton consists of cellulose. Some of these like cotton, wool and silk are obtained from nature. They are called natural fibres. Many of them are man-made like nylon, polyester, terylene, liakra, etc. They are called synthetic fibres. 21.4.1 Polymers Many things that we see around us and use are polymers. We use plastic buckets, containers, electrical switches, etc. The clothes that we wear are made of polymers like cotton, wool, terylene, etc. Polymers are big molecules which are formed when a large number of small molecules join one another. The word polymer means many parts. The small molecules which make a polymer are called monomers. For example, ethene (C2H4) molecules join together and form the polymer known as polythene. a) Nylon: Nylon is a polymer of small monomeric units called amide (-CO-NH-) i.e. it is a polyamide. It is prepared by reaction of adipic acid and hexamethylenediamine. Terylene is crease resistant, durable and is not damaged by insects like moths and by mildew (fungi that form a white growth on plants and materials like cloth and paper). b) Polysters: Polyesters are another category of polymers. One important member of this family is dacron which is also known as terylene. It is prepared by reaction between terephthalic acid and ethylene glycol. It is crease resistant, durable and is not damaged by insects like moths and mildew. Therefore, it is suitable for making garments because they can be set into permanent creases and pleats. It has also been used to repair or replace segments of blood vessels. In the form of thin sheets it is used for manufacture of adhesive tapes and recording tapes. 21.4.2 Rubber a) Natural rubber: Natural rubber is chemically poly-cis-isoprene which is formed from the monomer isoprene. It comes from the sap of the Para rubber tree, Hevea brasiliensis. Trees are tapped by making a spiral cut through the bark. The sap is called latex. It is a white milky liquid. It is a suspension of tiny particles of rubber in water. These particles can be separated when acid is added to it and solid rubber is obtained. Raw rubber is soft and pliable i.e. it can be easily bent. It does not possess the main property that we associate with rubber, elasticity i.e. the ability to return to its original shape after stretching. Rubber is made elastic by heating it with a small amount (1 to 3%) of sulphur. This process is known as vulcanization. Apart from sulphur other substances are also added to natural rubber to modify its properties. Carbon black is added to make it stronger, flexible and more resistant to wear and tear. For making car tyres, 2 parts of rubber are mixed

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with 1 part carbon black. If flexibility is not important fillers, such as clay or chalk, are added to make rubber hard and stiff. Rubber for floor tiles and mats contains fillers of this type. b) Synthetic rubber: Synthetic rubber supplements the natural rubber and helps save precious trees. Its properties are similar and sometimes better than those of natural rubber. The most common variety of synthetic rubber is made from the monomer butadiene CH2CH.CH.CH2. It can be vulcanized just like natural rubber. It has particularly good resistance to wear and tear, which makes it especially useful for making tyres. Other types of synthetic rubbers are made by mixing other monomers like styrene and chloroprene (commonly known as neoprene) with butadiene. 21.4.3 Plastics You must be using comb, toothbrush, jars and buckets in your house. All these items of daily use are made of plastic. Plastics are synthetic or man-made polymers. Let us learn about some of these. a) Polythene is a polymer made from ethene (CH2=CH2). It is one of the most commonly used materials. It is a soft plastic, which softens on heating. It is used for making bottles, buckets, and pipes, as covering for electrical wires and cables and as film for making bags. b) Polyvinyl chloride (PVC) is made from the monomer vinyl chloride (CH2=CHCl). It is used for making rain coats, handbags, toys including dolls, electrical goods and as a covering of electrical wires. c) Bakelite (Phenol-formaldehyde resin) is made by reacting phenol and formaldehyde. It is hard and quite a strong material. It is used for making combs, electrical switches, and plugs and for making handles of many kitchen utensils and electrical appliances like pans, pressure cookers, electric irons, kettles, and toasters. CHECK YOUR PROGRESS 21.4 1. What is a monomer? 2. What is the name of monomeric unit of natural rubber? 3. Why is sulphur added to rubber? 4. What is the full form of PVC? 21.5 MEDICINES Whenever we feel sick, we go to the doctor for medicines (also called drugs). Medicine is a substance used for treating diseases or illness. Let us study about some common types of medicines. 21.5.1 Anaesthetics Anaesthetics are drugs which produce a loss of sensation and consciousness. General anaesthetics result in loss of sensation and consciousness in the entire

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body. Examples are divinyl ethers, cyclopropane, etc. They are used during major surgical operations. Some anaesthetics like Novocain and Xylocaine which show their effect in a limited area are called local anaesthetics. They are used during small surgical operations and tooth extraction. 21.5.2 Antibiotics Antibiotics are medicines which are used to kill bacteria, fungi and moulds. The first antibiotic discovered was penicillin which is very effective for pneumonia, bronchitis, sore throat, etc. Ampicillin is a slight modification of penicillin. It has wider applications. Other commonly used antibiotics are streptomycin, tetracycline and chloramphenicol. 21.5.3 Analgesics Analgesics are used for relieving pain. Aspirin, paracetamol, morphine are some examples of analgesics. They must be used only under medical supervision. 21.5.4 Antacids Antacids are used to treat acidity in stomach. Digene, ranitidine and omeprazole are some examples of antacids. 21.5.5 Antipyretics Antipyretics are the medicines which are used to bring down body temperature in high fever. Their administration leads to perspiration which brings down the temperature. Common examples are aspirin, paracetamol, analgin and phenacetin. In this section you learned about some important types of medicines. However, it must be remembered that medicines should always be taken on the advice of a doctor. CHECK YOUR PROGRESS 21.5 1. What is the use of the drug paracetamol? 2. What is the use of ranitidine? 3. Name an antibiotic. 4. Which types of medicines are used for relieving pain? 21.6 HARMFUL EFFECTS OF MAN-MADE MATERIALS In this lesson you have learnt about various materials that are useful to us. Many of them are obtained from natural resources while a large number of them are man-made. These days the latter are being used extensively. However, after use their disposal becomes a problem. Many of them are toxic in nature and pollute air and water. Some of them are so stable that they are not degraded easily and they get accumulated in the environment. Such materials should be recycled in order to avoid such problems. In the next lesson you will learn about the harmful effects of man-made materials and the related environmental problems in detail.

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• • • •



• • • • •

• • • • •

• • • •

LET US REVISE Of all the materials that we see around us some are obtained from nature while others are prepared by man. Candles are made from a mixture of paraffin wax and stearic acid. Inks are coloured fluids or pastes that are used for writing or printing. Soaps are sodium or potassium salts of long chain fatty acids while detergents are sodium or potassium salts of long chain sulphonic acids. Detergents can give lather even with hard water whereas soaps cannot. Safety matches have a mixture of potassium chlorate and antimony trisulphide and glue at the head of match sticks and a mixture of red phosphorus and powdered glass on the striking surface. The heat generated when the match stick is struck starts the ignition. Cement is one of the most important building material manufactured from limestone, clay and gypsum. Concrete is a mixture of cement, sand gravel and water. It sets to an extremely hard structure. Glass is prepared by heating a mixture of washing soda, limestone and sand in a furnace. Soda glass is used for manufacture of bottles, ordinary crockery, laboratory apparatus, etc. Hard glass is made by using potassium carbonate in place of sodium carbonate. It can withstand very high temperatures and is used for making laboratory apparatus. Borosilicate glass is sodium aluminium borosilicate and can withstand rapid heating and cooling. It is used for making kitchen and laboratory ware. Flint glass is used for making lenses, prisms, spectacles, etc. Coloured glass is made by adding small quantities of oxides of different metals. Fibre glass is a mass of fine threads of glass used as an insulating material for heat, electricity and sound and reinforcing plastics and rubber. Washing soda (Na2CO3.10H2O) is prepared by Solvay process. It is used in the manufacture of glass, caustic soda, borax and soap powders. It is used for softening of water, as a laboratory reagent and as a starting material for many sodium compounds. Baking soda (NaHCO3) is the primary product of Solvay process. It is mainly used in baking industry and in fire extinguishers. Baking powder is a mixture of baking soda and tartaric acid. Bleaching powder (CaOCl2) is prepared by mixing chlorine and slaked lime. It is used for bleaching cotton, linen and wood pulp and for sterilization of water. Plaster of Paris (CaSO4. ½H2O) is prepared by heating gypsum (CaSO4.2H2O). It is used for making casts and patterns and for plastering the walls, pillars and ceilings and to make ornamental patterns on them.

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Polymers are big molecules formed when a large number of small molecules join together. Cotton, wool, terylene, etc. are some polymers. Nylon, polyesters, rubber and plastics are some important polymers. Medicine is a substance used for treating diseases or illness. Anaesthetics, antibiotics, analgesics, antacids and antipyretics are some important types of drugs that are used.

TERMINAL EXERCISES A. Multiple choice type questions. Choose the correct answer of the following: 1. The glass that can withstand rapid heating and cooling without breaking is (a) hard (b) soda-lime glass (c) borosilicate (d) flint 2. Novocain is an (a) antipyretic (b) analgesic (c) anaesthetic (d) antibiotic 3. Chloramphenicol is an (a) antibiotic (b) antipyretic (c) antacid (d) analgesic 4. Which of the following is not a raw material required for manufacture of washing soda? (a) Lime stone (b) Ammonia (c) Slaked lime (d) Sodium chloride 5. Which of the following is a man-made material? (a) Glass (b) Wood (c) Leather (d) Silk B. Descriptive type questions. 1. What are candles made of ? 2. What are the basic materials used for the manufacture of soaps? 3. What is concrete? 4. Mention two uses of bleaching powder. 5. Name the two substances used for making nylon. 6. For printing purpose why is ink used in the form of thick paste? 7. How striking the matchstick on the side of the matchbox helps in lighting it? 8. Why is gypsum added to the powdered clinkers during manufacture of cement? 9. Mention four uses of washing soda. 10. Give two examples each of antibiotics and analgesics. 11. What is an antipyretic? Give two examples. 12. What is vulcanization process? Why is natural rubber vulcanized? 13. List the raw materials required for manufacture of bleaching powder and describe its process of manufacture. 14. How is Plaster of Paris manufactured? Give its two uses. 15. Name three plastics and give one use of each one of them. 16. What is a candle made of? Explain the process of lighting it.

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17. Differentiate between soaps and detergents. Why soaps do not form lather with hard water while detergents can? 18. List the raw materials required for the manufacture of cement. Describe the process of manufacture of cement briefly. 19. How is soda-lime glass manufactured? Describe briefly. What changes are made in the raw materials in the manufacture of optical glass and Borosil glass? How is colour imparted to glass? 20. Describe the process of manufacture of washing soda giving appropriate chemical equations. Mention two of its uses. 21. What are the monomeric units of polythene and polyvinyl chloride? Give three uses of each of these. ANSWERS TO CHECK YOUR PROGRESS 21.1 1. Natural materials: Any two of the following – wood, silk, cotton, leather and rubber Man-made materials: Any two of the following – synthetic textiles like terylene and nylon, cement, glass, plastics, dyes, soap, detergents, fertilizers, insecticides and pesticides. Candles are made from mixtures of paraffin wax and stearic acid. Soaps are sodium or potassium salts of fatty acids. No, because soap is precipitated out as salts of calcium and potassium in hard water. Safety matches Sand and water Borosilicate glass To increase the strength of cement By adding small quantities of different metals Baking soda Solvay process Bleaching powder CaSO4. H2O or CaSO4.1/2H2O Monomer is a substance whose small molecules combine with one another and make a polymer. Isoprene To make rubber elastic Polyvinyl chloride

2. 3. 4. 5. 21.2 1. 2. 3. 4. 21.3 1. 2. 3. 4. 21.4 1. 2. 3. 4.

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21.5 1. 2. 3. 4.

As an antipyretic or to get relief from fever It is an antacid used to reduce acidity Ampicillin or penicillin Analgin or analgesic

GLOSSARY Analgesics: Medicines which are used for relieving pain. Antacids: Medicines which are used to treat acidity in stomach. Antibiotics: Medicines which are used to kill bacteria, fungi and moulds. Antipyretics: Medicines which are used to bring down body temperature in high fever. Bakelite : Phenol-formaldehyde resin made by reacting phenol and formaldehyde. Baking powder: Mixture of baking soda and tartaric acid. Baking soda: Common name of NaHCO3. Bleaching powder: Common name of CaOCl2. Borosilicate glass (Borosil glass): Sodium aluminium borosilicate and can withstand rapid heating and cooling. Concrete: Mixture of cement, sand, gravel and water. Dacron: Polyester prepared by reaction between terephthalic acid and ethylene glycol. Detergents: Sodium or potassium salts of long chain sulphonic acids. Fibre glass: Mass of fine threads of glass used as an insulating material for heat, electricity and sound and reinforcing plastics and rubber. Flint or optical glass: Lead-potash lime glass which is used for making lenses, prisms, spectacles, etc. General anaesthetics: Those drugs which result in loss of sensation and consciousness in the entire body. Hard glass: Variety of glass that can withstand very high temperatures. Ink: Coloured fluid or a paste, which is used for writing or printing. Local anaesthetics: Drugs which show their effect in a limited area. Man-made materials: Materials which are prepared by man. Medicine: Substance used for treating diseases or illness. Monomers: Small molecules which make a polymer by joining one another. Natural materials: Materials which we get from nature. Nylon: Polymer of small monomeric units called amide (-CO-NH-) i.e. it is a polyamide Plaster of Paris: Common name of CaSO4 ½H2O.

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Polymers: Big molecules formed when a large number of small molecules join together. Polythene: Polymer made from ethene (CH2=CH2). Polyvinyl chloride (PVC): Polymer is made from the monomer vinyl chloride (CH2=CHCl). Reinforced Concrete Cement (RCC): Concrete that is strengthened by filling it around or over a network of steel rods and allowing it to set. Rubber: Chemically poly-cis-isoprene which is formed from the monomer isoprene. Soaps: Sodium or potassium salts of long chain fatty acids. Synthetic rubber: Made from the monomer butadiene (CH2CH.CH.CH2). Vulcanization: The rocess of heating of rubber with a small amount (1-3%) of sulphur to make it elastic. Washing soda: Common name of Na2CO310H2O

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22

Environmental Problems
You have already learnt about the environment and its components in the previous lesson, and must have realized the importance of maintaining a life-supporting environment. The environment has undergone many changes over the period of time. Population explosion in the recent times has resulted in a number of environmental problems. In this lesson, you will learn about some natural and man-made environmental problems, their causes, effects and control. OBJECTIVES After completing this lesson, you will be able to: • explain how ecological balance is maintained in nature; • list some environmental problems (natural and man-made); • explain the causes, effects and control of forest fire; • explain the impact of increasing human population on the environment; • define pollution and list its types; • list the sources, consequences and means of control of air, water, soil and noise pollution; • explain the cause and effect of global warming and ozone layer depletion; • classify and define waste into biodegradable and non-biodegradable type. 22.1 MAINTENANCE OF ECOLOGICAL BALANCE IN NATURE 22.1.1 Ecological balance The rich diversity of life that inhabits the earth helps in maintaining a balanced environment. The perfect balance between the physical environment and the living organisms in nature is called ecological balance. Herbivores eat plants, and are themselves eaten by carnivores. The number of plants, herbivores and carnivores is maintained in such a way that there are enough organisms of different species to survive. However, various human activities cause interference and imbalance in nature. Ecological imbalances may lead to: • Destruction of natural habitat of wild life. For example, cutting of forests have resulted in the disappearance of Cheetah, and a falling number of tigers in India.

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Addition of various chemicals from industries in the Kalu River near Bombay has resulted in extinction of the Bombay duck, a favorite fish of the people living in this area. Capturing or killing of lions has led to an increased number of herbivores that compete for grass. They may uproot grass, making the soil barren that may lead to soil erosion and desertification. Disturbance in the food chain, which has resulted in an enormous increase in the population of a particular types of organisms, while others may become endangered.

22.1.2 Impact of human population on the environment The population of India has crossed the figure of 1 billion and the world population is estimated to have touched the 6 billion mark. To meet the demand of food, housing and energy, environmental resources are being exploited at a fast pace. Environment has the potential to replenish most of its resources in a certain period of time. However, over-exploitation of resources and human activities have altered it leading to many environmental problems, such as: • • • • • • deforestation, destruction of wild life, air, water and land pollution, diminishing fossil fuels (oil, coal and natural gas), concentration of pesticides in alarming proportions in organisms, and depletion of ozone layer and global warming.

22.1.3 Some environmental problems While there are many things to appreciate about the nature’s bounty, there also exist a number of environmental problems. Some of them are natural processes whereas others are man-made. Alterations made by man always affect life forms adversely including man himself, in the long run. All the problems listed above in (section 22.1.2) are man-made. Growth in human population leads to putting in more land under cultivation for food production, which means more water for irrigation, more fertilizers and pesticides. Forests are cleared to create space for housing, roads, educational institutes, industries, etc. 22.1.3a Deforestation Cutting of the natural forest cover is called deforestation. You are aware of the importance of forests as a major natural resource. They provide wood for multiple use, shelter to wild life, soil conservation and rainfall. Plants take up carbon dioxide for photosynthesis. Less forests mean more carbon dioxide in the atmosphere. Cutting down of forests may lead to the following: • destruction of habitat or living place for wild plants and animals leading to disappearance and extinction of many species, • reduced rainfall in that area, • lowering of water table or depth of ground water,

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soil erosion, loss of fertility of soil and lack of vegetation leading to desertification, and increased CO2 levels in the atmosphere and global warming.

22.1.3b What can be done? You would remember that replenishment of forests in nature takes a long time. This can be done by planting trees in place of cut down forests, known as reforestation. A reforestation programme may include the following: • • • • • enforcement of strict environmental laws against felling of trees, growing of at least three new plants for every single tree that has been cut, celebrating Van-mahotsava enthusiastically, which involves mass plantation, practising silviculture, the cultivation of forest trees, as it provides wood for industries and also increases area under the forest cover, plants are given great respect and worshiped in Indian culture, this is, mainly, due to their use in providing food and fodder for animals, shelter, fire wood for cooking, medicinal properties, agricultural implements, and many more, women in the sub-himalayan region have started a movement to prevent cutting and felling of trees by surrounding the tree with arms around them, plants and their products play an important role in festivals and important occasions like marriages in our country, and the great Indian medicinal system-Ayurveda, relies on plants and their products for their excellent medicinal properties.

• • •

CHECK YOUR PROGRESS 22.1 Fill in the blanks. 1. The number of animals, such as_______________ and_____________ is falling due to cutting of forests. 2. Need for _______________ leads to felling of trees. 3. Practice of ____________ and ______________ can help in reforestation. 4. Environmental problems, such as _______________ and ______________ are a result of increase in human population. 5. The practice of cultivating forests is called ____________________ 22.2 POLLUTION 22.2.1 What is pollution? Human life includes a number of daily activities. Bathing and washing of clothes with soaps and detergents add some chemical residue to water and change its quality. Cooking of food by using firewood may give out smoke in the air. Agricultural activities may dump fertilizers and pesticides in the environment. Each activity, human or industrial, discharges some unwanted substances in the environment. The addition of unwanted substances in wrong concentration

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that has an adverse effect on organisms and environment, is called pollution. Technological growth has given new devices for human comfort but has also added substances that may have an adverse effect on life and environment. An undesirable change in the physical, chemical and biological characteristics of the environment especially air, water and land that may adversely affect human population and the wild life, industrial processes, cultural assets (buildings and monuments), is called pollution. The agents that pollute the resources or cause pollution are called pollutants. Look at the picture given below. Is this the state of environment we live in? What major sources of pollution can you identify?

Fig 22.1 Activities leading to various types of pollution

22.3 TYPES OF POLLUTION Depending upon the area or the part of environment affected, pollution may be of the following types: • Air pollution • Water pollution • Land pollution • Noise pollution 22.3.1 Air pollution We all breathe in air, we can feel, and even smell the air and say whether it is fresh or stale. The pollution in air may not be noticed until we see smoke coming out

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from some source. All human activities from cooking at home to the working of highly mechanized industries contribute to air pollution. Table 22.1 gives an idea of some major air pollutants, their sources and effects. 22.3.1a Prevention and control of air pollution At domestic level, burning of wood and dung cakes can be replaced by cleaner fuel and use of biogas (formed by the decomposition of animal waste in a biogas plant). Automobile pollution can be reduced by: • pooling of transport or use of public transport, • use of unleaded petrol and CNG, • regular tuning and servicing of the engines, and • switching off the engine at red lights or when not in use. Table 22.1: Some major air pollutants, their sources and effects
Pollutant Carbon compounds (CO and CO2) Source Automobile exhausts, burning of wood and coal Power plants and refineries, Volcanic eruptions Motor vehicle exhaust, atmospheric reaction Automobiles and petroleum industries Thermal power plants, construction activities, metallurgical processes, and automobiles Textile and carpet weaving industries • • Harmful effect Respiratory problems Green house effect

Sulphur compounds (SO2 and H2S) Nitrogen compounds (NO and N2O)

• • • • • • • • • • •

Respiratory problems in humans Loss of chlorophyll in plants Acid rain on dissolving with water Irritation in eyes and lungs Low productivity in plants Acid rain damages material (metals and stones) Respiratory problems Cancer-causing properties Poor visibility, breathing problems Lead interferes with the development of red blood cells, causes lung diseases and cancer Smog (smoke+fog) formation leads to poor visibility and aggravates asthma in patients Lung disorders

Hydrocarbons (benzene, ethylene) SPM (Suspended Particulate Matter), (Any solid or liquid particles suspended in the air, (fly ash, dust, lead) Fibres (Cotton, wool)



Following measures can reduce industrial pollution: • • installation of tall chimneys, installation of devices that do not allow pollutants to be released in the environment, such as filters, electrostatic precipitators, scrubbers etc.,

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• •

closing down or shifting of industries polluting the atmosphere, and development and maintenance of green belt with adequate width.

22.3.1b Global environmental problems i) The ozone hole: depletion of the ozone layer The ozone layer present in the earth’s atmosphere prevents the entry of sun’s harmful ultraviolet (UV) radiations reaching the Earth’s surface. Industrial use of chemicals called chlorofluorocarbons (CFCs) in refrigeration, air conditioning, cleaning solvents, fire extinguishers and aerosols (spray cans of perfumes, insecticides, medicines, etc.) damage the ozone layer. Chlorine contained in the CFCs on reaching the ozone (O3) layer splits the ozone molecule to form oxygen (O2). Amount of ozone, thus, gets reduced and cannot prevent the entry of UV radiations. There has been a reduction by 30-40% in the thickness of the ozone umbrella or shield over the Arctic and Antarctic regions.
UV radiation

(a) Ozone layer blocks UV radiation

Ozone

Oxygen Chlorine from CFC

Chlorine monoxide

(b)

Chlorine from CFC reacts with ozone to form oxygen and chlorine monoxide

(c)

The area in the ozone layer where the ozone is depleted, allows UV radiation to pass.

Fig 22.2 Depletion of the ozone layer

Depletion of ozone layer may lead to the following hazards: • Sunburn, fast ageing of skin, cancer of skin, cataract (opaqueness of eye lens leading to loss of vision), cancer of the retina (sensitive layer of the eye on which image is formed)

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• •

Genetic disorders Reduced productivity at sea and forests

Damage to the ozone layer can be prevented by: • Reduced consumption of CFCs by adopting alternative technologies (substituting air conditioning gases by non-CFCs) • Discouraging the use of aerosol containing spray cans ii) Global warming – The greenhouse effect Greenhouse is referred to as a glass chamber where plants are grown in a closed warm environment as compared to the outside temperature. This is normally practiced in cold regions on the hills. The solar radiations bringing heat (in the form of infra-red rays from the sun) are trapped inside the chamber.

Sun

Radiant energy from the sun

phere e atmos etrate th n e p s th aveleng Short w

A propo rtio is absorb n of the long wa ed by th e atmos ves phere Warm s urface ra diates e nergy

back

Earth’s surface absorbs energy........ and warms up

Fig. 22.3 Greenhouse effect

Industrialization and urbanization has lead to deforestation and release of gases, such as CO2, CH4 and N2O intoatmosphere These gases have converted the earth’s atmosphere into a greenhouse. Heat contained in the solar radiations is allowed to come in, but the heat contained in it is not returned back due to increasing concentration of CO2. As a result, the earth’s average temperature is increasing each year leading to global warming.

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Effects of global warming Although the increase in global temperature in the last hundred years has been estimated to rise by only 1 degree, it has resulted in serious consequences, such as: • melting of snow caps/ glaciers and rising of sea level, • unpredictable weather patterns, • submerging of coastal areas of the Maldives islands in the Indian Ocean, • early maturation of crops leading to reduced grain size and low yields, and • interference with the hatching of eggs in certain fish. Control measures against further global warming include reforestation, reduced burning of wood and reduced vehicular pollution. CHECK YOUR PROGRESS 22.2 Fill in the blanks. 1. Addition of unwanted substances in the environment is called ___________ 2. Automobile exhaust gives out pollutants, such as _________ and ________ 3. Increased carbon dioxide level in earth’s atmosphere leads to the phenomenon of ___________________ 4. ________________ and _________________ are examples of Suspended Particulate Matter. 5. Air pollution can be prevented by installing ___________ and ___________ in industries. 22.3.2 Water pollution Addition of undesirable substances in water is called water pollution. Water pollution could be due to natural or man-made activities. Natural sources are soil erosion, leaking of minerals from rocks, and decaying of organic matter, while man-made sources include domestic, agricultural and industrial activities. Many water sources have become a dumping ground of wastes. Water pollution is one of the main causes of human diseases in India. Any physical, biological or chemical change in water quality that adversely affects living organisms or makes water unsuitable for desired use is called water pollution. On the basis of origin, water pollution may be caused by point or non-point sources. • • Point sources discharge pollutants from specific source, for example, factories, power plants, drain pipes, and sewage treatment plants, etc. Non-point sources of pollution have no specific location but arise from a larger area, such as surface runoff from fields, construction sites, etc.

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22.3.2a Types and effects of water pollutants Let us study about the sources and effects of certain water pollutants in the following table 22.2. Table 22.2: Some major water pollutants, their sources and effects Type of pollutant Infectious agents Organic chemicals Inorganic chemicals, fertilizers Examples Bacteria, viruses, and other parasites Pesticides, detergents, oil Acids, alkalis, metals, salts Sources Human and animal excreta Agricultural, industrial and domestic waste Industrial waste, household cleaning agents, surface runoff Mining and processing of ores, power plants, natural sources Effects Water-borne diseases Biomagnification Water unfit for drinking Genetic disorders

Radioactive Uranium, thorium, materials iodine

Table 22.3: Some major disturbances in the ecosystem due to water pollution Pollutant Nitrates, phosphates, ammonium salts Animal manure and plant residues Heat Oil slick Sources Agricultural fertilizers, sewage, manure Sewage, paper mills, food processing wastes Power plants and industrial cooling Leakage from oil ships Cause Plant nutrients Effect Eutrophication

Oxygen deficiency Thermal discharge Petroleum

Death of aquatic animals Death of fish Death of marine life due to non-availability of dissolved oxygen

Fertilizers and pesticides are widely used in agriculture. You will learn more about them in lesson 32 on Agricultural practices. Their excessive use to increase agricultural yield has led to the phenomenon of eutrophication and biomagnification. 22.3.2b Eutrophication With the use of high–yielding varieties of crops, the use of fertilizers and pesticides has increased a lot. Excess fertilizers may mix with surface water and may get drained into water bodies (surface runoff). The enrichment of water with nutrients such as nitrates and phosphates that triggers the growth of green algae is called

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eutrophication. This fast growth of algae followed by decomposition depletes the water body of the dissolved oxygen. As a result, aquatic animals die of oxygen shortage.
Sewage and /or fertilizer run off from fields

Enriched nutrient content in lakes (Eutrophication)

Algae multiply giving ‘algal bloom’

Algae use up oxygen and begin to die

Decomposers (bacteria) multiply and use more oxygen

Organisms (such as, fish) die due to lack of oxygen

Fig. 22.4 Sequence of events that may occur as a result of eutrophication

22.3.2c Biomagnification Non-biodegradable pesticides, such as DDT are widely used for crop protection. Once they enter the food chain, their concentration keeps on increasing with each trophic level (steps of a food chain). As a result, accumulation of these compounds takes place in the body of top consumers over a period of time. Entry of harmful, non-biodegradable chemicals in small concentration and their accumulation in greater concentration in the various levels of a food chain is called biomagnification. Consider the following food chain. Is there any difference in the concentration of DDT in water and that of the body of the Pelican bird? Water 0.2 ppm Algae 77 ppm Fish 500-600 ppm Pelican bird (top consumer) 1700 ppm

(ppm = parts per million) DDT used in small quantities to kill mosquitoes can enter the food chain and may get concentrated in large concentration due to its non-biodegradable nature in the body of birds (top consumer). This causes adverse effects, such as weak egg shells, resulting in decreased population. Death of vultures in large numbers has been reported due to eutrophication near Bharatpur area (Rajasthan).

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High concentration of DDT has been reported in milk from cattle and mother’s milk leading to various disorders in the newborn baby. 23.3.2d Control of water pollution In order to control water pollution, following measures can be adopted: • • • minimize the requirement of water by altering the techniques involved, maximum recycling of water after treatment (purification of waste water for reuse), and limiting the quantity of waste water discharge.

CHECK YOUR PROGRESS 22.3 Fill in the blanks. 1. _________and ________ are examples of natural sources of water pollution. 2. Thermal discharge into rivers may lead to the death of ________________ 3. Presence of________and_______ in water may lead to infectious diseases. 4. Enrichment of water bodies with nutrients coming from fields is called _____ 5. Non-biodegradable wastes, such as _______ may lead to biomagnification upon entering the food chain. 22.3.3 Soil pollution and land pollution Addition of substances that change the quality of soil by making it less fertile and unable to support life is called soil pollution. Soil pollution is caused due to: • • • Domestic sources: plastic bags, kitchen waste, glass bottles, and paper Industrial sources: chemical residue, fly ash, metallic waste, and Agricultural residues: fertilizers and pesticides.

Soil erosion leads to soil degradation due to uprooting of plants (over-grazing). It leads to the loss of the top fertile soil. Application of DDT, its entry in the food chain and accumulation in top consumers is also a part of soil pollution. 22.3.3a Recycling of waste materials for ecological balance The waste generated from various sources can be categorized into two types: i) Biodegradable waste includes substances that can be degraded by microbes into harmless and non-toxic substances. Agricultural and animal wastes like leaves, twigs, hay, dung, etc. are biodegradable wastes.

ii) Non-biodegradable waste cannot be easily degraded. Aluminium cans, plastics, glass, DDT, etc. are examples of non-biodegradable wastes. Radioactive wastes produced during nuclear reactions take a long time to decay and are harmful to human beings. If a waste material is processed by some means and converted to a product, we call the process recycling. Recycling helps in efficient management of wastes and also reduces the load on natural resources. For example, recycling of plastics

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and paper, converting municipal waste into manure, and rice husk into wood particle board. Use of cow dung for the production of biogas is a good example of recycling of waste for the production of energy. 22.3.4 Noise pollution You may enjoy listening to music. But if the volume is too high you may not enjoy it any longer. It may become irritating. Noise can be simply defined as “unwanted sound”. It is generally higher in urban and industrial areas than in rural areas. Workers using heavy machinery are exposed to high noise levels for long period of work hours every day. Intensity of sound is measured in a unit called decibel or dB. The lowest intensity of sound that human ear can hear is 10 dB. 22.3.4a Sources of noise pollution The major sources of noise pollution are: • Means of transport i.e. automobiles, railways, aircrafts, etc. • Use of loud speakers, loud music system and television at public places • Industrial activities • Noisy fireworks

Jet plane taking off

Noisy group

At a party

Heavy traffic

Fig 22.5 Sources of noise pollution

22.3.4b Effects of noise pollution • Temporary loss of hearing, earache, sometimes even leading to permanent deafness • Inability to concentrate, headache • Increased blood pressure, irregular heart beat • Ringing of ears (a feeling of sound coming from within the ear in a very quiet environment) • Inability to sleep, slow recovery from sickness. • Irritability and interference in communication 22.3.4c Prevention and control of noise pollution Following steps can be taken to control or minimize noise pollution: • • • • Control the noise emanating from your radio and television. Use automobile horn only in case of emergency. Do not burn fire crackers, they are noisy and also cause air pollution. Getting all machinery and engines of automobiles properly tuned and serviced

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• • •

at regular intervals and by the use of silencers. Use of soundproof cabins and sound-absorbing materials in the walls. A green belt of vegetation is an efficient absorber of noise. Not playing loudspeakers during odd hours. It is legally banned and should be reported to the police immediately. Radioactive pollution Disintegration of atomic nuclei in some elements such as radium-224, thorium232, and uranium-235 and uranium-238 is called radioactivity. The alpha, beta, and gamma particles produced during disintegration of radioactive substances in the environment cause ionization in the living cells. This may lead to genetic/ birth defects, cancer of body parts including leukemia (blood cancer). Overexposure to X-rays may lead to cancer. Pregnant females are advised not to get X-ray done for any diagnosis. Radioactive waste produced by nuclear power plants, and nuclear weapons cause serious pollution and require careful disposal.

22.4 NATURAL ENVIRONMENTAL PROBLEMS Some environmental problems are not man-made but are caused by natural forces. Floods, cyclones, earthquakes, volcanic eruptions, hurricanes, forest fires, etc. are a few examples. These are termed as natural disasters. The government of India has set up a High Powered Committee on Disaster Management to look into various disasters and suggest the ways to cope up with these disasters. Let us discuss about some such disasters and their impacts. 22.4.1 Flood India is one of the most flood-prone countries in the world. We regularly learn about the damage caused due to floods. This is because 75% of the total annual rainfall occurs in about four months of monsoon from June to September. As a result, most of the rivers are full of water during this period. For example, as per the report of the High Powered Committee on Disaster Management in India about 1400 lives were lost, and about three lakh hectares area of land was affected due to floods is Gorakhpur and adjoining districts in Uttar Pradesh alone in 1998. On an average, about eight million hectares of land area is affected by floods annually in our country. The following steps may be taken to prevent damage due to floods: • Timely cleaning and desilting of water channels and reservoirs by civic agencies • Safe disposal of surplus run-off water from river to river and drain to drain to ensure easy flow of water • To locate buildings like public institutes, schools, offices, telephone exchange, power supply stations, railway tracks and stations, roads and residential areas etc. sufficiently above levels corresponding to floods of last few years frequency

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Making buildings flood proof by raising their levels with the use of earth fill etc. Construction of rings around villages and residential areas Identify an evacuation center in the flood-prone area so that people can move there in emergency Stocking adequate stock of material / equipments to handle floods Ensure supply of drinking water by installing hand pumps above the highest flood level and storing adequate food and water Consuming boiled water and properly cooked food at the time of floods Preventing outbreak of epidemics during floods Keep away from high-held structures like walls and electricity poles in the event of flooding Did you know? Years 1955, 1971, 1978, 1988 and 1996 were the major flood years in India. In the year 1996 alone, about 7.42 million-hectare land was submerged, 39.4 million people were affected and over 2000 people died in the floods. The estimated economic loss amounted to Rs. 1.8 billion due to 1996 floods. Source: Source book of District Disaster Management, Ministry of Agriculture, Dept. of Agriculture & Co-operation, Government of India.

22.4.2 Cyclone India has a long coastline, which is vulnerable to the tropical cyclones in the Bay of Bengal and the Arabian Sea. Cyclones are intense low-pressure systems in the form of depressions, cyclone storms, severe cyclones associated with hurricane winds, etc. There are two cyclone seasons in India, the pre-monsoon season (AprilMay) and the post-monsoon season (October-December). The states of Orissa, Andhra Pradesh, Tamil Nadu and West Bengal are the most affected states due to cyclones. Balasore district in Orissa is the most vulnerable district for cyclone landfall. You would have heard about Orissa super cyclone that occurred in the state of Orissa on October 29, 1999 at a wind speed of 270-300 km per hour accompanied by heavy rains continuously for three days. The sea surged up to 7m high and seas waves travelled up to 15-20 km in land. This resulted in heavy losses. The agriculture, livestock, infrastructure, industries and environment were badly devastated during this cyclone. Steps to be taken before, during and after a cyclone • Build houses, buildings, etc. taking cyclone safety measures. Repair doors, windows, walls and roof tops, wherever necessary, before cyclone season. Remove decaying trees or any other loosely fixed objects. Demolish unsafe buildings. • Do not go into the areas where water level is high due to rains, coastal areas and where streams or rivers flow. • Have clean drinking water. • Store extra food, such as rice, pulses, sattu, etc. • Store enough drinking water. • Keep yourelf alert and updated to the latest weather warnings.

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• • • • • • • • • • •

Keep hurricane lantern filled with kerosene, and flashlights, matchbox, candles etc. ready. In case of a cyclone, head for the proper shelter or evacuation point, keep calm and remain there until informed that you may return back to your place. When you are moving to a shelter, move your valuable articles to upper floors so that they are not destroyed. Do not keep free objects like cans, tyres and other implements as they can cause injury during strong winds. Do not touch any loose electric wire to avoid electrocution. Do not spread rumours or listen to them. Board up glass windows and provide strong suitable support to outside doors. Make provisions for children and adults who require special diets. After the cyclone has passed get yourself inoculated against diseases and seek medical care for the injured and sick. Clear the house and dwellings of debris. Report any loss to the revenue authorities.

22.4.3 Earthquake An earthquake is the shaking, rolling or sudden shock of the earth’s surface. We are aware of the serious damages caused by earthquakes to life and property, at Bhuj and Anjar near Ahmedabad and some other places in Gujarat on 26th January 2002. Latur in Maharashtra also experienced a similar natural disaster on 30th September 1993. Earthquakes are a common phenomenon. Most earthquakes pass unnoticed. Earthquakes of greater intensity shake buildings, and loosen the bricks. Falling of walls may injure people and property. Earthquakes also cause breakage of water pipes, cut electric lines, damage rail and road routes. The intensity of earthquake is related to the amount of energy released when rocks give way to the forces within the earth. It is measured with the help of an instrument known as seismograph. The intensity of an earthquake is measured on the Richter scale (invented by the scientist C.F. Richter). Following values indicate the degree of damage. Intensity on Richter scale Up to 3 5 7 Above 8 Extent of Damage No damages Cracks in old buildings Cracks in roads Falling of buildings

22.4.3a Impact of a severe earthquake Most problems from an earthquake result due to falling objects and debris because of collapse of the building, collapse of the ceiling plaster etc., and not due to the ground movement. The possible areas of impact of a severe earthquake are given below: • Damage to property

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Damage to roads, bridges, dams, etc. that may leads to loss of human and animal lives and injuries Fires due to short-circuits or other means Damage to fields and settlements (landslides) Spreading of diseases sometimes may lead to epidemics

22.4.3b Preventive measures • Construct earthquake-resistant buildings, roads, dams, bridges, etc. • At home, locate beds away from the windows and heavy objects that could fall in event of an earthquake. Make sure that overhead plaster and lighting fixtures are well secured to the ceiling. Move heavy unstable objects away from the exit doors. In the event of an earthquake Keep away from buildings, specially old and tall ones, electricity poles, wires and walls that are liable to collapse. If travelling, stop the vehicle away from buildings, walls, slopes, trees, electricity poles and wires. Move out in the open. Do not rush to doors or exits, keep calm, never use lift and keep well away from windows, mirrors and furniture. Stand under strong beams that may not fall or creep under the dining table or a strong bed. If your home is badly damaged, come out of it immediately. Collect all emergency supplies like food, water, first aid kit, medicines, flashlight or torch, candles, matchbox, clothes, etc. If you are under a building and unable to move, cover your head and body with your arms, pillows or blankets to protect yourself from falling objects. If in a multi-storyed building stay on the same floor. Do not use elevators or run towards the staircase. They may sustain damage. Check for injuries. Apply first aid. Help others who require your help. Check for fire and structural damage and clear blocked exits.



India has experienced four earthquakes of destructive magnitude (more than 8.0 on Richter scale). These are, • • • • 4th April, 1905; Kangra (8.25) January, 1934; Pusa, Bihar (8.25) 26th June 1941; Andaman (8.1) 15th August, 1950; Assam (8.6) In addition, there have been many seismic contingencies of moderate magnitude

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(6.0 to 7.0 on the Richter scale) during the last decade or so. • 20th August, 1988; Bihar (6.5) • 21st October, 1991; Uttarkashi (6.5) • 30th September, 1993; Latur (6.2) • 22nd May, 1997; Jabalpur (6.0) • 29th May, 1999; Chamoli (6.8) • 26th January, 2001; Gujrat (6.9) 22.4.4 Forest fires and their control You are already aware of the benefits we derive from forests. Full benefits of forest resources can be obtained only if timber (wood) is protected from fire, diseases and insect pests. Fire is a great threat to forests because it can cause tremendous damage in a short time. Forest fire may be caused due to: • Human negligence, by carelessly dropping lighted matchsticks • Lightening striking the dry trees • Extreme heating of rocks, especially during the dry season 22.4.4a Fire fighting Damage caused due to a forest fire can be controlled by the following means: • Remove dry litter like dying twigs, leaves etc. during summer season. • Try to put out the fire by digging a circle around it or by water, and call a fire brigade. • Move farm animals and movable goods to a safe place. • Do not throw smouldering bidi, cigarette or leave burning wood sticks around. • Do not enter a forest if it is on fire. • Inform all members of your family and others about the ways in which a fire can be caused and the methods to prevent fire. CHECK YOUR PROGRESS 22.4 Fill in the blanks. 1. Domestic sources, such as _________ and _________lead to land pollution. 2. Unwanted sound may lead to_____________pollution. 3. Noise pollution may be caused by___________ and __________ 4. Intensity of earthquakes can be measured on ____________________ 5. Vegetable peels and paper are examples of__________ waste. LET US REVISE The perfect balance between the physical environment and the living organism in nature is called ecological balance. Ecological imbalances may lead to destruction of natural habitat of wild life and loss of vegetation leading to desertification. Increased population leads to over-exploitation of resources and many

• • •

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environmental problems, such as pollution, soil degradation, destruction of wild life, etc. • • • • Trees provide wood for multiple use, shelter to wild life, soil conservation and rainfall. Cutting down of trees may lead to environmental problems. Silviculture is the practice of reforestation; it includes planting of more trees to develop forest cover. Addition of unwanted substances in the environment is called pollution. Pollution could affect air, water, soil and noise quality. Loss of air quality is called air pollution, and is caused by the addition of gaseous and particulate pollutants from domestic, vehicular and industrial sources. Human, plant and animal life are adversely affected by air pollution. Water may be polluted from domestic, agricultural and industrial sources and makes it unfit for drinking and industrial use. Uranium-235, uranium-238, and radium-224 cause radioactive pollution that may lead to genetic or birth defects and cancer. Addition of nitrates and phosphates in water leads to eutrophication, followed by algal growth, depletion of oxygen and death of aquatic animals. Non-biodegradable chemicals, such as DDT, enter the food chain in small quantities but get accumulated in higher concentrations in top consumers. This phenomenon is called biomagnification. Soil pollution includes addition of substances that reduce the fertility of the soil. Waste can be classified into biodegradable (e.g. cow dung, vegetable peels, paper, wood etc.) and non-biodegradable (e.g. aluminium cans, glass bottles, plastics, DDT etc.). Recycling of wastes, such as cow dung, paper, sewage and rice husk, into useful products help in conservation of resources. Ozone provides a protective layer against harmful ultra-violet rays coming from the sun. Excessive use of chemicals, such as CFCs used in spray cans, gas used in refrigerators and air conditioners, lead to thinning of the ozone layer. Accumulation of high concentration of carbon dioxide has led to the phenomenon of global warming (greenhouse effect), and has resulted in increased earth’s temperature. Earthquakes, floods, and volcanic eruptions are examples of some natural environmental problems. Forest fires may be caused due to human negligence; lightening and extreme rise in temperature in rocky areas, and can be controlled by removing inflammable material from fire line. TERMINAL EXERCISES A. Multiple choice type questions.

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1. Which of the following may NOT lead to air pollution? a) Carbon dioxide b) Cooking oil c) Lead particles d) Carbon monoxide 2. Growing of forests is called a) monoculture b) horticulture c) silviculture d) agriculture 3. Which of the following chemicals lead to depletion of the ozone layer? a) Carbon dioxide b) Chloro-fluorocarbons c) Nitrogen d) Water vapour 4. Which of the following can be found in the body of top consumers in high concentration? a) Nitrates b) Phosphates c) DDT d) Vitamins 5. Soil erosion can be prevented by a) use of pesticides b) deforestation c) afforestation d) excessive use of fertilizers B. Descriptive type questions. 1. Which of the following are biodegradable? Aluminum foil, paper, ballpoint pen refill, grass 2. Which gaseous pollutant has the ability to absorb infra-red radiations? 3. A chemical factory in a village discharges its waste that is rich in nitrogen, in a pond. What phenomenon do you expect to take place? 4. Leakage of gases used in refrigerators and air conditioners for cooling are not considered eco-friendly. Why? 5. A ship carrying oil from the gulf region collides with huge rocks and gets damaged. Is this just news or has some serious consequences? Give your opinion in one sentence. 6. Give the term given to replenishment of the forests from where wood can occasionally be taken for commercial use? 7. List two ways to replenish forests. 8. To set up a new industry, a large forest area had to be cut. List four ways in which the environment in that area may be affected. 9. How does production of more paper in the world contribute to ecological imbalance? Use only four key phrases to support your answer. 10. What could be a major disadvantage for man being placed at the top of the food chain? Name the phenomenon that may cause this harmful effect. 11. List any three ways in which noise from various sources can affect the well-being of a person. Suggest few methods to control noise pollution.

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12. What does ‘Global warming’ mean? Name the gas responsible for this phenomenon and why should it be considered an environmental problem. 13. It was observed that a large number of vultures were dying around a crop field. Considering the fact that vultures are top consumers, explain the phenomenon that may have caused their death in large numbers. 14. How would you classify the waste generated at home? What is the difference between the different groups? How would you manage this waste so that it causes least pollution? 15. Name the instrument used to measure the magnitude of an earthquake. Suggest some ways to cope with them in earthquake prone areas. ANSWERS TO CHECK YOUR PROGRESS 22.1 1. 2. 3. 4. 5. 22.2 1. 2. 3. 4. 5. Cheetah, Tiger Housing, construction of roads, industrialization Silviculture, mass plantation Air pollution, water pollution, global warming Silviculture Pollution CO, NO, CO , NO (any two) 2 2 Global warming/ greenhouse effect Fly ash, lead particles, dust (any two) Tall chimneys, electrostatic precipitators, scrubbers (any two)

22.3 1. Soil erosion, leaking of minerals from rocks, decay of organic matter (any two) 2. Fishes 3. Virus, bacteria, protozoa (any two) 4. Eutrophication 5. DDT 22.4 1. 2. 3. 4. 5. Kitchen waste/ glass /plastic bags/ bottles Noise Fireworks, loudspeakers, moving automobiles Richter Scale Biodegradable waste GLOSSARY

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Deforestation: Cutting of natural forest cover. Reforestation: Plantation of trees to replenish forests. Silviculture: The cultivation of forest trees to increase forest area. Silviculture provides wood for industries. Pollution: Addition of unwanted substances in wrong concentration having an adverse effect on organisms and environment. Greenhouse effect / Global warming: Increase in average global temperature due to high concentration of carbon dioxide, methane etc. that trap heat (from solar radiations). Eutrophication: Enrichment of water bodies with nutrients such as nitrates and phosphates, leading to algal growth and death of aquatic life. Algal bloom: Tremendous algal growth covering the pond surface. Biomagnification: Entry of harmful, non-biodegradable chemical in small concentration and its accumulation in higher concentration at various levels of a food chain. Decibel: Measurable unit of sound intensity. Biodegradable: Organic compounds that can be decomposed / degraded by microbes, such as bacteria and fungus. You Would Enjoy Doing the Following Activities ACTIVITY 22.1 Aim: To compare the amount of particulate pollutants emitted from different vehicles. Material required: pieces of white cotton cloth 8”x 8”, rubber bands or thread to tie. Method: Tie a piece of cloth on the exhaust of a diesel bus and another on the exhaust of a CNG bus. Remove the cloth after 2-3 days and compare the two pieces. Do you notice any difference in the colour of the cloth? Is the patch on one piece very dark? Was it tied to the diesel bus? Record your observations. A comparison can be made between the amount of particulate pollutants emitted from different vehicles. ACTIVITY 22.2 Aim: To compare the level of particulate pollutants in different areas in a city. Material required: Some samples of leaves, hand lens, old white cloth/ tissue paper Method: Pluck few leaves from a plant or tree growing near a road on which heavy vehicular traffic runs. Pluck few leaves from an area with little traffic. Compare the two samples. Observe them for particulate matter. Which of the two show more particulate pollutants on their surface? Which of the two has a shiny surface?

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Gently wipe them with cloth or tissue paper. Which leaf makes it darker? ACTIVITY 22.3 Aim : To study effects of noise pollution in different places. Method : Conduct a survey among people living in very noisy areas, such as near railway crossings, place with heavy vehicular traffic, or a construction site. Do the people living in such places show signs of adverse effect of noise pollution, such as of stress, headache, and inability to concentrate, increased blood pressure, reduced or loss of hearing? Compare these with those living in an isolated place away from the city.

23

Diversity in the Living World
When you look around you see a large variety of living things. There are all kinds of birds, trees, insects, dogs, spiders, lizards and so on. In the countryside, you would see a still larger variety of organisms. There are all kinds of crop plants like wheat, maize and sugarcane. Then, there are wild plants growing of their own like keekar. In a forest you would see strange wild animals and plants. In a pond, one can see a variety of fishes, snails, waterweeds and even some water birds. If you dig out the soil you may find earthworms, beetles, ants, etc. In the sea, there are whales, sharks, corals, sea anemones and so on. Then, there is any number of parasites (like the tapeworms or bacteria) inside our own body and inside, practically, all other animals. All these living forms show similarities indicating mutual relationships. At the same time every kind of organism is very different from the other. Such a study amounts to classifying living organisms on the basis of their wide similarities and subtle differences, in other words, the study of their diversity. OBJECTIVES After completing this lesson, you will be able to: • recognize the vast diversity in the living world both in size and complexity; • explain the need for classifying living organisms; • argue in favour of binomial nomenclature over common names with examples; • outline the 5-kingdom classification mentioning its different basis; • classify the kingdom Plantae up to divisions, giving their characteristics and examples; • classify the kingdom Animalia up to phyla giving their characteristics and examples; • classify the phylum Chordata up to classes giving their characteristic features and examples. 23.1 DIVERSITY OF LIVING THINGS IN SIZE AND COMPLEXITY 23.1.1 Variety in size Think of the following: • • There are huge trees like banyan, peepal, pine, tamarind and so on. They have profuse branches and lots of leaves. There are tall trees like palms and coconuts with almost no branches.

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• •



There are medium to small-sized plants like guava, banana, rose, sugarcane, wheat and the almost shortest lawn grass. There are animals ranging from huge elephants or still larger whales in the sea through the medium-sized cow to the small insects like butterflies or ants. A full-grown whale may weigh as much as 30 adult elephants. There are such tiny organisms like the Amoeba and bacteria, which you can see only under microscope. Hundreds and thousands of bacteria will occupy a space hardly larger than the head of an ordinary pin.

23.1.2 Variety in complexity • Human body is extremely complex with so many different organs, each composed of a variety of cells performing different tasks. The human brain coordinates the thousands of activities going on inside the body. • A bird’s body is complex in some other ways. Birds have wings supported by bones and covered by feathers. • A frog’s body is less complex than ours. Frogs have a 3-chambered heart whereas we have a four-chambered one. • Fishes have no legs; instead they have fins to swim in water. The fish heart is only two-chambered. • Amongst plants, there are trees with tough wood and those producing flowers, fruits and seeds, there are trees like the pine tree which produce seeds but no fruits. • There are plants like ferns that produce neither seeds nor fruits but they do have leaves and roots. • There are single-celled organisms as opposed to the ones having trillions of cells. • There are organisms, which have neither leaves nor any stem nor roots. They only have a network of filaments. These are the fungi. • On one hand, there are green plants that have chlorophyll and can produce their own food. On the other hand, there are non-green plants like fungi and mushrooms, which decompose organic food and straightaway absorb it. Similarly, there are animals having no mouth or food canal like the tapeworm, which absorb the predigested food from the intestines of their host. CHECK YOUR PROGRESS 23.1 1. Mention if the following statements are true (T) or false (F). (i) Mouse is the smallest animal and the banana tree is the smallest plant. T/F (ii) Some animals have no food canal. T/F (iii) Mushrooms and bread mould are non-living things. T/F (iv) Some organisms are made of just one cell. T/F

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23.2 THE NEED TO CLASSIFY LIVING ORGANISMS There are different kinds of living organisms found on the earth. Some are closely similar to each other, some are distantly similar and some are very different. Still all of them are similar in being living organisms as distinct from the non-living objects. Grouping or classifying the organisms on the basis of their similarities and differences helps us to know about them even if we have not seen them directly Classification is the arrangement of organisms into groups or sets on the basis of their similarities and differences To illustrate the concept of classification look at the organisms shown in the figure (Fig. 23.1) given below.

Fig 23.1 Some familiar living organisms

• • • •

Can you recognize all the organisms shown in the figure? Think of features common to all of them? Yes, they grow and reproduce. Can you group them into any two clear categories in some way? Yes, one way could be that some are animals and others are plants. Can you further divide the animals into two groups. Yes, one way is that some of them have bones while the others do not have them. How are the three animals (rabbit, dog and horse) similar to each other? These are hairy, they give birth to young ones, and they suckle their babies on the milk they secrete from their milk glands. If we say that the whales and bats too belong to the same group as that of rabbits and dogs, can you mention some features you would expect to find



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both in the whale and bat? These features could be giving birth to young ones and having milk glands. That was about animals in the diagram. Now let us take the case of plants. • What is common between grass, rose and the tree? They all have green leaves. • Again, how is grass different from a rose plant or a jamun, guava or any other tree? Guess your own answer. Thus, what we did in the above-mentioned exercise was a kind of classification. 23.2.1 Advantages of classification • Classification makes the study of such a large number of living organisms easy. • It presents before us the vast variety of life at a glance. • It helps us in understanding the relationships among the organisms. • It helps to give an idea of evolution. • It serves as a basis for several allied branches of biology 23.3 NAMING AN ORGANISM – BINOMIAL NOMENCLATURE The common names of organisms are variable and very often confusing. Can you think of any animal or plant, which in India is known by several names? Ask your friends what they call the common vegetable pumpkin in different Indian languages. To mention a few of such names in Hindi belt alone are ‘sitaphal’, ‘kashiphal’, ‘kumhra’, ‘petha’, ‘kaddu’, and so on. Can you think of any more names in other Indian languages or in the languages of the different countries? Communicating any scientific information throughout the world by such local names as for the pumpkin would be impossible. Hence, arose the need of evolving scientific names for uniformity. The scientific name of pumpkin is Cucurbita pepo. ACTIVITY 23.1 Ask your friends and relatives about the names of any other common animal and a common plant in a few Indian languages. Judge for yourself the relevance of using the international scientific names instead of the local ones. 23.3.1 Two part scientific names The scientific names of all kinds of organisms are composed of two parts: • the genus (group) name, and • the species (particular organism) name. For pumpkin, the genus name is Cucurbita, which is the group of cucumbers and gourds, and the species (individual type) name is pepo the particular type of the cucurbit, here the pumpkin. Carl Linnaeus started the practice of using binomial nomenclature. Species is a group of individuals having common characteristics and which can interbreed to produce fertile offspring.

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Take the example of crow. We have two types of crows. One is the common house crow found in plains around our houses. The other is the hill or the jungle crow. The two crows differ in the intensity of black colour on the neck, and in the size and shape of the beak (Fig. 23.2). Both are crows but they cannot interbreed. Thus, they are different species. Do you know? Mule is the offspring (hybrid) of a cross between a male donkey and a female horse. It is sterile and cannot reproduce. Thus, the mule is not a species.

House crow (Corvus splendens)

Jungle crow (Corvus macrorhynchos)

Fig. 23.2 Two common Indian crows

Table 23.1 Scientific names of some common animals and plants Animals
Common Name Scientific Name

Plants
Common Name Scientific Name

Man Cat Tiger Honey bee Housefly House crow

Homo sapiens Felis domesticus Felis tigris Apis indica Musca domestica Corvus splendens

Peepal Banyan Rubber plant Mango Lady’s finger Lentil (masoor)

Ficus religiosa Ficus bengalensis Ficus elastica Mangifera indica Hibiscus esculenta Lens esculenta

Usually, scientific names are given with some appropriate meaning. In the above examples, domesticus refers to home, esculenta to eating, religiosa to sacred, sapiens to wise/intelligent, etc. Thus, the two categories of the Indian crow are: Corvus splendens (house crow) (Gk. corvus: crow, splendens: shining) Corvus macrorhynchos (jungle crow) (Gk. macro: large, rhynchos: beak/snout) 23.3.2 Categories higher than the genus and the species Family: A group of two more genera (plural of genus) with common characteristics make a family. For example, lion (Panthera leo), tiger (Panthera tigris) and the domestic cat (Felis domesticus) make the family Felidae. Order: A group of related families. For example, the family of cats (Felidae) and the family of dogs, foxes, etc. (Canidae) is grouped under the order Carnivora. Class: Related orders make a class. For example, several orders like those of the tigers, cats, dogs, monkeys, bats and humans belong to the class Mammalia.

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Phylum: A phylum is the largest category with related classes grouped together. For example, the classes of mammals, birds, reptiles, amphibians and fishes together constitute the phylum Chordata. In plants, the corresponding category is named division. Kingdom: Kingdom is the largest group of organisms differentiated on very general similarities. For example, plant and animal kingdoms. CHECK YOUR PROGRESS 23.2 1. Mention if the following statements are true (T) or false (T). (i) Classification means grouping the items according to some criteria. T/F (ii) Scientific names of all species consist of three components. T/F (iii) The scientific names are written in capital letters. T/F (iv) Horse, donkey and mule are three different species. T/F (v) Classification of the organisms gives an idea of their relationships. T/F 2. Rewrite the following scientific names in their correct form: Sapiens homo, Felis Domesticus, ficus religiosa 3. Rearrange the following in their correct sequence starting from the smallest category upwards to the highest: genus, species, class, family, kingdom, phylum, order 23.4 THE FIVE KINGDOM CLASSIFICATION Until some time ago we had been classifying the organisms into two primary categories—the Plant kingdom and the Animal kingdom. But this had some serious problems, such as: • Mushrooms and the bread moulds were grouped under plants. But we know that they have no leaves and no chlorophyll. Thus, it is incorrect to consider them as plants. Many organisms like the singlecelled bacteria and Euglena (Fig. 23.3) could neither fit properly with animals nor with plants. The bacteria have cell walls (as found in all plant cells) but they have no chlorophyll. Euglena-like organisms have only cell membrane and no cell wall (like the animal cells) but they have chlorophyll (a plant characteristic).
Cell mouth Flagellum

Eye spot Contractile vacuole



Chloroplasts Nucleus

Fig. 23.3 Euglena – a single-celled microscopic organism (highly magnified)

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To overcome such problems a new scheme of classification was recommended by R.A. Whittaker (1969). This scheme of classification comprises five kingdoms instead of two. The five kingdoms according to the new system of classification are Monera, Protista, Fungi, Plantae and Animalia. The main criteria in this classification are as follows: • • • Whether the organisms are single-celled or multi-celled. Whether the genetic material (chromosome) of the cell is enclosed within a nuclear membrane or lies freely in the cytoplasm. Mode of nutrition – whether produces food (autotrophic) by photosynthesis or dependant on others, either by eating them up (heterotrophic), or sucking or absorbing the food from them (saprotrophic). Let us now study the five kingdoms one by one.



23.4.1 Kingdom Monera (bacteria) It includes bacteria and blue green ‘algae’ (not really algae). Monera are single-celled. Their chromosome material is not enclosed within a nuclear membrane. It means that they have no compact nucleus. The Monera are described as prokaryotes meaning that their nuclear material is in a primitive form (pro: primitive, karyon: nucleus). As opposed to these, all other organisms from Protista onwards, are described as eukaryotes (eu: true) meaning that they have true nucleus. Characteristic features of bacteria • Size: Microscopic, rarely more than 0.01mm in length • Cell wall: Not made of cellulose • Chromosome material: Not enclosed in a nuclear membrane Coccus • Shapes: Spherical (cocci), rod-like (Sphericals) (bacilli), or spiral (spirilli) (Fig. 23.4) • Nutrition: Absorb food from the surroundings after digesting it by pouring out enzymes • Reproduction: Mostly by division into two Bacillus • Occurrence: Almost everywhere in soil, (Rod-like) in water, outside or inside the body of plants and animals Some of the bacteria are useful such as those making curd and the vinegar. Some are used in making antibiotics. And, many are beneficial in nature as in the carbon and the nitrogen cycles.
Spirillum (Spirals)

• •

Fig. 23.4 Common types of bacteria – spherical, spiral and

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Many bacteria are harmful. They cause diseases, such as tuberculosis and typhoid. Some bacteria spoil foodstuff. 23.4.2 Kingdom Protista These are single-celled (unicellular) organisms, and have a well-defined membrane-bound nucleus. Their modes of nutrition may be quite varied. • Active feeders: Some protists like Amoeba and Paramecium (Fig. 23.5) ingest food like most animals. Very often these are also referred to as Protozoa (protos: primitive, zoon: animal). • Photosynthesizers: Some protists like Euglena (Fig. 23.3) have chlorophyll and manufacture their own food like the plants. • Reproduction: Mostly asexual reproduction by fission and some reproduce sexually. • Occurrence: Many protists live freely in water or in soil and many are harmful parasites which cause diseases. Some of the protists are pathogenic, such as Entamoeba histolytica that causes dysentery and Plasmodium vivax that causes malaria.

Paramecium

Amoeba

Fig. 23.5 Two examples of freshwater protists: Amoeba and Paramecium

Bracket Fungus

Mushroom

Yeast

Fig. 23.6 Some examples of fungi

23.4.3 Kingdom Fungi Common bread moulds (Rhizopus and Mucor), mushrooms and toadstools are some common types of fungi. Most of these are mildly or severely poisonous. • Most fungi are made of thread-like structures called hyphae (as in bread mould). The hyphae grow in the form of a mat-like structure called mycelium. • Hyphae possess rigid cell walls not made of cellulose (the cell walls of the true plant cells are made of cellulose). • Multicellular in nature. • Absorb nutrients from dead or living organisms. • Produce spores in special rounded bodies called spore heads (sporangia) as in the common bread mould. One variety of mushrooms is edible, and it is grown in mushroom culture. Many moulds grow on fruits and vegetables, such as Penicillium notatum and Aspergilllus. Penicillium was the source of the first discovered antibiotic, penicillin. Yeasts (Saccharomyces) are widely used in baking bread and in winemaking, etc. Some fungi produce diseases, such as ringworm.

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23.4.4 Kingdom Plantae • These are multicellular forms. • Many of the body cells contain the green pigment chlorophyll for photosynthesis. • Cells have a cell wall made of cellulose. Kingdom Plantae is very large. It is divided into four divisions – Algae, Bryophyta, Pteridophyta and Spermatophyta. Division Algae • Found in all kinds of water • No proper roots, stem or leaves • Derive nutrition by simply absorbing mineral nutrients from the surrounding water. • Some of the algal seaweeds may be very tall. Laminaria (Fig 23 .7) can reach a length of two meters or even more. • Some algal seaweeds that are popularly called kelp are used as sources of food for humans and cattle.

Fig. 23.7 Laminaria – an alga

Division Bryophyta You must have often seen green velvety layers growing on damp soil, or on walls or inside the flowerpots. These are bryophytes, e.g. mosses and Liverwort liverworts (Fig.23.8). Moss • Mosses are generally small. Fig. 23.8 Types of bryophytes – mosses • They possess some root-like structures but not and liverworts the true roots. • They have small green leaves. • Some of the mosses may show long slender stalks growing out from them. Each such stalk ends in a capsule full of spores. After getting discharged from the capsule and settling at suitable damp places the spores germinate to produce new plants. The liverworts grow as spreading patches of green, forked or ribbon-like structures lying flat on moist ground. The liverworts are common on the shady moist slopes of hills. Division Pteridophyta Ferns are very commonly grown in gardens (Fig. 23.9). • Ferns have a single underground stem with true roots. • Their green leaves are often quite large. • The leaves bear spores for reproduction.

Fig.23.9 Fern – a pteridophyte

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The first three divisions of Plantae, namely Algae, Bryophyta and Pteridophyta are often collectively called non-flowering plants. They do not produce any flowers or seeds. Division Spermatophyta It includes a great variety of the seed-producing plants, such as pines, mango, maize, lotus, peas, etc. These are of two types: • plants that produce seeds openly (not contained inside the fruit) (Gymnosperms), and • plants that produce seeds contained inside the fruit (Angiosperms). a) Gymnosperms (Gk. gymno : naked, sperm: seed) Gymnosperms include conifers (cone bearing plants) like the pines (Fig. 23.10). They produce naked seeds, which are not enclosed in a fruit. Fig. 23.10 The pine tree (a gymnosperm) and its cone • The pinecone consists of hardmodified scale-like leaves, which support the seeds borne on their upper surface. Many species grow on mountains and hills including the Himalayas. They constitute the conifer forests. Such forests are useful in many ways. • They provide wood for construction, packing, plywood, etc. • Provide oils, such as the turpentine oil. • The edible chilgoza is the seed of a particular species of pine (Pinus gerardiana). • Some are the sources of drugs, such as ephedrine, from the plants of the genus Ephedra. b) Angiosperms (Gk. angio: a case or vessel, sperm: seed) These are flowering plants in which seeds are always contained inside the fruit (fig. 23.11). • • Flower is a special organ in which the male and female reproductive organs are grouped together. The seed contains an embryo together with the nourishment-containing cotyledons (one in some and two in others). The angiosperms with one cotyledon are called monocots, such as grass, maize and rice. The angiosperms with two cotyledons are called dicots, such as gram, mango, rose, etc. •

• •

Fig. 23.11 An angiosperm (flowering plant)

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SUMMARY OF THE CLASSIFICATION OF THE KINGDOM PLANTAE PLANTAE [Multicellular with chlorophyll, cell wall made of cellulose] ALGAE BRYOPHYTA PTERIDOPHYTA
[Underground stem; true roots; leaves bear spores]

SPERMATOPHYTA
[Seed bearing plants]

[No proper roots, [Root-like structures; stem or leaves] no true roots; green leaflets in some]

GYMNOSPERMS [No true flowers, seeds naked, not enclosed in fruit]

ANGIOSPERMS [Flowering plants; true flowers; seeds enclosed in fruit]

CHECK YOUR PROGRESS 23.3 1. What are the three basic criteria that have been taken into consideration for the five-kingdom classification of the living organism? 2. The five kingdoms of living organisms are __________, Protista, __________, __________ and__________ (Fill in the blanks). 3. Name the kingdoms to which the following belong: i) Mushrooms __________ ii) Algae__________ iii) Ferns__________ iv) Bacteria__________ v) Flowering plants__________ 4. Name the groups of angiosperms with one cotyledon and two cotyledons, respectively. 23.5 KINGDOM ANIMALIA Animals include a vast variety of organisms, such as sponges, fishes, insects, frogs, snakes, feathery birds, and hairy mammals including humans and, so on. Some of the characteristics of all animals in general: • All animals are multicellular, eukaryotic (true nucleus), heterotrophic (obtaining food by methods other than photosynthesis) • Almost all animals move about (locomotion) in the search of food or for other needs. • Most animals possess a nervous system with sense organs.

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Animals are found in all types of places – in water, on land, in soil, and in air, many are found as parasites living either inside the body of other animals and plants or on their body. [A point to remember – The heterotrophic unicellular Protistans like Amoeba used to be described as Protozoans under the animals. But according to the new five-kingdom classification. They to no longer belong the animal kingdom.] The kingdom Animalia is very vast and highly varied. It is subdivided into nine phyla (singular: phylum). i. ii. iii. iv. v. vi. vii. viii. ix. Porifera (sponges) Cnidaria (jellyfishes, corals, etc.) Platyhelminthes (flat worms) Aschelminthes ( round worms) Annelida (earthworms) Arthropoda (insects, spiders, crabs, etc.) Mollusca (snails, oysters, etc.) Echinodermata (starfishes, sea urchins, etc.) Chordata (animals with backbone) 23.5.1 Phylum Porifera (sponges) • Most organisms are found in the sea but a few are found in fresh water. • Body consists of a hollow tube, fixed to the substratum. • A vast number of pores are present in the body wall for the entry of water carying food and oxygen and a single large opening for the exit of water. • Body is supported by a skeleton of minute spicules or special kind of fibres. Examples: Sycon, bath sponge 23.5.2 Phylum Cnidaria (hydra, jellyfishes) • Body somewhat tubular or umbrella-like with a single (digestive) cavity that has a single opening the mouth at one of the ends. • Tentacles that surround the mouth capture the prey paralyzed by their stinging cells and push it into the mouth. The same mouth throws the undigested left out food out of the body again. Some members like the corals develop hard skeleton of calcium carbonate. • Reproduction is by budding as well as by sexual method.

Sycon

Bath sponge

Fig. 23.12 Examples of Porifera

Sea anemone

Hydra

Jelly fish Sea coral

Fig. 23.13 Examples of Cnidaria

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Hydra is a fresh water form found usually attached to the submerged rocks and plants in lakes, ponds and streams. It reaches a length of about 1cm when fully extended. 23.5.3 Phylum Platyhelminthes (flat worms) • Small, soft, flattened unsegmented worms • Alimentary canal with only a single opening, the mouth or no mouth at all. Mostly parasites, either external or internal, but a few are free-living forms found in the sea or in fresh water (Fig. 23.14).
Liver fluke Tapeworm



Fig. 23.14 Examples of Platyhelminthes
Mouth Exeretory pore

Examples: Liver fluke (in the liver of sheep), tapeworm (Taenia sp.) which is a parasite of the human intestine in case of non vegetarians who eat pork or beef), Planaria (freeliving aquatic form) (ctiofig. 23.14). Tapeworms appear to be segmented, but in reality they are not. In them, new segments continue to add on the front in the neck region while the old ones at the back continue to shed one after another. 23.5.4 Phylum Aschelminthes (round worms) • Long cylindrical and unsegmented body • Alimentary canal open at both ends (mouth and anus) • Mostly parasitic but some live freely in the soil Examples: Ascaris (Fig. 23.15) is found in human intestine. Eelworm is a parasite of potato plant. 23.5.5 Phylum Annelida (segmented worms) • Long cylindrical body divided into ring-like segments • Well-developed digestive system, alimentary canal open at both ends (mouth and anus)

Cloaca

Curved tail Anus

Fig. 24.15 Ascaris – an Aschelminth

Earthworm

Examples: Common earthworm Pheretima posthuma (Fig. 23.16) found in the burrows in damp soil, and the common leech Hirudinaria medicinalis found in ponds but readily sticks to the body of cattle and even human beings.

Leech

Fig.23.16 Examples of Annelida

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23.5.6 Phylum Arthropoda (joint-legged animals) • Jointed appendages, one pair each on some or all body segments •
Crab

Body covered by a hard chitinous skeleton During the growth period the exoskeleton is shed off (moulting) and a new one is produced



Millipede

This is the biggest phylum with four major kinds of organisms. i. Insects, such as cockroaches and butterflies, have three pairs of legs and usually two pairs of wings. Spiders and scorpions have four pairs of legs. Prawns and crabs have many pairs of legs. Centipedes and millipedes have paired legs on each body segment.

ii.
Butterfly

iii. iv.

Scorpion

23.5.7 Phylum Mollusca (snails, oysters) • Soft unsegmented body enclosed in a hard calcareous shell • Muscular foot for creeping or for other kinds of locomotion

Fig.23.17 Examples of Arthropoda

Examples: Snails, slugs, oysters, and octopuses and cuttlefish (foot divided into arms for swimming). 23.5.8 Phylum Echinodermata (starfishes) • Usually thorn-like spines on the body •
Water snail Octopus

Fig.24.18 Examples of Mollusca

Body radially symmetrical having similar parts (usually five) arranged regularly around a central region

Examples: Starfish, brittle star, sea urchin, sea cucumber, etc.

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23.5.9 Phylum Chordata (animals with backbone and some others) • Possess a flexible rod-like notochord along the mid-dorsal axis of the body in the embryos of all chordates including humans. The notochord is later replaced by a backbone (vertebral column). • Possess a hollow dorsal nerve cord. • Paired gill slits (in the pharynx) present either throughout life or at least in the embryonic stages of all chordates. • All possess a tail extending behind the anal opening. (In some cases, as in humans, the tail in the embryo gets ‘lost’ before birth). The phylum Chordata is divided into three subphyla. a) Subphylum Urochordata (uro: tail)

Starfish

Sea urchin

Brittle star Sea cucumber

Fig.24.19 Examples of Echinodermata

Notochord is confined to the tail region only and, that too, in the larval stages only. All forms are marine. Example: Herdmania b) Subphylum Cephalochordata (cephalo: head) Notochord extends up to the front end of the body. No head is formed. Single example: marine Amphioxus c) Subphylum Vertebrata Organisms possess a vertebral column (notochord replaced) and the head is well differentiated. Vertebrata is the largest group in Chordata. It is divided into five very distinct classes. a) Pisces (fishes) b) Amphibia (frogs) c) Reptilia (lizards) d) Aves (birds) e) Mammalia (animals with milk glands) i. Class Pisces (fishes) • Body covered with scales • Have fins and no limbs • Breathe by gills, no lungs • 2-chambered heart Fishes are mainly of two types – cartilaginous fishes and bony fishes. Cartilaginous fishes, such as the sharks, have their skeleton made of cartilage and their gills are exposed (not covered by any gill-cover).

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Amphibian Mammal Bird

Reptile Fish

Fig. 23.20 Examples of the five classes of Chordata

Bony fishes, such as rohu, catla, herring and trout, have their skeleton made of bones and their gills are covered by a gill-cover (operculum). ii. Class Amphibia (frogs, toads) • Live both in water and on land • Smooth moist skin without scales • Aquatic respiration by skin (when under water) as well as by lungs (when on land) • All larval stages as well as some adults breathe by gills. • Heart 3-chambered • Cold blooded (body temperature changes with that of the surroundings) • Ear drum (tympanum) on the surface of the skin • Eggs laid in water, no eggshell, larvae undergo metamorphosis iii. Class Reptilia (lizards, crocodiles) • Completely adapted to living on land, some secondarily aquatic (like the turtles) • Cold blooded (therefore live in warmer regions only) • Eggs with a leathery (non-calcareous) shell • Breathe by lungs right from birth • Rough horny scales on the skin • 3-chambered heart, but the ventricle is partially divided in crocodiles • Ear drum sunken into a tubular depression Examples: Lizards, snakes, tortoises, crocodiles, gharial, etc. (Gharial is found in India and in some adjoining countries of the east.) iv. Class Aves (birds) • Body covered with feathers • Only the two hindlegs present, forelegs are modified into wings. • Scaly legs • 4-chambered heart

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• • •

Bones with air cavities to lighten the body weight for flight Warm blooded (maintain constant body temperature, usually 380- 410C) Lay eggs with calcareous shell

Examples: Pigeon, sparrow, crow, owl, penguin, ostrich, emu, etc. v. Class Mammalia (mammae: breasts) • Most mammals give birth to young ones. Very few mammals lay eggs. • All feed their babies on the milk produced in their milk (mammary) glands • Possess hairy skin • Have projecting external ears (pinna) • Testes are external contained in the scrotal sacs • 4-chambered heart • Warm-blooded • Mature red blood cells without nucleus (except only in camels, a surprising situation difficult to explain). Examples: Cat, dog, cow, sheep, rat, bat, seal, monkey, apes and man CHECK YOUR PROGRESS 23.4 1. Name the phylum of each of the following animals: i) Sponge_____________ ii) Earthworm_____________ iii) Tapeworm_____________ iv) Cockroach_____________ v) Starfish_____________ 2. Name the phylum showing the following characteristics: i) Body flattened and the food canal with only one opening__________ ii) Body divided into ring-like segments and the food canal is open at both ends_____________ iii) Soft body enclosed in a hard calcareous shell_____________ iv) Body supported by a flexible rod like notochord_____________ 3. Tick-mark the correct matching pairs of an example and its Phylum / Class. i) Frog – Chordata ii) Whale – Pisces iii) Crocodile – Amphibia iv) Bat – Mammalia v) Pigeon – Reptilia • • LET US REVISE The living world varies in size from the tiny microscopic organisms to the very huge ones like the elephant and the whale. Organisms are varied in structure, made of either just one cell performing all the activities or of numerous highly complex tissues with different functions.

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• • • • • • •



• •



Classification is the arrangement of organisms into groups or sets on the basis of similarities and differences. Classification helps us in understanding the inter-relationships among the organisms leading to the idea about of evolution. Species is the lowest category in the classification and the kingdom is the highest with family, order, class and phylum in-between. Species is a group of individuals that can successfully breed among themselves to produce fertile young ones. Every organism is given a scientific name (binomial nomenclature) consisting of two components (genus and species). Scientific names of living organisms are universal and they remove any confusion arising from the local names in the different languages. The five-kingdom classification is based on three main criteria : whether the organisms are single-celled or multicellular, whether the genetic (chromosomal material) is enclosed by a nuclear membrane or not, whether the nutrition is of autotrophic (photosynthetic) type or of heterotrophic or saprotrophic (eating, sucking, or absorbing) type. The five kingdoms are: Monera (single-celled, no nuclear membrane) containing bacteria, Protista (single-celled, nuclear membrane) with forms, such as Amoeba and Paramecium, Fungi (no chlorophyll) with forms like bread mould and yeasts, Plantae (photosynthetic) that consist of the divisions Algae, Bryophyta (mosses), Pteridophyta (ferns) and Spermatophyta (seedbearers), and Animalia that includes all animals from sponges up to humans. The Spermatophyta are subdivided into Gymnosperms (naked seeds, and no fruit) and Angiosperms (seeds contained in the fruit). The kingdom Animalia includes nine phyla: Porifera (sponges), Cnidaria (hydra, jellyfishes), Platyhelminthes (flat worms), Aschelminthes (round worms), Annelida (earthworms), Arthropoda (prawns, spiders, insects), Mollusca (snails), Echinodermata (star fishes), and Chordata (animals with backbone) The phylum Chordata is composed of five classes: Pisces (fishes), Amphibia (frogs), Reptilia (lizards), Aves (birds) and Mammalia (cow, dog, monkey, man).

TERMINAL EXERCISES A. Multiple choice type questions. 1. Which one of the following names is written in the correct form? a) PANTHERA TIGRIS b) Mangifera Indica c) Homo sapiens d) ficus religiosa 2. Mushrooms belong to the kingdom a) Protista b) Spermatophyta

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c) Pteridophyta d) Fungi 3. Presence of hyphae and mycelium is a characteristic feature of one of the following kingdoms: a) Fungi b) Protista c) Monera d) Plantae 4. The seeds of angiosperms and gymnosperms differ in the aspect that: a) Angiosperms do not produce seeds but gymnosperms produce seeds. b) Gymnosperms do not produce seeds but angiosperms produce seeds. c) Angiosperms have naked seeds but gymnosperms have seeds enclosed inside the fruit. d) Gymnosperms have naked seeds but angiosperms have seeds enclosed inside the fruit. 5. The alimentary canal has a single opening in one of the following: a) Aschelminthes b) Annelida c) Arthropoda d) Platyhelminthes B. Descriptive type questions. 1. With the help of any two examples describe how the five-kingdom classification is better than the old system of just two kingdoms (plants and animals). 2. Match the items in column I (organisms) with their group in column II (draw connecting lines). Underline the items that do not match. Column I (Organisms) Fern Dog Yeast Fish Pine Mushroom Bacteria Sponge Spider Column II (Group) Arthropoda Monera Bryophyta Amphibia Pteridophyta Porifera Reptilia Mammalia Fungi

3. Why are scientific names of the living beings preferred over the local names? 4. Write two identification characteristics of each of the following: i) Chordata ii) Arthropoda iii) Pteridophyta iv) Monera 5. Given below is a list of some organisms each followed by three-characteristics/

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classification etc. Identify the correct one in each case and underline. i) Amoeba – nuclear membrane, Monera, segmented ii) Earthworm – Arthropoda, Chordata, Annelida iii) Pine – cone, flower, parasite iv) Bread mould – chlorophyll, spores, Bryophyta v) Whale – Pisces, milk glands, gills vi) Bacteria – Protista, Pteridophyta, Monera 6. List any three characteristics of the phylum Chordata. Classify it further into classes. 7. Differentiate between the following: i) Gymnosperms and Angiosperms ii) Amphibia and Reptilia iii) Protista and Fungi iv) Mollusca and Annelida 8. List the characteristics of Kingdom Plantae. Classify it into its various subdivisions. ANSWERS TO CHECK YOUR PROGRESS 23.1 1. 23.2 1. 2. 3. 23.3 1. 2. 3. 4. 23.4 1. 2. 3. (i) F, (ii) T , (iii) F, (iv) T

(i) T , (ii) F, (iii) F, (iv) F, (v) T Homo sapiens, Felis domesticus, Ficus religiosa Species, genus, family, order, class, phylum, kingdom Whether single-celled or many celled, nucleus or no well defined nucleus, autotrophs or heterotrophs or saprotrophs. Monera, Fungi, Plantae, Animalia (i) Fungi, (ii) Plantae, (iii) Plantae, (iv) Monera, (v) Plantae Monocots, dicots Porifera, Annelida, Platyhelminthes, Arthropoda, Echinodermata Platyhelminthes, Annelida, Mollusca, Chordata (i) and (iv)

GLOSSARY Classification: Arrangement of organisms into groups or sets on the basis of their similarities and differences. Class: A group of related orders. Family: A group of two or more genera with common characteristics. Kingdom: A group of organisms differentiated on very widespread similarities. Order: A group of related families. Phylum: A group of related classes. Species: A group of individuals having common characteristics that can interbreed to produce fertile offsprings.

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24

Cells, Tissues and Organs The Building Blocks of the Body
If we pull out or pinch off any tiniest bit from any part of a plant or an animal and examine it under microscope we will find hundreds and thousands of unit structures of well-defined shapes – the cells. In fact, every organism including human beings starts life only as a single microscopic cell. This single cell undergoes repeated divisions to produce more and more cells, which acquire different shapes to suit a variety of functions. OBJECTIVES After completing this lesson, you will be able to: • recognize that cell is the unit of structure and function of all forms of life; • draw and describe the structural details of a cell that are common to both plant and animal cells and state their functions; • differentiate between a plant cell and an animal cell; • recognize that basic functions of life occur both at the level of a cell as well as an organism; • explain the need for cell division as related to growth, development and reproduction; • describe and draw sketches of the different stages of mitosis in an animal cell; • explain briefly the role of meiosis (no description is required); • give a brief account of animal tissues – epithelial, connective, muscular and nervous tissues; • differentiate between protective (covering) and conducting tissues in plants (excluding finer details); • trace the increasing complexity of organization of life from cell to organ, to organ system and to the organism. 24.1 CELL: THE UNIT OF STRUCTURE AND FUNCTION OF LIFE All plants and all animals, whether tiny or large, are made of small units – the cells. Every function of the body is basically the outcome of the activity of the cells comprising the body.

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24.1.1 Function of cells in living beings • Growth: Growth is the result of new cells being produced by cell division. Any substance added to increase the bulk of the body of the organism is also due to the activity of the cells. • Reproduction: No matter how an organism reproduces, whether sexually or asexually, it is again the cells that carry out the process. The male sperm is a cell and so is the female egg. When you grow a new plant from a cutting, such as rose or sugarcane, it is again the cells in the cutting that re-divide and result in growth of a new plant. 24.1.2 Functions of cells in plants • Absorption of water and minerals from soil: Even the tiniest parts of the root are made of cells and these cells absorb water and minerals from the soil. • Production of food (starch): The food (starch), which the plant produces, is through the activity of the green cells of the leaf. The green cells contain a green pigment, chlorophyll, which traps sunlight for food synthesis. • Produce colourful flowers: The colour of flowers is due to the pigments developed inside the cells. 24.1.3 Function of cells in human beings • Movement: The movement of the limbs or the body as a whole (locomotion) is the result of contraction of muscle cells. • • • Tasting food while eating: Taste of any food that you have, is the result of the taste cells (sensory) of your tongue. Digestion of food and its absorption: The enzymes produced by cells of the digestive glands digest food, and the intestinal cells absorb it. Transport of oxygen in the body: The oxygen, supplied to the body parts, is absorbed by the red blood cells from inside the lungs and then transported to all parts of the body.

Similarly, you think of any activity inside a plant, an animal or a human being, you will find that there is always a cell carrying it out. CHECK YOUR PROGRESS 24.1 1. Mention whether the following statements are true (T) or false (F). i) Skin is made up of cells. T/F ii) Tears are secretions of the tear gland cells. T/F iii) Bones are made up of hard material without any cells. T/F iv) Petals have no cells. T/F v) Sperm is a cell but the egg is not. T/F 24.2 STRUCTURE OF A CELL All kinds of cells, whether in plants or in animals, contain the same basic structures. Each such structure also has the same basic function. A generalized cell consists of three main parts: plasma membrane, cytoplasm and nucleus (Fig. 24.1).

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a) Plasma membrane: It is the outermost membrane enclosing the cell. • It holds within and protects all the cell contents. • It is very thin and flexible. • It is a living membrane full of activity. • It allows some substances to pass inward or outward while preventing the others. Thus, it is selectively permeable.

Chloroplast Vacuole Mitochondrion Cell membrane Cytoplasm Nucleolus Nucleus Golgi bodies Lysosome Endoplasmic reticulum Cell wall

Fig. 24.1 A generalized animal cell

b) Cytoplasm: Cytoplasm is the living part of the cell enclosed by the plasma membrane excluding the nucleus. • It contains several structures that behave like ‘mini-organs in the cell’, each performing a particular task. Such structures are called organelles meaning ‘little organs’. An organelle is any structure in a cell in which certain functions and processes are localized. c) Nucleus: The nucleus is a small ovoid or spherical mass located somewhat in the centre of the cytoplasm. • This is the largest organelle. • It is bounded by a nuclear membrane. • The nuclear membrane surrounds a semi-solid substance, the nucleoplasm. • The nucleoplasm contains a network of darker fibres (chromosomes) called chromatin network. • Nucleus contains one or more rounded nucleoli (sing. nucleolus). Functions of the nucleus i) The nucleus coordinates the activities of the entire cell. ii) It plays an important part in cell division. iii) It contains genes, which determine the inheritance of characteristics from the parents to the offspring. 24.2.1 Organelles in the cytoplasm The main organelles found in the cytoplasm are: endoplasmic reticulum, ribosomes, mitochondria, golgi bodies, lysosomes, centrosome (in animal cells only) and plastids (in plant cells only) (Fig. 24.2). a) Endoplasmic reticulum (ER): An irregular network of double membrane distributed in the entire cytoplasm. • It provides a supportive framework to the cell. • It helps in the transport of various products from one part of the cell to the other or from within the cell to the outside.

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Cell membrane

Vacuole

Ground substance

Mitochondrion Centrioles Nucleolus Nuclear membrane Lysosome Golgi complex Secretory granules

b) Ribosomes: These are granules either scattered freely in the cytoplasm or attached to the endoplasmic reticulum. • Ribosomes are the sites for the synthesis of proteins. c) Mitochondria: These are minute bodies scattered in the cytoplasm. • They carry out cellular respiration. • They breakdown glucose by using oxygen and release energy in the form of a compound, adenosine triphosphate (ATP), for the activities of the cell.

Ribosomes

Fig. 24.2 A generalized animal cell showing finer details (organelles) as observed under an electron microscope.

d) Golgi bodies (also called Golgi apparatus or Golgi complex): Very small vesicles of various shapes generally located near the nucleus (similar structures in a plant cell are called dictyosomes). • These produce secretions of the cell such as enzymes, hormones, etc. e) Lysosomes: These are small vesicles of different shapes. • They contain digestive enzymes, which destroy and digest the worn out cell organelles or any foreign substances like bacteria that may enter the cell. • They help to digest stored food during the starvation of the cell. • Too many damaged cells are rapidly destroyed by the cell’s own lysosomes – a kind of self-destruction and hence these are also known as suicide bags. f) Centrosome (in animal cells only): It is located near the nucleus and contains 1 or 2 centrioles. • It initiates and regulates cell division. g) Plastids (in plant cells only): These are of various shapes – oval, spherical or disc-like. The most common ones are chloroplasts that contain chlorophyll. 24.2.2 Parts other than the organelles The vacuoles and granules are the non-living parts of a cell. a) Vacuoles: These are clear spaces with water or other substances in solution. • Plant cells often have several and more number of large-sized vacuoles while the animal cells have smaller and fewer ones. • Vacuoles help in storage of water and other substances.

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b) Granules: These are small particles, crystals or droplets. • Granules containing starch, fat, etc. serve as food for the cell. Table 24.1 : Basic differences between plant and animal cells Plant cell (special features not found in animal cells) Cell Wall: Rigid protective layer present outside the plasma membrane. • Chiefly made of cellulose • Supports and protects the cell • Freely permeable allowing substances to pass through in and out without any hindrance Chloroplasts: Oval-shaped green structures containing chlorophyll • Trap sunlight for preparing food (starch) Vacuoles: Very big and numerous and act as storage areas Animal cell (special features not found in plant cells) Centrioles: 1 or 2 centrioles enclosed in a centrosome located just near the nucleus, which participates in cell division

CHECK YOUR PROGRESS 24.2 1. Mention whether the following statements are true (T) or false (F). i) Cell division is necessary for the movement of the body. ii) Cell membrane permits inflow and outflow of all molecules. iii) Chloroplast and not chlorophyll is an organelle. iv) Ribosomes are often called suicide bags.

T/F T/F T/F T/F

2. Fill in the blanks. i) The cell wall is mainly formed of____________ ii) The _________ is selectively permeable. iii) Centrioles are found only in ______________ cells. iv) Inside nucleoplasm is the _____________network of _____________ 24.3 CELL DIVISION – THE NEED TO PRODUCE NEW CELLS New cells need to be produced for many reasons. a) Growth: To increase the number of cells for the growth in size of the organs as well as that of the body as a whole. b) Replacement: To replace the cells that are normally dying. For example, 20 million red blood cells in our body are destroyed every minute. These are replaced by new cells formed by the division of their parent cells in the bone marrow. Similarly, dead skin cells on the body surface are being replaced regularly by new cells.

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c) Repair: There may be cuts or injuries in the body. New cells produced by cell division of the bordering cells fill up the gap to repair these cuts or wounds. d) Reproduction: To produce sex cells in which the number of chromosomes is reduced to half of that of the normal body cells. When the sex cells (egg and sperm) fuse, the normal number of the chromosomes is restored. 24.3.1 Types of cell division There are two types of cell division. • • Mitosis: Cell division leading to growth and repair Meiosis: Cell division leading to the production of sex cells

a) Mitosis: Mitosis is the kind of cell division that occurs in all body cells, while meiosis takes place in sex cells only. Its major events are largely similar in both animal and plant cells but for the sake of simplicity, we will describe mitosis in an animal cell. The sequence of events in mitosis is as follows: • The chromosomal material (chromatin network) inside the nucleus condenses to form the chromosomes (the number specific for the species, e.g. 46 in humans) The centrosome (in animal cell) divides into two equal parts called centrioles, each of which migrates to the opposite poles of the cell. A spindle of ray-like fibres is formed between the centriole. The chromosomes duplicate themselves to form chromatids. Each chromosome consists of two chromatids held by a centromere. The nuclear membrane disappears. The chromatids (daughter chromosomes) of each chromosome separate from each other, move to the opposite poles of the spindlechromosomes then turn into a network of chromatin threads at the two poles. The nuclear membrane reappears around each of the two new clusters of the chromatin material. A furrow appears in the cell membrane at the two sides in the middle of the cell, which deepen to divide the parent cell completely into two new daughter cells.

• • • • •

• •

Two main differences in mitosis in a plant cell and an animal cell • In plant cells, there is no centrosome and no centrioles inside it. However, the spindle is formed. • Upon the completion of mitosis, the cytoplasm in plant cell does not constrict (furrow is not formed). Instead, a cell plate or a new cell wall is laid down in the cytoplasm at the middle of the cell. It divides the original cell into two daughter cells.

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ANIMAL CELL Cytoplasm Nucleus Chromatin threads A Centrosome Nucleus Nucleolus Interphase (Resting stage) Interphase (Resting stage) Centromere B Centrosomes moving apart Early prophase Chromosomes lie along the equatorial plane of the cell C Chromatin threads Nucleolus PLANT CELL

Chromatids Early prophase

Metaphase Chromatids separate and move to opposite poles D

Metaphase

Anaphase Cell plate forming

Anaphase

E

Daughter chromosomes Telophase

Furrow in cytoplasm Telophase

F

Cytokinesis Daughter cells Daughter cells

Fig. 24.3 Comparison of mitotic division in a plant cell and an animal cell

b) Meiosis: This type of cell division occurs in cells involved in sexual reproduction. Meiosis takes place in reproductive organs, such as the testis and the ovary, in animals that produce eggs and sperms, and in the anthers and the ovary, in flowering plants to produce pollen grains and the ovule, respectively. During meiosis the number of the chromosomes is halved in the resulting sex cells so that when the male cell and the female cell combine during fertilization, the normal number of chromosomes in the species is restored.

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A

Chromosomes

2n

B

Chromosomes in homologous pairs

Stages in meiosis Broadly, meiosis is completed in two phases or stages (Fig. 24.4). Stage I: A reduction division that involves production of two cells with half the number of chromosomes in each. Stage II: The immediately following second division is mitotic and produces four cells at the end.

E

Characteristic features of the first meiotic division • Chromatin fibres condense into Splitting of C chromosomes. chromosomes (still in pairs) • The chromosomes arrange in matching (or homologous) pairs . A matching pair 2n means one chromosome having been First division received from the mother and the (chromosome D pairs separated) corresponding one received from the father. n n • Each chromosome in such a pair is made Second division of two chromatids. Thus, each pair of (mitotic type) chromosomes is now a group of four n n n n chromatids. Fig. 24.4 Meiosis: The cell division that • The nuclear membrane disappears, the leads to formation of the sex cells homologous chromosomes separate and move apart. Thus, the pairs are broken. • The cytoplasm divides into two cells, each of which now has half the number of original chromosomes. At the same time, each chromosome is already split into two chromatids still held together by a centromere. • The two chromatids of each chromosome in the two cells separate and move apart to become surrounded by nuclear membranes and thus, four cells are formed.
2n

• • •



Meiosis in a human cell The 46 chromosomes organise in homologous pairs (23 pairs). Each pair breaks, but each separated chromosome is already split into two chromatids that are still held together. The cell divides into two daughter cells (this is the first meiotic division which actually is a reduction division) and now each of the two resulting cells has only 23 single chromosomes. Each of the two resulting cells undergoes the second (mitotic) type of division in which the two chromatids of each of the 23 chromosomes separate apart (just as in mitosis) and the two cells divide to form four cells (these are the sex cells).

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CHECK YOUR PROGRESS 24.3 1. List the four basic needs of organisms for which cell division is necessary. 2. Name the type of cell division that occurs during the following events: i) repair of skin and injury ii) formation of eggs and sperms in animals iii) increase in the length of the stem in plants 24.4 SPECIALIZATION OF CELLS – FORMATION OF TISSUES Most organisms are made of more than one cell, actually in millions and millions. These cells are variously specialized in their shape, size and function. Such specialized cells are called tissues. Groups of similar cells with similar functions are called tissues. All animals and plants have a large variety of tissues. Here, we shall describe the more common types of these tissues. 24.4.1 Animal tissues Animal tissues are grouped under four main categories: epithelial, connective, muscular and nervous tissues. a) Epithelial tissue • Thin protective layer (or layers) of cells • Generally located on the outer surface of the body, on the surface of the internal organs and the lining of the body cavities There are three distinct types of epithelial tissues (Table 24.2, Fig. 24.5). Table 24.2 Different types of epithelial tissues
Type Nature of cells Example/location Cells of the outermost layer of skin Function Protection of underlying parts in the body from injury, harmful substances and from drying up Secretion

Squamous Thin plates of somewhat epithelium hexagonal or irregular cells

Cuboidal epithelium

Thick and cuboidal cells

Columnar Tall-elongated cells epithelium arranged in a straight or folded row. At some places these cells have cilia at their free ends (ciliated columnar epithelium)

Some parts in kidney tubules and in glandular ducts Inner lining of the stomach and the intestine Inner lining of trachea (wind pipe)

Secretion, absorption

Lashing movement of cilia pushes the material forward

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Squamous

Cuboidal

Columnar

Ciliated columnar

Fig. 24.5 Different types of epithelial tissue

b) Connective tissue • Connect various tissues and organs or support them to keep them in position. The various types of connective tissues are given below (Table 24.3, Fig. 24.6). Table 24.3 Subcategories of connective tissue
Subcategory Nature of tissue Example/Location Tendon Ligament Adipose (fat) tissue Function Fibrous tissue Cells usually separated from one another by intercellular spaces. This space is filled with solid or liquid material Non-porous tissue, Cartilage thickened intercellular substance Semi-transparent and elastic Hard and porous, consists Bone of both living cells and rigid mass of non-living salts Contains both cellular and Fluid liquid parts connective tissue Connect muscle to bone Connect two bones Packing and binding of most organs, store fat In nose, ears, walls of Provide support and windpipe and at ends strength of long bones

Ribs, thigh bone, Provide support and backbone, etc. strength, help in movement Blood and lymph Transport of gases and chemical substances, protection from disease- causing germs

Cell Matrix

Matrix

Fibres

Nucleus Cell Cartilage

[
(b)

Empty Lacuna

(a)

Fig. 24.6 Types of connective tissue (a) fibrous tissue (b) cartilage

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Haversian Canal Concentric rings

Bone Bone cell Bone cell

Fig. 24.6 Types of connective tissue (c) Bone

c) Muscular tissue • Brings about all kinds of movements in the body. The various subcategories of muscular tissue are listed in Table 24.4 (Fig. 24.7). Table 24.4 Subcategories of muscular tissue
Subcategory Striped or striated (Voluntary) Nature of muscle Occur in groups of fibres, cells are multinucleated, show bundles of light and dark bands Slender tapering cells Example/Location Function Muscles of arms, legs, face, Cause movements that are under the neck, etc. control of will

Unstriped or unstriated (Involuntary)

Cardiac (heart Specialized striped muscles, short muscles) and branched (Involuntary)

Wall of blood vessels, urinary bladder, uterus, etc. Iris muscles regulate the size of pupil of the eye Only heart muscles

Movement of the parts or contents of the part not under the control of will Contract without will and without any outward stimulation, do not get tired

Nucleus Sarcolemma

Dark band Light band Nucleus

(c) (a) (b)

Fig. 24.7 Different types of muscular tissue (a) Striped muscle, (b) Unstriped muscle, (c) Cardiac muscle

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d) Nervous tissue Nervous tissue constitutes the nervous system (brain, spinal cord, sense receptors etc.) The nerve cells are called neurons. These are highly specialized. Each nerve cell consists of a cell body called cyton (or perikaryon) containing a nucleus in the centre and one or more elongated hair-like extensions called dendrons (or dendrites). One of these extensions, the axon, may be very long. It is usually covered by a medullary sheath, which is not continuous, the gaps in it are called the Nodes of Ranvier.
C Y T O N Nucleus Cytoplasm

Dendrons Neurilemma Myelin sheath Nucleus A X O N

Branch

Node of Ranvier

Terminal branches

Fig. 24.8 The nervous tissue–A nerve cell (neuron) and a nerve

A bundle of axon fibres forms a nerve. The dendrites carry the impulse (message) towards the cell while the axon carries the message away from the cell. The function of nervous tissue is perception of the stimuli from the environment and responding to them. 24.4.2 Plant tissues Plant tissues are basically of two types – meristematic and permanent. a) Meristematic tissue: It is found at the growing points of a plant such as at the tips of the roots, stems and branches. The chief characteristics of meristematic tissue are as follows: • The cells are small and have large nuclei. • The cells divide actively and add new cells to the plant. • The new cells produced are transformed into mature permanent tissues. b) Permanent tissue: It is made up of cells, which have lost their ability to multiply. According to their function, the permanent tissues are of three types. i. Protective tissue: This tissue is found on the surface of plant organs like the leaves, stem, roots, etc. The cells have thick walls. For example,

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ii.

iii.

epidermis (outermost layer of cells) of leaves, which secretes a waxy Sieve cell waterproof covering. Phloem Supporting tissue: It provides parenchyma support to various parts of the plant. cell It is of several types, such as • cells that fill up the interior of Companion cells potatoes, which store food, Seive plate • cells that provide temporary support to the plant, such as in the pith (central region) of roots A and stem, and those that fill up a) Longitudinal section the interior of the leaf (the chlorophyll-containing cells), Seive cell • cells that are more elongated Phloem and thick at the corners; found parenchyma Sieve plate in the leaf stalks and in the stems below the outer epidermis B Sieve and provide support, pits • have long, narrow and thick Companion cell cells, which have become dead, b) Transverse section have very thick walls , and Fig. 24.9 Conducting tissue in plants– phloem provide strength to the plant. Conducting tissue: It is also called the vascular tissue. It provides passage for the fluids to move up and down in the plant. It is of two types–xylem and phloem (Fig. 24.9). Xylem is located more towards the centre of the stem. It allows water and minerals absorbed from the soil to travel upwards in the plant. Phloem is located outward of the xylem and serves to conduct the food (sugar) synthesized in the leaves to flow downward and upward so as to reach all other regions.

CHECK YOUR PROGRESS 24.4 1. Choose the most appropriate answer. i. A tissue is a group of cells with a) same structure but different functions. b) different structures but similar function. c) same structure and same function. d) different structures and different functions. ii. Which one of the following is a matching pair of an example and its kind of tissue? a) Blood – Epithelial tissue b) Muscle – Connective tissue c) Cartilage – Nervous tissue d) Bone – Connective tissue

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Cells

The plant tissue which transports prepared food material from the leaves to other parts of the plant is called i) parenchyma. ii) collenchyma. iii) xylem. iv) phloem. 2. Name the kind of tissue found at the following places: i) Surface of the human skin ii) Inside the salivary glands iii) In the brain iv) Inner lining of the wind pipe 24.5 LEVELS OF ORGANIZATION – INCREASING COMPLEXITY FROM CELL TO ORGANISM There are various levels of organisation which increase in their complexity from the cell stage to the organismic level (Fig. 24.10). Cell is the lowest level of organization in all living beings. Every action of the organism is ultimately the outcome of the activity of the cell. Every cell has its own life. It feeds, respires, excretes, responds and even reproduces, and after getting old and aged it dies.

iii.

Tissue

Organ

Tissue is a group of similar cells that perform a particular function. Human body, for example, has a muscular tissue made of muscle cells, which brings about movement by contraction. Organ is formed of many tissues, which work in a cooperative and a coordinated manner to perform a specific function in the body. For example, the heart is an organ consisting of the muscle, nerve, and blood. But as a whole it is concerned with one or more very specific tasks. Similarly, the plant leaf is an organ formed of several tissues but its one main task is to manufacture food. Organ system is formed of many organs that act together to perform a specific life process, such as digestion. All the organs concerned with one specific process collectively constitute an organ system. The digestive system, respiratory system or the reproductive system are some of the organ systems in animal body. In plants, there are only two organ systems – the root system and the shoot system.

Organ system

Fig. 24.10 Levels of organisation in the living world

Organism is the whole living being by which different life processes are performed.

CHECK YOUR PROGRESS 24.5 1. Circle the organs out of the following: tongue, blood, bone, lungs, leaf, xylem, flower, finger

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2. Name any three organ systems found in the human body. 3. Which are the two organ systems found in a maize plant. 4. Rearrange the following in their correct sequence from the lowest to the highest level of organisation: organ, cell, organ system, organism, tissue • • • • • • LET US REVISE Cell is the smallest unit of structure and function in an organism. Every organism starts as a single cell. A cell primarily consists of cell membrane, cytoplasm and nucleus. Plant cells have an extra rigid cell wall made up of cellulose. Cytoplasm contains several organelles, each of which has a specific function. Ribosomes are the site of protein synthesis, mitochondria produce chemical energy (ATP), golgi apparatus produces secretions, lysosomes destroy foreign substances around them. Plant cells have plastids as very special organelles. The chloroplasts among them are concerned with production of food (starch). Nucleus contains the genetic material in the chromosomes. Also, it controls the activities of the cell. Similar cells with similar functions packed together form a tissue. Different tissues arranged together to perform some specific activities make up an organ. Related organs together constitute an organ system. Animal tissues constitute epithelial, connective, muscular and nervous tissues. Epithelial tissue consists of squamous epithelium, cuboidal epithelium, columnar epithelium, ciliated epithelium and glandular epithelium. Connective tissue consists of cartilage, bone, fat, blood, etc. Muscular tissue consists of striped, unstriped and cardiac muscles. Nervous tissue consists of neurons whose long axons are bundled together to form a nerve. Plant tissues are of two types – meristematic (actively dividing cells) and permanent. Permanent tissues include protective tissue (epidermis) and supporting tissues (parenchyma, collenchyma, sclerenchyma) and conducting tissues (xylem, phloem).

• • • • • • • • • • • •

TERMINAL EXERCISES A. Multiple choice type questions. 1. The structural and functional unit of the living body is a) Lungs b) Cell c) Stomach d) Tissue

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2. Transport of substances within the cell is performed by a) Nucleus b) Chromosomes c) Endoplasmic reticulum d) Lysosomes 3. Division of a cell into two daughter cells by the formation of a cell plate occurs in the body of a) Human beings b) Apple tree c) Cat d) Elephant 4. The connective tissue that connects muscles to bones is a) Tendon b) Ligament c) Blood d) Cartilage 5. Meristematic tissue in a plant is found in one of the following parts a) Tip of the leaf b) Tip of the root c) Base of the stem d) Base of the flower B. Descriptive type questions. 1. List any common three features found both in plant and animal cells. 2. Mention three features found only in plant cells and one found only in animal cells. 3. Differentiate between the following: i) Centrosome and chromosome ii) Nucleolus and nucleus iii) Organ and tissue iv) Conducting and protective tissue in plants v) Chromosome and chromatid vi) Cell and tissue vii) Organ and organelles viii) Organ and organism ix) Organ and organ system 4. State the major functions of the following: i) Plasma membrane ii) Lysosome iii) Golgi apparatus iv) Ribosomes v) Mitochondria

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5. “First meiotic division is the reduction division.” What does the word reduction refer to in this statement? 6. Why is it necessary that the sex cells (gametes) must be produced by meiosis? 7. The diagram alongside represents a stage in the mitotic type of the cell division. i) Is it a plant cell or an animal cell? ii) Which stage does it represent? iii) How many chromosomes have been shown in it? iv) Name the stage that precedes it and the one that follows it. 8. Given below are the jumbled spellings of some of the cell structures and tissues. A special point about each of them is also given on the side. Write the correct name of each of the item in the jumbled spellings. a) b) c) d) e) f) Organelles found only in plant cells HCRMOOOEMS ( ___________ ) Carriers of heredity LEMYX ( ___________ ) A conducting tissue ILIAC ( _________ ) Structures present on a kind of epithelial cells SOLESOMY ( ___________ ) An organelle that destroys foreign substances SUNCLUE ( ___________ ) The cell organelle that regulates cell activities ANSWERS TO CHECK YOUR PROGRESS 24.1 1. i) ii) iii) iv) v) i) ii) iii) iv) i) ii) iii) iv) T T F F F F F T F Cellulose Plasma membrane or cell membrane Animal Chromatin, chromosomes SPASDITL ( ___________ )

24.2 1.

2.

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24.3 1.

2.

i) ii) iii) iv) i) ii) iii) i) ii) iii) i) ii) iii) iv)

growth repair replacement reproduction mitosis meiosis mitosis c) d) d) Epithelial (squamous) Epithelial (columnar) Nervous Epithelial (ciliated)

24.4 1.

2.

24.5 1. 2. 3. 4.

Tongue, lungs, leaf, flower, finger Nervous system, digestive system, respiratory system, etc. Shoot system, root system Cell, tissue, organ, organ system, organism

GLOSSARY Axon: The process of a neuron that conducts impulses away from the cell. Cell: The structural and functional unit of the living body. Cell wall: A layer that surrounds the plant cells. Chlorophyll: The green-coloured matter contained in the chloroplast of plant cells. Chloroplast: The plant cell organelle that contains chlorophyll. Egg: The female sex cell also called the ovum or the female gamete. Heredity: Transmission of characteristics from parent to the offspring. Nucleolus: A well-defined part inside the nucleus. Pith: The soft spongy tissue in the centre of most stems. Tissue: A group of structurally similar cells that perform the same function.

25

Food and Nutrition
Why do we have food? We have food because we feel hungry. I s n ’t i t ?B e i n g h u n g r yi st h eb o d y ’s w a yo fs a y i n gt h a ti tn e e d sm o r ef u e lt ok e e pg o i n g .T h ef o o d we eat provides energ yf o ra l lb o d yf u n c t i o n sa n di sa l s ou s e dt of o r mn e wc e l l s f o rt h eb o d y. We e a tav a r i e t yo ff o o da c c o r d i n gt oo u rt a s t e ,b o d yr e q u i r e m e n t a n da v a i l a b i l i t y. S o m eo fu sm a yp r e f e rt oe a tr i c et ob r e a do rc h a p a t t i s .O t h e r s m a yl i k et oh a v ed o s a s ,i d l i s ,b u rg e r s ,n o o d l e s ,e t c . We m a yb eav e g e t a r i a no ra n o n v e g e t a r i a n .A l ll i v i n gb e i n g s ,b o t hp l a n t sa n da n i m a l sn e e df o o df o rg r o w t h , repair and maintenance. OBJECTIVES A f t e rc o m p l e t i n gt h i sl e s s o n ,y o uw i l lb ea b l et o : • d e s c r i b ev a r i o u sm o d e so fn u t r i t i o ni no rganisms; • d e f i n et h et e r mp h o t o s y n t h e s i s ,a n dl i s ti t sr a wm a t e r i a l sa n dp r o d u c t s ; • e x p l a i nt h ei m p o r t a n c eo fp h o t o s y n t h e s i sa sas o u r c eo ff o o df o ra l ll i f eo ne a r t h ; • l i s ta n dd e s c r i b et h ef a c t o r sa ff e c t i n gp h o t o s y n t h e s i s ; • l i s tt h ec o m p o n e n t so fab a l a n c e dd i e ta n ds t a t et h ef u n c t i o n so fe a c ho ft h e m ; • d r a wt h ep a r t so ft h ea l i m e n t a r yc a n a la n dd e s c r i b et h ef u n c t i o n so fe a c h ; • d e s c r i b es o m en u t r i t i o n a ld i s o r d e r s ,t h e i rc a u s e sa n dp r e v e n t i o n ; • define food adulteration, and list some common food adulterants. 25.1 FOOD Food provides the essential raw material our body needs to grow and stay healthy. 25.1.1 The need for Food How do you feel if you do not have food for a day or two? You may feel exhausted and weak. Think of a young child who is deprived of food for a few days. Wi l lt h e c h i l ds u r v i v ea n dg r o w ?T h ea n s w e ri s‘ N o ’ .A l ll i v i n gb e i n g sn e e df o o dt os u r v i v e . Food serves the following purposes: • p r o v i d e se n e rg yf o rv a r i o u sm e t a b o l i ca c t i v i t i e s( b i o c h e m i c a lr e a c t i o n st a k i n g p l a c ei nt h eb o d y ) ,s u c ha sr e s p i r a t i o na n dd i g e s t i o n . • h e l p si ng r o w t ho ft h eb o d ya n dr e p a i ro fw o r n o u tt i s s u e s . • p r o t e c t su sf r o md e f i c i e n c yd i s e a s e s .

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25.1.2 Nutrition Yo u rf o o dm a yi n c l u d ean u m b e ro fi t e m s ,i fi tm e e t sy o u re n t i r eb o d y ’s r e q u i r e m e n t a n di su t i l i z e db yt h eb o d y, i ti sc a l l e dn u t r i t i o n (n u t r i n e: t on o u r i s h ) . The process by which, org a n i s m so b t a i na n du t i l i s ef o o df o rt h e i rg r o w t ha n d d e v e l o p m e n t( f r o mt h e i re n v i r o n m e n t )i sc a l l e dn u t r i t i o n . 2 5 . 1 . 3 Types of nutrition Depending upon the mode of food uptake, nutrition could be of two b r o a dt y p e s – autotrophic n u t r i t i o n a n dh e t ro t rophic nutrition. a ) Autotrophic nutrition ( a u t o s :s e l f ;t ro p h o s : food) You must have noticed a gardener w a t e r i n gt h ep l a n t so ro c c a s i o n a l l y p r o v i d i n gt h e mw i t hf e r t i l i z e r s .A r e w a t e ra n df e r t i l i z e r sf o o df o rt h e m ? I si ta l lt h a ta l lp l a n t sn e e d ?
From soil through absorption

C O2 f r o ma i r Sun Chlorophyll + Wa t e r ↓ Glucose + Oxygen R e l e a s e di n t ot h ea i r

L i g h te n e rgy

To d i ff e r e n tp a r t so ft h ep l a n t

Fig. 25.1 Gre e np l a n t ss y n t h e s i s et h e i r

Green plants synthesize their own food food from water and carbon dioxide, i nt h ep r e s e n c eo fs u n l i g h t .T h i sp r o c e s si sc a l l e dp h o t o s y n t h e s i s . The gre e np l a n t s and certain bacteria which can manufacture t h e i ro w nf o o dw i t h i nt h e m s e l v e s , a re c a l l e da u t o t rophs, a n dt h e i rm o d eo fn u t r i t i o ni sc a l l e da u t o t r o p h i cn u t r i t i o n ( F i g .2 5 . 1 ) . b ) Hetro t rophic nutrition(h e t e ro s :d i ff e r e n t ;t ro p h o s :f o o d ) W e cannot make food inside our own body. All animals including man and nongreen plants cannot make their food and depend on green plants. The organisms, which depend on other org a n i s m sf o rt h e i rf o o d ,a re c a l l e dh e t e ro t rophs a n dt h e i r m o d eo fn u t r i t i o ni sc a l l e dh e t r o t r o p h i cn u t r i t i o n . O nt h eb a s i so ft h e i rf e e d i n gh a b i t sh e t e r o t r o p h sm a yb ec l a s s i f i e da s– sapro t rophs a n d parasites. i ) Sapro t rophic nutrition: You must have seen a white cottony growth developing on your wet leather shoes or belts especially when they get wet during rainy days. This is a fungal growth. The fungus grows and feeds on s u b s t a n c e s ,w h i c hw e r eo n c ep a r to ft h el i v i n go rg a n i s m s ,s u c ha ss t o r e df o o d , wood, leather and rotten plant products. Some common examples are bacteria, mushrooms, yeast, bread mould, etc. Org a n i s m st h a td e r i v et h e i rf o o df rom dead and ro t t e no rganisms are c a l l e ds a p ro t rophs ( F i g .2 5 . 2 ) .S a p r o t r o p h s help in cleaning the environment by decomposing the dead and recycling the n u t r i e n t s .

F o o da n dN u t r i t i o n : 175 :
Fungal spots S l i c eo fb r e a d

Fig. 25.2 Some sapro t rophs

i i ) P a r a s i t i cn u t r i t i o n : Have you ever been bitten by a head louse or a bed bug? Have you heard of some children having worms inside their body? These o rg a n i s m st h a tl i v eo no ri n s i d eo t h e rl i v i n go rg a n i s m s ,t od e r i v et h e i rf o o d a re c a l l e dp a r a s i t e s. S u c ham o d eo fn u t r i t i o ni sk n o w na sp a r a s i t i cn u t r i t i o n . Bed bug, head louse and leech remain outside the body. S o m eb a c t e r i a ,a n d worms, such as tapeworm and roundworm, live inside the body (Fig. 25.3). Dodder plant (Amar bel) i sap a r a s i t eo ng r e e np l a n t s .
Mouth Gut Mosquito Ovary Hookworm Head Mouth Sucker

Rare Sucker Tapeworm Leech

Fig. 25.3 Some parasites on human body

CHECK YOUR PROGRESS 25.1 1 . Which are the two major groups of org a n i s m so nt h eb a s i so fn u t r i t i o n ? 2 . Give two examples of saprotrophs. 3 . Which group of org a n i s m si sc a p a b l eo fp r e p a r i n gi t so w nf o o da sw e l la s nourishing others? 4 . D i ff e r e n t i a t eb e t w e e np a r a s i t i ca n ds a p r o t r o p h i cm o d eo fn u t r i t i o n . 5 . C l a s s i f yt h ef o l l o w i n ga ss a p r o t r o p h so rp a r a s i t e s : leech, yeast, head louse, mushroom 6 . Name one parasitic plant. 25.2 NUTRITION IN PLANTS Yo um u s th a v es e e na n i m a l s ,s u c ha sc o w s ,h o r s e s ,s h e e p ,e t cg r a z i n gi nt h ef i e l d s for food. How do plants get their food? Yo uh a v ea l r e a d ys t u d i e dt h a ta u t o t r o p h s ,

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s u c ha sg r e e np l a n t s ,c a ns y n t h e s i z et h e i ro w nf o o d .G r e e np l a n t su t i l i z ee n e rg y from sunlight to prepare food. The food that humans and animals eat, consists of p l a n tp r o d u c t s ,o rp r o d u c t so fa n i m a l st h a te a tp l a n t s . The process by which green plants manufacture food from carbon dioxide a n dw a t e ri nt h ep r e s e n c eo fs u n l i g h ti sc a l l e dp h o t o s y n t h e s i s ( photos:l i g h t ;s y n t h e s i s: t oc o m b i n e ) . 25.2.1 Where does photosynthesis occur? I to c c u r si nt h ec e l l so fg r e e nl e a v e sa n do t h e rg r e e np a r t so ft h ep l a n tt h a ta r e e x p o s e dt ol i g h t .T h e s ec e l l sp o s s e s st i n ys t r u c t u r e sc a l l e d chloro p l a s t s. T h e s e structures remain packed with chlorophyll, a green pigment, about which you h a v ea l r e a d ys t u d i e di nl e s s o n2 4 .P l a n t sr e q u i r ee n e rg yf o rp h o t o s y n t h e s i s .L e tu s s e eh o wp l a n t sh a r v e s t( g a t h e r )t h i se n e rg yf o rt h ep r o c e s so fm a k i n gf o o d . 25.2.2 How does photosynthesis occur? I nt h i sp r o c e s s ,p l a n t su s ec a r b o nd i o x i d ea n dw a t e ra sr a wm a t e r i a l st ob u i l d e n e rgy containing chemical compounds. Glucose is one such compound. Such compounds are needed by all living beings for energy production. The process of photosynthesis is completed in two steps – l i g h t reaction a n d dark reaction.

C O2 Sun Chlorophyll Glucose + Wa t e r + Oxygen Glucose + Wa t e r + Oxygen Sun

Wa t e r

F i g .2 5 . 4T h ep ro c e s so f p h o t o s y n t h e s i si nal e a f

F i g .2 5 . 5T h e products o fp h o t o s y n t h e s i s

i )

Light re a c t i o n : T h ef i r s ts t e po fp h o t o s y n t h e s i so c c u r si nt h ep r e s e n c eo f l i g h t .D u r i n gt h i ss t e p ,c h l o r o p h y l lc o n t a i n e di nt h ec h l o r o p l a s to fp l a n tc e l l s a b s o r b sl i g h te n e rg y. T h i se n e rgy is converted into another form, which can b es u p p l i e df o rt h ec o m p l e t i o no ft h ed a r kr e a c t i o n .

i i ) Dark re a c t i o n : T h i ss e c o n ds t e po fp h o t o s y n t h e s i sd o e sn o tr e q u i r el i g h t , a n di sc a l l e dd a r kr e a c t i o n .I tc a na l s oc a r r yo ni nt h ep r e s e n c eo fl i g h t .D u r i n g t h i ss t e p ,e n e rgy generated during light reaction is used to combine carbon dioxide and water molecules to form energy rich compounds, such as glucose. O x y g e ni sa l s or e l e a s e di nt h i sp r o c e s s .

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Green plants – The green lungs Green plants constantly absorb carbon dioxide from the environment and r e t u r ne n o u g ho x y g e ni n t oi t .I si tn o tw o r t ha p p r e c i a t i n gt h a tw ed on o th a v et o b u yo x y g e nf i l l e dc y l i n d e r sf o ro u rs u r v i v a l !O x y g e ni sn a t u r a l l ya d d e dt o the environment by the plants. They are sometimes called the g reen lungs a st h e y help in keeping the environment clean by maintaining low levels of carbon dioxide. The following equation summarizes the raw materials and products of photosynthetic process: R AW M ATERIALS 6CO2 + 12H2O c a r b o n w a t e r d i o x i d e s u n l i g h t c h l o r o p h y l l PRODUCTS C 6H 12O 6 + 6H2O + 6O2 g l u c o s e w a t e r o x y g e n

(Wa t e ra n dc a r b o nd i o x i d ea r eu s e di ne q u a lp r o p o r t i o n si nt h es y n t h e s i so f o rganic compounds.) 25.2.3 Factors that influence photosynthesis T h er a t eo fp h o t o s y n t h e s i si si n f l u e n c e db y external a n d internalf a c t o r s . a ) External factors These include l i g h t ,c a r b o nd i o x i d e ,w a t e ra n dt e m p e r a t u r e . • • L i g h t :T h er a t eo fp h o t o s y n t h e s i sd e p e n d sd i r e c t l yo nt h ei n t e n s i t yo fl i g h t . G l u c o s ei sn o tf o r m e di nt h ea b s e n c eo fl i g h t . Carbon dioxide: H i g hc a r b o nd i o x i d ec o n c e n t r a t i o ni n c r e a s e st h er a t eo f p h o t o s y n t h e s i su pt oac e r t a i ne x t e n t .G l u c o s ec a n n o tb es y n t h e s i z e di ni t s a b s e n c e . Wa t e r :I ti sa ne s s e n t i a lr a wm a t e r i a l ,i t sl o wa v a i l a b i l i t yr e d u c e st h er a t eo f photosynthesis, whereas the excess present is removed by transpiration. Temperature :M o s to ft h ep l a n t sw o r kb e s ta ta no p t i m u mt e m p e r a t u r eo f2 5oC . o Ar i s ea b o v e3 5 Cl e a d st oad e c r e a s ei nt h er a t eo fp h o t o s y n t h e s i s .P l a n t st h a t g r o wi nt h et r o p i c sc a ne ff i c i e n t l yp r o d u c es t a r c he v e na tah i g h e rt e m p e r a t u r e .

• •

b ) Internal factors These include chlorophyll content, number of stomata, and the shape, structure a n da g eo ft h el e a f .C h l o r o p h y l li st h em o s ti m p o r t a n ti n t e r n a lf a c t o r. T h er a t eo f p h o t o s y n t h e s i sd e c r e a s e sw i t ha ni n c r e a s ei nt h ea g eo fl e a f . T h ec y c l eo fl i f e L o o ka tt h eF i g u r e2 5 . 6 . Yo uh a v ea l r e a d ys t u d i e dt h es t r u c t u r ea n df u n c t i o n s o fm i t o c h o n d r i aa n dc h l o r o p l a s t s .L e tu ss t u d yt h ew a yt h e ya r ef u n c t i o n a l l y i n t e r r e l a t e d .

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T h ea c t i v i t i e st h a t o c c u r i n c h l o r o p l a s t a n d Sun mitochondria make life Oxygen Mitochondrion possible. Inside the chloroplast, energy Chloroplast f r o mt h es u ni sc a p t u r e d and stored in the Carbon dioxide AT Pf o rc e l la c t i v i t i e s : A c t i v et r a n s p o r t and water glucose molecules, P l a n t s Movement Animals Growth with the release of Reproduction Fig.25.6 Chloroplasts and mitochondria – Repair oxygen. Inside the t h e i ri n t e rr e l a t i o n s h i p mitochondria, the energy stored in g l u c o s ei su s e dt oc a r r yo u to t h e rc e l la c t i v i t i e s .I na d d i t i o n ,o x y g e np r o d u c e d i nt h ec h l o r o p l a s ti su s e di nt h eb r e a k d o w no fg l u c o s e .
Photosynthesis Respiration Glucose

25.2.4 Materials synthesized by plants as a sourc eo ff o o d You may have seen farmers caring for their crops. Young plants of wheat, maize a n dp a d d yg r o wt oy i e l dg r a i n s .T h i sp r o d u c t i o no ff o o dg r a i n so rg r o w t ho ff r u i t s and vegetables is a result of photosynthesis. Products of photosynthesis are i m p o r t a n tf o rt h en o u r i s h m e n ta n ds u r v i v a lo fa l ll i f ef o r m so nt h ee a r t h . Glucose formed during photosynthesis is converted into starch and a number of other useful forms by undergoing chemical changes or combining with other molecules. Following table indicates materials synthesized by green plants and t h e i ru s ea sas o u r c eo ff o o d . Ta b l e2 5 . 1 : Nutrients synthesized by plants that are used as food Type of nutrient Carbohydrates
l l l l l

Food source ( some examples ) Grapes A l lf r u i t st h a tt a s t es w e e t Sugarcane and beet root, common sugar P e e l so ff r u i t sa n dv e g e t a b l e s ,w h o l eg r a i n s( b r a n–g o o d source of roughage) Cereals (wheat, rice, maize, barley), and vegetables (potato, sweet potato, tapioca, onion, banana, water c h e s t n u to r singhara) P u l s e s( s o y a b e a n ,b e a n s ,p e a s ,l e n t i l s ,g r a m ) ,n u t s Groundnut, mustard seeds, coconut

Glucose Fructose Sucrose C e l l u l o s e S t a r c h

Pro t e i n s Oil and fats

CHECK YOUR PROGRESS 25.2 1 . W h e r ed o e sp h o t o s y n t h e s i st a k ep l a c ei nt h ep l a n tc e l l ? 2 . During which step of photosynthesis are carbohydrates synthesized – light or d a r kr e a c t i o n ?

F o o da n dN u t r i t i o n : 179 :

3 . N a m ea n yt w op l a n t st h a ta r ear i c hs o u r c eo fs t a r c h ? 4 . W h i c hf o r mo fs u g a ri sp r e s e n ti ns u g a r c a n ea n db e e t r o o t ? 5 . G i v et h eo v e r a l lc h e m i c a lr e a c t i o ni n v o l v e dd u r i n gp h o t o s y n t h e s i s . 25.3 OUR DIET The food that we have on regular basis forms our diet. You may have diff e r e n t t y p e so ff o o di ny o u rd i e t . You may prefer to take more of one and less of another. D o e sy o u rd i e tf u l f i l ly o u rb o d y ’s r e q u i r e m e n t s ?S h o u l di ts a t i s f yy o u rt a s t eb u d s or body needs? For healthy growth and development of the body, y o un e e dt oe a tf o o d st h a t provide enough of the essential nutrients. What does the term nutrient mean? Nutrients are the chemical constituents present in our food that arerequire d for the nourishment of our body. 25.3.1 Components of diet and their functions From the wide variety of food items that we consume, we get mainly six types of n u t r i e n t s .M o s tf o o d sp r o v i d e ,a tl e a s t ,s m a l la m o u n t so fe a c hk i n do fn u t r i e n t . T h e s en u t r i e n t sa r ec a r b o h y d r a t e s ,f a t s ,p r o t e i n s ,v i t a m i n s ,m i n e r a l sa n dw a t e r. a ) Carbohydrates Carbohydrates are compounds made up of three elements – carbon,hydrogen a n d oxygen. These are the main source of energy in our diet. One gram of carbohydrates on complete oxidation yields 17 kJ ( 4k i l o c a l o r i e s )o fe n e rg y. Carbohydrates may be in the form of s u g a r s ,s t a rc ho rc e l l u l o s e. • Sugars a r ea v a i l a b l ei nt h ef o l l o w i n gf o r m s :g l u c o s e ,f r u c t o s e( f r u i ts u g a r ) , lactose (natural sweetness in milk) and sucrose (common sugar made f rom sugarc a n ej u i c e ). G l u c o s ep r o v i d e sa l m o s ti n s t a n te n e rg y. I ti sa l s o g i v e nt ot h ep a t i e n t sw h oc a n n o td i g e s tf o o d . Starc hc a nb ee a s i l yd i g e s t e di no u rb o d y. I tf o r m st h eb u l ko fo u rd i e t .P o t a t o , wheat, rice, sweet potato and banana are few good sources of starch. C e l l u l o s ec a n n o tb ed i g e s t e di no u rb o d yy e t ,i ti si m p o r t a n tt oh a v es o m ec e l l u l o s e ( i nt h ef o r mo f roughage) i nt h ed i e t .R o u g h a g eh e l p si ne a s ym o v e m e n to f f o o dt h r o u g ht h ef o o dc a n a lp r e v e n t sc o n s t i p a t i o na n dh e l p si nd i g e s t i o n .W h o l e g r a i n s ,p e e l so fm o s tf r u i t sa n dv e g e t a b l e sa r eg o o ds o u r c e so fr o u g h a g e .

• •

b ) Fats Much like carbohydrates, fats are composed of carbon, hydrogen, and oxygen but i nd i ff e r e n tp r o p o r t i o n s .Af a tm o l e c u l ec o n s i s t so ft w op a r t s : glycero la n df a t t y a c i d s . On complete oxidation each gram of fat provides around 37 kJ ( 9 k i l o c a l o r i e s )o fe n e rg yt ot h eb o d y. F a t sp e r f o r mt h ef o l l o w i n gf u n c t i o n s : • • Keep body warm by providing extra energ y F a td e p o s i t si nt h eb o d yp r e v e n tl o s so fb o d yh e a t

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• A c ta ss h o c ka b s o r b e ra n dp r o t e c ti n t e r n a lo r g a n sa g a i n s ti n j u r y • H e l pi nt h et r a n s p o r to ff a t s o l u b l ev i t a m i n s S o m ec o m m o ns o u r c e so ff a t sa r ee d i b l eo i l ,g h e e ,b u t t e r, m e a ta n dn u t sl i k eg r o u n d n u t s . c ) Proteins Yo um u s th a v eo f t e nh e a r dy o u rm o t h e ri n s i s t i n go nh a v i n gag l a s so fm i l ko rab o w lo f c o o k e dp u l s e s (d a l s) o re v e na ne g g .A l lt h e s ea r er i c hi np r o t e i n s .P r o t e i n sa r em a d e up of molecules of carbon, hydrogen, oxygen, and nitrogen, and sometimes sulphur a l s o .G r o w t ho fb o d yt i s s u e si st h em a i nf u n c t i o no fp r o t e i n s .D u r i n gs t a r v a t i o np r o t e i n s a l s os e r v ea sas o u r c eo fe n e rg y. O nt h eb a s i so ff u n c t i o np e r f o r m e dp r o t e i n sm a yb eo f f o l l o w i n gs i xt y p e s : • • • • • • Structural proteins h e l pb u i l du pt i s s u e sa n dr e p l a c ew o r no u tc e l l s ,f o re x a m p l e c o l l a g e na n de l a s t i n . Enzymes r e g u l a t et h ec h e m i c a lr e a c t i o n sg o i n go ni n s i d eo u rb o d yl i k ed i g e s t i o n a n dr e s p i r a t i o n ,f o re x a m p l ep e p s i na n dt r y p s i n . P r o t e c t i v ep r o t e i n sp r o v i d ep r o t e c t i o nt ob o d ya g a i n s ti n f e c t i o n sw i t ht h eh e l po f a n t i b o d i e s ,f o re x a m p l eg a m m ag l o b u l i n s . C o n t r a c t i l ep r o t e i n sh e l pi nm o v e m e n ta n dl o c o m o t i o no fb o d yp a r t s ,f o re x a m p l e a c t i na n dm y o s i n . Transportp ro t e i n sc a r r yd i ff e r e n ts u b s t a n c e si nt h eb l o o dt ob o d yt i s s u e s ,f o r e x a m p l eh a e m o g l o b i ni nt h eb l o o dt r a n s p o r t so x y g e n . Hormones serve as chemical messengers, which regulate body functions, for example insulin and thyroxine.

d ) Vitamins You have often heard your mother saying ‘Eat carrots and your eyesight will improve’. This is because carrots contain vitamin A. What are vitamins? Vi t a m i n s ( v i t a: e s s e n t i a lo ri m p o r t a n t )a r ec o m p l e xo rg a n i cc o m p o u n d se s s e n t i a lf o rl i f e . W e cannot make vitamins for ourselves and so must get them from our diet. Ta b l e 2 5 . 2l i s t sc e r t a i nv i t a m i n st h a ta r ee s s e n t i a lf o rh u m a n s .T h e ya r en e c e s s a r yf o r normal growth, and maintenance of the body, a n da r er e q u i r e di nr e l a t i v e l ys m a l l a m o u n t s .D e f i c i e n c yo fap a r t i c u l a rv i t a m i nf o ral o n gp e r i o dc a u s e sd i s e a s e . Overdose of certain vitamins, such as vitamins A and D, also proves harmful. O nt h eb a s i so fs o l u b i l i t yi nw a t e rv i t a m i n sm a yb ew a t e r s o l u b l eo rf a t s o l u b l e . VITAMINS

Wa t e r s o l u b l e Vitamins B-complex n dC ( B1,B2,B4,B12) a

F a t s o l u b l e Vitamins A, D, E and K

F o o da n dN u t r i t i o n : 181 :

Ta b l e2 5 . 2 : Types of vitamins, their sources, functions and deficiency diseases
Vitamin A Retinol B1 Thiamine B2 Riboflavin B4 Niacin Sourc e s Milk, green leafy vegetables, b u t t e r, c a r r o t s ,t o m a t o e s , c o d l i v e ro i l ,e g g Milk, peas, cereals, green vegetables, sea food, meat Peas, yeast, egg, meat, Whole cereals, potatoes, tomatoes, meat, fish Functions Deficiency disease Normal growth, keeps Night blindness (poor eyes and skin healthy v i s i o ni nd i ml i g h t ) Growth and development Healthy skin, growth Healthy skin, digestive and nervous system Formation of red blood corpuscles Healthy growth, strong blood vessels Formation of strong bones and teeth Beri-beri (a disease which a ffects the nervous system) Skin disease and retarded growth Pellagra (a disease which a ff e c t st h es k i n , alimentary canal and nervous system) Anaemia (deficiency of red blood corpuscles) Scurvy (a disease in which gums swell up and bleed) Rickets (a disease which a ffects bones in children making them soft and deformed) Aff e c t sf e r t i l i t yt os o m e e x t e n t Excessive bleeding from wounds

B 12 Liver, e g g s ,m i l k ,f i s h Cyanocobalamine C Amla, tomatoes, green leafy Ascorbic acid v e g e t a b l e s ,c i t r u sf r u i t s ,w a t e r chestnut D Sunlight, milk, butter, whole Calciferol grains and vegetables

E Tocopherol K Phylloquinone

Ve g e t a b l eo i l s ,m i l k ,b u t t e r, whole grains, vegetables

P r o t e c t st h ec e l l membranes

Green vegetables like spinach H e l p si nt h ec l o t t i n g and cabbage, soya bean oil of blood

e ) Minerals M i n e r a l sa r ei n o rg a n i cs u b s t a n c e sr e q u i r e db yt h eb o d yi ns m a l lq u a n t i t i e s .M i n e r a l s , s u c ha si r o n ,c a l c i u m ,p h o s p h o r u s ,i o d i n e ,s o d i u ma n dp o t a s s i u m ,a r ee s s e n t i a lf o r t h ef o r m a t i o no fb o d yt i s s u e s .T h e ya l s oh e l pi nr e g u l a t i n gb o d yf u n c t i o n sa n d m e t a b o l i s m ,i . e .t h ev a r i o u sc h e m i c a lr e a c t i o n st a k i n gp l a c ei nt h eb o d y. F o l l o w i n g t a b l ei n d i c a t e st h es o u r c e sa n df u n c t i o n so fs o m ei m p o r t a n tm i n e r a l s . Ta b l e2 5 . 3 : Some important minerals, their sources and functions
Mineral I r o n Calcium Phosphorus Potassium Sodium Iodine Sourc e s Functions Green vegetables, turnip, Formation of haemoglobin, which is the oxygens p r o u t s ,y e a s t ,l i v e r, e g g s , m e a t carrying pigment in RBCs Milk and milk products Formation of strong bones and teeth, muscle contraction, clotting of blood Tapioca, green leafy vegetables For the development of strong bones, teeth, making n e rgy-rich compounds in our bodies Whole grains, meat, eggs, fish e For growth and keeping osmotic balance of cells and Green and yellow vegetables blood Proper functioning of the nervous system, osmotic Common salt balance Sea food, iodized salt Body metabolism, development of brain

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) f Wa t e r Wa t e ri sa ni m p o r t a n tp a r to fo u rd i e t .I tm a k e s6 5 7 0 %o fo u rb o d yw e i g h t . Wa t e r does not provide any energ y, y e ti ti sc o n s i d e r e da ni m p o r t a n tc o n s t i t u e n to f b a l a n c e dd i e t .I th a st h ef o l l o w i n gf u n c t i o n s : • Wa t e rr e g u l a t e st h eb o d yt e m p e r a t u r e . • Provides means of excretion of body wastes. • P r o v i d e sm e d i u mf o rb i o c h e m i c a lr e a c t i o n s ,s u c ha sd i g e s t i o n ,r e s p i r a t i o n . • P l a y sa ni m p o r t a n tr o l ei na b s o r p t i o n ,t r a n s p o r t a t i o na n du s eo fn u t r i e n t s . 25.3.2 Balanced diet Now that you are aware of the components of diet, try to analyze your own food intake. Do you include all the components in your diet? For healthy growth and development of the body, y o un e e dt oe a tf o o d st h a t p r o v i d ee n o u g ho fa l lt h ee s s e n t i a ln u t r i e n t s .E a t i n gav a r i e t yo ff o o d si np r o p e r q u a n t i t ye v e r yd a yp r o v i d e s a balanced diet.A balanced diet contains adequate a m o u n to fe s s e n t i a ln u t r i e n t ss u c ha sc a r b o h y d r a t e s ,f a t s ,p ro t e i n s ,v i t a m i n s , minerals and water.The amount of these nutrients in diet depends upon a number o ff a c t o r s ,s u c ha sa g e ,s e xa n dn a t u r eo fw o r ka ni n d i v i d u a lp e r f o r m s . CHECK YOUR PROGRESS 25.3 1 . S u g g e s to n eu s eo fi n c l u d i n gr o u g h a g ei no u rd i e t . 2 . Which group of functional proteins serves as chemical messengers? 3 . Which of the two will provide greater amount of energy – one gram of starchy food or one gram of fatty food? 4 . C a t e g o r i z ev i t a m i n so nt h eb a s i so ft h e i rs o l u b i l i t y. 5 . H i g h l i g h to n ed i fference between vitamins and minerals. 25.4 THE PROCESS OF NUTRITION IN HUMAN BEINGS T h ef o o dt h a tw ee a ti si nq u i t ead i ff e r e n ts t a t ef r o mt h eo n et h a tc a nb eu s e db y t h ec e l l si nt h eb o d y.Conversion of complex food material into smaller units so t h a tt h ec e l l sc a na b s o r bi ti sc a l l e dd i g e s t i o n . The digestive system enables c o n v e r s i o no fi n g e s t e df o o di n t oi t ss i m p l e rf o r m .D i g e s t i o nr e q u i r e ss p e c i f i c c o n d i t i o n sf o rd i ff e r e n tn u t r i e n t sp r e s e n ti nt h ed i e t . The digestive system includes the food canal (mouth, pharynx, esophagus, s t o m a c h ,s m a l li n t e s t i n e ,l a rg ei n t e s t i n e , rectum), and the glandular organs ( s a l i v a ry g l a n d s ,l i v e ra n dp a n c re a s ). T h el o n gt u b e ,s t a r t i n gf r o mt h em o u t ht o t h ea n u s ,i sc a l l e d alimentary canal a n dt h ed i g e s t i v ep r o c e s si sc a l l e d e x t r a c e l l u l a rd i g e s t i o n. Digested food is transferred from the external environment to body’si n t e r n a l e n v i r o n m e n t .H e r ei tc a nb ed i s t r i b u t e dt oa l lb o d yc e l l sb yt h ec i r c u l a t o r ys y s t e m . 25.4.1 Enzymes The process of digestion requires a number of enzymes for the conversion of complex molecules into simpler ones.

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E n z y m e sa r ec h e m i c a l sn e e d e df o rt h ec o m p l e t i o no fc h e m i c a l r e a c t i o n st a k i n gp l a c ei na l ll i v i n gc e l l s . A l le n z y m e sa r ec o m p l e xp r o t e i n sa n dr e m a i nu n c h a n g e dd u r i n gt h er e a c t i o n .T h e y c a nb eu s e dr e p e a t e d l y. S i n c et h e ys p e e du pt h er a t eo fc h e m i c a lr e a c t i o n si nt h eb o d y t h e ya r ea l s ok n o w na sb i o c a t a l y s t s .E n z y m e sm a yh e l pi nj o i n i n go rs p l i t t i n go f b i o m o l e c u l e s . 2 5 . 4 . 2N u t r i t i o n S u mt o t a lo fc e r t a i np r o c e s s e st h a te n a b l eac e l lt ou t i l i z en u t r i e n t si sc a l l e dn u t r i t i o n . T h ee n t i r ep r o c e s so fn u t r i t i o ni n c l u d e st h ef o l l o w i n gs t e p s :i n g e s t i o n ,d i g e s t i o n , absorption, assimilation and egestion. a ) I ngestion and digestion T h ep r o c e s so ft a k i n gi no ff o o dt h r o u g h t h em o u t hi sc a l l e di n g e s t i o n .T h e d i g e s t i o no ff o o ds t a r t sf r o mt h em o u t h Mouth Salivary gland a n de n d si nt h ei n t e s t i n e s .
Wi n dp i p e

) i

i i )

i i i )

Mouth: The food is (trachea) Oesophagus ingested through the Diaphragm mouth. Carbohydrates, Spleen s u c ha ss t a r c h ,a r eb r o k e n Liver Stomach down or digested to form Gall bladder Pancreas Ascending colon s u g a r. T h es a l i v ac o n t a i n s Transverse colon S m a l li n t e s t i n e an enzyme salivary Descending colon Appendix amylase t h a th e l p si nt h e Rectum d i g e s t i o no fs t a r c hi n t o sugar. The saliva also Fig. 25.7 Alimentary canal in human beings h e l p si nl u b r i c a t i n gt h ef o o d a n dm a k i n gi te a s i e rf o rs w a l l o w i n g .T h et o n g u eh e l p si nr o l l i n ga n dp u s h i n g o ff o o di n t ot h eo e s o p h a g u s . S a l i v a r ya m y l a s e S t a r c h M a l t o s e Oesophagus: T h eo e s o p h a g u so rt h ef o o dp i p eh e l p si np u s h i n gt h ef o o d into the stomach. The expansion and contraction of muscles of the o e s o p h a g u si sc a l l e dp e r i s t a l s i so rp e r i s t a l t i cm o v e m e n t . Stomach: T h es t o m a c hi sah i g h l ym u s c u l a ro r g a n .T h eg a s t r i cg l a n d sp r e s e n t i ni t sw a l l ss e c r e t eg a s t r i cj u i c e sa n dh e l pi nt h ed i g e s t i o no ff o o d .T h e s e j u i c e sc o n t a i nh y d r o c h l o r i ca c i d( H C l )a n de n z y m e sl i k ep e p s i n. H C lc r e a t e s a na c i d i cm e d i u mf o rt h ea c t i v a t i o no fe n z y m e sa n dk i l l sb a c t e r i a .T h e s e e n z y m e sb r e a kd o w nt h ep r o t e i n si n t os m a l l e rf r a g m e n t sc a l l e d peptones. T h em u s c l e so ft h es t o m a c hh e l pi nc h u r n i n gt h ef o o ds ot h a ti ti sp r o p e r l y m i x e dw i t ht h ed i g e s t i v ej u i c e s . Pepsin Pro t e i n s P e p t o n e s( p a r t l yd i g e s t e dp r o t e i n s )

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Pepsin i v ) Milk pro t e i n s Calcium paracaseinate Small intestine: The food moves from the stomach to duodenum, w h i c hi st h eu p p e rp a r to ft h es m a l li n t e s t i n e .H e r et h ee m u l s i f i c a t i o n o ff a t( f a ti sb r o k e ni nt of a td r o p l e t s )t a k e sp l a c ew i t ht h eh e l po ft h e b i l ej u i c es e c r e t e db yt h el i v e r. T h eb i l ej u i c ei ss t o r e di nt h eg a l lb l a d d e r. P a n c r e a ss e c r e t e st r y p s i n,amylase a n dl i p a s e( p a n c r e a t i cj u i c e s )w h i c h are poured into the duodenum. Trypsin P e p t o n e s Amino acids ( c o m p l e t e l yd i g e s t e dp r o t e i n s ) Amylase Glucose Maltose and Sugars Lipase F a t s Fatty acids + Glycero l

T h ef o o dm o v e st oi l e u m ,w h i c hi st h el o w e rp a r to ft h es m a l li n t e s t i n e . T h ei n n e rs u r f a c eo ft h ei l e u mc o n t a i n st h i nf i n g e r l i k ep r o j e c t i o n sc a l l e d v i l l i. T h e s ea r er e s p o n s i b l ef o ri n c r e a s i n gt h es u r f a c ea r e ao fa b s o r p t i o n o fd i g e s t e df o o di nt ot h eb l o o d .T h eb l o o dt h e nc a r r i e st h ea b s o r b e d f o o dt od i ff e r e n tp a r t so ft h eb o d ya n du n d i g e s t e df o o di sp u s h e di n t o t h el a rg ei n t e s t i n e . v ) Large intestine: T h i sp a r to ft h eb o d ya b s o r b sw a t e rf r o mt h eu n d i g e s t e d f o o da n ds o l i dw a s t ei sl u b r i c a t e dt of o r mt h ef a e c e s .T h ef a e c e sp a s s o nt ot h el o w e rp a r to ft h el a rg ei n t e s t i n e ,c a l l e dt h er e c t u m ,a n dt h r o w n o u to ft h eb o d yt h r o u g ht h ea n u s . b ) Absorption The simple soluble food molecules are absorbed from the small intestine into the b l o o dw h i c ht a k e st h e mt oa l lt h ec e l l so ft h eb o d y. T h i si sk n o w na sa b s o r p t i o n . c ) Assimilation The absorbed food supplied to cells is used to release energy and build up the cell components. This is called assimilation. For example, glucose from digested food is broken down into carbon dioxide and water along w i t ht h er e l e a s eo fe n e rgy. Amino acids are used to make proteins required b yt h ec e l l s . d ) Egestion The process by which the undigested food material or waste is released from the b o d yi sc a l l e de g e s t i o n . CHECK YOUR PROGRESS 25.4 1 . W h a ta r et h ef i n g e r l i k ep r o j e c t i o n sp r e s e n ti ns m a l li n t e s t i n e sc a l l e d ? 2 . Name the enzyme that converts proteins into peptones in the stomach? 3 . What is the movement of muscles of oesophagus that pushes down food called? 4 . Name the two glands associated with digestion.

F o o da n dN u t r i t i o n : 185 :

5 . N a m et h ea c i dt h a tt a k e sp a r ti nd i g e s t i o np r o c e s s . 25.5 DEFICIENCY DISEASES OR NUTRITIONAL DISORDERS Ad i s e a s et h a to c c u r sd u et ol a c ko fa d e q u a t ea n db a l a n c e dd i e ti s c a l l e dd e f i c i e n c yd i s e a s e . E a t i n gt o om u c ho fan u t r i e n to rd e f i c i e n c yo fan u t r i e n tm a yl e a dt oan u m b e ro f nutritional disorders.Intake of improper or inadequate diet in human beings is c a l l e d malnutrition. I n a b i l i t yo ft h eb o d yt oa b s o r bn u t r i e n t sp r o p e r l ym a ya l s o l e a dt om a l n u t r i t i o n .M a l n u t r i t i o ni sh a r m f u lf o rc h i l d r e na si tr e t a r d st h e i rp h y s i c a l growth and may cause mental disabilities. Deficiency diseases caused due to m a l n u t r i t i o na r eo ft h r e et y p e s : • Protein Energy Malnutrition (PEM) • Mineral deficiency diseases • Vi t a m i nd e f i c i e n c yd i s e a s e s 2 5 . 5 . 1 Protein energy malnutrition (PEM) D e f i c i e n c yo fp r o t e i n si nt h ed i e tm a yl e a dt om a l n u t r i t i o n i nc h i l d r e n .T h i si st h ep r i m er e a s o nw h yy o u rp a r e n t si n s i s t t h a ty o us h o u l dd r i n km i l k ,e a tp u l s e sa n do t h e rs o u r c e so f proteins. PEM is the most common nutritional disorder among children. Two diseases caused due to PEM are – marasmus and kwashiorkor.

( a )

( b )

F i g .2 5 . 8E f f e c to f

(a) Marasmus, and a ) Marasmus (b) Kwashiorkor I ta ff e c t sc h i l d r e nu pt oo n ey e a ro fa g e .T h i so c c u r si n deprived children of mother’ s milk. The symptoms of this disease include: • l o s so rw a s t i n go fm u s c l e s , • b o d yd e v e l o p sl o o s ef o l d so fs k i n , • ribs become prominent, • digestion becomes weak, • body growth and development slows down. I tc a nb ec u r e db ye n s u r i n gm o t h e r’ sm i l kf o ri n f a n t s ,b yd e l a y i n ga n o t h e rp r e g n a n c y i nc o n t i n u a t i o na n db yh a v i n gad i e tr i c hi np r o t e i n ,c a r b o h y d r a t e s ,f a t s ,v i t a m i n s a n dm i n e r a l s .

b ) Kwashiorkor Amongst children of age group 1-5 years protein deficiency causes kwashiorkor. The symptoms of this disease are: • e n l a rg e m e n to fl i v e rd u et ow a t e rr e t e n t i o n , • darkening of the skin with scaly appearance, • hair become reddish-brown, • legs become thin, and • r e t a r d a t i o no fp h y s i c a la sw e l la sm e n t a lg r o w t h . E a t i n gap r o t e i n r i c hd i e tt h a tc o n s i s t so fm i l k ,m e a t ,g r o u n d n u t ,s o y a b e a n , j a g g e r y, e t c .c a nc u r ei t .

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25.5.2 Mineral deficiency diseases Yo ua r ea w a r eo ft h ei m p o r t a n c eo fc e r t a i nm i n e r a l si ny o u rd i e t( r e f e r Ta b l e2 5 . 3 ) d e f i c i e n c yo ft h e s em i n e r a l si ny o u rd i e tm a yl e a dt oc e r t a i nd e f i c i e n c yd i s e a s e s . Let us study about two common mineral deficiency diseases – goitre and anaemia. a ) Goitre I o d i n ei sr e q u i r e df o rt h es y n t h e s i so fh o r m o n e ,t h y r o x i n e ,p r o d u c e db yt h et h y r o i d g l a n dl o c a t e di no u rn e c kr e g i o n .P r o l o n g e di o d i n ed e f i c i e n c y c a u s e se n l a rg e m e n to ft h y r o i dg l a n di . e .g o i t r e .S e a f o o di sa g o o ds o u r c eo fi o d i n e .P e o p l el i v i n gi nc o a s t a lr e g i o nd o n o ts u ff e rf r o mi o d i n ed e f i c i e n c y. I o d i z e ds a l t ,e s p e c i a l l y f o rp e o p l el i v i n gi nt h eh i l l yr e g i o n so re v e np l a i n si s recommended to reduce incidence of goitre. b ) Anaemia This is a very common diet related condition in which the level of haemoglobin becomes lower than normal. Iron is F i g .2 5 . 9G o i t re : e n l a rgement an important constituent of haemoglobin, the respiratory o ft h et h y roid gland pigment of our blood. Iron deficiency causes deficient production of haemoglobin, resulting in the following symptoms: • Body becomes pale, • l a c ko fa p p e t i t e , • e x h a u s t i o n , • l o s so fb o d yw e i g h t , • retarded growth. A ni r o n r i c hd i e tc o n s i s t i n go fs p i n a c h ,a p p l e ,b a n a n a ,g u a v a ,e g g s ,g r o u n d n u t s , e t c .c a nh e l pt oc u r ea n a e m i a . 25.5.3 Vitamin deficiency diseases a ) Xerophthalmia Lack of Vitamin A leads to Xerophthalmia, a disease in which the following symptoms are observed: • • • • cornea (white area of the eye ball) may become dry, foggy or cloudy and may u l t i m a t e l yl e a dt ot o t a lb l i n d n e s s , retarded growth, d r ys c a l ys k i n ,a n d n i g h tb l i n d n e s s( i m p r o p e rv i s i o ni nd i ml i g h t ) .

T h i sc a nb ea v o i d e db yp r o p e ri n t a k eo fg r e e nl e a f yv e g e t a b l e sl i k eS p i n a c h ,y e l l o w vegetables and fruits, such as carrots, pumpkin, papaya and ripe mango. Liver, c o dl i v e ro i l ,b u t t e ra n dg h e e also provide vitamin A. b ) Rickets Milk and liver are good sources of vitamin D, calcium and phosphorus. Beans, green vegetables, whole gram and tapioca are other sources of calcium.

F o o da n dN u t r i t i o n : 187 :

P h o s p h o r u si sa l s oi nb a j r a ,g r e e nl e a f yv e g e t a b l e sa n d n u t s .C a l c i u ma n dp h o s p h o r u sa r et h em a j o rc o n s t i t u e n t so f b o n e sa n dt e e t h .T h e i rd e f i c i e n c ym a yr e s u l ti nad i s e a s e c a l l e dr i c k e t si nc h i l d r e n . Symptoms of this disease are pigeon chests and bone d e f o r m i t i e s ,p a r t i c u l a r l yo ft h el o n gb o n e s ,a st h e yc a n n o t s u s t a i nb o d yw e i g h t ,l i k eb o wl e g s . c ) Beri-beri Deficiency of Vitamin B1 i nt h ed i e tl e a d st ob e r i F i g .2 5 . 1 0R i c k e t s: b e r i .I ti sad i s e a s eo fh e a r ta n dn e r v e s .T h es y m p t o m so f d e f o r m i t i e si nl e g s t h i sd i s e a s ei n c l u d e : • s w e l l i n go ft i s s u e sa n dw a t e ra c c u m u l a t i o ni nt h e body, • extreme weakness, • headache, • p a r a l y s i sa n de v e nh e a r tf a i l u r e . This disease is observed more in people consuming more of polished rice in t h e i rd i e t . d ) Pellagra Deficiency of vitamin B4 r e s u l t si np e l l a g r a .T h i sd i s e a s ec a u s e s : • reddening and drying of skin (eczema), • swelling of gums and tongue, along with diarrhoea, and • m e n t a ld i s o r i e n t a t i o n . Consuming a lot of maize interferes with the absorption of Vitamin B4 i nt h eb o d y. P e l l a g r ac a nb ea v o i d e db yh a v i n ga d i e tf u l lo fw h o l eg r a i nc e r e a l s ,b e a n s ,g r e e nv e g e t a b l e s ,t o m a t o , p o t a t o ,f i s ha n de g g s .

Normal hand

P e l l a g r av i c t i m ’s h a n d

25.6 FOOD ADULT E R ATION p e r s o ns u f f e r i n gf rom W h yd ow ep r e f e rt ob u yf o o dp r o d u c t ss o l di ns e a l e dp a c k e t s ? pellagra Why do we prefer to buy items made by a standard reliable c o m p a n y ?As i m p l ea n s w e ri st h a tt h em a n u f a c t u r e rs e l l i n gi t sp r o d u c t si ns e a l e d p a c k e t so rb r a n d se n s u r e sd e l i v e r yo fq u a l i t yo fi t sc o n t e n t st ot h ec o n s u m e r.Any a t t e m p tt om i xp u re f o o ds u b s t a n c e sw i t hc h e a p e r, s u b s t a n d a rd ,e d i b l eo ri n e d i b l e s u b s t a n c e si sc a l l e d food adulteration. Adulterants n o to n l yd e t e r i o r a t et h eq u a l i t ya n df o o dv a l u eo ft h ep r o d u c t b u tm a ya l s oc a u s es e v e r ei l le ffects. Mixing water in milk may reduce its food value. Mixing colour (complex org a n i cd y e s ) ,s t o n e s ,t o x i cc e r e a l sa n dr o t t e n ingredients in grains and pulses causes severe damage to body parts and hence s i c k n e s s . Ta b l e2 5 . 4g i v e nb e l o wl i s t ss o m eo ft h ea d u l t e r a n t su s e di nd i ff e r e n t f o o dm a t e r i a l s .

F i g .2 5 . 11 Hands of a

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Table 25.4 : Some food items and their common adulterants Food item C e r e a l s P u l s e s Wheat flour,maida, s u j i,e t c . Milk E d i b l eo i l s Honey Tu r m e r i c( h a l d i ) Coriander Black pepper C h i l l i e s Common adulterants Straw, h u s k ,m u d ,s t o n e s ,g r i t ,i n f e r i o rq u a l i t yg r a i n s , i n f e c t e do ri n s e c ti n f e s t e dg r a i n s Straw, k e s a r id a l ,i n f e r i o rq u a l i t yg r a i n s ,i n f e c t e d grains, metanil yellow dye G r i t ,i n f e s t e ds t o c k ,e x c e s so fb r a n S t a r c h ,w a t e r, m i l ko fo t h e ra n i m a l s ,e x t r a c t i o no f f a t s ,s y n t h e t i cm i l k M i n e r a lo i l ,a rg e m o n eo i l ,a r t i f i c i a lc o l o r s Sugar syrup, jaggery Starch coloured with chromate or metanil yellow dye Powdered cow/horse dung, saw dust, starch Dried papaya seeds Saw dust, colour dust

25.6.1 Prevention of food adulteration To p r e v e n ta d u l t e r a t i o no ff o o dp r o d u c t s ,o u rg o v e r n m e n th a si s s u e dc e r t a i nl a w s . T h e s ei n c l u d e : Prevention of Food Adulteration Act and Rules a n d Food Product Orders w h i c hs e r v et h ef o l l o w i n gf u n c t i o n s : • • • lay a minimum standard for the quality of food requires date of manufacture and expiry to be mentioned on the packet of the food item q u a n t i t yo ft h ec o n t e n tt ob ei n d i c a t e d

I nI n d i a ,t h e Bureau of Indian Standards c a r r i e so u tt h ec e r t i f i c a t i o no f food products at the manufacturer’ se n d . CHECK YOUR PROGRESS 25.5 1 . Give the full form of PEM. 2 . Name any two diseases caused due to lack of vitamins. 3 . W h i c ht y p eo fs a l ti n t a k ec a np r e v e n to c c u r r e n c eo fg o i t r e ? 4 . List any two symptoms of anaemia. 5 . Name one common adulterant used in edible oils. 6 . Name the org a n i z a t i o nt h a tc e r t i f i e sf o o dq u a l i t yi nI n d i a . LET US REVISE • Food is the raw material that our body needs to grow and stay healthy. • Nutrition amongst org a n i s m sc o u l db ea u t o t r o p h i co rh e t e r o t r o p h i c( p a r a s i t i c a n ds a p r o t r o p h i c ) . • The process by which green plants synthesize their food is called p h o t o s y n t h e s i s .

F o o da n dN u t r i t i o n : 189 :

• T h er a wm a t e r i a l so fp h o t o s y n t h e s i sa r ec a r b o nd i o x i d ea n dw a t e r. T h ee n dp r o d u c t s a r eg l u c o s ea n do x y g e n . • E x t r ag l u c o s em a yg e tc o n v e r t e di n t os u c r o s e ,f r u c t o s e ,c e l l u l o s e ,s t a r c h ,f a t s , o i l s ,p r o t e i n s ,e t c .i no u rb o d y. • Ab a l a n c e dd i e ti n c l u d e sa l lt h ee s s e n t i a ln u t r i e n t s ,i nt h er e q u i r e dp r o p o r t i o n , along with water and roughage. • Components of balanced diet are carbohydrates, proteins, fats, vitamins and m i n e r a l s .T h er a t i oo ft h ea b o v e m e n t i o n e di t e m s ,i nt h ed i e t ,n e e d st oc h a n g e w i t ht h ea g e ,s e xa n dp r o f e s s i o n . • L a c ko fb a l a n c e dd i e tl e a d st ov a r i o u sn u t r i t i o n a ld i s o r d e r s . • T h ep r o c e s so fn u t r i t i o ni n c l u d e ss t e p so fi n g e s t i o n ,d i g e s t i o n ,a b s o r p t i o n , a s s i m i l a t i o na n de g e s t i o n . • C o n v e r s i o no fc o m p l e xf o o dm a t e r i a li n t os m a l l e ru n i t ss ot h a ti tc a ne n t e rt h e c e l l si sc a l l e dd i g e s t i o n . • Certain chemicals called enzymes play an important role in the process of d i g e s t i o n. • Hormones are the chemical messengers, which regulate body functions. • S a l i v a r yg l a n d si nt h em o u t h ,l i v e ra n dp a n c r e a sh e l pi nd i g e s t i o na n da r e c a l l e dg l a n d u l a ro rg a n so ra s s o c i a t e dg l a n d s . • D i g e s t i o no fp r o t e i n sy i e l d sa m i n oa c i d s .D i g e s t i o no fo i l sa n df a t sg i v e sf a t t y a c i d sa n dg l y c e r o l . • D i g e s t i o ns t a r t si nt h em o u t ha n dc o n t i n u e su pt ot h el a rg ei n t e s t i n e . • T h el o n gt u b eo rc a n a lo ft h ed i g e s t i v es y s t e mi sc a l l e da l i m e n t a r yc a n a l . • L a c ko fb a l a n c e dd i e tm a yl e a dt on u t r i t i o n a ld i s o r d e r s . • D e f i c i e n c yd i s e a s e sm a yb ed u et op r o t e i n s ( k w a s h i o r k o ra n dm a r a s m u s ) ,m i n e r a l s ( g o i t r ea n da n a e m i a ) o rv i t a m i n s (x e r o p h t h a l m i a ,b e r i b e r i ,p e l l a g r a ,r i c k e t s ) • Mixing pure food substances with cheaper, s u b s t a n d a r d ,e d i b l eo ri n e d i b l e s u b s t a n c e si sc a l l e df o o da d u l t e r a t i o n . TERMINAL EXERCISES A. Multiple choice type questions. 1 . O n eo ft h ef o l l o w i n gi sn o tas t e po fn u t r i t i o n a ) I n g e s t i o n b ) Assimilation c ) S e c r e t i o n d ) Egestion 2 . R i c k e t si sc a u s e dd u et od e f i c i e n c yo f a ) I r o n b ) Vitamin D c ) P r o t e i n s d ) Carbohydrates

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3 . One gram of a substance was oxidized. The energy released amounted to 9.0 Kcal. The substance was of the type: a ) Carbohydrates b ) F a t s c ) Vi t a m i n s d ) P r o t e i n s 4 . Ap e r s o nl i v i n gi nt h eh i l l yr e g i o n so fS h i m l ad e v e l o p e ds w e l l i n gi nh i sn e c k region. The doctor said his thyroid gland got swelled up. Can you name the n u t r i e n td e f i c i e n ti nh i sd i e t ? a ) Calcium b ) I r o n c ) Phosphorus d ) I o d i n e 5 . T h ev i t a m i nt h a th e l p si nt h ec l o t t i n go fb l o o di s a ) Vitamin A b ) Vitamin D c ) Vitamin E d ) Vitamin K B. Descriptive type questions. 1 . List the major components of food. 2 . D e f i n eb a l a n c e dd i e t . 3 . If equal amounts of fats or carbohydrates were oxidized, which of them would yield more energy? 4 . How would you establish the presence of starch in a given sample? 5 . What are vitamins? Name the diff e r e n tt y p e so ff a t s o l u b l ev i t a m i n s . 6 . L i s tt h ef u n c t i o n so ff o o d ? 7 . D e f i n ea d u l t e r a t i o ni nf o o d .N a m ea na g e n c yt h a tc e r t i f i e sr e l i a b i l i t yo ff o o d produced. 8 . Name five common adulterants in food. 9 . D i ff e r e n t i a t eb e t w e e np a r a s i t i ca n ds a p r o p h y t i cn u t r i t i o n . 1 0 . What are the main steps of photosynthesis? Is sunlight essential for photosynthesis and why? 11 . Give the chemical equation of photosynthesis. 1 2 . Ap a t i e n tc o m p l a i n so fl a c ko fa p p e t i t e ,e x h a u s t i o na n di sl o s i n gw e i g h t . Diagnose the deficiency. W h a tk i n do fd i e tw o u l dy o us u g g e s tf o rt h ep a t i e n t ? 1 3 . Deficiency of which vitamin causes night blindness. What would you suggest t op r e v e n tt h i sd e f i c i e n c y ? 1 4 . W h yi sw a t e ra ne s s e n t i a ln u t r i e n to fab a l a n c e dd i e t ? 1 5 . Draw a neat and labelled diagram of the human alimentary canal.

F o o da n dN u t r i t i o n : 191 :

1 6 .D i s c u s st h ef i v es t e p si n v o l v e di nt h ep r o c e s so fn u t r i t i o n . 1 7 .W h e r ed o e st h ed i g e s t i o no fs t a r c h ,p r o t e i n sa n df a t st a k ep l a c ea n dw h a ti st h e r o l ep l a y e db yt h ea s s o c i a t e dg l a n d s ? 1 8 . Which component in your diet will not be digested if the enzyme lipase is not s e c r e t e d ?A l s on a m et h es e c r e t i o nt h a th e l p si nt h ea c t i v i t yo ft h i se n z y m e . 1 9 .W h a ta r et h eb u i l d i n gb l o c k so fp r o t e i n s ?C l a s s i f yp r o t e i n so nt h eb a s i so f their functions along with one example. ANSWERS TO CHECK YOUR PROGRESS 2 5 . 1 1 . 2 . 3 . 4 . 5 . 6 . 2 5 . 2 1 . 2 . 3 . 4 . 5 . Autotrophs and heterotrophs Mushrooms, bread mould, bacteria, yeast (any two) Autotrophs/plants P a r a s i t e s :L i v eo no ri n s i d eo t h e rl i v i n go rg a n i s m st od e r i v et h e i rf o o d Saprophytes: Derive their food from dead and rotten organisms P a r a s i t e s :l e e c h , Cuscuta ( d o d d e rp l a n t ) ,h e a dl o u s e Saprotrophs: yeast and mushroom D o d d e rp l a n to r Amar bel Chloroplast Dark reaction P o t a t o ,o n i o n ,t a p i o c a( a n yt w o ) Sucrose s u n l i g h t 6CO2 + 12H2O c a r b o n w a t e r c h l o r o p h y l l d i o x i d e

C 6H 12O 6 + 6H2O + 6O2 g l u c o s e w a t e r o x y g e n

2 5 . 3 1 . 2 . 3 . 4 . 5 . 2 5 . 4 1 . 2 . 3 . 4 . 5 .

Roughage adds bulk to the food and helps in digestion. Hormones, such as insulin, growth hormone, thyroxine One gram of fatty substance yeilds more energy upon oxidation; Carbohydrates: 4.2 Kcal/g; Fats: 9 Kcal/g Wa t e rs o l u b l e : Vitamins B and C; Fat soluble: Vitamins A, D, E and K Vi t a m i n sa r eo rganic molecules, while minerals are inorg a n i cs a l t s . Vi l l i(s i n g.Vi l l u s ) Pepsin P e r i s t a l s i s S a l i v a r yg l a n d s ,l i v e ra n dp a n c r e a s HCl (hydrochloric acid)

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2 5 . 5 1 . 2 . 3 . 4 . 5 . 6 .

P r o t e i nE n e r g yM a l n u t r i t i o n N i g h tb l i n d n e s s ,p e l l a g r a ,b e r i b e r i ,r i c k e t s( a n yt w o ) U s eo fi o d i z e ds a l t L a c ko fa p p e t i t e ,l o s so fb o d yw e i g h t M i n e r a lo i l ,a rgemone oil (any one) Bureau of Indian Standards

GLOSSARY Nutrition: The process by which org a n i s m so b t a i nm a t e r i a lf o rt h e i rg r o w t h and development (from their environment). Autotrophs: O rganisms that can manufacture their own food. Hetero t rophs: O rganisms that depend upon other org a n i s m sf o rt h e i rf o o d . Sapro t rophs: O rganisms that derive their food from dead and rotten o rganisms. P a r a s i t e s :O rg a n i s m st h a tl i v eo no ri n s i d et h eb o d yo fo t h e rl i v i n go rganisms t od e r i v et h e i rf o o d . Photosynthesis: The process by which green plants manufacture food from c a r b o nd i o x i d ea n dw a t e ri nt h ep r e s e n c eo fs u n l i g h t . Nutrients: C h e m i c a lc o n s t i t u e n t sp r e s e n ti no u rf o o da n dr e q u i r e df o rt h e nourishment of our body. Balanced diet: D i e tt h a tc o n t a i n sa d e q u a t ea m o u n t so fe s s e n t i a ln u t r i e n t s , s u c ha sc a r b o h y d r a t e s ,f a t s ,p r o t e i n s ,m i n e r a l s ,v i t a m i n sa n dw a t e r. D i g e s t i o n :C o n v e r s i o no fc o m p l e xf o o dm a t e r i a li n t os m a l l e ru n i t ss ot h a ti t c a nb ea b s o r b e db yt h ec e l l s .

26

Transport of Materials in Plants and Animals
All plants need water. The wilted leaves recover when water is added to the soil, which means that water has been conducted upward into the leaves. You have also learnt that the leaves for photosynthesis need water. Likewise, the food produced in the leaves has to be transported to other parts of the plant including the stem, the roots flowers and fruits etc. All this transportation is the function of conducting tissues. Similarly, in animals, the food absorbed by the gut has to be carried to all the body parts, oxygen absorbed in the lungs has to be transported to every cell of the body, the carbon dioxide produced in the cells has to be carried to the lungs for elimination, and the poisonous body wastes like urea has to be transported to the kidneys for elimination in urine, and so on. All such functions are the outcome of a transport system. You will read about these aspects of plant and animal life in this lesson. OBJECTIVES After completing this lesson, you will be able to: • explain the need for a system of transport in plants and animals; • list and explain mechanism for movement of molecules such as diffusion, osmosis and active transport; • explain the structure and function of xylem and phloem in plants; • recognise the importance of blood as a medium of transport; • explain the structure and function of human heart; • describe the composition of blood; • differentiate between arteries, veins, and capillaries; • list the major blood groups and state the matching groups for blood transfusion; • mention disorders of circulatory system. 26.1 MECHANISMS FOR MOVEMENT OF MOLECULES Molecules move in and out of a cell through the cell membrane, which forms the boundary of each cell. The cell membrane is selectively permeable to substances, which means that it permits entry and exit of certain molecules only. The movement of molecules takes place by diffusion, osmosis, and active transport

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26.1.1 Diffusion Molecules move out from their region of higher concentration to the region of lower concentration. For example, during respiration, oxygen-laden air in lungs being at a higher concentration moves into blood capillaries having lower concentration of oxygen in them. Such movement of particles or molecules from a region of their higher concentration to a region of their lower concentration is termed diffusion.
Semi-permeable membrane Sugar molecule

Watar molecule

Watar Watar molecules at high concentration

Sugar solution Watar molecules at low concentration

26.1.2 Osmosis Osmosis is the movement of water molecules from a region having more water molecules to a region having less water molecules when separated by a semipermeable membrane. Semipermeable membrane means a membrane, which allows some molecules (e.g. water molecules) to pass through it but not some other larger molecules (Fig. 26.1). No energy is spent during diffusion or osmosis.

Fig. 26.1 The process of osmosis

26.1.3 Active transport In active transport, molecules have to move (against concentration gradient) i.e., from a region of their lower concentration to a region of their higher concentration. Energy is required in active transport. 26.2 TRANSPORT OF MATERIALS IN PLANTS

26.2.1 Transport of water Roots of plants take up water and minerals from the soil. How does this water move up from roots to leaves for needs like photosynthesis? You have already learnt about conducting tissues of plants – xylem and phloem in lesson 24. Tracheids and vessels (Fig. 26.2), which are non-living cells of xylem, transport water picked up by root hairs (Fig. 26.3) from soil to the leaves.
Open end of vessel

Lignified wall Lignified thickening to give the wall extra strength Root hair

Cavity carries water and mineral salts

Root tip

Root cap

Fig. 26.2 Vessels in xylem

Fig. 26.3 Root hairs

Transport of Materials in Plants and Animals : 195 :

The upward movement of water and minerals termed ‘ascent of sap’ is against gravity and is due to transpiration pull. Transpiration is the process in which a lot of water evaporates (as water vapour) from pores on the surface of leaf called stomata (Fig. 26.4). This evaporation creates a vacuum and pulls up water through the xylem. 26.2.2 Transport of food material Sugars and other food molecules synthesised in the leaves are transported to other parts of the plant through phloem. Sieve tubes are living cells of the phloem, which transport food (Fig. 26.5). Transport of food material from leaves to other parts of the plant is called translocation. This food may be stored in fruits, stem or roots. CHECK YOUR PROGRESS 26.1 1. In which type of molecular movement is energy required? 2. Define osmosis. 3. Name the two kinds of cells of xylem. 4. Which cells of phloem pass on food from one part of the plant to another? 5. Which out of the following are non-living parts: tracheids, vessels, sieve tubes?
Fig. 26.4 Structure of stomata

Nucleus

Stomatal pore

Guard cell epidermal cell

Chloroplast

End wall perforated by pores

26.3 TRANSPORT OF MATERIALS IN ANIMALS In the body of majority of animals, substances are transported from one part of the body to another through blood. Thus blood is the “tissue for transport” and circulates throughout the body. Circulatory system consists of organs, which make blood circulate throughout the body. Blood transports nutrients, respiratory gases, hormones and waste material from one part of the body to another.

Cellulose wall

Cavity contains very fine strands of cytoplasm

26.3.1 Human circulatory system Fig. 26.5 Sieve tubes in phloem Human circulatory system consists of (i) Centrally located muscular pump called heart, and (ii) Blood vessels, which are tube-like structures, connected to the heart (Fig. 26.6). Blood vessels are of three kinds: • Arteries: Carry blood from heart to various parts of body. • Veins: Bring blood from various parts of body to the heart. • Capillaries: Thin vessels between the artery and the vein. The capillaries allow the exchange of materials between blood and tissues.

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Jugular vein

Carotid artery Subclavian artery Aorta

Subclavian vein

Pulmonary vein

Heart

Vena cava Hepatic vein

Pulmonary artery Lung

Liver Hepatic portal vein Gut Renal vein

Hepatic artery

Kidney

renal artery

mesenteric artery Iliac vein Iliac artery

Fig. 26.6 Circulatory system in human beings

Sinoatrial node

Left auricle

Right auricle

26.3.2 Heart a) Structure: Heart is a powerful muscular organ lying between lungs in the upper part of thorax of our body. It is four-chambered- two (right and left) atria (sing. atrium, also called auricles), and two (right and left) ventricles. (Fig. 26.7). The heart is made of specialised muscle cells (also called cardiac muscle fibers), which contract and relax all the time without getting tired. The contraction and relaxation follows a rhythm called heartbeat to pump blood into the vessels.

Right ventricle

Left ventricle

Fig. 26.7 The human heart

Rhythmic heart beat results in the proper transport of substances to the various organs. In one minute, normal human heart beats about 72 times. Abnormalities in heartbeat can be seen by taking ECG or Electrocardiography (Fig. 26.8).

Transport of Materials in Plants and Animals : 197 :

b) Functions of heart: A large vein, the vena cava collects impure or deoxygenated blood (blood low in oxygen and high in carbon dioxide) through veins from all parts of the body and empties into the right atrium. At the same time vein from the lungs brings oxygen-laden blood to left atrium. At this time all the four chambers of the heart are relaxed. Then the atria contract and impure blood (blood full of carbon-dioxide) from right atrium enters the right ventricle and purified blood (blood full of oxygen) from left atrium enters the left ventricle. Valves within the heart prevent blood from flowing back. Next, the ventricles contract while the atria relax. Blood to be purified is transported to the lungs from right ventricle through two pulmonary arteries. The oxygen laden blood from the left ventricle gets pumped into a large artery called aorta. It carries oxygenated blood to all parts of the body (Fig. 26.9). You must have noticed that veins bring impure blood to the heart and the arteries take the pure blood away from the heart. But here are two exceptions – the pulmonary artery carries impure blood and the pulmonary vein carries pure blood.

Fig. 26.8 Electrocardiograph

Head

Anterior vena cava

Lungs Pulmonary vein

Carotid artery

Great veins (venae cavae)

Pulmonary artery Heart

RA LA

RV LV Aorta Posterior vena cava Hepatic vein Liver Hepatic artery

Hepatic portal vein Gut

Rest of Body

CHECK YOUR PROGRESS 26.2 Fig. 26.9 General plan of the human 1. What are the different parts of human circulatory system circulatory system? 2. What are capillaries? 3. In which category of blood vessels exchange of nutrients and respiratory gases occur between blood and tissues? 4. Name the kind of muscle fibres that make the heart? 5. What is the function of valves in the heart? 26.3.3 Blood Blood is a connective tissue that circulates throughout the body. It is made up of a fluid medium called plasma in which float three types of blood cells, called red blood cells, white blood cells and blood platelets. Blood cells are manufactured in the bone marrow. (Fig. 26.10) a) Red blood cells (RBC or Erythrocytes)

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These are circular in shape, and contain a red coloured pigment called haemoglobin No nucleus is present in RBCs RBC carry oxygen to tissues and bring back carbon dioxide from tissues About 5 million mm 3 erythrocytes occur in circulating blood


Section through red cell (a) Red cells


Blood platelets Bacteria

Nucleus



Phagocyte

Lymphocyte (c) White cell engulfing bacteria

(b) Two types of white cells

Fig. 26.10 Types of blood cells

b) White blood cells (WBC or Leucocytes)

• • • •

In the circulating blood 5000 to 7000 mm3 WBCs are present Since they carry no pigments, therefore, they so are colourless WBC have irregular shape They prevent body from infections by eating up germs or by producing antibodies

c) Blood platelets (Thrombocytes) • These are very small fragments of cells • They have no nuclei • They participate in clotting of blood Functions of blood: Blood carries nutrients, oxygen, carbon dioxide, hormones and waste material to the relevant parts of the body. Some medicines when taken in the body are also distributed through blood. 26.4 BLOOD GROUPS AND BLOOD TRANSFUSION You must have heard that blood has to be arranged for a person undergoing a surgery (operation) or in the case of an accident. This arrangement is to replace blood lost from the patient. Injecting blood into the body from outside is called blood transfusion. Blood transfusion is successful only when the blood of donor (who gives blood) and of the recipient (who receives blood) match. Unmatched blood transfusion causes agglutination (clumping together) of red cells due to which the recipient may even die. Blood of all human beings belongs to one of four blood groups named A, B, AB and O. the blood group is inherited from parents. Table 26.1 shows the matching blood groups. Table 26.1 : Various blood groups in humans

Transport of Materials in Plants and Animals : 199 :

BloodGroup A B AB O

Can donate to blood group A, AB B, AB AB A, B, AB, O

Can receive blood from blood group A, O B, O A, B, AB, O O

The same may be depicted in a simple form as follows: You must have noticed that persons with blood group O can donate blood to all and ‘O’ group is called universal donor and AB group can receive blood from all and is called universal recipient.

A
Universal donor

O

AB

Universal recepient

26.5 LYMPHATIC SYSTEM B Lymph is also a circulatory fluid and flows in the lymph vessels. • It is light yellow in colour. • It always flows only in one direction from tissues to heart. • Cells called lymphocytes present in lymph eat up germs and prevent body from infections. • Lymph carries digested fats from intestine to other parts. • It returns proteins and fluid from circulation to tissues. 26.6 DISORDERS RELATED TO CIRCULATORY SYSTEM 1. Heart attack: Like all other organs, heart also needs food and oxygen. When arteries supplying the heart become thick due to age or faulty diet consisting of excessive fatty food, muscle cells of the heart cannot beat in the proper rhythm. Heart attack occurs which can be detected in an abnormal ECG and there are methods of treatment. 2. Anaemia: When haemoglobin level falls below a certain point the condition is called anaemia. It makes the person weak and look pale and inactive. Iron in the diet helps remove anaemia. 3. Leukemia: This is blood cancer. The bone narrow makes excessive WBCs at the cost of RBCs. 4. Hypertension: It is high blood pressure and leads to headache, dizziness and fatigue. Normal blood pressure is 120/80. High blood pressure is caused by anxiety also. Proper diet, exercise, medicines and tension free mind helps to cure high blood pressure. CHECK YOUR PROGRESS 26.3 1. What are the components of blood? 2. State one function each of RBC, WBC, and blood platelets. 3. Which category of blood cells do not have nuclei? 4. Which blood group is called “universal donor”? 5. In which direction does lymph flow? LET US REVISE

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• • • • • • • • • • • • • • • • • • • • • • • • •

Molecules move in and out of cells by diffusion, osmosis or active transport. Diffusion is movement of molecules from region of their higher concentration to the region of their lower concentration. In osmosis, water molecules move from their region of higher concentration to that of their lower concentration. In active transport, molecules move against concentration gradient. Energy is required for active transport. In plants, water is absorbed from soil by root hairs and reach leaves and other parts through xylem vessels. Tracheids and vessels are cells of xylem. They are non-living. Ascent of sap is facilitated by transpiration pull. Food in plants is translocated by phloem. Sieve tubes, the cells of phloem are living structures. In most animals, blood circulates through heart and blood vessels to reach all parts of body. Blood flowing through the body transports food, nutrients, oxygen, hormones, metabolic waste and carbon dioxide. Heart in humans is four-chambered, two upper chambers are called atria and lower chambers are ventricles. Heart is made of cardiac muscle fibres. Heart pumps blood into blood vessels for transport by relaxing and contracting in a rhythmic manner called heartbeat. Heartbeat is recorded as ECG or Electrocardiogram. Of the blood vessels, artery carries blood away from heart, vein carries blood towards heart. Capillaries are thin blood-vessels between an artery and a vein. Blood is made of plasma, a fluid and three types of blood cells called RBC, WBC and blood platelets (cell fragments). RBCs are circular, non nucleated and carry respiratory gases. They contain a red pigment, haemoglobin. WBCs are colourless and of varied shape. They protect the body from infections. Blood platelets play a role in blood clotting. Blood transfusion can save life when blood loss occurs due to accident or surgery. Every human being belongs to one of four blood groups: A, B, AB and O. Blood transfusion can be between matching blood groups. O group is universal donor and AB blood group is universal recipient. Lymphatic system is made of lymph vessels in which a colourless fluid called lymph flows. Lymph flows only from tissues to heart and serves to transport proteins and digested fat. TERMINAL EXERCISES

Transport of Materials in Plants and Animals : 201 :

A. Multiple choice type questions. 1. Which cells of conducting tissues of plants are dead? a) Sieve tubes b) Tracheids c) Stomata d) Phloem 2. Which kind of muscle fibres is found in the human heart? a) Striated b) Unstriated c) Cardiac d) Voluntary 3. What is a lymph? a) A fluid which flows in one direction only b) A fluid which carries material from heart to tissues c) Another name for blood d) A fluid with red coloured cells 4. What happens when the atria contract? a) Blood from left ventricle flows into aorta. b) Blood from right ventricle flows into pulmonary artery. c) Blood from pulmonary vein enters left atrium. d) Blood which is almost without oxygen flows from right atrium to right ventricle. 5. Pulmonary artery carries carbon dioxide laden blood while all other arteries carry oxygenated blood. It is still called an artery because, a) its structure is like that of a artery b) it carries blood away from heart c) it transports blood towards the heart d) it brings blood from lungs to heart B. Descriptive type questions. 1. Name the three kinds of blood cells. 2. How many chambers does the human heart have? What are the lower chambers called? 3. Name the two kinds of cells of xylem. 4. Through which pores on the leaf does transpiration occur? 5. Mention one point of distinction between (a) artery and vein(b) vein and capillary 6. What happens to blood when (a) right atrium contracts (b) left ventricle contracts 7. From donor of which blood group can a person with blood group O receive blood? 8. State two functions of lymph. 9. In plants, where is food synthesised and through which tissue is it translocated? 10. What does “ascent of sap” mean?

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11. Describe the events in the heartbeat. 12. Make a flow chart to show the flow of blood from one chamber of heart to the other and to the lungs and other parts of the body. 13. Draw a simple labelled diagram of the internal structure of human heart. 14. Write a note on lymph. 15. Write a note on composition of blood. 16. Name two disorders related to the circulatory system and write a note on any one of them. C. Difficult but try Rahul’s blood group is A, Gita’s blood group is AB and Ravi’s blood group is O. Who can donate blood to whom in case of an emergency? ANSWERS TO CHECK YOUR PROGRESS 26.1 1. 2. 3. 4. 5. 26.2 1. 2. 3. 4. 5. 26.3 1. 2. Active transport Net movement of water molecules from a region of higher concentration of water to a region of lower concentration of water. Tracheids and vessels. Sieve tubes Tracheids, vessels Heart and blood vessels like artery, vein and capillaries Thin walled blood vessels through which exchange of material takes place. Capillaries connect artery to vein. Capillaries Cardiac muscle fibres To permit blood to flow only in one direction / to prevent back flow of blood. Plasma and blood cells like RBC, WBC and blood platelets. RBC – To carry oxygen to tissues from lungs / carbon dioxide from tissues to lungs. WBC – To eat up foreign particles, to produce antibodies, to fight against disease Blood platelets – Factor required for blood clotting RBC Group O From tissues to heart GLOSSARY

3. 4. 5.

Transport of Materials in Plants and Animals : 203 :

Selectively permeable: That membrane which permits transport of only certain molecules through it and not others. Diffusion: Process of movement of molecules from the region of their higher concentration to the region of their lower concentration. Osmosis: Process of movement of molecules of water from region of their higher concentration to a region of lower concentration of water. Active transport: Movement of molecules, with consumption of energy against the concentration gradient that is from a region of their lower concentration to that of their higher concentration. Transpiration pull: Ascent of water against gravity because of pull exerted by transpiration of water from leaves. Translocation: Transport of food materials in plants from leaves to other parts. Atria: Upper chambers of the human heart. Ventricles: Lower chambers of the human heart. Blood transfusion: Introduction of blood from one person into another. Universal donor: A blood group in whose case blood can be donated to all other groups. Blood group O is considered as the universal donor. Universal recipient: A blood group in whose case blood from any other group can be received during blood transfusion. Heart attack: A condition of the muscles of heart in which rhythm of heartbeat becomes abnormal. Leukemia: Blood cancer in which the number of WBCs increase in blood beyond normal number. Hypertension: High blood pressure.

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27

Respiratory Gaseous Exchange and Elimination of Body Wastes
We can live without food for several days but we cannot live without breathing even for a short while. Breathing provides oxygen to the cells of our body for oxidation of food in order to generate energy for various activities. Breathing along with utilization of oxygen in the cells and release of carbon dioxide is included in the process of respiration. Another vital function of life is excretion. Excretion is the process of eliminating certain body waste, which if retained in the body would act like a poison and make us ill or even kill us. In this lesson, you shall learn how oxygen reaches all the cells and how carbon dioxide and other wastes are removed from our body. Plants too need to respire as well as need to remove wastes from their body. You will also learn about respiration in plants in this lesson. OBJECTIVES After completing this lesson, you will be able to: • • • • • • • • • • • • distinguish between breathing and respiration; explain the need for respiratory gaseous exchange; explain the structure of stomata and their role in respiratory gaseous exchange in plants; sketch the human respiratory organs; explain the mechanism of breathing in the human body; explain briefly the exchange of gases at the level of tissues; name few respiratory disorders; define the term excretion; give a brief account of excretion in plants; list the different parts of human excretory system and draw them; explain briefly the mechanism of waste formation and its elimination; suggest a treatment for kidney failure.

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27.1 NEED FOR RESPIRATORY GASEOUS EXCHANGE Every cell of our body needs to produce energy for its activities. This energy is produced by oxidising the food (glucose), which the cell receives as product of digestion. Oxygen is required for oxidation of glucose in the cell. The intake of oxygen for the release of energy by its action on glucose is termed as respiration. 27.2 BREATHING AND RESPIRATION The mechanism by which organisms obtain oxygen from the environment and release carbon dioxide into it is termed breathing. Respiration in ordinary sense is a wider term, it includes breathing as well as (i) exchange of oxygen and carbondioxide in the tissues, and (ii) action of oxygen on glucose inside the cell to release energy (oxidation). 27.3 RESPIRATION IN PLANTS Plants do not have any special respiratory organs. Roots take up oxygen by means of root hair (Fig. 27.1). Root hair are embedded in the soil. Oxygen in the air surrounding them diffuses into the root hair and from there into Lateral root the roots. The carbon dioxide given out, similarly, diffuses out through roots. You may check the mechanism of diffusion in the lesson Primary root 26 on transportation.
Root hairs

Apical meristem Root cap

Tiny apertures called stomata (Fig. 27.2) are found on the surface of the leaf. They have a mechanism for opening and closing. They open to let in oxygen and release carbon dioxide. In the older parts of roots or bark of woody plants, tiny openings called lenticels are present. It is through these lenticels that oxygen reaches the Thick cell wall inner living tissues and carbon dioxide moves out. CHECK YOUR PROGRESS 27.1 1. Roots are present below the soil. Do they pick up oxygen from air surrounding the root hair or from the water surrounding them? 2. Name the apertures found on the green stems and leaves that let in oxygen.

Fig. 27.1 Root hairs
Flaccid guard cell Closed Turgid guard cell Open

Stoma closed

Stoma open

Thin cell wall When a plant has plenty of water, the guard cells become turgid. The cell wall on the inner surface is very thick, so it cannot stretch as much as the outer surface. So as the guard cells swells up, they curve away from each other, opening the stoma.

When a plant is short of water, the guard cells become flaccid closing the stoma.

Fig.27.2 Opening and closing of stomata

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3.

The bark of woody plants is dead but the inner layers inside the bark are living. How do they get oxygen and release carbon dioxide? 4. Differentiate between breathing and respiration. 5. How does respiration help in the release of energy? 27.4 RESPIRATION IN ANIMALS

Animals have special organs for respiration. Most aquatic animals have gills (e.g. fish, prawn). The major organs for respiration in land animals are the lungs.

Nostril Tongue Trachea (windpipe)

Rib Bronchiole

Left lung Bronchi

(a) Fish (gill breather)

Diaphragm (b) Human (lung breather)

Heart

Fig. 27.3 Gill and lung breather

27.4.1 Respiration in human beings Like other land animals, human beings take in oxygen from the surrounding air and release carbon dioxide into it. 27.4.1a Respiratory system Respiratory system of human beings has the following parts (Fig. 27.4). • • • • • External nares or nostrils Nasal cavities inside the nose Internal nostrils opening into pharynx Pharynx that leads into the wind pipe or trachea Trachea divides into two bronchi (sing bronchus) which lead into the two lungs

Branch of pulmonary artery

Bronchiole

Alveoli covered with capillaries

Branch of pulmonary vein

Voice box

Alveoli Wind pipe Alveoli cut open Bronchus Ribs Right lung Bronchiole Heart Rib

Diaphargm

Fig. 27.4 Respiratory system in human beings

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The opening of the pharynx into the trachea is called glottis. Trachea is thin walled but its walls do not collapse even when there is negligible amount of air in it as it is supported by rings of cartilage. Lungs enclose within them branches of bronchi called bronchioles which branch further and end in very thin walled sac-like structures called air sacs or alveoli (sing. alveolus). 27.4.1b Mechanism of breathing or Ventilation of lungs Lungs are located in the chest cavity or the thoracic cavity. Below the chest cavity is the abdominal cavity. These two cavities are separated from each other by a dome-shaped (upwardly arched) muscular sheet called diaphragm (see figure). The movements of this diaphragm help in breathing. Breathing, also called ventilation of the lungs involves two processes • inhalation (taking the air inside) • exhalation (forcing the air out) (i) Inhalation (drawing the air inwards) (Fig. 27.5a) is the result of increase in the volume of the thoracic cavity. This increase is caused by the changes that take place in the position of diaphragm and ribs. • Diaphragm straightens out • Ribs are raised upward and outward and volume of chest cavity increases. • The air drawn in brings in oxygen which diffuses into the alveolar air. (ii) Exhalation (Fig. 27.5b) is the result of decrease in the volume of the thoracic cavity. This decrease in the volume is caused due to the following: • Diaphragm relaxes and resumes its domeshape arching upwards.
Diaphargm springs up Volume of thorax decreases, forcing air out of the lungs

Rib cage is raised

Volume of thorax increases, so air is drawn into the lungs Diaphargm is pulled down

(a) Inhalation Trachea

Rib cage drops down

• Ribs are lowered downward and inward. The thoracic cavity is compressed and the pressure inside the lungs is increased. Air is pushed out through the trachea and nose. The alveolar carbon dioxide diffuses out. This breathing out of carbon dioxide laden air is called exhalation. You can breathe heavily and feel your chest go up and down.

(a) Exhalation

Fig. 27.5 How the thorax changes shape during breathing

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Breathing rate When at rest, an adult human breathes about 16 to 18 times per minute. Breathing rate increases during physical exercise, disease, fever, pain and under stress. Exchange of gases between blood and tissues Inhalation fills in the alveoli of lungs with oxygenated air. This oxygen has to reach the various tissues of the body. Thus as the first step, blood capillaries on alveoli (Fig 27.6) pick up oxygen from alveoli and carbon dioxide brought by the capillaries from the tissues is exchanged for oxygen and diffuses into alveoli.
Air moves in and out Bronchiole Cell in wall of capillary Wall of alveolus Wall of capillary

Cell in wall of alveolus CO2 diffuse O2 diffuse in out Alveolus
Blood vessels bring blood without much oxygen from the pulmonary veins

Air space in alveolus
Blood vessels return oxygenated blood to the pulmonary veins

Red blood Elastic fibre cell
White blood cell, which can destroy bacteria that get into the alveolus

Layer of moisture

Red blood cell

(a) Alveoli

(b) Section through part of a lung (magnified)

(c) Gaseous exchange in an alveolus

Fig. 27.6 Exchange of gases between blood and alveoli

In the tissues, oxygen gets used up and carbon dioxide is accumulated which is now exchanged for oxygen. The carbon dioxide picked up by blood from tissues is carried to the heart through veins. 27.4.1c Cellular respiration Once inside the tissues, oxygen acts upon the digested food (glucose) which has reached the cells of the tissues. As a result energy and carbon dioxide are released. This occurs in the mitochondria of the cells and is called cellular respiration. Respiration suffers at high altitudes and great depths. Do you know why mountaineers and sea divers carry oxygen cylinders and wear oxygen masks? As we climb higher and higher altitudes, the air pressure becomes lower and lower. Reduced oxygen supply causes breathing troubles and oxygen masks facilitate breathing. People living in hilly areas have evolved adaptation such as increased number of red blood corpuseles and large thoracic cavity. Divers carry oxygen masks because we derive our respiratory oxygen from air and not water.

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27.4.1d Artificial respiration A victim of an accident like drowning, electric shock or inhalation of poisonous gas suffers from “asphyxia” or the condition of lack of oxygen. The symptoms are blueing of lips, fingernails, tongues and stoppage of breathing. In such cases mouth-to-mouth respiration is given. You must have realised how important respiration is for survival. Medical technology has introduced certain gadgets like the “oxygen mask” and “ventilators” which aid in respiration when a patient develops breathing problems. Often these help the patient to overcome respiratory problems. 27.4.2 Respiratory disorders Two common diseases of the respiratory system are bronchitis and pneumonia. 27.4.2a Bronchitis In bronchitis, the bronchi and bronchioles get inflamed and their cavities become narrow so that air cannot pass in and out of lungs easily. The pathway gets constricted either due to accumulation of mucus on the walls of the bronchi or bronchioles. This happens due to excessive smoking. Also infection of the accumulated mucus leads to inflammation of walls of the lungs and bronchi, which narrow the airways and cause difficulty in breathing. 27.4.2b Pneumonia Pneumonia is caused by pneumococci bacteria. These bacteria attack the trachea and bronchi and spread to the terminal bronchi. Symptoms of pneumonia are shivering, vomiting and continuous fever. Antibiotics have to be administered to cure bronchitis and pneumonia. CHECK YOUR PROGRESS 27.2 1. Why does the trachea not deflate (collapse) when the air is pushed out? 2. Name the parts of the human respiratory system in a sequence starting from the nose. 3. State the events which occur during inhalation. 4. In which organelle of the cell does cellular respiration occur? 5. Why are the alveoli supplied with capillaries? 27.5 EXCRETION Many chemical reactions take place inside the body cells. Some products of these chemical reactions are not needed by the body. They may even be harmful. Most of these waste products contain nitrogen and therefore they are termed nitrogenous waste products. Their removal from the body is called excretion. We shall now learn about the excretory organs and mechanism of excretion. 27.5.1 Excretion in plants In plants, breakdown of substances is much slower than in animals. Hence accumulation of waste is much slower and there are no special organs of excretion

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in plants. Carbon dioxide released during respiration gets utilized during photosynthesis. However, a number of chemical substances which are formed as byproducts during certain activities of plants, are known to be thrown out of the plant and deposited on the bark, old wood, old leaves etc. These substances may be nitrogenous such as alkaloids, or non-nitrogenous such as oils, resins and crystals of silica. The alkaloids include Quinine, which deposits in the bark of the cinchona tree and is a medicine for malaria; Morphine in poppy fruits was used as an anaesthetic. Caffeine, which yields the beverage coffee is deposited in coffee leaves. The non-nitrogenous substance exuded by plants include: tannins found in tea leaves, essential oils such as are deposited in leaves of tulsi and lemon and Eucalyptus, resins thrown out are deposited on the bark of pine trees. We use resins in varnish and polish. In certain grasses crystals of silica are deposited by the plant. 27.5.2 Human excretory system In human beings, excretion is carried out by an organ system known as the urinary system or the excretory system. See the figure (Fig.27.7) and locate the following parts: • Two bean shaped kidneys, located below the diaphragm in the abdomen and towards the back. Two excretory tubes or ureters, (one from each kidney). One urinary bladder, ureters open into it. A muscular tube called urethra arises from the bladder. The urinary opening is at the end of urethra.

Blood vessels Diaphragm

Kidney (makes urine)

• • •

Ureter (carries urine to the bladder) Bladder (stores urine)

Sphincter muscle (when relaxed urine can leave body)

Urethra tube (leading from bladder out of body)

27.5.2a Structural and functional unit Fig.27.7 Human excretory system of the kidney — Nephron Each kidney is made of tube like structures called nephrons (renal tubules). A nephron is the structural and functional unit of the kidney. The cup-shaped upper end called Bowman’s capsule, has a network of capillaries within it called glomerulus. Glomerulus is a knot of capillaries formed from the artery which brings blood containing wastes and excess of water to the kidney. Bowman’s capusle leads into a tubular structure. The tubular part of the nephron or renal tubule has three sub-parts, the proximal convoluted tubule (PCT), a thinner tube called loop of Henle and the

Respiratory Gaseous Exchange and Elimination of Body Wastes : 211 :

distal convoluted tubule (DCT) (Fig. 27.8). Blood capillaries surround these tubules.
Renal artery

Renal vein

27.5.2b Mechanism of excretion Blood leading into the glomerulus gets filtered in the Bowman’s capsule and is called the nephric filtrate. The red blood corpuscles and proteins do not filter out. The filtrate which now comes into the renal tubule not only contains waste but also useful substances. The useful substances get reabsorbed from the tubule into the blood capillaries surrounding the tubule. Excess water and salts like sodium and chloride also get reabsorbed into the blood from the renal tubule. Thus, the waste alone which is primarily in the form of urea enters into collecting tubules from various renal tubules. It is the urine. From the kidneys, the urine enters the ureters to reach the urinary bladder where it is stored temporarily. The urine is thrown out periodically through the urinary opening.

Ureter (a) A Kidney

Urine

Branch of renal artery Glomerulus Bowman’s capsule
Distal convoluted tubule Proximal convoluted tubule

Capillaries Branch of renal vein Loop of Henle Collecting duct Capillaries

27.5.2c Functions of the kidneys Fig. 27.8 Structural and functional • Excretion of nitrogenous wastes, unit of the kidney — Nephron • Regulating the water content of the body (osmoregulation), and • Keeping the normal mineral balance in the blood. When this balance is upset, a person can fall sick. 27.5.3 Other organs that remove waste from our body Apart from kidneys, some other organs of the body also remove waste from the body. These organs are as follows (Fig. 27.9)
Skin Liver Amino acids Blood Excess Heat Kidney Urea Excess water and minerals Oxygen Glucose Heat Cells Lungs

(b) One nephron (highly magnified)

Carbon dioxide

Fig. 27.9 Some organs of our body that remove waste

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• Sweat glands in the skin remove excess salts when we perspire. • Lungs remove carbon dioxide. • Rectum (large intestine) removes undigested food. 27.5.4 Maintenance of the internal environment A person gets sick if the balance of substances such as mineral ions, water or even hormones inside the body is upset. Maintenance of the correct amount of water and mineral ions in the blood is termed osmoregulation. Osmoreulation is a function of the kidney. Homeostasis means maintaining a steady state inside the body. It requires the regulation of all substances inside the body in the correct amount and proportion. Kidneys and liver play an important role in maintenance of homeostasis. 27.5.5 Kidney failure, dialysis and kidney transplant Certain diseases or sometimes an accident may lead to kidney failure. Since the number of nephrons is as large as almost one million in each kidney, a person can survive even with one kidney. However, in case both the kidneys are damaged, it is difficult to remain alive. Modern technology can now save such patients with the helps of new techniques like dialysis and kidney transplant. As shown in the figure (Fig. 27.10) an artificial kidney is employed. A tube is inserted in an artery in the patient’s arm or leg. The tube is connected to the kidney machine. This plastic tube has two membranes so as to form one tube within the other. In the inner tube flows blood from patient’s artery. This blood is surrounded by fluid (dialysis fluid) in the outer tube, separated from it by the membrane of the inner tube. Wastes move out of blood into the fluid. The blood cleaned of its waste goes back from the kidney machine into the vein in the arm or leg and back into the body. The kidney dialysis fluid carrying waste is removed from the machine. This technique is termed dialysis. Nowadays, surgeon sometimes remove a nonfunctioning kidney from a patient and replace it with a kidney donated by another person. Care, however, has to be taken so that a foreign kidney gets accepted by the body. CHECK YOUR PROGRESS 27.3 1. Define excretion. 2. Name the organ of the excretory system, which stores urine before its removal from the body.
Line from apparatus to vein Line from artery to apparatus Pump Tubing made of a selectively permeable membrane

Dialyzing solution

Fresh dialyzing solution

Fig. 27.10 Kidney dialysis

Used dialyzing solution (with urea and excess salts)

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3. In which part of the nephron does filtration occur? 4. What happens to the useful substances that get filtered into the renal tubule? 5. What is osmoregulation? TERMINAL EXERCISES A. Multiple choice type questions. Select the most appropriate answer of the following. 1. Which of the following is NOT a step in the process of respiration? (a) Breathing (b) Diffusion of oxygen from blood to tissues (c) Diffusion of oxygen from tissues to blood (d) Production of energy 2. From which part of the respiratory system is oxygen picked up by the blood? (a) Trachea (b) Bronchus (c) Alveolus (d) Nostrils 3. Which one of the following is not a part of nephron? (a) Loop of Henle (b) Proximal Convoluted tubule (PCT) (c) Distal Convoluted Tubule (DCT) (d) Seminiferous tubules. 4. Identify the process involved in the functioning of the artificial kidney. (a) Renal transport (b) Dialysis (c) Renal failure (d) Catalysis 5. Which is the correct sequence of the following parts of the urinary system? (A) Kidney (B) Ureter (C) Urethra (D) Urinary bladder (a) B A C D ( b) D C B A (c) A B C D (d) A B D C B. Fill in the blanks. 1. Excretion is a process of removal of _______________ waste. 2. Nephrons are the functional units of __________________ 3. The main excretory nitrogenous product in human beings is _____________ 4. The openings in plant leaves through which gaseous exchange takes place are called _____________________ C. Descriptive type questions. 1. State one point of difference between each of the following: (i) Breathing and respiration (ii) Inhalation and exhalation (iii) Ureter and urethra (iv) Homeostasis and osmoregulation (v) Bowman’s capsule and glomerulus (vi) Bronchi and bronchioles 2. Which step occurs earlier than the other - breathing or cellular exchange of gases? 3. What happens to the size of thoracic cavity when we breathe in air? 4. Describe the mechanism of breathing in human beings.

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5. 6. 7. 8. 9.

How are respiratory gases exchanged between blood and tissues? Draw the urinary system in the human body and label its parts. What is glottis? Mention its function. Explain the mechanism of excretion. Write notes on the following: (i) artificial kidney (ii) glomerular filtrate (iii) organs of excretion in human beings ANSWERS TO CHECK YOUR PROGRESS

27.1 1. Air 2. Stomata 3. Through lenticels 4. Breathing is the mechanism for obtaining oxygen from the environment and release carbon dioxide into it / respiration is the intake of oxygen as also its utilization by cells for release of energy. 5. Energy is released through oxidation of food (glucose) during respiration in cells. 27.2 1. The cartilaginous rings around the trachea prevent its collapse. 2. External nostrils, nasal cavity, internal nostrils, pharynx, trachea, bronchi, lungs. 3. The diaphragm contracts, thoracic cavity increases in volume, air from outside rushes into lungs. 4. Mitochondria 5. They pick up oxygen from alveoli and carbon dioxide carried by them diffuses into alveoli. 27.3 1. Excretion is the process of removal of nitrogenous waste products. 2. Urinary bladder 3. Glomerulus 4. They are reabsorbed into blood 5. Maintaining the normal amount of water and mineral ions in blood is termed Osmoregulation GLOSSARY Bowman’s capsule: Thin walled cup-shaped part of the nephron with the glomerulus lying within the cup. Bowman’s capsule leads into the renal tubule. Breathing: The mechanism in which oxygen from the environment is taken into the lungs and carbon dioxide present in the lungs removed.

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Bronchitis: A respiratory disease in which the air passages in lungs become inflamed. Cellular respiration: The oxidation of glucose in the mitochondria of the cell. Dialysis: The mechanism of cleansing the blood of its waste outside the body by using a ‘kidney machine’. Diaphragm: A muscular partition between the thoracic cavity and abdominal cavity of mammals which participates in breathing. Excretion: The process of elimination of nitrogenous waste products from the body. Exhalation: Removal of carbon dioxide from the lungs during breathing. Glomerulus: A network of capillaries, which is a part of nephron. Inhalation: Intake of oxygen-laden air into the lungs during breathing. Lenticels: Tiny openings in older parts of roots and bark of woody plants for exchange of gases. Nephron: The structural and functional unit of the kidney. It is made of glomerulus and renal tubule. Pneumonia: The inflammation of lungs due to fluid accumulation in the alveoli caused by bacterial infection. Stomata: Openings in leaves which open and close for exchange of gases. Respiration: The intake and utilization of oxygen for oxidation of glucose in the cells for the liberation of energy. Renal tubule: The tubular part of the nephron.

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28

Control and Coordination
In the earlier lessons you have studied that the body of all living organisms is made up of cells. These cells aggregate and differentiate to form tissues and assembly of different tissues forms different organs. The various organs perform their functions at the right time so that they can work together efficiently. Therefore, some form of control is needed to coordinate their functions. For example, when we eat food, our eyes help in locating the food, our nose senses the food, our hand brings the food to our mouth and our jaw muscles help the teeth to chew the food. All these activities occur in a coordinated manner, and if any of these activities misses or does not occur in time then the body will not get nutrition. In case of animals, including man, the chemicals produced by ductless (endocrine) glands also bring about coordination. This coordination by chemicals is brought about by the endocrine system. On the other hand the nervous system consists of a series of nerve cells throughout the body. Signals from one part of the body are transmitted to another part through these nerve cells. You know that our sense organs are gateways for receiving information or stimuli from the environment and help in maintaining a state of stability between the internal conditions of an organism and its external environment. In this lesson we will learn about the nervous system, the endocrine system and sense organs of our body. OBJECTIVES After completing this lesson, you will be able to: • relate nervous system and endocrine system with the function of control and coordination; • recognise sense organs as gateways for receiving information from the environment; • recall nerve cell as the basic structural and functional unit of nervous system and explain the terms synapse and nerve; • define nerve impulse; • identify the components of central nervous system and explain what is grey matter and white matter; • describe the major regions of human brain and list their functions;

Control and Coordination: 217:

• • • • • • • • •

describe the location and structure of spinal cord and recognise its function relating to reflex action; name the parts of the eye and explain vision in simple terms; explain accommodation of the eye and give reasons for short sightedness (myopia), long sightedness (hypermetropia) and their correction; explain the structure and working of the ear; describe various ways of taking care of sense organs; draw an outline diagram of human body and show the location of various endocrine glands; list the hormones secreted by pituitary, thyroid and pancreas; give a brief idea of feedback mechanism in hormonal activity; state the symptoms and cause of cretinism, goitre and diabetes mellitus.

28.1 NERVOUS SYSTEM The organ system in an animal that serves to coordinate and control the functioning of all other organ systems in the body is known as nervous system. Nervous system works with the endocrine system to communicate, integrate and coordinate the functions of various organs and systems in our body and helps the body to respond to the external stimuli. In humans, the nervous system has two main divisions: • The central nervous system (CNS) • The peripheral nervous system (PNS) The central nervous system consists of brain and spinal cord. It is regarded as the ‘thinker’ or ‘information processor’ in the body. The peripheral nervous system includes the sensory and motor nerves and connects the central nervous system with the sense organs, muscles and glands of the body. The peripheral nervous system is regarded as ‘actor’ or ‘performer’ in the body. The organisation of nervous system is given in Fig. 28.1. NERVOUS SYSTEM Central nervous system Brain Spinal cord Peripheral nervous system Sensory (afferent) nerves Motor (efferent) nerves Autonomic nervous system Parasympathetic

Somatic nervous system Sympathetic

Fig. 28.1 Organisation of nervous system in humans

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Dendrites Nucleus Cytoplasm

]

Cell body

Schwann Cell nucleus Node of Ranvier Myelin sheath Axon Neurofibrils

Nissl granules

28.1.1a Structure of the neuron Each neuron has a central area Fig. 28.2 A neuron (highly magnified) called the cell body or cyton. The cell body has a large central nucleus and cytoplasm. Several short, thread like branches called dendrites arise from the cell body. One branch arising out of the cell body is very long in comparison to others. This branch is called axon or nerve fibre. Axon may or may not be covered by a fatty sheath called myelin sheath. This covering is missing at intervals. These gaps on the sheath are known as nodes of Ranvier. 28.1.1b Types of neurons
Sensory nerve ending e.g. in skin Motor nerve ending in muscle (or gland)

Motor nerve ending in muscle (or gland)

28.1.1 Nerve cell or neuron A neuron is the basic unit of nervous tissue. Our nervous system contains about 10 billion nerve cells, which communicate with each other in a specific manner.

i.

Sensory neurons, which transmit impulse from receptor (sense organ) to coordinator (brain or spinal cord).

Nerve fibre or axon

Sensory neuron

ii. Motor neurons, which transmit impulse from modulator to effectors (muscle or glands). iii. Connecting neurons, which connect sensory and motor neurons, found in the grey matter. 28.1.2 Nerves Nerves are thread like structures, which emerge from brain and spinal cord and branch out to almost all parts of the body. The nerves are composed of axons or nerve fibres bundled together like the strands of an electric cable (Fig. 28.4).
Nerve fibre with cover (sheath) of fat

Motor neuron Sheath of electrical insulating material

Cell body (cyton)

Dendrites

Connector neuron

CNS (brain or spinal cord)

Connective tissue

Fig. 28.3 Types of neurons

Fig. 28.4 A nerve is a bundle of nerve fibres

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28.1.2a Kinds of nerves There are three kinds of nerves. These are: i. Sensory nerves: These nerves contain sensory fibres. Sensory nerves bring impulse from sense organs to the brain or the spinal cord. ii. Motor nerves: These nerves contain motor fibres. Motor nerves carry impulse from brain or spinal cord to the effector organ like muscle or glands. iii. Mixed nerves: These nerves contain both sensory and motor nerve fibres and perform a mixed function. 28.2 FUNCTIONING OF THE NERVOUS SYSTEM The nervous system functions in a coordinated manner. It receives a stimulus through a receptor organ like eye, ear, tongue, etc. The stimulus through sensory nerves reaches the brain and spinal cord, which integrates it and give action. The motor nerves pass on the action to the required organ (muscle or gland) and this way a response is generated.
Stimulus Sense organ Nerves Central Nervous System (CNS) Receives information makes a plan of action Nerves Effector Response

Red hot object

Temperature Nerves sensory cells in skin

Nerves Sends instructions

Muscles of arm and shoulder

Hand pulled away

Fig. 28.5 Nervous system works in a coordinated manner

28.3 NERVE IMPULSE 28.3.1 What is an impulse? Let us understand this by an example. Suppose your finger is pricked, you have felt the sensation. Then your brain senses the prick and generates a response and you withdraw your hand. This flow of message through the nerve is called impulse. Nerve impulse upon generation passes along a neuron in only one direction. The neuron is connected to a sensory receptor that receives the message or stimulus and converts it into electrochemical waves. These electrochemical waves are carried by the neuron. The stimulus from the receptor organ is received by the dendrites, conducted to cell body (cyton) of the neuron and finally to the effector organ. 28.3.2 Synapse The axon of one neuron is close to the dendrites of cell body of the next neuron. This junction of two neurons is called synapse. There is a space at the synapse between the end of axon of first neuron and cell body or dendrite of the next neuron. This is called synaptic cleft.

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Axon Synaptic vesicle containing neurotransmitters

Mitochondrion Synaptic bulb

Through the synapse the impulse passes from one neuron to the next neuron. There are many synapses between the millions of nerve cells. When the impulse reaches the end of axon of first neuron, a neurotransmitter (a chemical substance) is released in the synaptic cleft of the synapse, which helps in passage of nerve impulse from one neuron to the next neuron.

Presynaptic membrane Postsynaptic membrane Synaptic cleft

Dendrite

Fig. 28.6 A synapse

28.3.3 What does a synapse do? • It allows the information to pass from one neuron to another. • It ensures the passage of nerve impulse in one direction only. • It helps in information processing by combining the effects of all impulses received. • It filters out low-level stimuli. 28.4 CENTRAL NERVOUS SYSTEM- BRAIN AND SPINAL CORD 28.4.1 Brain The human brain is a highly developed organ situated in the skull. It weighs about 1200-1400g in an adult. It has three main parts: • Cerebrum • Cerebellum • Medulla oblongata a) Cerebrum The cerebrum is the largest and most prominent part of the brain. Among all vertebrates cerebrum of humans is most highly developed. It is divided into left and right hemispheres by a deep median longitudinal groove. Each hemisphere contains two regions - the outer region and the inner region. The outer region of cerebrum contains grey matter, which contains cell bodies of the neuron. The inner region of cerebrum contains white matter, which contains nerve fibres or axons of the neurons. The cerebrum performs the following functions: i. It governs our mental abilities like thinking, reasoning, learning, memorising and intelligence. ii. It controls our will, emotions and speech. iii. It controls feeling of love, admiration and hatred. iv. It controls all involuntary functions. b) Cerebellum It is a small area of brain lying below the mid-brain which is under the large cerebrum. Like cerebrum, it also has grey matter in its outer region and white matter in the inner region.

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Brain

Spinal nerves

Spinal cord Hole between vertebrea from which spinal nerves emerge

Spinal cord

Nerves (b) Vertebral column (enlarged view)

Dorsal root of spinal nerve (Sensory) Dorsal root ganglion

Grey matter

White matter

Ventral root of spinal nerve (Motor)

(c) Transverse section of spinal cord (a) The nervous system in human beings

Fig. 28.7 Components of the human nervous system

The cerebellum performs the following functions: i. It maintains equilibrium (balance) of the body. ii. It controls posture of the body. iii. It coordinates muscular movement. c) Medulla oblongata It is the lowermost part of the brain located at the base of the skull. The medulla oblongata performs the following functions: i. It controls the internal organs like movement of lungs, heart etc., by regulating breathing and heart-beat. ii. It controls vital reflex centres such as cardiac centre, respiratory centre and centres for swallowing, sneezing, coughing and vomiting (Fig. 28.8).

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Do you know? Our brain sends out certain waves, which are different in nature at different times depending on our body activity. An instrument called electroencephalograph can record this activity of our brain. For doing this, electrodes are taped on different parts of the scalp and the activity is recorded in the form of an electrocephalogram (EEG).
Cerebrum Thalamus

28.4.2 Spinal cord The spinal cord is a long cord that extends from the medulla oblongata and continues downward inside the vertebral column. Spinal cord has within it a narrow canal and this central canal of the spinal cord is filled with cerebrospinal fluid. The arrangement of the grey and white matter is just reversed in the spinal cord. The grey matter lies on the inner side while the white matter on the outer side. The spinal cord performs the following functions:

Cerebellum

Hypothalamus Pituitary gland Medulla

Spinal cord

Fig. 28.8 Different parts of the brain

i. It controls the reflexes below the neck region. ii. It conducts sensory impulses from the skin and muscles to the brain. iii. It conducts motor response from brain to the muscles of trunk and limbs. CHECK YOUR PROGRESS 28.1 1. Fill in the blanks. i) ii) iii) iv) The central nervous system consists of _________ and ___________ Pathway meant for transmission of the message from the receptors to modulators is called _____________ pathway. ___________________ nerves carry impulse from brain or spinal cord to the effectors. The stimulus from the receptor organ is received by the __________, conducted to the cell body of neuron and finally to the __________ organ. A synapse is the point of contact between the terminal branches of the _________ of one neuron with the _________ of another neuron.

v)

2. List any two functions of cerebellum. 3. Name the main organs of our body regulated by medulla oblongata.

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28.5 PERIPHERAL NERVOUS SYSTEM The peripheral nervous system includes nerves that carry impulse to and from the central nervous system. These nerves are of two types: • Afferent or sensory nerves, which carry information from sensory receptors into central nervous system, and • Efferent or motor nerves which carry information from the central nervous system to the effector organ. The peripheral nervous system is further subdivided into two systems: a) Somatic nervous system It receives and processes information from receptors in the skin, voluntary muscles, tendons, joints, eyes, tongue, nose and ears and thus gives an organism the sensation of touch, pain, heat, cold, balance, sight, taste, smell and sound. It also controls voluntary actions like movement of arms and legs. b) Autonomic nervous system or visceral nervous system It consists of a pair of chains of ganglion (a ganglion is a group of cell bodies of neurons) and nerves found on either side of the backbone. It is subdivided into sympathetic and parasympathetic nervous systems. It controls the involuntary actions of the internal organs of the body like heart etc. You will learn more about autonomic nervous system in higher classes. 28.6 REFLEX ACTION AND REFLEX ARC There are many actions in our body which are spontaneous and do not require any processing by brain. These responses are called reflex actions. Reflex actions are controlled by spinal cord. For example, we blink our eyes in response to high beam of light that falls on our eyes. Similarly we withdraw our hand immediately if we prick our finger or touch a hot object. A reflex action may be defined as a spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain. 28.6.1 Components of a reflex arc A reflex arc has the following components: i. a receptor or sensory neuron which perceives the stimulus, ii. a sensory nerve which carries the message from sensory neuron to spinal cord, iii. a relay or intermediate neuron of spinal cord which transmits the impulse from sensory to motor neuron, and iv. motor nerve which carries the message from spinal cord to effector organmuscle or gland.
Stimulus (a short blow below the knee cap) Sensory organ Motor neuron Spinal cord Response (leg straightens)

Sensory neuron

Effector organ

Fig. 28.9 Components of a reflex arc

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Stimulus received by the sensory receptors in the sensory organ Impulse generated and carried along by the sensory neuron toward the spinal cord Impulse arrives at the nerve endings of sensory neuron in the grey matter of spinal cord Neurotransmitter released at nerve endings Impulse pass across the relay neuron to motor neuron Impulse travels away from spinal cord along motor neuron The nerve endings of motor neuron connect effector organ like muscle Response produced by effector organ
Fig. 28.10 Sequence of events in a reflex arc

CHECK YOUR PROGRESS 28.2 1. Fill in the blanks. ii. __________ carry information from sensory receptors to central nervous system. iii. iiii. __________________ system receives and processes information from receptors in the skin, voluntary muscles and eyes. The pathway followed by sensory or motor nerves in a reflex action is called __________________

2. Define reflex action. 3. What are the various components of a reflex arc? 28.7 OUR SENSE ORGANS What are sense organs? Sense organs are the organs through which we sense or feel change in the external environment.

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We all touch, taste, smell, hear and see because of our sense organs. When a sense organ detects a stimulus it sends messages along the nerves to brain. The brain gives us feelings or sensations. Our sense organs and their functions are given in Table 28.1. Table 28.1: Different sense organs in our body Sense organ Skin Tongue Nose Ears Eyes Sensitive to stimuli Pressure, heat and cold, pain Chemicals in food and drink Chemicals in air Sound and movement Light Senses Touch Taste Smell Hearing and balance Sight

28.7.1 Skin The sense of touch is produced by the ends of nerve cells called nerve endings or receptors because they receive stimulation from the outside world. These nerve endings are of different types for different stimulations. • Touch and pressure: These receptors are concentrated on fingertips. They detect the texture of objects, whether they are rough, smooth, hard or soft. Touch receptors are attached to hair. Pain: Pain receptors are evenly distributed over the skin. • Temperature: There are separate cold and heat receptors. These detect changes in temperature. The fingertips can detect temperature differences as small as 0.5 oC. In a human adult the surface area of the skin is 1.5 to 1.7 sq. meters. The thickness of the skin varies from about 0.5 to 3 mm. The skin is composed of two distinct layers: i) epidermis, which contains hair, nails, sweat glands, etc. ii) dermis, which is made up of connective tissue mixed with blood vessels and nerves. 28.7.1.a Functions of skin • Skin protects the body from mechanical injuries, bacterial infections, heat and cold. • Skin is sensory to touch, pain and temperature. • Skin regulates our body temperature. Excessive heat is lost through evaporation of sweat otherwise it is conserved by fat and hair in the skin. •

Cold

Light/ Touch

Pain

Pressure

Heat

Fig. 28.11 Different types of sensory cells of skin

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• • •

Oily substances are freely absorbed by skin. The excess of water, salts and waste products are excreted through the sweat. Vitamin D is synthesized in the skin. Table 28.3: Common skin diseases Nature Disease
Fungal Allergic Ring worm Eczema, dermatitis

Symptoms
Itching/rashes/burning sensation Itching, scaly skin

Prevention Personal hygiene Most of the allergy can be prevented by avoiding offending substances Personal hygiene and domestic hygiene

Parasitic Scabies

Itching

Eyebrow

Tear gland Duct Upper lid Eye lash

We should take care of our skin! • The skin must be washed daily because it gets dirty by dust and sweat. • It should be protected from injury. • It should be protected from sun rays and fire.

Cornea

28.7.2 Eyes Eyes are well-protected organs of our body through which we see. The eyes are lodged within the skull. When we close our Iris Lower lid Pupil eyes a layer of skin with hair (eye lashes) in its margin covers each eye. It is an eyelid. Fig. 28.12 The human eye This eyelid protects our eye from an external discomfort. Different parts of the eye are cornea, iris, pupil, retina etc. as shown in fig. 28.12. How do we see? The light rays enter our eyes through transparent structures (conjunctiva, cornea, aqueous humour, lens and vitreous humour). The curvature of cornea and lens bend the light rays to form an image on the retina. The image formed on retina is inverted and real. The nerve impulses are produced in retina, which are transmitted to the brain (visual area of cerebrum). The brain interprets the image and the image that was formed inverted on the retina is viewed or perceived here correct and upright. 28.7.2a Focusing and accommodation (i) Eye focused on a distant object Lens is less convex (somewhat flattened) due to being stretched by suspensory ligament, the ciliary (circular) muscles along the suspensory ligament are relaxed.

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(Fig. 28.13a). (ii) Eye focused on a near object Ciliary (circular) muscles contract. This reduces tension of the suspensory ligament and the lens turns thicker and more convex (Fig. 28.13b).
Radial muscle (contracted) Circular muscle relaxed Suspensory ligament Lens Pupil (wide) Radial muscle (relaxed) Pupil (narrow) Circular muscle(cntracted) Suspensory ligament Lens

Light from a distant object

(a)

Light from a near object

(b)

Fig. 28.13 Focussing and accomodation of the eye a) Distant object b) Near object

28.7.2b Defects of the eye i) First, understand the normal sight Both distant and near objects can be focused on the retina (Fig 28.14a). (ii) Long sightedness or hypermetropia It occurs when the eyeball is shorter than normal. In this defect distant objects can be focused properly, but the point of focus for an object close to the eye is behind the retina (Figs. 28.14 b,c).
Small short eye ball

Focus behind retina

(a) Normal sight
Eye ball

(b)Long sightedness or hypermetropia
Long, oval eyeball Eye ball

Convex lens

Focus in front of retina

Concave lens

Fig. 28.14 The normal sight and the defects of vision (c) Correcting hypermetropia using convex lens (d) Short sightedness or myopia, (e) Correcting myopia using concave lens

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(iii) Short sightedness or myopia It occurs when the eye-ball is longer than normal. In this defect objects close to the eye can be focussed properly, but the point of focus for distant objects is in front of the retina (Fig. 28.14 d,e). We should take care of our eyes! • Do not read in the dark or when the light is too bright. You must keep your book at a proper distance from your eyes. While reading, maintain correct posture. Do not rub your eyes with unclean hands because germs can enter into your eyes. When dust, insects or other object goes into your eyes, do not rub them. Rinse the objects away with plenty of clean water. Wash eyes daily carefully. Eyes should be protected from direct sunlight sparkling and injuries. In case of an injury consult the doctor immediately.
Semi-circular canals External ear Nerve to brain

• • • •

Ear canal Ear drum

Eustachian tube

Sacculus

Fig. 28.15 Structure of the ear

28.7.3 Ears Ears help us in hearing different sounds and balancing our body. The air around us is full of vibrations called sound waves. We have one ear on each side of the head. Ears change vibrations in the air into nerve impulses, which travel to brain where they are interpreted as sound.

28.7.3a Functions of ears The part, which we call our ear, is a flap of skin in the shape of a funnel. This is the external ear. This leads to a tunnel – the ear canal, at the end of which is a thin sheet of skin called the eardrum. Sound waves are collected by the outer ear and directed inside the ear canal, where they set the eardrum vibrating. The eardrum is connected to the inner ear by three small bones or semicircular canals called ear ossicles. These are hammer (malleus), anvil (incus) and stirrup (stapes). These bones transmit and amplify the vibrations increasing their force by about 20 times. The ossicles are connected to an oval window. Due to vibrations, oval window moves in and out causing vibrations through the cochlea. The cochlea contains a carpet of tiny hair like structures, which are connected to nerves. They are actually sensory cells which help us to hear the sound.

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Our ears helps us to balance Our ears tell us if we are standing upright or not. The semicircular canals of our inner ear tell us to keep balance or to move. The semicircular canals are three tubes full of liquid. When we move the liquid moves. Sensitive hair cells inside the tubes detect this movement and send impulses along nerves to the brain. Our brain detects loss of our balance and sends impulses to muscles to keep us upright. 28.7.3b Deafness—disorder of the ears The vibrations of the eardrum cause disturbance within the middle ear. This space is linked with the back of a canal – the Eustachian tube. We know that when the air pressure changes, we feel a strong sensation in our ears until we open our mouth, and the air in the mouth and the pressure is equalized. Unfortunately, the Eustachian tube may become a channel for infection. This may happen for a brief period during a cold and if neglected the infection may spread to the middle ear and cause inflammation. The eardrum may become thickened and the little bones may have Bitter their articulations affected. This may cause deafness. Deafness may also be due to the injury to the ear nerve. Sweet Sour We must take care of our ears! • • • We should clean our ears with towel after bath every day. Never use a pin or stick to remove wax from the ear. We should protect our ear from injury, cold and dirt.

Sour

Sweet and salt

Fig. 28.16 Our tongue

28.7.4 Tongue You know that your tongue helps you to talk and helps in moving food inside the mouth and swallowing the food. Tongue is a sense organ, which distinguishes different tastes. Our tongue contains taste buds. Taste buds are groups of sensory cells. These are sensitive to chemicals, which must dissolve in saliva, before we can taste them. Taste buds send messages to brain by taste nerves for analysis, resulting in the sensations. This is why dry food has no taste until we chew it with saliva. We must take care of our tongue! • • It should be cleaned daily by tongue cleaner. If there are any rashes or cut on the tongue it should be treated as per doctor’s advice.

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28.7.5 Nose We can detect about 3000 different kinds of smells. Smell helps animals to hunt food and find their way. Smell can also warn if there is certain danger. Our nose is sensitive to smell. Smell is basically detecting chemicals in the air. The chemicals dissolve in moisture on lining of our nose. The stimulation of nerve endings in our nose send message to the brain which produces the sensation of smell. Smell receptors are called olfactory receptors. CHECK YOUR PROGRESS 28.3 1. Name the five sense organs in our body. 2. Fill in the blanks. i) Skin is made up of ________________ and ____________________ ii) Oily substances are freely absorbed by __________________ 3. Match the items in column A with those in column B:
A B

i) ii) iii) iv)

Eustachian tube Cornea Nerve ending Olfactory organ

a) b) c) d)

Eye Nose Ear Skin

Hypothelamus Pineal gland Pituitary gland

Parathyroid gland

Thyroid gland

Thymus

Kidney Pancreas

28.8 ENDOCRINE SYSTEM Our body has a number of organs called endocrine glands. Their main function is to produce chemical secretions and these secretions are known as hormones. The term hormone has been derived from the Greek word hormaein meaning to set in motion or to spur on. Hormones play an important role in control, coordination and regulation of the functioning of tissues and organs in the body. For the smooth and normal functioning of the body, different hormones are required in different quantities. Hormones are secreted by ductless glands or endocrine glands (Greek: endo means within, krinein means to separate). The endocrine system is responsible for chemical coordination in the animals including man.

Ovary (in females) Testis (in males)

Fig. 28.17 Location of various endocrine glands in the human body

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What are hormones? A hormone is a chemical secreted by an endocrine gland and carried by blood or lymph to a target organ elsewhere in the body to stimulate a specific activity. There are different endocrine glands for secretion of different hormones (Fig. 28.17). Table 28.2 lists some important hormones, glands secreting them and their effects on the functioning of our body. Did you know? Hyperactivity (overactivity) or hypoactivity (underactivity) of endocrine glands cause disease. 28.8.1 Pituitary gland • Hyperactivity of cells of pituitary gland cause Cushing’s disease. In this disease excessive growth of hair occurs in males. In some cases this disease may even cause atrophy of testes leading to impotency. In females, this disease causes sterility, musculisation, growth of beard, moustaches, etc. • Deficiency (hypoactivity) of growth hormone (GH) or somatotrophic hormone (STH) secreted by pituitary gland causes dwarfism (retarded growth of the long bones) while its excessive secretion or hyperactivity causes gigantism (excessive growth of long bones) making a person very tall. 28.8.2 Thyroid gland • Hypoactivity of thyroid gland causes hypothyroidism causing cretinism in young children. In this disease the child has stunted growth, short club like fingers, deformed bones and teeth. The skin becomes rough, dry and wrinkled with scanty hair growth. The abdomen gets pot-bellied and the child is mentally retarded. • Hypoactivity of thyroid gland also causes abnormal swelling of thyroid called goitre. 28.8.3 Pancreas • Hyposecretion of insulin secreted from pancreas, causes diabetes mellitus, in which glucose present in excess in the blood sometimes appears in urine. Table 28.2: Major hormones secreted in the human body, their sources and effects Endocrine glands and their location
Pituitary gland

Hormone secreted

Effects

(It is attached to the lower surface of the brain. It has three lobes-anterior lobe, Adenocorticotropic hormone Controls the growth and functioning of middle lobe and posterior (ACTH) adrenal cortex. Stimulates adrenal cortex lobe) to produce steroid hormones called glucocorticoids.

Growth hormone (GH) or Controls the overall growth of the body, Somatotrophic hormone (STH) muscles and bones.

:232: Control and Coordination Thyroid stimulating hormone (TSH) Follicle stimulating hormone (FSH) Controls the growth and functioning of thyroid gland. Stimulates thyroid gland to produce thyroxin. Stimulates the maturation of ovarian follicle and secretion of estrogen by ovary in females; and in males stimulates the process of spermatogenesis. In females stimulates the ovulation and secretion of progesterone and hence helps in preparation and maintenance of pregnancy. In males it stimulates the secretion of testosterone. Enhances development of mammary glands and milk production in females. Controls the production of melanin pigment in skin. Controls the uterine muscle contraction at the time of child birth (parturition). Controls reabsorption of water in kidney tubules. Stimulates the cellular metabolism and oxidation. In general it controls the growth and metabolism of the body.

Luteinizing hormone (LH)

Prolactin (PRL) Melanocyte stimulating hormone (MSH) Oxytocin Antidiuretic hormone (ADH) Thyroid gland (It is situated in the neck region on the ventral side of the body. It has two lateral lobes,one on either side of the trachea). Pancreas (Situated in the abdominal region. Its endocrine cells - Islets of Langerhans secrete hormones. Thyroxin

Insulin

Regulates the conversion of glucose to glycogen. Regulates the conversion of glycogen and some non-carbohydrates back to glucose.

Glucagon

CHECK YOUR PROGRESS 28.4 1. Fill in the blanks. i) ii) iii) iv) v) A hormone is carried by _________ or ________ to the target organ. Thyroid stimulating hormone is secreted by ___________ ________ hormone regulates the conversion of glucose to glycogen. ___________________ hormone controls the reabsorption of water in kidney tubules. Hypoactivity of thyroid gland leads to__________



LET US REVISE Nervous system works with the endocrine system to communicate, integrate and coordinate the functions of various organs and systems in our body and responds to the external stimuli.

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• •

In humans the nervous system has two divisions, the central nervous system and the peripheral nervous system. The central nervous system comprises of brain and the spinal cord, while the peripheral nervous system includes the nerves, which connect the central nervous system with sense organs, muscles and the glands in the body. Nerves are thread like structures that emerge from brain and spinal cord and branch out to almost all parts of the body. A neuron is the basic unit of nervous system. There are three types of neurons - sensory neurons, motor neurons and connecting relay or intermediate neurons. A synapse is the junction of the terminal branches of the axon of one neuron with the dendrites or cell body of another neuron. It is the site of transfer of nerve impulse from one neuron to another. The brain has three parts - cerebrum, cerebellum and medulla oblongata. A reflex action is a spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord without the involvement of the brain. The pathway followed by sensory or motor nerves in a reflex action is called reflex arc. Sense organs are the organs by which you detect changes in the external environment. The five sense organs are eyes, ears, skin, tongue and nose. Messages from the sense organs are carried to the brain by nerves. Brain analyses these messages and as a result the sensations are produced. Without our sense organs we would know nothing about our environment. Therefore we should take care of them and protect them from injury and disease. TERMINAL EXERCISES

• •



• • • • • • •

A. Multiple choice type questions. Tick the most appropriate answer of the following. 1. Which of the following carry impulse from brain to effector? a) Sensory neuron b) Motor neuron c) Connecting neuron d) Mixed nerve 2. Short thread like branches of nerve cell are called a) dendrites b) synapse c) nodes of Ranvier d) neuron 3. A chemical known as neurotransmitter is released from the ends of a) axon b) synapse c) nodes of Ranvier d) neuron

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4. The pituitary gland is found a) in the neck c) beneath the stomach

b) d)

at the base of the brain near the kidneys

5. The transparent window at the front of the eyeball is called a) cornea b) iris c) cone d) retina 6. Hormones are carried around in the body by a) blood b) nerves c) lymph d) both blood and lymph 7. Which of the following glands secretes the hormone thyroxin? a) Pituitary gland b) Thyroid gland c) Brain d) Pancreas 8. Which of the following hormones is secreted by the pancreas? a) Growth hormone b) Thyroxin c) Insulin d) Prolactin 9. The disease cretinism is caused due to a) hypoactivity of pituitary gland b) c) hypoactivity of thyroid gland d) 10. Hyposecretion of insulin causes a) Goitre c) Diabetes insipidus B. Descriptive type questions. 1. Define the following: (i) central nervous system, (iii) receptor (v) nodes of Ranvier, (vii) synapse, (ix) reflex arc, and b) d) hyperactivity of pituitary gland hyperactivity of thyroid gland Cretinism Diabetes mellitus

(ii) (iv) (vi) (viii) (x)

hormone, neuron, impulse, reflex action, power of accommodation

2. Differentiate between the following: i) Sensory nerve and motor nerve ii) Cerebrum and cerebellum iii) Somatic nervous system and autonomic nervous system iv) Grey matter and white matter v) Hypermetropia and myopia vi) Insulin and glucagon 3. What are nerves? Classify nerves into different types stating their functions. 4. What are sensory neurons? How do they help in transmission of nerve impulse in our body? 5. What is a synapse? What is the main function of a synapse? 6. State the main functions of cerebrum and medulla oblongata.

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7. Mention one function of each of the five sense organs of our body. 8. Draw a labelled diagram of the human eye. 9. What is the function of sweat glands? 10. What are endocrine glands? How do their secretions reach various parts of our body? 11. Name various hormones secreted by pituitary gland stating functions of each one of them. 12. Endocrine glands are ductless glands, then how do their secretions reach the target site? 13. Name the hormone secreted by thyroid gland and state its main functions. 14. What is Cushing’s disease? Name the endocrine gland responsible for this disease. ANSWERS TO CHECK YOUR PROGRESS 28.1 1. i) ii) iii) iv) v) brain and spinal cord sensory pathway motor dendrites, effector axon, dendrites

2.

Any two functions of cerebellum like, maintenance of equilibrium of the body, controlling the posture of the body, coordinating muscular movement, etc. Internal organs of the body like lungs, heart, etc.

3. 28.2 1.

i) Afferent nerves ii) Somatic nervous system iii) Reflex arc A spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain is called reflex action. Components of a reflex arc i) A receptor or sensory organ which perceives the stimulus, ii) A sensory nerve which carries message from receptor to spinal cord, iii) A relay neuron of spinal cord which transmits the impulse from sensory to motor neuron, and iv) Motor nerve which carries the message from spinal cord to effector organ - muscle or gland.

2.

3.

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28.3 1. Eyes, Nose, Ear, Skin and Tongue 2. (i) Dermis, epidermis (ii) Skin 3. (i) (c) (ii) (a) (iii) (d) (iv) (b) 28.4 1. i) ii) iii) iv) v)

Blood, lymph Pituitary gland Insulin Antidiuretic hormone Goitre

GLOSSARY Nervous system : The organ system in an animal that serves to coordinate and control all the physiological systems in its body. Neurons : The nerve cells that transmit messages throughout the body. Nerves : Thread like structures that emerge from brain and spinal cord and branch out to almost all parts of the body. They are bundles of axons or nerve fibres enclosed in a sheath. Synapse : The junction between the terminal branches of the axon of one neuron with the dendrites or cell body of another neuron. Nodes of Ranvier : Regular gaps on the medullary sheath covering the axon. Neurotransmitter : A chemical released at the synapse which helps in the transmission of nerve impulse from one neuron to another. Cerebrum : The largest and most prominent part of the brain. It controls intelligence activities, motor activities, etc. Cerebellum : The region of the brain under the large cerebrum which controls balance of the body. Medulla oblongata : The lowermost part of the brain located at the base of the skull. It controls cardiac and respiratory activities. Spinal cord : A long cord that extends from the medulla oblongata and runs inside the vertebral column. Reflex action : The action in our body which are spontaneous and do not require any processing by brain. Sense organs : The organs through which we sense or feel change in the external environment.

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Hypermetropia : The defect of the eye in which the eye can focus the distant objects clearly but the point of focus for an object close to the eye is behind the retina. Myopia : The defect of the eye in which the eye ball is longer than normal. In this defect objects close to the eye can be focused properly but the point of focus for distant objects is in front of the retina. Hormone : A chemical secreted by an endocrine gland and carried by blood or lymph to a target organ elsewhere in the body to stimulate a specific activity.

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29

Reproduction
Reproduction is the process by which a living organism is able to produce more of its own kind. The continuity of life on earth, from its origin to the present day, has been possible only because of reproduction. Living organisms reproduce in two ways—asexual and sexual reproduction. In this lesson we will learn about the modes of reproduction in plants and animals especially humans, population growth and its control and sexually transmitted diseases. OBJECTIVES After completing this lesson, you will be able to: • define reproduction and differentiate between asexual and sexual reproduction; • describe different modes of reproduction in plants; • illustrate male and female reproductive systems in humans and state functions of each part; • describe the physical and physiological changes occurring during puberty and menstrual cycle; • describe the main events in the process of reproduction in humans starting from the production of gametes to pregnancy and parturition; • recognize the factors responsible for the growth of population and explain the consequences of rapid increase in population; • reason out the importance of contraception and suggest methods for control of population growth; • emphasize the importance of reproductive health and suggest ways to prevent transmission of sexually transmitted diseases. 29.1 TYPES OF REPRODUCTION Living organisms reproduce in two ways—asexual and sexual reproduction. 29.1.1 Asexual reproduction Asexual reproduction involves the production of an offspring from body parts other than reproductive organs. It is a common process of reproduction in lower plants and animals.

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Basic features of asexual reproduction i) It involves only one organism i.e. different sexes are not involved. ii) The cell divisions during this type of reproduction are either mitotic or amitotic. iii) New individuals produced are genetically identical to the single parent. iv) It is a fast mode of multiplication. 29.1.2 Sexual reproduction Sexual reproduction is a type of reproduction in which two sexes, the male and the female, are involved. This type of reproduction occurs both in plants and animals. Basic features of sexual reproduction i) It is the production of offspring by the fusion of egg and sperm, which are the sex cells or gametes. ii) Upon fertilization, the male and female gametes unite to form a zygote, which develops into a mature organism. iii) It results in the combination of genetic material from two parents. 29.2 REPRODUCTION IN PLANTS Like animals plants also reproduce both asexually and sexually. Asexual reproduction in plants is either by fission, budding, fragmentation and regeneration, spore formation or by vegetative propagation or vegetative reproduction of plant parts. Sexual reproduction is by fusion of male and female gametes and it occurs in flowering plants. 29.2.1 Asexual reproduction 1. Fission Fission is of two types: Binary fission and multiple fission. Binary fission: In binary fission, two individuals are formed from a single parent. This type of reproduction is found in organisms like bacteria, yeast and Amoeba (Fig. 29.1).
Divison of nucleus Division of cytoplasm

Daughter cells

Mother cell

Fig. 29.1 Binary fission in Amoeba

Multiple fission: In multiple fission, many individuals are formed from a single parent. This type of reproduction by multiple fission occurs during unfavourable conditions.

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Cyst

Parent cell

Daughter cells

Fig. 29.2 Multiple fission in Plasmodium

In this type of reproduction, the unicellular organism develops a protective covering called cyst over the cell. The nucleus of the cell divides repeatedly producing many nuclei. Many daughter cells are produced within the cyst. The cyst breaks and small offsprings are liberated. This type of reproduction is seen in many algae and in some protozoans, such as the malarial parasite (Plasmodium) (Fig. 29.2). 2. Budding In this type of reproduction, a bulb-like projection or outgrowth arises from the parent body known as bud, which detaches and forms a new organism.

Hypostome Parent Hydra Parent Hydra Bud (Protuberance)

Daughter Hydra

Tentacles

Basal disc

For example, Hydra Fig. 29.3 Budding in Hydra reproduces by budding (Fig. 29.3). A small protruberance arises from one side of its body, which grows, develops tentacles and gets detached to lead an independent life. 3. Regeneration or Fragmentation In this type of reproduction, the body of an individual breaks up into two or more parts and each part develops into a complete individual. Examples: Spirogyra, and Planaria. 4. Spore formation In lower forms of life like the alga, Chlamydomonas, the protoplast of the cell divides to form 4–8 spores. These being motile are termed as zoospores. When spores are released in the surrounding medium they develop into new plants. 5. Vegetative propagation or vegetative reproduction in plants Vegetative reproduction (or vegetative propagation) is a form of asexual reproduction in plants in which a bud grows and develops into a new plant. In this type of reproduction, any vegetative part of the plant body like leaf, stem or root develops into a complete new plant. Vegetative reproduction can take place by two methods—natural and artificial.

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I) Vegetative reproduction by natural methods This type of vegetative reproduction can involve roots, stem or leaves. Some common modes of vegetative reproduction are given below: i) By roots The roots of sweet potato and mint bear adventitious buds. When these roots are planted in the soil, new plants are produced

ii) By stem In many plants the stem develops buds on it. The part of the stem that bears buds serves as an organ for vegetative multiplication, e.g. the modified parts of stem, such as runners of grass, suckers of mint and Chrysanthemum, bulbs of onion and tulip, rhizomes of ginger, corms of gladiolus and Colocasia, and tubers of potato, etc.

Stem Scale leaves Scale leaves Storage leaves Auxillary buds Roots Stem Stem Adventitious roots Old corn (previous year)

Fig. 29.4 Vegetative propagation by bulb in onion

Fig. 29.5 Vegetative propagation by corm in Gladiolus

Node

Bud

Germinating bud Scale leaf

Young plant Potato tuber

Fig. 29.6 Vegetative propagation by rhizome in ginger

Fig. 29.7 Vegetative propagation by tuber in potato

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New plant Parent plant

Stem of parent plant

New plant

Runner

Scale leaf Sucker Tap root

Tap root Lateral roots Adventitious roots

Lateral roots

Fig. 29.8 Vegetative propagation by runner in grass

Fig.29.9 Vegetative propagation by sucker in mint

iii) By leaves In some plants, e.g. in Bryophyllum and Bigonia, adventitious buds are developed in the margins of their leaves. When the leaf falls on moist soil, these buds develop into small plantlets, which can be separated and grown into independent plants (Fig. 29.10). b) Vegetative propagation by artificial methods Some plants can be propagated artificially. The methods of artificial propagation include grafting, layering, cutting and tissue culture. i) Grafting: It is the method of obtaining a superior quality plant from two different plants, taking the root system of one plant and the shoot system of another plant. The plant whose root system is taken is called stock. The plant whose shoot system is taken is called scion. The ends to be grafted, of the stock and the scion, are cut obliquely and placed face to face and are bound firmly with tape (Fig. 29.11). The stock supplies all the desired nutrients to the scion. This technique has been used in raising superior quality plants of mango, apples, roses, rubber and citrus..
Obliquely cut ends of stems Cambia of each stem in close contact Stock and scion bound firmly

Bud

New plant

Fig. 29.10 Vegetative propagation by leaves of Bryophyllum

Fig. 29.11 Vegetative propagation by grafting

ii) Cutting: In some plants like rose, sugarcane, Bougainvillaea, etc. this method is used quite frequently. Stem cuttings with nodes and internodes are placed

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in moist soil which give rise to adventitious roots, and grow into new plants. iii) Layering: Layering is the development of roots on a stem while it is still attached to the parent plant. The stem or the branch that develops adventitious roots while still attached to the parent plant is called a layer. It is a means of reproduction in black raspberries, jasmine (Jasminum), Magnolia, etc. iv) Tissue culture: This is a modern technique of vegetative propagation. In this technique, a small piece of tissue is cut from a plant and is transferred to a container with nutrient medium under aseptic conditions. The tissue utilizes nutrients from the medium, divides and re-divides, and forms a callus. Small portions of this callus are transferred to another medium which induces differentiation and plantlets are produced. These plantlets are transplanted in soil to form an adult plant. Orchids, Chrysanthemum, Asparagus and many other plants are now being grown by using plant tissue culture technique. CHECK YOUR PROGRESS 29.1 1. Name the two main methods of reproduction found in living organisms. 2. Give one example each of organisms which reproduce by (a) binary fission (b) multiple fission (c) budding (c) fragmentation (d) vegetative propagation by leaf 29.2.2 Sexual reproduction in plants In flowering plants, flower is the reproductive part of a plant. Most flowers have both male and female reproductive organs. A typical flower has four whorlscalyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels) (Fig. 29.12). The androecium and gynoecium are directly concerned with sexual reproduction.

Gynoecium Androecium Corolla Thalamus Calyx Pedicel (a) Section through a flower (b) Stamen (magnified view) (c) Section through a stamen Filament Filament Anther Connective Pollen grain Pollen sac

Fig. 29.12 Parts of a flower

The androecium is the male part of the flower. It consists of stamens. Each stamen has anther and a filament. Each anther possesses many pollen grains, which are the male gametes in pollen sacs. Gynoecium is the female reproductive part of a flower. The female part

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contained in this whorl is called pistil. Each pistil consists of three parts—an upper flat stigma, a medial, long, cylindrical style, and a lower, swollen ovary. • •


The stigma receives pollen grains during pollination. The style bears the stigma at a suitable position to receive the pollen grains. The ovary contains ovules that are found attached to the placenta. Ovules are the structures in which embryo sacs develop, and mature into seeds after fertilization. The arrangement of ovules in the ovary is called placentation.

Pollination Pollination is the process of transfer of pollen grains from the anther to the stigma of a flower. It is of two types: i) Self-pollination: If the pollen grains from the anther of a flower are transferred to the stigma of the same flower, it is termed as self-pollination or autogamy (auto: self; gamy: marriage) e.g. pea and china rose. ii) Cross pollination: If the pollen grains from anther of one plant reach the stigma of a flower on another plant of the same species, then this is called as cross pollination or allogamy (allos: other; gamy: marriage). Cross pollination has the advantage of increasing the chances of variations.

Fertilization • After pollination, the pollen grains Germinating germinate on the stigma to produce a pollen grains Stigma pollen tube. • This tube grows down through the style Style Pollen tubes and finally reaches the ovule. • The ovule contains the egg cell inside the embryo sac. • The tip of the pollen tube ruptures in the Ovary ovule and discharges two male gametes wall Ovule into it. Embryo sac • One of the male gametes fuses with the egg to form the zygote. This fusion is called fertilization. Secondary nucleus • The other male gamete fuses with the Egg nucleus diploid secondary nucleus and forms the endosperm nucleus. Male nuclei • The zygote that is formed as a result of Tube nucleus fertilization divides several times and gives rise to an embryo. The endosperm nucleus grows to form the endosperm of the seed. Fig. 29.13 Zygote formation Following fertilization, the sepals, petals, style and stigma degenerate and usually fall off. The ovary wall ripens and forms the pericarp of the fruit. Each ovule develops into a seed. The seed contains a potential plant or embryo. The whole ovary after fertilization changes into a fruit.

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CHECK YOUR PROGRESS 29.2 1. Define the following terms. (a) Self-pollination (b) Cross-pollination 2. Name the specialized organs meant for sexual reproduction in flowers. 3. Which part of the flower usually changes into fruit? 29.3 REPRODUCTION IN HUMANS Humans reproduce sexually. Reproductive organs in humans are described below. 29.3.1 Male reproductive system
Urinary bladder Ureter Ejaculatory duct Seminal vesicle Vas deferens Epididymis

Prostate gland Urethra Penis

The male reproductive system in humans consists of the following organs—a pair of testes, a pair of epididymis, a pair of vasa deferentia, an ejaculatory duct, a urethra, penis and accessory glands (Fig. 29.14).

The testes produce, sperms, the male gametes. The process of Erectile tissue formation of sperms in the testes of Testis Prepuce an organism is called Scrotal sac Glans penis spermatogenesis . Each testis Fig. 29.14 Male reproductive contains certain coiled tubes called system in humans seminiferous tubules that are actually responsible for the production of sperms. These sperms are released from the testes and stored in the epididymis until mating. At the time of mating, the sperms are passed from the epididymis through the vas deferens to the ejaculatory duct. The ejaculatory duct opens into the urethra. In human males, the urethra is a common passage for sperms and urine. The urethra passes through an organ called penis, which is the copulatory organ (organ for transfer of sperms during mating or copulation) in humans. During their passage from the epididymis to the urethra, the sperms are mixed with certain secretions from the accessory glands. The sperms along with the secretions form the semen. During copulation, semen is discharged. The process of discharging of semen is called ejaculation. In one ejaculation about 200,000,000 (2 × 108) sperms are discharged. 29.3.2 Female reproductive system The female reproductive system consists of a pair of ovaries, a pair of oviducts (or fallopian tubes), uterus and vagina(Fig. 29.15). A pair of ovaries lies in the lower part of the abdominal cavity, one on each side of the body. Ovaries produce ova and secrete female sex hormones, oestrogen and progesterone. The process of formation of egg in the ovary is known as

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oogenesis. There is a pair of oviducts or fallopian tubes in the human female reproductive system. One end of each oviduct is funnel-shapped. It collects the eggs released by the ovary. Both fallopian tubes open into the uterus. The uterus is a pear-shaped, muscular, thick-walled organ. the lower end of the uterus opens into the vagina that opens to the outside by a genital opening. Vagina is the organ where the penis is inserted during coitus for the discharge of semen. It serves as the birth canal during childbirth. In a human female, the urethra and the genital duct have separate openings.

Oviduct Ovary

Space in which th baby develops

Uterus

Funnel of the oviduct Cervical canal

Cervix Vagina

Vulva

Hymen

Fig. 29.15 Female reproductive system in humans

29.3.3 Puberty The reproductive organs in human beings become functional at an age of 13–14 years in males and 12–13 years in case of females. This age is known as puberty. During sexual maturity, hormonal changes take place in males and females, and under the influence of these hormones secondary sexual characteristics are developed. • Development of secondary sexual characteristics in males include deepening of voice, widening of shoulders, appearance of beard and moustaches, and growth of axillary and pubic hair. • Development of secondary sexual characteristics in females include growth of axillary and pubic hair, widening of pelvis and hip, enlargement of breasts and initiation of the menstrual cycle. CHECK YOUR PROGRESS 29.3 1. At what age do human males and females attain puberty? 2. Name the tubules present in the human testis. 3. Name the various parts of the following. i) Human male reproductive system ii) Human female reproductive system 4. Describe three secondary sexual characteristics each in human male and human female. 29.4 SEXUAL CYCLE IN HUMAN FEMALES (MENSTRUAL CYCLE) The period of life during which a female has the capacity to produce young ones is called the fertility period. In human females, it extends from about 12–13 years (puberty) up to 45–50 years (menopause). Between puberty and menopause, the female reproductive system passes through a regular monthly sequence of events called the menstrual cycle (Fig. 29.16). The events of menstrual cycle are given here.

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• •





During each menstrual cycle, an ovum matures and is released once every 28 days. The menstrual cycle starts with menstrual flow, during which cellular lining of the uterus is shed off alongwith blood flow. This process continues for 3–4 days. From the 5th up to the 13th day of the onset of menstrual cycle, growth and maturation of the graafian follicle takes place. It consists of an ovum and a mass of cells surrounding it. The graafian follicle produces the female hormone, oestrogen.
CHANGES IN THE EGG CELL

Growing follicle

Graafian follicle

Rupturing follicle

Corpus luteum

Regressing corpus luteum

CHANGES IN THE UTERINE WALL

Menstruation CHANGES IN THE ENDOMETRIAL LINING

Uterus grows a new lining of blood vessels and glands

Menstrual phase CHANGES IN HORMONE LEVELS IN THE BLOOD

Follicular phase

Ovulatory phase

Luteal phase

Progesterone Oestrogen

0

1

2

3 4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Most likely period of ovulation (Fertile period)

Menstruation

Fig. 29.16 Sexual cycle in females

• •



The cells lining the uterus grow rapidly and develop a dense network of blood vessels. The release of the ovum from the ovary is called ovulation. Ovulation takes place 12–13 days after the onset of menstruation. The graafian follicle ruptures to release the ovum. The cells of the ruptured follicle form the corpus luteum, which secretes the hormone, progesterone.

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• • •

The ovum reaches the uterus via the fallopian tube on the 13th or 14th day and remains there up to the 16th day (for 48–72 hours). If the ovum does not receive any sperm during this period it starts degenerating. At the end of the 28th day this ovum is rejected along with the uterine lining. This marks the start of a slow disintegration of the thickened lining of the uterus and the next menstrual cycle.

What happens if the ovum receives sperm? If the ovum receives sperm it is in the fallopian tube, the two unite to form a zygote. This is called fertilization. Fertilization occurs in the fallopian tube. The zygote immediately begins to divide and forms a mass of cells called morula, which passes down to the uterus and fixes itself to the wall of the uterus (known as implantation). Menstruation does not occur and the female is said to be pregnant. The developing young one or the foetus is attached to the uterus by a tissue called placenta. Placenta supplies oxygen and nourishment from the maternal blood to the foetus. It also transports carbon dioxide and excretory waste from the foetal blood to the maternal blood. Placenta also produces two hormones— progesterone and oestrogen. Under the influence of these hormones neither ovulation nor menstruation take place till pregnancy continues. The Umbilical cord is a tough structure that serves as the blood vascular connection between the foetus and uterine wall. From the first few weeks of development, the embryo is enclosed in a sac called amnion, which is filled with amniotic fluid. This fluid acts as a shock-absorber and helps to protect the embryo from damage. 29.4.1 Test tube babies In some women, the fallopian tube gets blocked, which prevents the ova from being fertilized. This problem can be overcome by the test tube baby technique. In this technique, one or more mature ova are sucked from a woman’s ovaries using a special syringe. The sperms are taken from her husband. These sperms and ova are kept together in a container for a few hours for fertilization to take place. When a sperm fertilizes an ovum a zygote is formed, which divides repeatedly to form an embryo. This embryo is them inserted into the woman’s uterus where it gets implanted and develops into a baby. Fertilization of an egg by a sperm outside the body of the female is called in-vitro fertilization or IVF. 29.4.2 Twins In every reproductive cycle, usually, an ovary releases only one ovum. But, sometimes more than one egg may be released and fertilized by more than one sperm or an ovum may divide into two or more cells after fertilization which separate and develop as different individuals. This is how twins, triplets and quadruplets etc. are produced. a) Identical twins When a fertilized egg divides into two independent sets of cells, both of which

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continue to divide, two identical embryos are produced from the same egg. The twins thus produced are identical twins. b) Non-identical or fraternal twins When two eggs are produced at the same time and a different sperm fertilizes each egg, non-identical or fraternal twins are produced. 29.5 POPULATION CONTROL Reproduction serves to replace the older generation. It is also a phenomenon that leads to increase in the number of individuals of a species to ensure that at least some will survive in the struggle for existence. In humans, due to a variety of reasons more and more children have been surviving. This has currently led to what we call the population explosion. The increase in population has created many problems like problems of food, shelter, clothing, etc. So it has become very essential to limit the human population. There are various ways to prevent fertilization and hence to check the increase in population. Let us study about few such methods. 29.5.1a Education Imparting education to the people about various ways of fertility control is the most effective method of population control. Education helps to make people aware of the advantages of a small family and the disadvantages of a large family. 29.5.1 b Preventive methods These methods prevent the fusion of the egg and the sperm. Two important preventive methods are discussed below. (i) Vasectomy This is a method of sterilization in males. In this method, each vas deferens is cut and tied at both cut ends by a thread (ligature). Tubectomy This is a method of sterilization in females. In this method, the fallopian tube is cut and the two ends are tied to prevent passage of ova down the fallopian tubes. Thus, in this method, the eggs continue to be released but do not reach the fallopian tube and no fertilization takes place.

(ii)

29.5.1c Contraception methods These methods involve prevention of fertilization and conception. The main methods of contraception are given below: i) • Natural methods of contraception Rhythm method of contraception: In this method copulation is avoided for those days when the ovum is available for fertilisation. Thus, fertilization can be avoided. Coitus interruptus: In this method, the penis is withdrawn from the vagina prior to ejaculation.



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ii) Mechanical methods of contraception In this approach, various mechanical methods are used to prevent the passage of semen to the fallopian tube or to prevent implantation. • Condoms: It is a thin rubber tube worn over the penis before sexual intercourse. The ejaculate gets collected in this tube and is not discharged into the vagina. Diaphragm: It is fitted over the cervix in a woman’s body by a doctor to prevent the entrance of sperms into the cervical canal. Intra uterine device (IUD): IUD or loop is made of plastic or stainless steel. It is inserted in the uterus, which releases certain secretions that prevent the implantation of embryo in the uterine wall.

• •

iii) Chemical methods of contraception Spermicides: Strong spermicidal (sperm-killing) creams, jellies, etc. are applied in the vagina before copulation, which kill the sperms and prevent fertilization. • Oral contraceptives or pills: The oral contraceptives or pills are taken daily, which prevent ovulation in females. These pills prevent ovulation but allow monthly shedding of the uterine lining through menstrual bleeding. iv) By Medical Termination of Pregnancy (MTP) MTP methods are also known as if conceptive methods. There are applied if conception has taken place. Abortion and aspiration are two corrective methods in which pregnancy can be terminated by either mechanical method or by using hormones. CHECK YOUR PROGRESS 29.4 1. Name the hormone secreted by graafian follicle? 2. Name the term given to the sterilization process in the following. (i) human males (ii) human Females 3. Name the commonly used contraceptives in the following: (i) human males (ii) human female 4. Write the full form of IUD. 29.6 SEXUALLY TRANSMITTED DISEASES Diseases which spread through sexual contact are called sexually transmitted diseases (STD). Sometimes microganisms may infect areas around reproductive parts. During the act of sexual intercourse, these microorganisms may be easily transmitted from one person to another. Three important sexually transmitted diseases are: i) Syphilis ii) Gonorrhoea

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iii) Acquired Immuno Deficiency Syndrome (AIDS) 29.6.1 Syphilis and Gonorrhoea Causative organism Both these diseases are caused by bacteria. Syphilis: Treponema pallidum Gonorrhoea: Neisseria gonorrhoeae Modes of spread Sexual contact with the infected person Incubation period Symptoms of gonorrhoea disease occur in about 2-5 days and that of syphilis are seen in 10-90 days. Symptoms The common symptoms of these bacterial diseases are given below: i) ii) iii) iv) v) Fever and sores appear on the skin, in the throat and urinogenital areas especially vagina or penis, anus, rectum and mouth. Break out of rashes on hands, feet and palms. White patches in the mouth. Acne-like warts in the groin area. Hairfall occurs in patches from infected areas.

Prevention and cure i) Having sexual intimacy with only one person ii) Avoiding prostitution and homosexuality iii) Taking appropriate medical treatment 29.6.2 Acquired Immuno Deficiency Syndrome (AIDS) AIDS is caused by the Human immunodeficiency virus (HIV) (Fig. 29.17). once the virus enters the body it lives and grows in the body fluids and blood cells of the infected person. Mode of transmission (i) HIV may be transmitted in the following ways. (ii) Sexual contact with the affected person i.e. through semen or vaginal fluid. (iii) Exposure to infected blood and blood products by using the same syringe already used by an infected person, and by use of infected

Fig. 29.17 HIV virus

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blood during blood transfusion. (iv) Organ transplant from an affected person to a healthy person. (v) During pregnancy, from an infected mother’s blood to her baby’s blood. Incubation period The average incubation period of HIV virus is about 28 months (range 15–57 months). Symptoms i) The person feels fatigued or tired, suffers from loss of weight and fever, and sweats profusely. ii) Persistent dry cough, oral rash and shortness of breath may be observed. iii) Headache, visual disturbance, vomitting and fits are also witnessed. iv) Gastro-intestinal problems like mild diarrhoea may occur. v) Skin blotches, eczema, fungal infection and sometimes skin cancer may be observed. vi) Nervous system may be affected, the brain may be badly damaged leading to a loss of memory, and ability to speak and to think. vii) A completely infected AIDS patient may die within three years of infection. Prevention and control Although there is no cure for AIDS, the HIV infection can be prevented by i) ii) iii) iv) v) Avoiding multiple sex partners Using a condom or other method of contraception Avoiding prostitution and homosexuality Screening of blood before transfusion Treatment of all blood and other products used in transfusion to destroy the HIV vi) Avoiding sharing of injection needles vii) Avoiding pregnancy if the mother is HIV positive viii) Educating people

CHECK YOUR PROGRESS 29.5 1. What are sexually transmitted diseases? 2. Name any two diseases that are spread by sexual contact. 3. Give the full form of AIDS. 4. Name the causative organism of the following diseases. (a) Syphilis (b) Gonorrhoea • LET US REVISE The process by which living organisms produce more of their own kind is called reproduction. It is of two types- asexual reproduction and sexual reproduction.

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• • • • • • • •

• • • • •

In asexual reproduction only one organism is involved, no gametes are produced and no fertilization takes place. In sexual reproduction both male and female gametes are produced and fertilization occurs. Some methods of asexual reproduction are - fission, budding, fragmentation and spore formation. Some artificial methods of propagation of plants are grafting, cutting, layering and tissue culture. A typical flower has four whorls—calyx, corolla, androecium and gynoecium. Each member of the androecium is called stamen and each member of the gynoecium is called pistil. Most animals and some plants reproduce sexually. Sexual reproduction involves two main processes, i.e. meiosis and fertilization. The age of 13–14 years in males and 11–12 years in females is called puberty in human beings. At this age, sex organs get matured and several secondary sexual characteristics appear in them. Placenta is an association between maternal and foetal tissues meant for physiological exchange. Twins are of two types—fraternal and identical twins. Unchecked population control has led to population explosion. Fertility control methods can be preventive or corrective. We can control the rising population by fertility check. Diseases that spread through sexual contact are known as sexually transmitted diseases. TERMINAL EXERCISES

A. Multiple choice type questions. Select the correct answer from the following statements. 1. In potato, vegetative propagation takes place by a) leaves b) stem c) root d) seeds 2. Bryophyllum plant reproduces vegetatively by a) leaf bud b) adventitious buds c) root d) stem 3. In the process of grafting, the plant forming the shoot system is known as a) scion b) stock c) sucker d) bulb

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4. Pollen sacs are present in a) thalamus b) anther c) ovary d) corolla 5. The transfer of pollen grains from anther to the stigma of the same flower is a) self pollination b) ovulation c) cross pollination d) fertilization 6. In the human female, fertilization of the ovum takes place in a) vagina b) ovary c) fallopian tube d) uterus 7. The process of release of the egg from the ovary is called a) ovulation b) oogenesis c) menstruation d) spermatogenesis 8. Which of the following is the sperm storage organ in human males? a) Epididymis b) Penis c) Vas deferens d) Testis B. Descriptive type questions. 1. Define reproduction. Name the two types of reproduction that occur in the living beings. 2. Give one example each of organisms, which reproduce by i) Budding ii) Fragmentation iii) Fission 3. Give one example each of the plants, which reproduce by vegetative propagation of the following parts: i) Stem ii) Leaves iii) Layering iv) Grafting 4. What is vegetative propagation? Write various methods of artificial vegetative propagation. 5. What is a zygote? How is it formed? 6. Where does fertilization take place in plants and in animals?

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7. 8. 9. 10.

Name the organs of male reproductive system in humans. Name the organs of female reproductive system in humans. Name any two mechanical methods of contraception. Give one word for the following statements. i) Process of transfer of pollen grains from the anther to the stigma. ii) Male reproductive whorl of the flower. iii) Diseases spread through sexual contact. iv) Site of sperm production in males. v) Site of fertilization in females. 11. Differentiate between binary fission and multiple fission. 12. What is placenta? 13. A woman gave birth to twin daughters. Both the daughters looked exactly alike. What type of twins could they be? 14. What is meant by population explosion? 15. What are contraceptives? Name any two contraceptives used by females. 16. How does the process of pollination differ from that of fertilization? 17. Explain the different methods of vegetative reproduction in plants. ANSWERS TO CHECK YOUR PROGRESS 29.1 1. Asexual reproduction and sexual reproduction. 2. i) Amoeba ii) iii) iv) v) 29.2 1. i) ii) Self- pollination: If the pollen grains from the anther of a flower are transferred to the stigma of the same flower, it is termed self-pollination. Cross pollination: If the pollen grains from anther of one plant reach the stigma of a flower on another plant of the same species, then this is called as cross pollination Plasmodium Hydra Spirogyra Bryophyllum

2. Androecium and gynoecium 3. ovary 29.3 1. 13-14 years in males and 12-13 years in females. 2. Seminiferous tubules

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3. i) ii)

Human male reproductive system: a pair of testes, a pair of epididymis, a pair of vasa deferentia, urethra, penis and accessory glands

Human female reproductive system: a pair of ovaries, a pair of fallopian tubes, uterus, vagina 4. i) Human male: deepening of voice, appearance of bread and moustaches, growth of axillary and pubic hair, widening of shoulders (any three) ii) Human female: Growth of axillary and pubic hair, widening of pelvis and hip, enlargement of breasts 29.4 1. Oestrogen 2. i) Males: Vasectomy ii) Females: Tubectomy 3. i) Males: Condoms ii) Females: Intra uterine devices, spermicides, diaphragm, oral contraceptive pills etc. 4. IUD: Intra Uterine Device.

29.5 1. Diseases spread through sexual contact are called sexually transmitted diseases. 2. AIDS, Gonorrhoea, Syphilis etc. 3. Acquired Immuno Deficiency Syndrome. 4. i) Syphilis: Treponema pallidum ii) Gonorrhoea: Neisseria gonorrhoeae GLOSSARY Reproduction: A process by which a living organism is able to produce more of its own kind. Asexual reproduction: Production of an offspring from body parts other than the reproductive organs. Sexual reproduction: Production of an offspring by the fusion of egg and sperm which are the sex cells or gametes. Binary fission: Process in which two individuals are formed from a single parent. Multiple fission: Process in which many individuals are formed from a single parent. Vegetative propagation: Method in which any vegetative part of the plant, such as leaf, stem or root, develops into a new plant. Androecium: The male part of a flower. Gynoecium: The female part of a flower. Placentation: The arrangement of ovules in the ovary of a flower.

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Autogamy (self pollination): Pollen grains from the anther of a flower are transferred to the stigma of the same flower. Allogamy (cross pollination): Pollen grains from the anther of a flower are transferred to the stigma of another flower of the same species. Spermatogenesis: The process of formation of sperms in the testes of an organism. Oogenesis: The process of formation of eggs or ova in the ovaries of an organism. Semen: The sperms along with the secretions. Puberty: The age at which the reproductive organs become mature and functional in human beings. Fertilization: The process of fusion of the egg and the sperm. Zygote: The product of the fusion of the egg and the sperm. Identical twins: When two embryos are formed from the same egg due to division of the fertilized egg into two sets of cells. Non-identical or fraternal twins: When two embryos are formed from two different eggs produced at the same time and fertilized by two different sperms.

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30

From Parents to Children – Elements of Genetics
Collect a few photographs of your family members and close relations. You will be surprised to find marked resemblances in physical features such as the shape of nose, eyes, hands, feet, forehead, colour and texture of hair and many other observable characterics. Similarities between members of a family are due to ‘heredity’. Heredity means passing down of characteristics from parents to children. Differences between members of the same family are due to different combinations of parental characteristics. These differences are termed ‘variations’. Heredity and variation are due to genes and gene combinations and study of heredity is termed ‘Genetics’. In this lesson, you will learn about some basics of genetics. OBJECTIVES After completing this lesson, you will be able to: • define heredity and variation; • highlight Mendel’s and Sutton’s contributions to genetics; • state the number of chromosomes in a normal human being; • state the distinction between autosomes and sex chromosomes; • explain the chromosomal basis of sex determination in humans; • name at least three genetic disorders; • state the symptoms and explain the cause of haemophilia, colour blindness and thallasemia. 30.1 MENDEL AND SUTTON’S CONTRIBUTION TO GENETICS Gregor Johann Mendel (1822-1884) an Austrian monk, was the first to observe the manner in which characteristic features pass down from parents to offsprings. He performed his experiments on the garden pea plant, which has striking contrasting characteristics such as, purple or white flowers, tall or dwarf plants, green or yellow seeds, which may also be either round or wrinkled. He selected

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seven pairs of contrasting features in the pea plant and carried out selective breeding. For example, he chose a tall plant whose seeds always produced tall plants, and a dwarf plant from whose seeds only dwarf plants could be raised. He used the pollen of a tall plant to pollinate and fertilise the pea flower of a dwarf plant. Such a type of pollination that is done manually is known as artificial pollination. Similarly, he artificially pollinated plants with other contrasting features. After experimenting for several generations he was able to formulate certain ‘laws of inheritance’. That was the beginning of genetics. One of Mendel’s laws states that for every feature or character (e.g. colour of flowers, height of plants, etc.) there is a pair of ‘factors’. One factor each from each pair goes into the gamete (sperm or egg). Upon fertilisation, these factors express themselves according to a set pattern. Gregor Johann Mendel was born in 1822. He grew up on a small farm in Northern Moravia, then in Austria. In 1847, he became a priest. In 1856, in the monastery of St. Thomas, Mendel began his historic research work with the garden pea and published his work entitled “Experiments on plant hybrids” in 1866. Unfortunately his work was rediscovered Fig. 30.1 Gregor Johann Mendel sixteen years after his death in 1900. The (1822 - 1884) first significant contribution in the field of genetics was given by Mendel and so he is known as “the father of genetics”. Later in 1920, Sutton while observing grasshopper chromosomes confirmed that ‘Mendelian factors’ are present on chromosomes. The factors later got to be known as genes. It was accepted that genes are responsible for heredity. In other words, genes are the units of heredity. These are present at fixed loci (locations) on the chromosomes. ACTIVITY 30.1 Check your ear lobes and those of your friends and family members. The lower end of the ear lobe may be attached or free. This feature of the ear lobe is hereditary. Observe the ear lobes of your parents and your siblings (brothers and sisters) and note from which of your parents you have inherited this feature. You may similarly try and observe the rolling of your tongue and notice who all in your family can roll their tongues and notice who all in your family can curve the tip of the thumb and who all cannot, for this ability is also hereditary. Also, note any two other features such as colour of eyes or shape of the nose or any other feature among your friends. Differences that you note are variations.

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Ear lobes Tongue rolling

Free ear lobe

Attached ear lobe

Shapes of Nose

Roman

Straight

Up turned

Fig. 30.2 Some variations found in people

30.2 HUMAN CHROMOSOMES Every cell in the human body contains 46 (23 pairs) chromosomes. You have already learnt that chromosomes are present in the nucleus of a cell. Chromosomes are present in pairs. One chromosome of each pair comes from the father and the other from the mother. The chromosome number is thus a “diploid” (i.e. paired) number and is represented as 2n. The number of chromosomes remains constant in all normal human beings. Of the 23 pairs of human chromosomes (2n = 46), one pair represented as X and Ychromosomes have genes that determine the sex of an individual. X and Y chromosomes are, therefore, called sex chromosomes while, the rest 22 pairs are termed autosomes. You can see the chromosomes arranged according to size and also based on certain other considerations in the Fig. 30.3. Chromosomes can be seen only during cell division. Pairs of similar chromosomes (called homologous chromosomes) are selected and arranged in the mitotic metaphase of a dividing cell. You have

Chromosomes of a normal female

1

2 A

3

4 B

5

6

7

8

9 C

10

11

12

13

14 D 20 F

15

16

17 E

18

19

21 G

22

X X

Chromosomes of a normal male

1

2 A

3

4 B

5

6

7

8

9 C

10

11

12

13

14 D

15

16

17 E

18

19 F

20

21 G

22

X Y

Fig. 30.3 Human chromosomes

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already learnt about cell division earlier and know that at metaphase chromosomes are clearly seen lying at the equator. CHECK YOUR PROGRESS 30.1 1. 2. 3. 4. 5. Who proposed that hereditary units are located on chromosomes? What are ‘Mendelian factors’ called today? How many autosomes do humans have? Why are X and Y-chromosomes called sex chromosomes? What is the diploid number of chromosomes in human body cells?

30.3 CHEMICAL NATURE OF GENES By now you know that genes are bearers of hereditary characters and they are present on chromosomes. From the work of many scientists, today we know that genes are segments of chemical molecules called DNA or deoxyribonucleic acid. One chromosome contains one molecule of DNA and genes are fragments of this DNA molecule. You might have heard that criminals can now be identified by DNA tests called “DNA fingerprinting”. This is because DNA of an individual is same in each and every cell of the body and also resembles the DNA of parents. Needless to say this is because children inherit DNA from parents. Just like the fingerprint, DNA of every individual is unique and even if a hair or drop of blood or semen of the criminal is left at the site of the crime, it can be used to detect the DNA of the criminal and compare with the suspect to ascertain the truth. Dr. Hargobind Khorana: the creator of man-made gene It is a matter of pride that Nobel laureate Dr Hargobind Khorana who was born in our country synthesized an artificial gene in the laboratory for the first time. Dr Khorana got the Nobel Prize in 1970 for this contribution.
Fig. 30.4 Dr. Hargobind Khorana

30.4 SEX DETERMINATION IN HUMANS In the earlier section you have learnt about autosomes and sex chromosomes. The gametes, i.e., sperms or eggs have haploid or half the number of chromosomes as you have learnt earlier in lesson 29 on gamete production and fertilization. Gamete has 22 autosomes and 1 sex chromosome. When an egg of the mother and sperm of the father fuse to produce a zygote, the diploid number is restored. Zygote develops into an individual whose sex depends on whether there are two X chromosomes or one X and one Y-chromosome. Zygotes having two X-chromosomes develop into females and zygotes with one X and one Y-chromosome develop into males.

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Eggs are of one kind only. These contain 22 autosomes and a single X chromosome. Sperms are of two kinds (i) having 22 autosomes and one X chromosome, or (ii) having 22 autosomes and a Y chromosome (See figure below). When X bearing sperm fuses with egg, a female child results with 44 autosomes and two X chromosomes. If Y bearing sperm fuses with egg then a male child results with chromosomal constitution 44 autosomes (Fig. 30.5) and X and Y chromosomes.

Parents

44 + XY

44 + XX

22 + X

22 + Y

22 + X

44 + XX

44 + XY

Note : Thus, the chromosomes in a male Fig. 30.5 Chromosomes - the basis of sex human are 44 autosomes + XY and that determination in humans in a female are 44 autosomes + XX. It is, therefore, wrong to blame a woman if she does not bear a male child as is done in some ignorant families of our country. Sex of an individual is purely due to chance and neither the mother nor the father can be blamed. CHECK YOUR PROGRESS 30.2 1. What is a gene made of? 2. Why is DNA fingerprinting a foolproof test? 3. If a Y bearing sperm fuses with an egg, what will be the sex of the individual developing from the zygote? 4. How many X chromosomes can be found in the cells of (i) a boy, and (ii) a girl. 5. How many molecules of DNA are present in one chromosome? 30.5 INHERITANCE OF BLOOD GROUPS You have already learnt in lesson 26 that every human being belongs to one of the four blood groups i.e., A, B, AB or O. The blood group of a person is inherited from parents and depends on the combination of genes for blood group inherited from either parent. One gene for blood group is inherited from the father and the other from the mother. These genes are designated as IA, IB and i. The following table shows the combination of genes and the resulting blood group. Table 30.1: The combination of genes and the resulting blood group Gene combination IA IA or IA i IBIB or IB i I I Ii
A B

Blood group A B AB O

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Similarly the Rh+ (Rhesus positive) blood group is inherited when one or two genes for Rh+ antigen are present in a person. A person with Rh- (Rhesus negative) blood group lacks Rh+ gene. Thus, Rh+ Rh+ or Rh+ Rh- combinations result in Rh+ blood group and Rh- Rh- into Rh- (Rh negative) blood group. 30.6 HEREDITARY (GENETIC) DISORDERS Sometimes a defective gene present in a parent may be passed down to the offspring. The defective gene may not express itself in the parent. This is because the expression of the defective gene may be masked by its pair, which is normal. But the child may inherit one defective gene from each parent and hence have both genes defective. Such a child suffers from the genetic disorder as shown below. Parents: Normal mother (defective gene masked)
+ –

Normal father (defective gene masked)
+ –

Gametes : +



+



Offsprings : + + Normal

+ –

+ –

– –

Normal

Normal

Abnormal (Genetic disorder)

There are several kinds of hereditary disorders, some of which may be caused due to the presence of only one defective gene or sometimes as shown above by the presence of two defective genes. Genetic disorders cannot be cured by medicines. Scientists are trying to discover methods by which a defective gene occurring in an individual may be removed or replaced by a normal gene. This is called gene replacement therapy. Three common hereditary disorders are Thallasemia, Haemophilia and colour blindness. a) Thallasemia Patients suffering from this disorder are unable to manufacture haemoglobin, the pigment in red blood corpuscles which carries oxygen to tissues. This is because the pair of genes controlling hemoglobin production are defective. Thallasemics (persons suffering from thallasemia) require frequent blood transfusion in order to survive.

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b) Haemophilia Those persons suffering from haemophilia have either a defective gene or lack genes, which control production of substances responsible for blood clotting. In the absence of such substances blood does not coagulate. So, once bleeding starts, it does not stop. c) Colour blindness Different kinds of colour blindness are met with but commonly those suffering from this genetic disorder are unable to distinguish blue colour from green. Again, this is due to the presence of a defective gene or absence of a gene. Both haemophilia and colour blindness genes are located on X-chromosomes, and hence, the disorder is passed down form mother to the son. In the mother with two X-chromosomes, the defect may not show up. Also, in the daughter, the effect of defective gene on X-chromosome from mother may be masked by a normal gene on the X chromosome derived from the father. But males have only one X-chromosome, which is inherited from the nother and if it bears the defective gene, the person suffers from the genetic disorder. (1)
XC-chromosome + (colour blindness gene in mother’s X–chromosome) XC (From mother) + X-chromosome (normal gene in father’s X-chromosome) Y (From father) XCX (daughter carrying colour blindness gene but not suffering from it) XCY Son born colour blind does not have any gene for colour vision so son with defective gene suffers.

(2)

Thallasemia is an autosomal genetic disorder, while, haemophilia and colour blindness are sex-chromosomal or X-chromosomal disorders. CHECK YOUR PROGRESS 30.3 1. What will be the blood group of an individual with genetic combination IAIB? 2. How can a person be normal for a trait even when carrying one defective gene for that trait. 3. On which chromosome are genes for haemophilia and colour blindness located? 4. On which kind of chromosome–autosome or sex chromosome is defective gene causing Thallasemia located? 5. Name the therapy in which defective gene is substituted by normal gene. LET US REVISE Passing down of characters from parents to children is called heredity. Children of same parents differ because they posses different combinations of parental genes. This is called variation.

• •

From Parents to Children - Elements of Genetics : 265 :

• • • • • • •

• • • • •

Heredity and variation are due to genes and their varied combinations. Study of heredity is called genetics. Mendel was the first to postulate laws of inheritance (heredity) and said heredity was due to “factors”. Sutton explained that “Mandelian factors” were the genes and that genes are present on chromosomes. The diploid number of chromosomes in humans is 46, of which 22 pairs are autosomes and 2 chromosomes X and Y are sex chromosomes. Genes are made of DNA. One Chromosome has one molecule of DNA. Genes are fragments of DNA. Sex determination in humans is based on combination of sex chromosomes. Females have two X-chromosomes, while males have one X and one Y chromosome. Defective genes or absence of genes may cause genetic disorders e.g. thallasemia, haemophilia and colour blindness. Thallasemics lack genes responsible for production of haemoglobin so they need frequent blood transfusion for survival. Haemophiliacs are bleeders. Their blood cannot coagulate as they lack genes responsible for production of substances required for blood coagulation. Colourblind people cannot distinguish blue colour from green due to defective genes for colour vision located on X-chromosomes. Thallasemia is an autosomal genetic disorder while, haemophilia and colour blindness are sex chromosomal disorders. TERMINAL EXERCISES

A. Multiple choice type questions. Select the correct answer in the following. 1. Which statement is true for ‘genes’? (a) Genes are imaginary factors. (b) (c) Genes are present in the (d) ribosomes of the cell.

Genes are fragments of DNA. Genes are not inherited.

2. In which genetic disorder is the patient unable to manufacture haemoglobin? (a) Haemophilia (b) Thallasemia (c) Tuberculosis (d) Jaundice 3. The number of chromosomes in a human sperm is, (a) 46 (b) 44 (c) 23 (d) 22 4. The sex chromosomes in females are (a) XX (c) XY (b) (d) one X and no Y one Y and no X

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5. Who can be called the founder or father of genetics? (a) Sutton (b) Mendel (c) Darwin (d) Bateson B. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Descriptive type questions. Name the scientist who gave the laws of inheritance. What are “factors” named by Mendel called today? What is the chemical nature of a gene? Where are genes located? Why is haemophilia called bleeder’s disease? State two differences between autosomes and sex chromosomes. Define: heredity; variation; genetic disorder; sex chromosomes. What has been the contribution of Mendel and Sutton to science of genetics? State in one sentence for each of the two scientists. State any two facts about human chromosomes. Why is haemophilia found mostly in boys? With the help of a line diagram explain the chromosomal basis of making of a male child. What is the basis of sex determination in humans? Why is DNA fingerprinting a sure test for identification of a person? Write notes on any one genetic disorder. What is meant by “gene replacement therapy”?

16. Difficult but try Rahul’s maternal grandfather (mother’s father) was colourblind. What are the chances of Rahul being colour blind if his father has normal colour vision? ANSWERS TO CHECK YOUR PROGRESS 30.1 1. 2. 3. 4. 5. 30.2 1. 2. 3. 4. 5. Sutton Genes 22 pairs or 44 They determine sex of a person. 46 DNA DNA of a person is unique Male (i) one (ii) two One

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30.2 1. 2. 3. 4. 5.

AB The normal gene masks the effect of defective gene. X chromosome autosome Gene replacement therapy

GLOSSARY Autosomes: Chromosomes containing genes for characters other than those for sex determination. Colour blindness: Genetic disorder in which a person cannot distinguish between blue and green colours due to defective genes. DNA: Deoxyribonucleic acid, chemical substance of which genes are made. DNA fingerprinting: A technique by which a person’s identity can be established by the study of his DNA. Diploid: Full (double) set of chromosomes in pairs in a cell. Genetics: Science of heredity and variation. Heredity: Passing down of characteristics from parents to offsprings. Haemophilia: Genetic disorder in which blood does not clot because of the presence of a defective gene. Sex chromosomes: Chromosomes containing genes for sex determination (Designated X and Y). Thallasemia: Genetic disorder in which haemoglobin cannot form in RBCs due to the presence of defective gene. Variation: Genetic differences between individuals.

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31

Health, Hygiene and Diseases
You must have heard the saying ‘health is wealth’. Most of you must be in good health. If you keep good health your parents may not have to worry about your health. Health is of prime concern for individuals as well as for the community at large. Good health requires certain efforts and cannot be purchased. In this lesson we will discuss the characteristics of good health and the various factors that help to maintain it. Cleanliness inside and outside the house, along with proper sanitation helps in keeping the environment disease free. Knowledge of first aid can be of great help in saving a victim’s life in case of an emergency. You will learn about some first aid techniques also in this lesson. OBJECTIVES After completing this lesson, you will be able to: • define health and differentiate between personal and community health; • explain the role of proper nutrition, healthy habits and physical exercise in maintaining good health; • define hygiene and suggest ways to show that health and hygiene are interrelated; • define disease and classify diseases into communicable and noncommunicable types; • mention the cause, mode of transmission, symptoms and preventive measures of some common communicable diseases; • define immunity and list the various national immunisation programmes; • define first-aid and identify some of its methods. 31.1 HEALTH AND HYGIENE What is good health? Different people may consider good health differently. But to define it formally, health is a state of complete physical, mental and social well-being. We take health as being free from diseases but it is much more than just the absence of a disease. Good health may enable us to do well at work and in life. Good health involves proper functioning of all body organs. It also involves feeling well both in body and in mind. People enjoying good health are cheerful, free from stress, and enjoy life to the fullest. Only if you are in good health you can be of help to others and the community.

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Do you consider yourself to be in good health by the above-mentioned definition? To keep ourselves free from diseases and to have good health, we should be careful about hygiene. The various practices that help in maintaining good health are called hygiene. The word hygiene comes from a Greek word hygiea that means ‘Goddess for health’ and deals with personal and community health. Thus, health and hygiene go hand in hand or they are interrelated. Proper nutrition, physical exercise, rest and sleep, cleanliness, and medical care are essential parts of maintaining good health. Health includes both personal and community health. 31.2 PERSONAL HEALTH Taking care of oneself to remain healthy and free from diseases is personal health. Some important aspects of good personal health are as follows: 1. Balanced diet: You have already studied about the need and importance of balanced diet in lesson 25. Obtaining a balanced diet depends on one’s choice and what one can usually afford. It also includes the correct proportion of carbohydrates, proteins, vitamins, minerals and roughage in your diet. 2. Personal hygiene: There are some activities you perform everyday in order to keep yourself clean. Can you list them out? These activities are: • • Regular toilet habits: Regular bowel movements keep us free of body wastes generated inside the body. Washing hands before eating: Having food with dirty hands may make us sick because the dirt in our hand might carry certain diseasecausing germs. We should wash our hands after going to the toilet. Washing hands with soap make them germ free.

Bathing regularly and wearing clean clothes: Dirt is a place for germs to grow. Bathing regularly keeps your body free of dirt, body lice and germs (Fig. 31.1). • Cleaning the teeth: After eating food, some food particles may remain Adult Louse sticking to your teeth. These food particles form a medium for the germs to grow, harm your gums and teeth, and cause bad breath. Brushing of teeth Eggs every day do not let the germs grow. Magnified Eggs on hair Brushing of teeth before going to bed is a very good habit. Fig. 31.1 Regular cleaning and combing keeps hair free from lice • Washing hair, cleaning eyes, ears and nails: Regular washing and combing of hair helps in preventing dirt accumulation to keep the germs away. Nails should be clipped regularly; nail biting is unhygienic and must be avoided.



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3. Domestic hygiene • House should be kept clean and free from dirt, flies and germs. • Cooking utensils, plates, cups and other utensils should be kept clean. 4. Clean food and water • Fruits and vegetables should be washed in clean water to make them free from germs and pesticides (chemicals sprayed on plants to keep them insect free) before consumption and cooking. • Water used for drinking, cooking, bathing and washing utensils should be from a clean source. 5. Cooking with care: Food should be prepared in a clean kitchen and in a clean manner. • While cooking food, it is important to heat it to high temperature to kill any germs present in it. • Cooked food should be eaten fresh or stored in cool, fly-proof place. • Milk stored in the refrigerator or outside should be boiled again to make it germ free. 6. Abstaining from habit-forming substances: To keep healthy, one should avoid smoking, chewing of betel nut, gutka and tobacco, and drinking alcohol. Intake of such habit-forming substances may lead to health problems such as liver damage, kidney failure and heart failure. 7. Exercise: Regular walking and physical exercises have a good effect on health. Outdoor games and sport maintain the heart and circulatory system in good condition. Walking keeps the joints of bones healthy. 8. Regular sleep and relaxation: These also play an important part in maintaining sound mental health. They also help in the repair of body tissues. CHECK YOUR PROGRESS 31.1 1. Define good health. 2. List two precautions that should be taken while storing cooked food. 3. Intake of alcohol and narcotics may cause damage to ____________ and__________ 4. Washing of fruits and vegetables makes them free from _________ and ___________ 5. Balanced diet includes correct proportions of _________, __________, _______, __________, and ________________ 6. List any two activities that keep heart in good condition. 31.3 COMMUNITY HEALTH Activities, undertaken at the Government or local organisation level to maintain health of the people (for controlling diseases) are known as community health. We often read in the newspaper or see on television about the fast spread of certain diseases in a particular area. Many people seem to get affected. This may not be an individual problem, but the problem of community and requires immediate attention. Local or government organisations may take steps to control

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spreading of a disease, by creating awareness and ensuring adequate supplies of medicines. You must have seen notices and banners put up by the government agencies stating the date and time of immunization programmes and the precautions to be taken against different diseases. Such awareness is regularly created through nationwide campaigns against the spread of diseases such as malaria, dengue, AIDS, polio, leprosy, and Hepatitis B. There are several organisations working towards good community health. Some of these are listed below. 1. Government hospitals, and dispensaries 2. The National Malaria Eradication (removal) Programme 3. The Tuberculosis (T. B.) Eradication Programme 4. National Immunization Programme 5. National Pulse Polio Programme Some of the important tasks, which the community health centres undertake are: • • • To maintain proper cleanliness by disposing off the sewage from colonies. To provide safe and germ free drinking water. To run various immunization (vaccination against various diseases) programs and other health awareness programmes wherever there is danger of spreading of a disease. To provide health education. To spray insecticides to kill harmful insects. To maintain food standards, regular inspection at food stores, meat and milk outlets. To prevent mosquito breeding, cover open drains and pour kerosene oil on the surface of stagnant water.

• • • •

Concrete drains to drain soil

Clean compounds Oiling surface of stagnant water Fish eat larvae Use Mosquito nets on beds

Spraying insecticides on walls

Clean and airy rooms

Fig. 31.2 Some efforts made towards maintenance of community health

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31.4 ENVIRONMENTAL HYGIENE You can keep your body clean but what will happen if you live in dirty surroundings? If so, you are sure to fall sick. Thus, to have a healthy living one must live in clean surroundings. Unclean surroundings may become breeding ground for flies and germs, thus, leading to spread of diseases. Environmental hygiene includes environmental sanitation or keeping the surroundings clean. To keep the environment healthy, we should be careful about the disposal of the garbage. Some of the practices for disposing the garbage are: • Keeping the house clean: The house must be cleaned every day. We must sweep and mop the house to remove dirt from every nook and corner of the house. The furniture must also be wiped clean. The cobwebs from the walls and roof should be cleared at least once a week. • Throwing garbage in dustbins: Do not throw your household garbage on the roadside. This makes street dirty and allows flies, mosquitoes and other animals to breed. This garbage not only gives a dirty look but also produces foul smell. Garbage should be thrown inside the dustbins. The bins should also be cleaned after emptying the garbage. • Keeping dustbins covered: To prevent entry of insects and other animals inside the house dustbins should be kept covered. CHECK YOUR PROGRESS 31.2 1. Name any two diseases for which awareness is being spread at the national level. 2. List any two national organisations working towards good community health. 3. Fill in the blanks. i) Mosquito breeding may be prevented by pouring ___________ on stagnant water. ii) Unclean surroundings become breeding ground for __________ and ____________

31.5 DISEASE A disease is defined as any deviation from health or any state when body is not at ease. Disease may be the sickness of the body or the mind. A disease can be as mild as a sore throat, common cold, and stomach upset or as serious as cancer. Disease can strike almost any part of the body and anybody at some stage or the other. They can also affect a person’s mental and emotional health. In this section we will mainly discuss diseases of the body. You may have heard of some common diseases or may be you have seen people suffering from some diseases, such as typhoid, malaria, rickets, jaundice, scurvy, common cold, etc. Can these diseases be categorised on some basis? One

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of the bases could be the cause of the disease. Diseases that are transmitted through air, water and physical contact or spread through vectors like flies and mosquitoes are termed communicable diseases. Diseases Communicable Diseases that spread from infected person to another Caused by pathogens, such as viruses, bacteria, fungi, protozoa and worms Some examples are malaria, typhoid, common cold, measles and tuberculosis Non-communicable Do not spread from an infected person to another Pathogens are not involved These diseases may be caused due to dietary deficiency (rickets, scurvy, kwashiorkor), genetic defects, hormonal imbalances, allergy, etc.

• •

• • •



Epidemics Sometimes you would have seen or heard about a disease affecting a large number of people in a small period. A disease that affects a large population in a particular area is considered to be an epidemic. Sometimes, cholera takes an epidemic form in our country. Cholera is a bacterial disease and marked by uncontrolled vomiting and diarrhoea. It may affect large number of people, leading to dehydration and death. What is a communicable disease? Diseases that spread from one person to another by the entry of pathogens are called infectious or transmissible or communicable diseases. How do communicable diseases spread? We all know that there are a lot of germs or pathogens (disease causing organisms) in the environment we live in. To carry on their life cycle, the pathogens try to come out of the body of an infected person and reach out to more hosts for their survival. They produce toxins in the host’s body which leads to symptoms, such as fever and eruption of rashes, etc. These pathogens may be transferred from one person to another by the following methods. • Direct method • Indirect method Direct method: by contact with the infected person. Indirect method may include the following: • Touching and sharing items used by the infected person: Using the same towel or sharing a handkerchief or same bed with the patient may also spread diseases. Contaminated food and drink: Food and drinks may get infected by flies and insects carrying germs.



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• •

• •

Carriers: These organisms carry germs from one place to another, for example housefly, cockroach, etc. Vectors: These are agents that harbour germs but they themselves remain unaffected. For example, animals such as dogs and monkeys, or mosquitoes. Air: Through droplet method, i.e. coughing and sneezing by the infected person (Fig. 31.3). During blood transfusion or other equipment such Fig. 31.3 Droplet method of spread of communicable disease as infected needles.

31.6 CLASSIFICATION OF VARIOUS COMMUNICABLE DISEASES We can classify various communicable diseases according to the type of causative organism or pathogen (Table 31.1). Table 31.1: Diseases caused by certain pathogens
Type of pathogen Virus (Jaundice), Bacteria Fungi Protozoa Helminths (worms) Diseases caused Influenza (common cold), Hepatitis Chickenpox, Measles Cholera, Tetanus, Tuberculosis, Ring worm Amoebic dysentery, Malaria Filariasis

The following table 31.2 will give you an idea of cause and symptoms of some diseases and the different ways to prevent them. Table 31.2: Symptoms of some common infectious diseases, the causative organism, mode of transmission and preventive measures against the disease I. Viral diseases
Disease Causative organism Mode of transmission Direct or Indirect contact Symptoms Fever Body pain Sore throat Sneezing Weakness Rise in body temperature Yellowing of urine, eyes and nails Loss of appetite, nausea and vomiting Prevention/ Cure Taking precautions Antibiotics to prevent secondary infections Intake of treated water Vaccination Avoiding contact with an infected person and his and his articles

Influenza Influenza virus

Hepatitis Virus (Jaundice)

Contaminated water

II. Fungal diseases
Disease Ringworm Causative organism Fungus Mode of transmission Direct contact Symptoms Ring like discoloured patches over the skin and scalp Itching, redness Prevention Personal cleanliness

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III. Bacterial diseases
Disease Causative Mode of organism transmission Direct contact with infected person Coughing Contaminated food and drinks Symptoms Difficulty in breathing, chest pain; low grade fever especially in the evenings over long period; loss of weight; blood in sputum; night sweating Acute diarrhoea; vomiting; dehydration; muscle cramps Prevention BCG vaccination at birth

Tuberculosis Bacteria

Cholera

Bacteria

Contaminated food and water From germs present in faeces of patients

Use of clean, treated water. Vaccination. Prevention of contamination.

IV. Protozoan
Disease Malaria Causative organism Protozoa Mode of transmission Symptoms Female Anopheles mosquito bite Intermittent high fever; Chilliness during periods of high fever; headache; Enlargement of spleen and liver Prevention
Prevent accumulation of water in surrounding; Protection from mosquito bite; taking anti-malarial drugs

Amoebiasis Protozoa (amoebic dysentery)

Contaminated water and food Unwashed vegetables House flies

Abdominal pain; five to Proper disposal of six blood and mucus human excreta; containing stools per day Preventing food and
vegetables from contamination; Drinking safe water

V. Helminthic diseases
Disease Causative organism Mode of transmission Female Culex mosquito Symptoms Prevention

Filariasis Helminthic worm (Elephantiasis)

Fever; swelling of lymph nodes; permanent swelling of feet, legs and thighs; accumulation of large number of worms causing elephant leg-like swelling (Fig. 31.4) in the feet.

Prevention from mosquito bite; Taking preventive medicines in disease prone areas.

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31.7 MEASURES TO PREVENT DISEASES Contracting infectious diseases can be prevented by adopting measures such as: • • • • personal and community hygiene, intake of balanced diet, proper disposal of waste material, imparting education on habit-forming substances, and • immunization against communicable diseases. Protection from communicable diseases by immunization Immunity is body’s ability to defend (fight and protect) against diseases. Mother’s milk during infancy is very important as it provides immunity against diseases to a newborn baby. Immunity can be of two types: • Innate immunity (present from birth) • Acquired immunity (achieved during one’s Fig. 31.4 Elephantiasis (elephant-like lifetime legs) caused by helminthic worms Ways to acquire immunity • Exposure to a disease: A person suffering from a disease, such as chicken pox, measles or mumps, develops life-long immunity against the disease. • By vaccination: By taking vaccines against diseases, such as polio, tuberculosis, hepatitis, etc. Vaccines are weakened germs. When introduced into the body, they make the body develop body resistance to fight against disease but do not themselves cause disease. To prevent the occurrence of a number of communicable diseases, immunization through vaccines is highly effective. Vaccines are available against Polio, Chicken pox, Tetanus, Diphtheria, Whooping cough, Tuberculosis and various kinds of Hepatitis, etc. Most of the immunization for life long immunity should be provided at an early age. Under National Immunization Programme vaccination facilities are available at Government run clinics and hospitals for protection against some common communicable diseases. Table 31.3: Vaccines given to a newborn child and mother
Age 2-6 weeks 3-12months Vaccine Immunity against disease Tuberculosis Diphtheria Pertussis (whooping cough or kaali khansi) Tetanus Measles

Child
BCG DPT

Measles vaccine

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5-6 years 10 years

Diphtheria and Tetanus booster dose Diphtheria and Tetanus Tetanus Toxoide-booster dose Tetanus and Typhoid Typhoid vaccine

Mother (During pregnancy)
16-24 Weeks 24-32 Weeks First dose of Tetanus toxoid Booster dose of Tetanus toxoid Protection against tetanus during child birth from surgical instruments

IMMUNITY

Innate immunity (Inborn or natural)

Acquired immunity

Non-specific Specific (For infections in general) (For particular infections)

Active (Produced in one’s own body)

Passive (Supplied from outside)

Natural (By previous infection)

Artificial (By vaccination)

Natural
(Antibodies received from mother)

Artificial
(Readymade antibodies having been produced in other animals)

CHECK YOUR PROGRESS 31.3 1. List any two diseases transmitted from an infected person to other healthy person. 2. Are rickets and diabetes examples of communicable or non-communicable diseases? 3. Name any two diseases that can be prevented by taking vaccines. 4. Name the body organ(s) affected by hepatitis (jaundice). 5. Name a disease caused by the same group of organism that causes amoebic dysentery. 31.8 FIRST AID Activities that can prevent serious deterioration of a victim’s condition before he gets proper medical attention are called first aid activities.

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You often share work with your parents at home or go outside to play or work. Sometimes you or your friends may get hurt. In case of a medical emergency it may not be possible to get medical attention at once. Immediate care given to a victim of an accident, sudden illness or other medical emergency can save life. All this comes under first-aid. Some first-aid techniques are given here. 31.8.1 BLEEDING Severe bleeding due to deep injury may lead to acute loss of blood, low blood pressure and even death. To stop bleeding: • • • Press directly on the wound with thumb. Keep sterilised dressing or clean handkerchief. Make the victim lie down and elevate the bleeding part above the rest of the body.

31.8.2 Nosebleed • Make the victim sit up and lean forward to minimise blood flow from that part. • Press nostrils for a short while. • Place an ice-cold cloth on the victim’s face. • Consult a doctor if bleeding doesn’t stop. 31.8.3 Fainting It is a brief, sudden period of unconsciousness. In most cases it occurs when a person is standing motionless for too long and may fall to the ground. • Loosen the clothing and raise the feet slightly. Blood will flow back in the head and consciousness will be regained.

31.8.4 Dehydration It is a condition when water is lost from body cells. Early symptoms include severe headache and dizziness. Acute dehydration can result in death. Dehydration may be caused due to reasons, such as, extreme heat, excessive physical activity and inability to drink water, frequent vomiting and diarrhoea. • Victim should be made to drink small quantities of Oral Rehydration Solution (ORS) at frequent intervals. ORS can be made by adding one teaspoon of sugar and a pinch of salt in a glass of (about 200mL) water.

31.8.5 Animal bite It can result in serious infections and diseases if left untreated. • • • Wash the area of bite thoroughly with soap and water and cover it with a gauze dressing. In case of dog bite, the dog should be kept under observation to determine if it has rabies (aversion from water or hydrophobia). Consult the doctor immediately for anti-rabies treatment.

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31.8.6 Burns The first-aid treatment of burns depends upon the severity of the injury. Firstdegree burns produce a reddening of the top layer of skin. Second degree burns damage the deeper skin and may form blisters. To treat the first and second degree burns: • • Place the injured area in cold water to relieve the pain. Blot the area and apply a dry sterile dressing.

Third degree burns destroy the deepest layer of skin and should not be treated with water. They should be immediately covered with thick dressing, clean towel or cloth sheet. A doctor should be consulted immediately. Chemical burns caused by acids or alkalis should be flushed with large amounts of water for at least 10 minutes. 31.8.7 Fractures and dislocations A fracture is a break in the bone and a dislocation occurs when the end of the bone is forced out of its normal position in a joint. This may happen when we fall or injure ourselves while playing, driving or working etc. Signs of fracture and dislocation include pain, unusual position of a joint or bone, and tenderness and swelling around the injury. Victim may not be able to move the affected body part. What needs to be done? • • Do not move the victim until the expert help arrives. Improper handling may cause more damage. Apply a splint in that area if victim has to be taken for further treatment. Splint is a support given to the injured area that prevents movement of the bones. Things, such as a walking stick, big scale, stick, umbrella, rod, etc. can be used as a splint. Splint can be padded and tied to remain in place (Fig. 31.5). Do not tie it very tight, as this may interfere with blood circulation. Do not move a person who has suffered neck or spinal injury.

• •

Fig. 31.5 Technique showing application of splints

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CHECK YOUR PROGRESS 31.4 Fill in the blanks. 1. Activities that can prevent any deterioration before medical help is available to a victim are called _________________ 2. Items such as _________ and ________may serve as a splint in case of a fracture. 3. Cases of first and second-degree burns should be immediately dipped in ________________ 4. In case of animal bite, affected areas should be washed with _______and_______ 5. Extreme pain on movement, tenderness and swelling around the area are signs of ________________ LET US REVISE • • Health can be defined as a state of physical, mental and social well being. Basic conditions for good health are: balanced diet, personal hygiene, clean food, water and air, exercise and relaxation and abstaining from habit-forming substances. The various practices that help maintain health constitute hygiene. Hygiene could be personal and community (environmental). Personal hygiene includes clean habits such as: daily bath, washing of hands before eating food and going to the toilet. Keeping nails, hair and teeth clean. Community hygiene includes keeping the surroundings clean and not letting germs breed and cause diseases. Environmental hygiene and health means keeping the house clean and not letting environment get dirty by throwing of the garbage. Organisations such as government hospitals and dispensaries, and programmes such as: pulse polio, malaria eradication, leprosy and tuberculosis control aims at good community health. Diseases can be communicable and non-communicable. Communicable diseases spread from an infected person to another person through air, water, food and articles (objects). Communicable diseases may be caused by viruses, bacteria, fungi, protozoans, and worms (helminths). Polio, influenza (common cold), hepatitis are caused by viruses. Tuberculosis and cholera are bacterial diseases. Protozoans cause diseases such as: malaria, amoebic dysentery etc. Elephantiasis (Filariasis) is caused by worms. Immunization by vaccines is an effective way of protecting body against communicable diseases. Activities that can prevent serious deterioration of a victim’s condition before the person gets proper medical attention are called first aid.

• • • • • •

• • • • • • • • •

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TERMINAL EXERCISES A. Multiple choice type questions 1. Which one of the following diseases is caused by bacteria? a) Polio b) Hepatitis c) Tuberculosis d) Ringworm 2. Which of the following is a communicable disease? a) Rickets b) Scurvy c) Marasmus d) Cholera 3. Communicable diseases are those which are a) caused by bacteria b) carried from one person to another c) caused by the deficiency of nutrients d) carried from one organ of the body to another 4. Immunity against tuberculosis is provided by which of the following vaccines? a) DPT b) Tetanus Toxoide c) BCG d) Booster dose 5. The causative organism for malaria is a: a) bacteria b) virus c) fungus d) protozoa B. Descriptive type questions. 1. Define hygiene. 2. Why is it insisted to use water from a reliable source? 3. What is an epidemic? Give one example. 4. Name any two organisations working towards community health. 5. Name the vaccine given to the mother during pregnancy. 6. Name any two viral diseases. 7. List any two ways in which food and water get contaminated. 8. A patient comes with symptoms of swollen feet, legs and thighs showing an elephant leg like appearance. Identify the disease and the category of causative organism. 9. Name any two diseases, against which protection is usually provided by vaccination.

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10. People in a certain village have been drinking water from a pond and eating unwashed vegetables plucked from the fields. After a few months they started complaining of symptoms such as abdominal pain, five to six mucous and blood containing stools/ motions per day. Identify the disease and the category of the causative organism. 11. List any two precautions that should be taken while disposing the garbage. 12. What is personal hygiene? Discuss any four activities that are included in personal hygiene. 13. Differentiate between communicable and non-communicable diseases. List any four ways of spread of communicable diseases. 14. What is the difference between first and third degree burn? What important precaution should be taken while handling them? 15. Why is community health important? List any five major tasks undertaken by community health centres. 16. What is immunization? List any four vaccines and age at which they should be taken as per National Immunisation Programme specifying the diseases. C. Difficult But Try 1. Perform a survey in your area to list precautions people usually take to ensure good health for their family. 2. Make a list of diseases people have suffered in the last six months in your locality. Classify them on the basis of causative organisms and symptoms. 3. Visit a government hospital and find out about the immunizaton programme followed in our country. Tabulate the information giving the name of vaccine, age at which it is given and its functions. ANSWERS TO CHECK YOUR PROGRESS 31.1 1. A state of physical, mental and social well being. 2. Food should be kept covered, at a cool place. 3. Liver, kidney, heart (any two) 4. Pathogens/germs and pesticides. 5. Carbohydrates, fats, proteins, minerals and vitamins. 6. Walking, playing 31.2 1. Malaria, Hepatitis-B, Tuberculosis, Polio, AIDS 2. Government hospitals and dispensaries. 3. Kerosene 4. Flies and mosquitoes

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31.3 1. Influenza, Hepatitis, Tuberculosis 2. Non-communicable 3. Polio, Tuberculosis, Typhoid, Hepatitis, Diphtheria, Tetanus (any two) 4. Liver 5. Filariasis/ Elephantiasis 31.4 1. First aid 2. Stick, umbrella, long scale rod (any two) 3. Cold/ ice cold water 4. Soap and water 5. Fracture GLOSSARY Antibiotics : Chemicals secreted by bacteria and some fungi for their own protection, also used to cure certain infectious diseases. Dehydration : Excessive loss of water from body tissues. Epidemic : A disease that affects a large number of individuals in a population in a particular area. Hygiene : Keeping personal body and surroundings clean. Immunity : Body’s ability to fight and protect against diseases. Toxins : Poisonous substances Vaccination : Introduction of weakened germs in the body to develope body’s resistance against communicable diseases.

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32

Agricultural Practices and Animal Husbandry
We all need food to survive. Food is the basic need for all living beings, as it provides energy for doing work, and raw material for building and repair of various parts of the body. You know that our country has a large population, and therefore, we need to produce a lot of food. You also know that to produce such a large amount of food we need a large area of land. However, our land availability is limited. Indian scientists have experimented and researched and suggested ways and means by which more food can be grown than before, on the same piece of land. Improved methods of agriculture have led to the production of about 360m tonnes of plant food products and about 88m tonnes of animal food products. OBJECTIVES After completing this lesson, you will be able to: • state reasons for human dependence on plants and animals for food; • define and differentiate between agriculture and horticulture; • list and explain the various steps for raising an improved crop; • differentiate between manures and fertilizers with the help of examples; • explain various agricultural practices adopted for improvement of food such as, crop rotation and multiple cropping; • state the need for protection of crops; • explain the terms and give examples of weedicides and insecticides; • suggest methods of storage of agricultural produce; • explain the meaning of green revolution; • state the need for animal husbandry; • cite examples of three groups of domesticated animals; • explain methods adopted for management of live stock for better production; • state common diseases of domestic animals and their prevention. 32.1 HUMAN DEPENDENCE ON PLANTS AND ANIMALS FOR FOOD Our food items are either plant products, such as grains, vegetables and fruits or animal products like milk, egg, mutton, chicken etc.

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We eat various parts of plant as food. For example, grains of rice, wheat and corn are seeds; radish and carrot are roots; potatoes and ginger are the stem. We also eat leaves and stem of spinach and plenty of fruits. Thus, human beings depend on plants and animals for food. 32.2 AGRICULTURE AND AGRICULTURAL PRACTICES The branch of science which deals with methods of food production is known as agriculture. Besides studying the new methods of food production, in this branch of science we also study about how new and better varieties of crops can be grown, how animals and birds like cows, hens, etc. can be reared well and made to give more milk or better quality eggs? All these new methods which scientists develop come under agricultural practices. We need vegetables, fruits, cereals, pulses, etc. as food. For our clothes, we need the fibre of plants or animals. We get all these foods and fibres by farming or agriculture. ACTIVITY 32.1 Make a list of things which you use every day. Categorise those items which you get directly or indirectly from agriculture. Does your list look like the one given below? For easy reading, agricultural products have been divided into the following groups as given in the table 32.1. Table 32.1: Various categories of food items
Examples Sorghum (Jowar), Ragi (finger millet) and Bajra (pearl millet) Arhar (Tur), Black gram (Urad), Green gram (Moong), and Bengal gram (Channa) Beans Peas, Soyabean, Cowpea, Lentil Oilseeds Mustard, Groundnut, Soyabean, Sunflower, Linseed, Castor and Cotton seed Root crops Carrot, Turnip, Sweet potato Tuber crops Potato, Tapioca, Ginger and Turmeric Sugar crops Sugarcane and Beet root Plantation crops Coffee, Tea, Rubber and Coconut Category Millets Pulses

32.3 HORTICULTURE Did you observe that something is missing from the list of food items which we eat every day. What is it that we have not listed here in table 32.1? Yes, we have neither included vegetables nor fruits in this list. Vegetables and fruits are essential items of our diet and their growth and production are studied under a branch of agriculture called horticulture. Horticulture is derived from two latin words: hortus which means garden, and culture which means cultivation.

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The branch of agriculture that deals with growing and production of vegetables, fruits, ornamental plants and management of orchards is called horticulture. Horticulturists research to find new ways by which better varieties of fruits and vegetables can be grown in large quantities. 32.4 STEPS IN RAISING IMPROVED AGRICULTURAL PRODUCE To increase our food production we can sow good quality seeds and improve the methods of sowing. We can make the soil more rich and even use better techniques for harvesting the crops. Some of the agricultural practices which scientists have developed and which our farmers have started are explained here. 1. Preparation of soil This is an important practice which helps to enrich the soil and make it more fertile and aerated. It involves addition of manure followed by turning, loosening and levelling of the soil, using agricultural implements like spade, plough or mechanical farm implements. 2. Seed treatment Seeds can easily be attacked by micro-organisms. The crops that grow out of diseased seeds will also be unhealthy. So farmers treat these seeds by dipping them in certain chemicals like cerosan or agrosan. These chemicals do not allow the microorganisms to attack the seeds and damage them. Such chemicals are called Fungicides. Once the seeds are treated, they can be sown. 3. Preparing the seed bed and care of the seedlings In certain crop plants like paddy and some of the vegetables, seeds are not sown directly in the main field. First these seeds are sown in a nursery bed. Once they grow to a certain age they are transferred and planted in the main field. These small plants are called seedlings. When the farmers prepare a nursery bed they take care of the following: • The soil of the bed should be soft and loose so that the tender roots of the seedlings can grow well. This can be achieved by digging or ploughing the field well. • The seed bed or where the seedlings are planted should be even so that when we water the plants, the water distributes itself uniformly all over the field. • All weeds or unwanted plants in the field must be removed. Do you know why? It is because these weeds also take water and nutrients from the soil and as a result the desired plants cannot get enough of the nutrients. The seedlings also need to be protected from diseases and pests. This is done by spraying chemicals like Parathion, Sevin, Dimecron and Rogor on the seedlings. 4. Transplanting The process of removing the seedlings from the nursery bed and planting them in the main field is called transplanting. When we transplant, we must select those seedlings which have 4 to 5 healthy

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leaves. These are sowed at proper distance from each other. The main field must be ploughed and manured before transplanting. Generally rice and vegetables like tomato and brinjal are sown by transplanting. Transplanting of seedlings is a very important practice. This enables us to select good and healthy seedlings and get a better crop. Besides, when we transplant seedlings, their roots are able to go deep into the soil and get more nutrients. When seedlings get good food, they grow into healthy plants and give a better yield. 5. Adding fertilizers Crops need nutrients like phosphorus, calcium, nitrogen etc. for their growth and pick up these nutrients from the soil. It is very important to add fertilizers to the soil. They provide nutrients to the soil and help to obtain a better crop yield. Depending on the type of soil and the crop to be grown, we use different fertilizers. The way we use a fertilizer also depends upon what type of fertilizer is being added to the soil. A fertilizer which contains nitrogen (nitrogenous fertilizer) is generally given in two or three doses. Other fertilizers are phosphatic and complex fertilizers. Some fertilisers are added to the soil before transplanting. You must have heard about the most commonly used fertilizer ‘NPK’. The letter N stands for nitrogen, P for phosphate and K for potassium. While fertilizers are manufactured from chemicals in factories, manure is made from organic substances and contains nutrients in small quantities. Some of the commonly used manure are: Farmyard manure, as the name suggests is a mixture of decomposed cattle dung (excreta) and urine, left over fodder (cattle feed) and litter (bedding provided to cattle in the farm). Compost is manure made from vegetable and animal refuse collected from domestic waste, straw, weeds etc., dumped in a deep pit to decompose. Vermicompost is compost broken down by earthworms. Like fertilizers manures too add nutrients to soil. 6. Use of plant growth regulators Plant growth regulators are certain chemicals which regulate the growth of plants. All plants have growth regulators which determine how tall the plant would be, how big its fruit will be, etc. We can now add some plant growth regulators like auxins, gibberellins, cytokinins, abscisic acid etc. to get a better yield of crops. You will learn more about these plant growth regulators in higher classes. 7. Irrigation Irrigation is necessary for proper development of plants. Roots fail to develop and penetrate in the dry soil. The crop is irrigated according to its requirement and soil characteristics. Irrigation is essential during the seedling, flowering and grain filling stages of the crop. Rice crop needs standing water.

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8. Harvesting Harvesting machines have now replaced the back breaking job of hand harvesting with the sickle and scythe. Harvesting machines cut or dig out the plant or its parts as required. The machines gather the plant parts, separate desired parts and eliminate parts not needed. Certain harvesting machines may even load the crop for transport. However, the above mentioned functions of harvesting machines depend on kind of crop, plant parts to be harvested, crop use, stage of maturity, etc. 32.5 SOME OTHER DIFFERENT AGRICULTURAL PRACTICES 32.5.1 Rotation of crops If you stay in a village you must have seen that the wheat crop is planted during the month of November and harvested in March and April. The rice crop is planted in June-July and harvested in October and November. The land that lies fallow in between these two cereal crops, can be used by the farmers for sowing a leguminous crop at this time. A leguminous crop does not take as long as wheat or rice to grow. So by the time the farmer has to plant the cereal crops (rice, wheat etc.) the pulse is ready to be harvested. Leguminous crops include pea, beans, grams and pulses. They harbour nitrogen fixing bacteria in nodules of their roots (Fig. 32.1). These bacteria convert free nitrogen from atmosphere into usable form. Thus, after the leguminous crop is harvested, the soil is left fertile for other crops. The process of growing a different crop preferably a leguminous crop in between raising of two similar crops is called rotation of crops.
Fig. 32.1 Nitrogen fixing bacteria in the root nodules

Crop rotation has a lot of benefits, (i) the land gets utilized, (ii) the pulse crop uses up different nutrients from the soil but it fixes the nitrogen from the air and makes the soil richer in nitrogen and so more fertile. This way the next cereal crop gives a better yield. If we do not practice crop rotation by growing different crops on a piece of land, but continue to grow the same crop, year after year, they will keep on using the same nutrients from the soil till all the nutrients in the soil get used up. The newly grown plants get poor nourishment from the soil and grow up to be weak and of bad quality. When plants are weak the insects can easily attack them and destroy them. Thus, crop rotation restores the fertility of

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the soil, it gives better yield, prevents crop from diseases and pests and reduces the dependence on chemical fertilizers. 32.5.2 Multiple cropping Growing two to four crops one after the other in a year in the same field is called multiple cropping. Multiple cropping is possible, when we make use of crop varieties that grow for a short period of time. However, to get best results there must be a properly managed field. In fact, multiple cropping is the best solution for a country with food problem because same piece of land is used to grow different kinds of crops. ACTIVITY 32.2 Here is something you can do. Visit a nearby agricultural farm or vegetable garden. Observe and note down the agricultural practices being used there. All the above mentioned practices are meant to ensure that plants have a healthy growth and yield a good crop. Along with these developments in our country we have also brought under cultivation more and more land. The increased cultivation of agricultural crops is in order to meet requirements of a growing population. 32.5.3 Improving the variety of seeds You must have often heard or read advertisements which encourage farmers to buy new and better varieties of seeds. Some of these new varieties are resistant to diseases and give a very good crop. Some of the improved high-yielding crop varieties which our scientists have developed are given in table 32.2. Table 32.2 Improved high-yielding varieties of crops
Crop Rice Wheat Maize Lady’s finger (Bhindi) Brinjal Variety I R-8, Jaya, Padma, Bala Sarbati sonara, Sonalika, Kalyan sona, Hira-moti, RR-21 and UP 301 Ganga 101, Rankit and Deccan hybrid Pusa savani Pusa purple, Pusa kranti and Muktabeshi

Do you know what name is given to scientists who develop such new varieties of seeds? They are called plant breeders. Plant breeders have not only raised better quality seeds but also better quality fruits. Mango has been named the ‘king of fruits’ and in our country we grow many varieties of mangoes. Some of them are Alphonse, Langra, Chausa, Saroli, Dussehri, Himsagar, Safeda, Sinduri, Mulgoba, Amini. 32.6 PROTECTION OF CROPS IN THE FIELD As crops grow in the field, they have to be protected such that they produce a healthy yield. The weeds growing along with crops have to be removed and growing crops have to be saved from the attack of pests especially insects pests.

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32.6.1 Weed control The undesirable plants that compete with the main crop for sunshine, water and space in the field are called weeds. Weeds must be removed as they use up the nutrients in the soil and thereby make them unavailable for the crop itself. Weeds can be divided into two groups: (i) graminaceous (Monocotyledonous), and (ii) nongraminaceous (Dicotyledonous). Hariali or Doob grass is a graminaceous weed, while Choulai is Convolvulus a non-graminaceous weed. Amaranthus Before sowing or transplanting seedlings, weeds are removed by hand or with the help of a plough or harrow. If some of these weeds start growing again during the crop growth they must be removed. They can be removed by hand or by spraying weed killing chemicals called weedicides like 2, 4-D; MCPA and Simazine.
(Choulai) Chenopodium

Wild Oat

Doob grass (Common weeds)

Fig. 32.2 Some common weeds

32.6.2 Control of plant diseases and pests A lot of plants die due to some diseases and pests which attack and damage them. Generally plant diseases are caused by fungi, bacteria, and viruses. These diseases are transmitted either through the seed itself (seed-borne) or by air (airborne) or soil (soil-borne). Rust of wheat and Blast of rice are two common fungal diseases of plants. Insects are generally pests which eat and destroy crops (Fig. 32.3). To control plant diseases and pests we can spray fungicides and pesticides on the crops or on the soil. Apart from chemical methods, biological control methods are also used. For example aquatic weeds are eaten up by certain fish. Some insect Fig. 32.3 Some insect pests of crops pests are controlled by introducing their predator insects. 32.7 PRESERVATION AND STORAGE OF AGRICULTURAL PRODUCTS Once harvested, food grains have to be safely stored. They have to be saved from being attacked and eaten up by rodents, birds or insects. Also they have to be

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protected from spoilage due to improper temperature and moisture in the storage place or due to growth of fungi. Some of the methods to prevent loss and spoilage of agricultural products are as follows: • • Drying: The grains can be dried in the sun or by blowing hot air on them. Maintaining storage containers: Godowns or gunny bags or tanks or earthen pots used for storage should be free of the cracks and holes and should be clean. Chemical treatment: Spraying or fumigation (insecticide solution converted into fumes) of godowns and containers with insecticides and fungicides should be done before storage. Care should be taken to ascertain that the grains for consumption by human beings are not treated with chemicals poisonous to human beings. Grains are often treated with neem kernel powder or pepper or mineral oil which prevent laying of eggs by insect pests. • Use of improved storage structures: Structures which are airtight, rat proof, moisture proof and can maintain a steady temperature are now used for storage. Few of Fig. 32.4 Silos them are named Pusa bin, Pusa cubicle and Pusa kothar. Fig. 32.4 shows a type of of storage structure called ‘silos’. 32.8 GREEN REVOLUTION A general improvement in crop yield and food production occurred in our country between 1960 and 1980 and marked a turning point in Indian agriculture. This is commonly referred to as the golden era of agriculture or the green revolution. As a result of this we have become self-sufficient in food. In fact we are able to have surplus crop to stock and use in natural calamities like drought and floods. The credit for green revolution goes to a great agricultural scientist of our country, Dr. M. S. Swaminathan. He is the recipient of World Food prize for fighting against hunger. Thus, we find that modern agriculture needs the support of: • • • industries to produce farm implements, pumps, fertilizers and pesticides; irrigation and power projects to provide timely supply of water and power; and research and development institutions to breed newer, sturdier, pest resistant and better yielding varieties of crops and animals.



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CHECK YOUR PROGRESS 32.1 1. Fill in the blanks. i) The branch of science which deals with the study of the cultivation of land, and breeding and management of crops is called ___________________ ii) The branch of agriculture, which deals with growing and production of vegetables, fruits, ornamental plants and management of orchards and parks is called _______________ iii) The improved varieties of plants are resistant to diseases and give high ________ iv) 2, 4-D is a _____________ v) A nitrogenous fertilizer is applied in ________________ doses. 2. Name two improved varieties of wheat. 3. Name three kinds of organisms, which cause diseases in plants. 4. Give one point of difference between crop rotation and multiple cropping. 5. Give two examples of weeds. 6. Name any two plant growth regulators. 32.9 ANIMAL HUSBANDRY The branch of science, which deals with the study of various breeds of domesticated animals and their management for obtaining better products and services from them is termed animal husbandry (the term husbandry comes from ‘husband’ which means one who takes care). • • • Milk giving (milch) animals: Cows, buffaloes and goats who give us milk. Meat and egg giving animals: Pigs, cattle, goat, sheep, fowls and ducks which are the main source of meat. From hens and ducks we get eggs.

Working (draught) animals: Bullocks, buffaloes, camels and horses are draught animals used for doing work in the field and for transportation of goods and human beings. Mules are also used especially by the army to take things from one place to another in the hilly areas. We also get horns, feathers and leather from some of these animals which can be used for making various things. Their urine and droppings help to make the soil fertile by acting as manure. 32.9.1 Need for animal husbandry We have a large number of animals in our country. Yet we do not get as much food from these animals as we possibly can and need for our large population. Besides the food, which we get from animals, we need them to do a lot of our work. In India, we have about 80.4 million cattle, which work in the fields. If we take the ratio of working cattle to the area of land, which is being used for cultivation we find that only two individuals of cattle are available to plough 3.8 hectares of land.

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You all know that cattle wastes like urine and faeces are natural manure which enrich our soil. Unfortunately, in India we do not use all the cowdung available and a lot of it goes waste. Gobar gas plants have been developed so that we can make use of the cattle dung both for fuel as well as to make manure. Thus, we find that animal husbandry is a very important field which helps us to improve our livestock and other useful animals and make the maximum use of them. 32.9.2 Management of livestock When we study about improving our livestock we learn how they must be sheltered, fed, and mated, what kind of drinking water should be given to them and how the sick and diseased animals ought to be treated? This way we learn to manage our livestock for better production and utilization. 1. Feeding of animals All animals must be fed properly. The food should contain the requisite nutrients i.e. carbohydrates, proteins, fats, minerals, vitamins and water. The food which is given to cattle can be divided into two categories: • • Concentrates like cotton seeds, oilcakes, cereal grains, bran etc. They are very rich in most of the nutrients. Roughage includes fibrous and rough food like straw and stems of cereal crops. Generally roughage has a low nutrient content.

An average Indian cow eats about 15-20 kg of green fodder and 4 to 5 kg drygrass, which is mixed with a sufficient amount of grain. A cow drinks about 32 litres of water. Goat and sheep eat grass, herbs and waste products from the farms. Pigs are usually given cereals and their products to eat. Poultry birds are given a mixed feed consisting of cereals, bone meal, minerals and vitamins. 2. Housing of animals We must protect our animals from too much heat, rain and cold. We must, therefore, be careful where we house them. Their houses should have proper sanitation and ventilation. Too many animals should never be kept in a small space. Different animals require different types of houses. Hens and fowls are kept in cages while sheep and goats stay in open yard, which is partially covered with roof made of straw. This open yard should have a hedge of iron wires all around to prevent the animals from running away. 3. Water and its supply To keep these animals healthy they should be given clean water to drink and in sufficient quantities. For example, on an average a cow consumes about 27-36L of water, pigs require 5-23L, camel 8-90L and poultry birds require about 240mL of water. Besides this we must also bathe the cattle with clean water.

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4. Some common diseases of animals and vaccination Sometimes domestic animals may be afflicted by diseases. Some of the common diseases of animals are listed below. Viral diseases: Pox in cattle, goats, sheeps, and fowls; dermatitis in goats and sheep; foot and mouth disease in cattle. Bacterial diseases: Tuberculosis in cattle and poultry birds; cholera in fowls; diphtheria in calf; diarrhea in chicks; foot rot in sheep. Most of these diseases can be prevented by proper sanitation, a controlled diet, proper housing and also by vaccinating the animals against these diseases at the proper time and age. 5. Animal breeding Breeding means to reproduce. In case of animals, breeding is done to obtain animals with desired characters. The two individuals of desirable characters can be selected as parents. These are then crossed to obtain new breeds of animals, e.g. by cross breeding a cow of low milk yielding breed, we can get breeds of cow which produces more milk. Artificial insemination is an important and effective method of breeding. The process involves injecting the semen obtained from desired bull belonging to high milk yielding breed into the reproductive tract of female during heat period. It generally gives important breeds, and is widely used to improve the qualities of cow, buffaloes, poultry, horse and goat etc. Important breeds of cow In India, improved breeds of dairy cows have been developed at National Dairy Research Institutre (NDRI), Karnal, Haryana. Some examples are: Karan Swiss (Crossbreed of brown Swiss and Sahiwal) Karan Fries (Crossbreed of Tharparkar and HolsteinFriesian) Frieswal (Crossbreed of Holstein-Friesian and Sahiwal) Over the last two decades, improved practices of raising animals have resulted in the development of new breeds of dairy animals, poultry and pigs. This has substantially increased our milk, egg and meat production.
Holstein-Friesian cow

Murrah

Sahiwal cow

Fig. 32.5 High yield breeds of cows

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There is no dearth of milk, the most wholesome food in the country. The credit for increased milk production goes to Dr. V. Kurien. Dr Kurien is the founder chairman of National Dairy Development Board which designed and implemented “Operation flood” – the programme which led to the “white revolution” or self sufficiency of the country in dairy products. CHECK YOUR PROGRESS 32.2 1. Write the importance of domesticated animals. 2. Define management of livestock. 3. Name any two diseases that are caused by virus in cattle? • • LET US REVISE To increase food production we must use improved agricultural practices, have proper knowledge of animal husbandry and prevent soil erosion. Various agricultural practices which we can use to increase our food production are preparation of soil, improving the seed variety, seed treatment, preparation of seed bed, transplanting, use of fertilizers, irrigation, weed control, control of plant diseases, use of plant growth regulators, rotation of crops, and multiple cropping. Green revolution through use of improved techniques has led our country to attain self sufficiency in food. Domestic animals are very useful for us. They give us milk, meat and eggs. They also help in ploughing our fields and for transporting things. We must look after them properly, make proper houses for them, give them good food and water and keep them free from diseases. Management of livestock involves proper feeding, housing, vaccination and breeding of animals. Artificial insemination is an important breeding activity to improve high yielding animals. TERMINAL EXERCISES A. Multiple choice type questions. Select the most correct answer of the following: 1. Corosan or agrosan are chemicals belonging to a group of (a) pesticide (b) fungicide (c) weedicide (d) fertilizer 2. Which of the following is the proper sequence of agricultural steps? (a) Seed treatment, preparation of soil, addition of fertilizers, preparation of seed bed (b) Preparation of soil, seed treatment, preparation of seed bed, addition of fertilizers (c) Preparation of seed bed, preparation of soil, seed treatment, addition of fertilizers

• •

• •

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(d)

Addition of fertilizers, preparation of soil, seed treatment, preparation of seed bed

3. Choose the high yielding variety of wheat (a) IR-8, Jaya, Padma (b) Ganga 101, Rankit, Deccan hybrid (c) Sarbati sona, Sonalika, Hira moti (d) Pusa purple, Pusa savani, Muktabeshi 4. Credit of ‘Green revolution’ in our country goes to, (a) Aryabhatta (b) Dr V. Kurien (c) Dr M.S. Swaminathan (d) Dr. H.G. Khorana 5. Food items such as cotton seeds, oil cakes, cereal grains and bran belong to which of the following category? (a) Roughage (b) Concentrate (c) Minerals (d) Vitamins B. Descriptive type questions. 1. Define the terms agriculture and horticulture. 2. Why is it advisable to cultivate pulse crops in between two successive cereal crops? 3. Give one improved variety of each of the following crops—wheat, rice, maize, and lady’s finger. 4. Give names of two viral diseases of domesticated animals. 5. To meet increased demand of food, what steps would you suggest? 6. List and briefly discuss major aspects of animal husbandry. ANSWERS TO CHECK YOUR PROGRESS 32.1 1. (i) agriculture (ii) horticulture (iii) yield (iv) weedicide (v) split 2. Any two of the wheat varieties as given under varietal improvement. 3. (i) Seed borne (ii) Air borne (iii) Soil borne 4. Crop rotation means growing a pulse crop between two cereal crops. 5. Doob grass and Chaulai 6. Auxin, Gibberellin, Cytokinin, Abscisic acid (any two) 32.2 1. (i) They provide milk

(ii) They provide meat and eggs (iii) They are used for work 2. Taking proper care of the livestock. 3. Pox, Foot and mouth disease.

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GLOSSARY Agriculture: Branch of Science dealing with methods of production of food crops. Agricultural practices: Methods used in agriculture for growing better quality and high yield varieties of crops. Animal husbandry: Branch of Science dealing with study of various breeds of domesticated animals and their management for obtaining better products and services from them. Biological control: Killing insect pests by predators. Dermatitis: Disease of skin. Draught animals: Animals used to carry goods or working in the fields. Fungicides: Chemicals that kill fungi or moulds growing on crop plants. Horticulture: Branch of Science dealing with production of vegetables, fruits and ornamental plants. Multiple cropping: Growing two to four crops one after the other in a year in the same field. Plant breeders: Scientists who develop new varieties of plants and seeds. Seedlings: Plantlets growing out of seeds. Transplanting: Process of removing seedlings from the nursery bed and planting them in the main field. Weed: Undesirable plants growing in the same field as the main crop and competing for nutrients, water and sunshine with the main crop. Weedicide: Chemicals, which can kill weeds.

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33

Space Exploration
Man-made satellites orbiting the earth beyond the atmosphere have, now a days, become a part of our everyday life. Daily weather forecast and a picture of clouds taken from a satellite on your TV, a cricket match live on TV which is being played in Australia or any other country, reaches the local TV station through satellite. You talk to your friend far away while electromagnetic waves carry your massage via a satellite. Satellite pictures estimate forest cover and (on finding that it is decreasing fast) you are advised to save paper, and so on, the list is endless. Space means the vast, limitless and continuous expanse (or region) beyond the earth’s atmosphere. Sometimes we call it outer space in order to distinguish it from space occupied by atmosphere. In this lesson you will study how we use space with the help of space vehicles. (i.e. satellites orbiting the earth or space probes which leave the earth) for various purposes of importance to mankind, (e.g. for the study of earth’s atmosphere or surface or heavenly object like planets, or for communication). This field of knowledge is called space exploration. OBJECTIVES After completing this lesson, you will be able to: • • • • • • • • explain the meaning of space exploration and state its need and importance; recall the efforts made by different countries for space exploration; distinguish between natural and artificial satellites; give an elementary idea of how a satellite is launched; differentiate between the different types of launch vehicles on the basis of their capacity; define the nature of path of different types of artificial satellites; examine the applications of artificial satellites in the field communication, remote sensing and weather forecasting; mention the aim and objective of Indian space programme and identify the Indian achievements in the field of space science.

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33.1

KINDS OF SATELLITES AND SATELLITE ORBITS

33.1.1 Natural and artificial satellites You all are familiar with the Moon. It revolves around Earth. Hence, it is a satellite of Earth. The planet Jupiter has 16 satellites revolving around it. Man has no role in the existence of these satellites. Hence, these are natural satellites. Now-aday we have acquired technology to launch satellites revolving around Earth or any other planet for our own purposes, e.g. scientific data collection. A satellite launched by man around any planet for our own purpose is called an artificial satellite or man-made satellite. Sputnik-I, Explorer-I, GSAT-I and GSAT-II (recently launched by India) are examples of artificial satellites. 33.1.2 The path of a satellite The path of a satellite revolving around the Earth is called its orbit. It is a circle or an ellipse lying in a plane passing through the center of Earth, shown at O in Figure 33.1. The following three parameters define the orbit of a satellite.

Fig. 33.1 Parameters that define the orbit of a satellite

Apogee: It is a point on the orbit where vertical distance of the satellite from the Earth’s surface is maximum. The maximum distance of the satellite from Earth’s surface is also called apogee of the orbit of the satellite. Perigee: It is a point on the orbit where vertical distance of the satellite from the Earth’s surface is smallest. The smallest distance of the satellite from the Earth’s surface is also called perigee of the orbit of the satellite. Inclination: The angle between the plane of orbit of the satellite and plane of the equator of Earth is called inclination of the orbit. 33.1.3 Types of orbits If the inclination of the orbit of a satellite is 90o (Fig. 33.2), then during one revolution around the Earth, the satellite passes once vertically above the north pole of Earth and once above the south pole of the Earth. Such an orbit is called a

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polar orbit. The center of Earth, North Pole and South Pole, all lie in the plane of a polar orbit, which is perpendicular to the plane of equator. The satellite moving in a polar orbit is called a polar satellite. Consider a satellite whose orbit is in the plane of equator (Fig.33.3), i.e. its inclination is 0o. It is at a height of about 36000 km above the equator and keeps this distance constant. Thus, it is a circular orbit. At this height, the satellite makes one revolution around earth in just as much time as the earth itself takes to spin 360o around its axis. Hence, relative to any location on earth, the position of the satellite is stationary. This orbit is called geo-stationary orbit. A satellite revolving in this orbit is called a geo-stationary satellite. The time, which a satellite takes to make one complete revolution in its orbit is called its time period. Thus, the time period of a geo-stationary satellite is precisely one day, which is also the time period of rotation of earth.

36000 km

N Equator of Earth

Fig. 33.2 A satellite in a polar orbit

Fig. 33.3 A satellite in the geo-stationary orbit

Referring to Fig. 33.1 or 33.2, consider a satellite whose time period is such that it makes exactly an integral number of revolutions (usually 13, 14 or 15) around earth in 24 hours. After passing over a certain place on Earth, next day it will again pass over the same place at the same time of day. While Earth spins one rotation, relative to sun in 24 hours, the satellite makes an accurately integral number of revolutions. Thus, satellite will be able to look at that place and photograph it on consecutive days in identical illumination, Sun being in the same position relative to that place. Such an orbit is called a sun-synchronous orbit. The satellite moving in this orbit is called a sun-synchronous satellite. To be precise, earth spins through an angle a little more than 360o in 24 hours, say (360o + θ) (Fig. 33.4). In the same time it revolves around Sun through angle θ. Thus, the position of Sun relative to any place on Earth is same after 24hours. Thus, the illumination at that place on Earth is the same. But the position of Sunsynchronous satellite is not precisely above that place after 24 hours. It is to the west of that place through angle θ in longitude, though its latitude is same.

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Fig. 33.4 E1 is the first position of Earth and E2 the position after 24 hours. It revolves through angle θ around Sun and spins 360o + θ

CHECK YOUR PROGRESS 33.1 1. What is meant by the statement ‘apogee of the orbit of a satellite is 900 km’? 2. What is meant by the statement ‘perigee of the orbit of a satellite is 450km’? 3. Draw a labelled diagram to show the orbit of a satellite having parameters; apogee 900 km, perigee 300 km and inclination 90o. 4. Time taken by an artificial satellite for revolving once around Earth is same as the time which earth takes to complete one rotation about its axis. Name the type of this orbit. Give two other features of this orbit. 5. What are the parameters of a polar satellite? 6. State two features of a sun-synchronous orbit? What are its parameters? 33.2 NEED AND IMPORTANCE OF SPACE EXPLORATION Launching a satellite in orbit and designing and fabricating a satellite, which serves useful purpose, both are extremely expensive tasks. In the beginning of space research, this activity was considered a waste of money, to be done only by some rich countries. With development of technology, cost came down and newer applications were developed. Thus, today it has become an essential part of our everyday life due to its many applications. What are the areas in which it finds application? Some areas of application are given herewith. 33.2.1 Satellite communication Sending massages to long distances using a geo-stationary satellite is called satellite communication. The satellite S (Fig. 33.5) receives signals from an earth station A and transmits them to Earth in different directions. Because its direction and distance relative to any ground station A, or B, or C, or D, etc. remains fixed, any ground station can send signals to it or receive signals from it with the help of a dish antenna whose direction is adjusted once for all. Dish antenna is of parabolic shape. It focuses the microwaves coming from the satellite to its focus F. Wavelength of these waves is of the order of a centimeter so that these can travel from satellite to ground unhindered by atmosphere or

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even by clouds, and can be focused by an antenna of about 3 m diameter, like light rays are focused by a parabolic mirror. The technique of satellite communication is being used now-a-day for many purposes, e.g. telephonic conversations and conferencing, television broadcast, FAX and computer related network services. A satellite being used for this purpose is called a communication satellite. We build high television towers to reach longer distances. A communication satellite is like a 36000 km high television tower, and signals broadcast from it reach almost half the Earth. 33.2.2 Weather monitoring and forecasting by satellite Satellites are very useful in weather monitoring and forecasting. For this purpose a geo-stationary satellite is used. It is equipped with cameras and other sensors by which photographs of cloud formations and many other data about atmosphere in a vast area can be quickly obtained. The satellite being stationary relative to any place on earth, it can monitor the movement of clouds accurately. It is like a fixed observation station at a height of approximately 36000 km (Fig. 33.6).

S

Dish Antenna

A B

C

D E

Earth

Fig. 33.5 Signal sent by station A to geo-stationary satellite S is retransmitted to TV-stations in almost half the Earth

The data collected by the satellite is sent by it to a ground station. The data is analyzed and weather forecast is done. It is now possible to get prior information about an S emerging cyclone or flood or possible draught condition. This enables the government to take A appropriate measures to minimize loss of lives and property. Satellite used for this purpose is O called a weather satellite (or meteorological satellite). 33.2.3 Study of world resources (remote sensing) Fig. 33.6 A geostationary satellite is For this purpose we use a satellite in sun- like a fixed observation station synchronous orbit. It is equipped with cameras and other sensors, by which data about Earth’s resources can be obtained. These equipments observe and photograph Earth’s surface illuminated by sunlight, using

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Remote sensing satellites have served many practical purposes like, forestry and estimation of A A A A A A forest cover, preparing waste land maps, ground A water surveys, draught assessment, estimation of Fig. 33.7 Satellite in a polar orbit yield of various crops, detection of crop diseases, detection of potential fishing zones in the ocean, and survey for exploration of minerals. This list keeps on expending with time.
7 6 5 4 3 2 1

Anticlockwise rotation of Earth

selected wavelengths in ultra-violet, visible and infrared electromagnetic spectrum. Atmosphere is transparent for these wavelengths. This technique is called remote sensing, because the data is observed from a large distance (almost a thousand kilometres). A satellite used for this purpose is called remote-sensing satellite. It photographs a particular location on Earth each day (Fig. 33.7).

The most significant feature of this technology is that it offers some special advantages: i) A remote-sensing satellite can provide information about the areas/objects, which are very difficult to be reached physically, (i.e., which are inaccessible) like dense forests.

ii) A remote-sending satellite can survey a vast area in a very short time. iii) A remote-sending satellite can survey any region repetitively at regular intervals. Repetitive surveys of the same regions make a comparative study possible. 33.2.4 Scientific experiments and collecting information about heavenly bodies This is done by sending unmanned spacecrafts (called space probes) to target destinations, e.g. Mars, Venus, and other planets. These are equipped with cameras and other sensors suitable for the objective of the project. Another method is by launching a satellite in a suitable orbit above the Earth’s atmosphere equipped by a telescope and suitable sensors. The first noteworthy attempt of the second method was the launching of Cos-B, a gamma ray observatory in 1975 jointly by five European countries. Then came the launching of Hubble Space Telescope by the US in 1990. This telescope observes the visible, ultra-violet and infrared waves coming from heavenly bodies and sends the data back to Earth. It was soon followed by launching of Einstein X-ray Telescope and Chandra X-ray Telescope in space by the U.S.A., to study X-rays coming from heavenly bodies. The era after 1970s is thus called the Golden Era of Astronomy and Astrophysics. Atmosphere creates many problems for the earth-based telescopes. It absorbs most of the wavelengths of electromagnetic spectrum. Thus, earth-based telescope cannot study heavenly bodies by those wavelengths. Again, atmosphere is like a

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wavy windowpane through which we cannot see things clearly. A telescope in orbit above the atmosphere overcomes these problems. 33.2.5 Satellite launch vehicles For a satellite to stay in an orbit close to earth Orbit of (just above the atmosphere in the plane of equator, Satellite Fig. 33.8), it has to be given a horizontal speed of about 8 km per second. At this speed attraction of Earth is precisely equal to the force required Earth to keep the satellite on the circular orbit, instead of going in a straight line. The satellite makes a revolution in about 90 minutes, i.e. it makes about 16 revolutions in a day. If it moves in the same direction as rotation of Earth (anti-clockwise as Fig. 33.8 Satellite in low orbit seen from north pole), then it has a relative speed of about 15 revolutions per day, or about 7½ km/ second with respect to Earth’s surface. If it moves opposite to direction of rotation of Earth, then it has a greater relative speed (8½ km/second) with respect to Earth’s surface. Hence, it is easier to launch a satellite in the same direction as rotation of Earth. A rocket used for launching the satellite is called a satellite launch vehicle. Its operation is based on Newton’s III law of motion. Burning of fuel in the vehicle produces gases at high temperature and pressure. These are ejected backwards through a jet. Then due to reaction applied by the gases, the vehicle is pushed forward (Fig. 33.9). There exists no fuel which gives so much energy per kg of its weight on burning which it can impart a speed of 7½ km /second. Hence, satellite-launching vehicle usually has 3 or more stages, which Fig. 33.9 SLV is accelrated forward by the force of reaction applied by hot gases function one after the other. In order to launch a polar satellite, it has to be given a speed of 8 km/second relative to ground. The (Fig. 33.9) SLV is accelerated forward by the force of reaction applied by hot gases. Thus the vehicle must give more kinetic energy to the polar satellite than to the satellite in an orbit of low inclination, in the ratio (16/15) 2. Therefore, a vehicle, which launches a polar satellite, must have more powerful rocket motors, than the one for launching a satellite with small angle of inclination. In order to launch a geo-stationary satellite, it has to be lifted to a great height also (about 36000 km). Hence, a geo-stationary satellite launch vehicle has to

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give far more energy to the satellite than a PSLV gives. A cryogenic engine (or cryogenic rocket motor) is an essential last stage of a vehicle for launching geostationary satellite. It uses hydrogen as its fuel, which is the fuel having highest energy output per kilogram of its weight. The process of launching of satellite is quite simple in principle. The first stage rocket motor lifts the satellite out of the atmosphere along the shortest path (i.e. vertically upwards) so that the least amount of energy is spent against friction of air. The second and subsequent stages provide it speed in horizontal direction and simultaneously bring it into the orbit at desired height. CHECK YOUR PROGRESS 33.2 1. The orbit of a satellite is perpendicular to equator and it takes exactly 1.6 hours to complete one revolution around the earth. State two purposes for which it can be used. 2. What is a remote-sensing satellite? Why is it placed in a sun-synchronous orbit? 3. What band of electromagnetic waves is used to carry audio-signals of telephone conversation in satellite communication? What is the order of their wavelength? State one reason to select this band for the purpose. 4. Name the orbit of a meteorological satellite. How is it able to monitor accurately the movement of clouds? 5. What are the four areas in which space technology finds application? State the kind of orbit in which satellite is placed for each. 33.3 HISTORICAL PERSPECTIVE

33.3.1. Efforts of different countries in space exploration The first step into space was taken on 4th October 1957 when USSR (it has now been split up into several countries, biggest among them being Soviet Russia) successfully launched Sputnik-I weighing 84 kg. Due to friction with air, it soon came down. Sputnik–II a month later carried a dog whose health in space was closely monitored. Data about the health of the dog in space helped to better plan the journey of first man in space. Space age really began on 12 April 1961 when Yuri Gagarin of USSR made a journey into space in Vostok-I. He made a single revolution around Earth. The whole journey took 108 minutes. Soon after, on 5 May 1961, the first American astronaut made a journey into space. On 20th February 1969, the first human being, Neil Armstrong of USA set foot on the moon, traveling in Apollo-XI. Some landmarks in the history of development of space technology are given in table 33.1

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Table 33.1 Some landmarks in the field of technology
S.No. Date of launching 1. 2. 3. 04-10-1957 03-11-1957 31-01-1958 Name of space flight or space mission Sputnik-I* Sputnik –II* Explorer –I* Achievement Fist ever man-made satellite launched in space by USSR. First satellite to carry a living animal (dog) into space (USSR). First spacecraft by USA, first scientific discovery by a spacecraft (Van Allen Radiation Belt in upper atmosphere). The first space flight by a man (USSR). The first space flight by a woman (USSR). First successful soft landing by a space-probe on the Moon’s surface (USSR). Neil Armstrong of USA becomes the first human being to set foot on the moon on 2007-1969. First landing of a space probe on the planet Mars (USSR) First space probe to (a) explore the asteroid belt between Mars and Jupiter and to (b) take photographs of Jupiter from a close distance (USA). First satellite dedicated to remote- sensing (USA). First journey to all the outer planets of the solar system and photographing them from close distance. After 10 years of flight, Voyager-II flew past Neptune precisely on the planned path and time (USA). First gamma-ray observatory in space, operational till 1982 (five European countries). First space craft to carry astronauts from earth to an orbiting satellite and back – spacecraft usable several times (USA) (Fig. 33.10) The first space flight by an Indian, Sqn. Leader Rakesh Sharma. More than a year (366 days) of stay in orbit by two-person crew (Soviet Russia). First telescope in orbit to study heavenly bodies by infrared, visible and ultra-violet light. (USA) (Fig. 33.11).

4. 5. 6. 7.

12-04-1961 04-12-1963 21-10-1968 16-07-1969

Vostok-I* Vostok –III Luna –IX Apollo –XI*

8. 9.

19-05-1971 02-03-1972

Mars – II Pioneer – X

10. 11.

July 1972 05-09-1977 20-08-1979

Landsat-I Voyager-I Voyager-II

12.

09-08-1975

Cos-B

13.

12-04-1981

First space shuttle ‘Columbia’* Space station ‘Mir’ ‘Hubble space telescope’*

14. 15. 16.

03-04-1984 1986 25-04-1990

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S.No. Date of launching 17. 18. 19. April, 1991 April, 1992 Prior to 1994

Name of space flight or space mission
Compton gamma-ray observatory

Achievement Second gamma-ray observatory in space (USA).

By using a space shuttle, American astronauts repaired a satellite in space itself and put it back into its original orbit.
Einstein X-ray observatory First true X-ray telescope in space. X-rays do not reflect or refract in usual experiments (USA).

20.

1999

Chandra X-ray observatory* Second X-ray telescope in space achieved are – second resolution, named after Professor S. Chandrashekhar (USA).

* The more significant space flights. It should not be inferred from this table that US and USSR (now Soviet Russia) are the only countries doing significant work in this field till now, though most of the ‘firsts’ go to their credit. Several other countries, including India, are noteworthy partners. On April 3, 1984 Sqn. Ldr. Rakesh Sharma became the first Indian to journey into space, with the co-operation of USSR. He stayed there until April 11, 1984.

Fig. 33.10 Space shuttle Columbia to carry astronauts from Earth to satellite and back

Fig. 33.11 Hubble space telescope

33.3.2. Space science in India The foundation of modern space research in India was laid in 1961, when Department of Atomic Energy was asked to develop a programme for space

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research. Following objectives for space research in India were set then. Even today these are the most important objectives. i) Rapid development of mass communication and education, particularly in widely dispersed rural communities, and ii) Timely survey and management of the country’s natural resources. India entered the space age on 19th March 1975 when the first Indian satellite Aryabhata (Fig. 33.12) was launched. It was designed and fabricated by Indian scientists but was launched with the help of USSR. It enabled our scientist to: i) Develope the skills of staff members and physical facilities for designing and fabricating satellite and monitoring their performance during journey. ii) Establish ground facilities for Fig. 33.12 Aryabhata – The first communicating with satellite, tracking it, Indian satellite and to command it for carrying out various tasks. iii) Conduct some experiments in the fields of X-ray astronomy, solar physics and meteorology. Today, India is one of the six nations in the world, which has the technical know-how for putting a satellite in any orbit around the earth. The Indian space programme has been simultaneously pursuing two objectives. The programme aims at developing i) expertise in planning, designing and fabricating space satellites for various purposes, and ii) the necessary technologies, facilities and skills for the development of suitable launch vehicles to place satellites in predetermined orbits around the earth. However, less progress in one area is not allowed to delay the other. For example, if satellite fabrication is achieved, its launching is carried out in collaboration with one of the advanced nations without waiting for the availability of an Indian launch vehicle, if it is not available at that point of time. 33.3.3 Indian satellite launch vehicles India started working in this area with the launch of a 75mm diameter meteorological rocket in 1963 for investigation of ionosphere over the geomagnetic equator at Thumba near Thiruvananthapuram. The first success in the launching of an Indian satellite by an indigenously developed launch vehicle was achieved on 18th July 1980. The launch vehicle for carrying the satellite was a four-stage rocket SLV-3. It carried a 35 kg satellite named ‘Rohini’ into an orbit with an apogee of 900 km and perigee of 300 km.

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The main objective of this launch was to test the performance of the fourth stage of the launch vehicle. The second generation of India launch vehicles was called Augmented Satellite Launch Vehicle (ASLV). The historic event of launching of a more than 100 kg Indian satellite on an India vehicle took place on 20-05-1992 by ASLV-D3. It was 23 m tall having five stages and used solid fuel. It launched 106 kg satellite named SROSS-C into an orbit 450 km above earth. The first successful Indian polar satellite launch vehicle was PSLV-D2. On 15-10-1994 this 44 m tall, four-stage rocket launched the 804 kg remote sensing satellite IRS-P2 in polar sun-synchronous orbit.

Fig. 33.13 Indian satellite launch vehicles

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The first successful Indian geo-stationary satellite launch vehicle was GSLVD1. In April 2001 this 49 m tall, three-stage rocket launched the experimental satellite GSAT-1 of 1540 kg into a geo-synchronous orbit. It is planned to develop this GSLV further to carry a satellite of 2500 kg. 33.3.4 Indian satellite programme India has been launching satellites for all the four purposes discussed earlier, viz. telecommunication, study of weather, exploration of earth resources and scientific experiments. It has following series of satellites i) Indian National Satellite System (INSAT) These are geo-stationary satellites used for telecommunication and study of weather. This programme was established in 1984 when INSAT-1B was commissioned for being used for these two purposes. It lead to the expansion of TV and telecommunication network to remote areas. It also helped in better whether forecasting. Above all the success of INSAT-1B provided the needed boost to efforts in developing space research further. The second generation of satellites in this series started with the launch of INSAT-2A (fig. 33.13) on July 10, 1992 and of INSAT2B on July 23, 1993. The third generation of satellites started with the launch of INSAT3B in March 2000. India’s INSAT is one of the largest Fig. 33.14 INSAT –2A, first fully Indian built successful satellite communication satellite system in the world for communication and study of with five active satellites in orbit till March weather 2002: INSAT-2C, INSAT-2DT, INSAT-2E, INSAT-3B and INSAT-3C. These are being used for telecommunication, television broadcasting, weather monitoring and weather forecasting. An exclusive meteorological satellite METSAT has also since been launched. These are sun-synchronous satellites, which are being used for the study of earth resources. This programme started with the launch of IRS-1A in 1988 and IRS –1B in 1991 (Fig. 33.15).

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Fig. 33.15 India’s remote sensing satellite, IRS-1B

The Indian remote sensing satellite system, IRS, has the biggest constellation of satellites with five operational satellites: IRS –1C, IRS-1D, IRS-P3, IRS-P4 (OCEANSAT dedicated exclusively for the study of oceans) and TES (Technology Experiment Satellite). The TES can take photographs with a resolution of 1 m on the ground (i.e. about 0.3 arc second in terms of angle). These are being used for all the eight applications discussed earlier. iii) Stretched Rohini Satellite Series (SROSS) These are launched for purpose of scientific experiments carried out above earth’s atmosphere. Their contribution in the study of gamma ray burst events is noteworthy. At present Indian satellites of INSAT and IRS series are quite advanced and at par with those of any other advanced country. Data collected by these is commercially used by many countries of the world. Significant events of Indian space research programme are summarized in table 33.2. Table 33.2: Significant events in the Indian space research programme
S.No. Sateliite Date Launching country/ Launching vehicle USSR, India’s first satellite USSR India (SLV-3), India’s firest success to launch a satellite French Guyana (ARIANE) USSR India (SLV-3) USSR USSR India (ASLV)

1. 2. 3.

ARYABHATA* BHASKAR-1 ROHINI*

March 19, 1975 June 7, 1970 July 18, 1980

4. 5. 6. 7. 8. 9.

APPLE BHASKAR-2 ROHINI IRS-1A* IRS-1B* SROSS-3

June 19, 1981 Nov. 20, 1981 April 17, 1983 March 17, 1988 Aug. 29, 1991 May 19, 1992

: 316 : Space Exploration S.No. Sateliite Date Launching country/ Launching vehicle India (PSLV-D2) USSR India (PSLV-C1) USA, First major expansion of communication network in India by satellite in 1984 USA India (ASLV-D3). India’s succes to launch a more than 100 kg satellite French Guyana (ARIAN E) Frech Guyana (ARIANE) India (PSLV-D2). India’s success to launch a 1000kg class satellite in polar orbit French Guyana (ARIANE) Purchased from ARABSAT after a snag in INSAT-2D so that services are not disrupted International Telecommunications Satellite Organization (INTELSAT) French Guyana (ARIANE) French Guyana (ARIANE) India (PSLV-C3), launched three satellite inlcuding Belgian PROBA and German BIRD India (GSLV-D1), India’s success to launch a geo-stationary satellite

10. 11. 12. 13.

IRS-P2 IRS-1C IRS-1D INSAT-1B*

Oct. 15, 1994 Dec. 18, 1995 Sept. 29, 1997 Aug. 30, 1982

14.

INSAT-1D* SCROSS-C*

June 12, 1990 May 20, 1992

15. 16.

INSAT-2A* INSAT-2B IRS-P2*

July 10, 1992 July 23, 1993 Oct. 15, 1994

17. 18.

INSAT-2C INSAT-2DT

Dec. 7, 1995 Oct., 1997

19.

INSAT-2E

April 3, 1999

20. 21. 22.

INSAT-3B INSAT-3C Technology experiment satellite (TES) GSAT-1 Experiemental Satellite* METSAT

March 22, 2000 Jan. 24, 2002 Oct. 22, 2001

23.

April, 2001

24.

Sept. 12, 2002

India (PSLV-C4), exclusively dedicated to study weather, launching a geostationary satellite by a vehicle of PSLV class is a technological feat

* The more significant launches by India.

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CHECK YOUR PROGRESS 33.3 1. Explain how are TV programmes transmitted to remote areas through INSAT satellite? 2. Explain how does IRS-1D (launched in 1997) estimates the forest cover of India and detect its decrease. 3. Why was a dog first sent into space before sending a man? 4. Name the first Indian who went into space. How long did he stay in space? Did he go into space by India’s own launch vehicle? • • • i) ii) iii) LET US REVISE Now-a-days man has the technology to launch artificial satellites revolving around Earth or any other planet for scientific purposes. Orbit of a satellite is defined by its apogee, perigee and inclination. Satellite may be launched to revolve around Earth in different types of orbit for different purposes: Geo-stationary orbit: inclination 0O, apogee = perigee = 36000 km (approx.) Polar orbit: inclination 90o, apogee and perigee of any value depending on the objective of the project. Sun-synchronous orbit: apogee and perigee so selected that it makes precisely an integral number of revolutions in 24 hours, and inclination of any value depending on objective of the project. Artificial satellites revolving around Earth and space-probes find application for several areas of human activities: Communication over long distances: telephonic conversation and conferencing, television broadcast, FAX and computer related network service. Weather monitoring and forecasting. Exploration of resources, which mother Earth, provides. Scientific purposes like experiments in zero gravity and/or in near perfect vacuum; observation of other planets and stars (including the Sun) etc. Low inclination satellites are launched revolving in the same direction as rotation of Earth, so that less kinetic energy per unit mass of satellite need be given to them. More kinetic energy needs to be given to a satellite for launching it in polar orbit. Highest amount of energy per unit mass of satellite needs be given to launch a satellite in geo-stationary orbit. For launching a satellite, it is first lifted vertically out of the atmosphere, so that least amount energy is spent against friction of air. Thereafter the task of providing it speed in horizontal direction and placing it into desired orbit is carried out. Now days, Man can look down on Earth from space, using ultra violet, visible and infrared rays. Similarly Man can study heavenly bodies from above the atmosphere, using gamma rays, X-Rays, ultra-violet rays, visible light and infrared rays, eliminating all the disadvantages that atmosphere creates in

• i) ii) iii) iv) •

• •



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such studies. Thus, the era after 1970s is called the golden era of Astronomy and Astrophysics. India entered the space age with launching of Aryabhata in 1975. Since then India has been developing space science with two objectives: i) Designing and fabricating satellites for various purposes along with ground satellite to utilize the data provide by these satellites. ii) Developing suitable launched vehicles to place satellites in desired orbits around the earth. TERMINAL EXERCISES What is meant by space (outer space)? What is a satellite? What is meant by orbit of a satellite? What is the height of a geo-stationary satellite above Earth’s surface? What do you understand by space exploration? What are two types of satellites? Give one example of each. Name the parameters that define the orbit of a satellite around Earth. Time period of revolution of a satellite around earth is 24 hours with reference to Sun. In which type of orbit is it? State its parameters. What is a communication satellite? Name any three areas of application of space science and one characteristic feature of the satellite used in each case? State four purposes for which remote-sensing satellite is used? What bands of electromagnetic waves are used to study world resources by a satellite in outer space? What is the special advantage of using those bands? When was the first step into space taken and by which country? Name the first Man who went into space? When was the first step taken on the Moon, by whom and in which spacecraft? What does IRS-1A refer to? Mention any two uses of it. “Successful launching of INSAT-1B has brought revolution in the field of communication in India”. Give two reasons in support of this statement. What is a geo-stationary satellite? State its two applications. State for one of the applications why a geo-stationary orbit is used. Name India’s geo-stationary satellite, which has been launched by India’s own launch vehicle, and name that vehicle too. Write the full forms of following abbreviations: IRS, INSAT, SROSS, ASLV, PSLV, GSLV ANSWERS TO CHECK YOUR PROGRESS

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

18.

33.1 1. At the point where the satellite is farthest from Earth, its height above Earth is 900 km.

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2. At the point where the satellite is closest to Earth, its height above Earth is 450km. 3. Please refer fig. 33.16. 4. Geo-stationary orbit. Features: (i) Apogee = 36000 km (Approx.), perigee = 36000 km (Approx.) (or circular orbit), and (ii) inclination = 0o (or in the plane of equator). 5. Inclination = 90o, apogee = any value, perigee= any value. 6. i) It makes precisely an integral number of revolutions of Earth in 24 hours. ii) It looks at (or photographs) any location on Earth on consecutive days in identical illumination. Inclination = any value, apogee and perigee are so chosen as to satisfy the first feature. 33.2 1. Number of revolutions in 24 hours = 15 precisely. It is a sun-synchronous orbit. The satellite is usable for remote sensing (for purposes refer to 33.2.3). 2. Remote sensing satellite is one by which we study the surface of Earth to explore its resources and other phenomena useful to mankind. It is placed in sun-synchronous orbit so that it can take repeated photographs of a location on consecutive days in identical illumination and very meaningful comparison of photographs can be done. 3. Microwaves are used for satellite communication. Their wavelength is of the order of a centimeter. These are not hindered by atmosphere and not even by clouds. 4. A meteorological satellite is placed in a geo-stationary orbit. Its position with respect to any location on ground is fixed. Thus it is like a fixed observation station 36000 km high. It can see almost half of Earth. Being in a fixed position relative to Earth’s surface, it can accurately observe movements and formations of clouds. 5. The areas are: i) Communication to far-off places: Geo-stationary orbit. ii) Monitoring and forecasting weather: Geo-stationary orbit. iii) Study of world resources: Sun-synchronous orbit. iv) Scientific experiment and collecting data about heavenly bodies: Orbit depends upon the objectives of experiment. For study of heavenly bodies a satellite may be placed in a suitable orbit or a space probe may be sent to the target heavenly body. 33.3 1. INSAT is 36000km above equator in a fixed position relative to Earth, in the geo-synchronous orbit. A beam of microwaves from the transmitting station carries the signal to the satellite. The satellite re-broadcasts it. This re-broadcast signal can be received by any one in almost half the world (refer Fig. 33.5).

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2. IRS-ID is a remote sensing satellite in sun-synchronous orbit. Photographs of various areas of India illuminated by sunlight are taken by it. Entire country is quickly covered by the satellite (in three weeks). The photographs clearly show-up forest areas. Their total area is measured, which gives the forest cover of India at that point if time. Year after year values of forest cover clearly tell the yearly decrease of the forest cover. 3. The health of dog in space was closely monitored. This data about a living dog helped very much to better plan the journey of first man in the space. 4. First Indian to go into space was Sqn. Ldr. Rakesh Sharma. He stayed in space for eight day. He did not go into space by India’s own vehicle. It was the launch vehicle of USSR.

GLOSSARY Apogee: The highest point of the orbit or height of that point above earth’s surface. Artificial satellite: A man-made satellite. Communication satellite: A geo-stationary satellite, which is used for purpose of telecommunication between distant locations on earth. Geo-stationary orbit: The circular orbit in the plane of equator in which a satellite remains stationary with respect of any location on earth. Inclination: Angle between the planes of equator and of the orbit. Meteorological satellite: A geo-stationary satellite being used for observing weather related data and sending it to ground stations. Orbit of a satellite: The path along which the satellite revolves around a planet. Perigee: The lowest point of the orbit or height of that point above earth’s surface. Polar orbit: An orbit passing over north and south poles of earth. Remote sensing: Study of world resources by cameras and other sensors placed in a satellite in outer space. Remote sensing satellite: A satellite in sun-synchronous orbit being used for study for world resources by cameras and other sensors placed in it. Satellite: A natural or man-made object revolving around earth or any planet. Satellite communication: The entire activity of telecommunication between various distant locations on earth with the help of geo-stationery satellites. Satellite launch vehicle: Rocket of 3 or more stages that lifts a satellite and places it in a desired orbit. Space/outer space: Vast limitless and continuous region beyond earth’s atmosphere.

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Space exploration: Study of earth’s atmosphere or surface or of heavenly bodies by man-made space vehicles. Space-laboratory: A laboratory set up in a satellite orbiting the earth for experiments in zero gravity, or for observation of rays or particles coming towards earth. Space telescope: A telescope placed in a satellite orbiting the earth above atmosphere in order to overcome the disadvantages to observing process caused by the atmosphere. Sun-synchronous orbit: An orbit in which satellite makes accurately an integral number of revolution in 24 hours. Time period of orbit: The time in which a satellite in the orbit makes one complete revolution.

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