Biology Chapter 6

Biology Chapter 6.1 Test Revision (+chapter 2.3)
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Monosaccharides are single sugar units
Disaccharides consist of 2 monosaccharides linked together.
(e.g. maltose is made by linking 2 glucose molecules togethere.g.2 sucrose is made by linking a glucose and a fructose)
Polysaccharides consist of many monosaccharides linked
together (e.g. starch, glycogen and cellulose- all made by
linking together glucose molecules

 Lipids and carbohydrates are both used for energy
storage in humans
 Lipids usually used for long term energy storage
 Lipids that are used as fats are stored in specialised
groups of cells called adipose tissue (located beneath
the skin and also around some organs e.g. the kidneys)
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Amount of energy released in cell respiration per gram
of lipids is double the amount released from a gram of
carbohydrate
Stored lipids have some secondary roles that could not
be performed as well by carbohydrates
Because lipids are poor conductors of heat- can be used
as heat insulators
Fat is liquid at room temperature- can also act as a
shock absorber- reason for adipose tissue around the
kidneys and some other organs
Glycogen is the carbohydrate that is used for energy
storage- in liver + some other muscles
Glycogen is used for short term storage
Because glycogen can be broken down to glucose
rapidly and then transported easily by the blood to
where it is needed.
Glucose can be used in either anaerobic or aerobic
respiration
Whereas fats and fatty acids can only be used in
aerobic respiration

 Health risks of fats
 Positive correlation between saturated fatty acids
intake and rates of CHD (coronary heart disease)
 However, finding a correlation doesn’t prove that
saturated fats cause the disease
 Populations that don’t fit the correlation

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Kenya has a diet that is rich in meat, fat, blood &
milk
Therefore high consumption in of saturated fats
yet CHD is almost unknown among the Maasai
High fats leads to obesity

Mouth

Chewing- saliva moistens food to
make a bolus for swallowing salivary
amylase begins chemical digestion
for starch

Salivary glands

Secrete saliva, includes amylase to
being digestion of starch

Oesophagus

A wave of muscle contractions
pushes the bolus into the stomach

Stomach

Muscular contractions continue
mechanical digestion- acid kills
bacteria-pepsin begins digestion of
protein

Liver

Secretion of surfactants in bile to
break up liquid droplets

Gall bladder
Pancreas

Storage and regulated release of bile
Secretion (taking from outside to
inside) of lipase, amylase and
protease
Bile from the liver and gall bladder
neutralises acid and emulsifies fatspancreatic amylase and lipase digest
carbohydrates and fats- trypsin
digests polypeptides to amino acids

Small intestine (duodenum)

Small intestine (ileum)

Lower half of small intestine absorbs
nutrients into the blood via the villi

Large intestine

Water is reclaimed and returned to
the blood leaving semi-solid faecesstored in rectum

Rectum
Anus

Stores faeces temporarily
Faeces- containing undigested food,
dead cells + other waste- is forced
out of anus

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Need for digestion of large food molecules- to break down
the diverse mixture of large carbon compounds in food to
yield ions and smaller compounds that can be absorbed
Need for enzymes in digestion- digestion requires
surfactants to break up lipid droplets and enzymes to
catalyse reactions

 The contraction of circular and longitudinal muscle of
the small intestine mixes the food with enzymes and moves
it along the gut
 Food is moved by peristalsis (wave of contractions moving
food along the digestive system, especially the intestine)
 Smooth- not striated muscle-short cells. It exerts force most
of the time-moderate force mostly-occasionally high level of
force when required to move food-it is divided into
longitudinal and circular muscles.
 In small intestine to churnin (movement here is very slow)
allowing digestion to take place- best by mixing substrate and
enzyme
Amylase  digest starch
Lipases  to digest triglycerides and phospholipids
Proteases  to digest proteins and peptide
 Digestion in the small intestine
 Enzymes digest most macromolecules in food into
monomers in the small intestine
 Enzymes secreted by the pancreas into the lumen of
the small intestine carry out these hydrolysis
reactions
-Starch is digested to maltose by amylase
-Triglycerides are digested to fatty acids and
glycerol or fatty acids and monoglycerides by
lipase
-Phospholipids are digested to fatty acids, glycerol
and phosphate by phospholipase

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-Proteins and polypeptides are digested to shorter
peptides by protease
Because of the great length of the small intestine, food takes
hours to pass through, allowing time for digestion of most
macromolecules to be completed
Some substances remain largely undigested- because
humans cant synthesise the necessary enzymes
Cellulose for example is not digested and passes on to
the large intestine as one of the main components of
dietary fibre
The process of taking substances into cells and the blood
is called absorption
In the human digestive system nutrients are absorbed
principally in the small intestine
The rate of absorption depends on the surface area of the
epithelium that carries out the process
The small intestine in adults is approx 7m long and 25-30mm
wide and has lots of folds on its inner surface giving a
large surface area
Villi and micro-villi increase the surface area
Villi are small projections of the mucosa on the inside of the
intestine wall
A villus is between 0.5mm and 1.5mm long and there can be
as many as 40 of them per square mm of small intestine wall.
They increase the surface area by a factor of about 10
Glucose cant pass through the plasma membrane by
simple diffusion because its polar and therefore
hydrophilic
Sodium-potassium pumps in the inwards-facing part of the
plasma membrane pump sodium ions by active transport
from the cytoplasm to the interstitial spaces inside the
villus and potassium ions in the opposite direction
To have balance concentration
This creates a low concentration of sodium ions inside the
villus epithelium cells
Sodium-glucose co-transporter proteins in the microvilli
transfer a sodium ion and a glucose molecule together
from the intestinal lumen to the cytoplasm of the
epithelium cells
This type of facilitated diffusion is passive but it depends
on the concentration gradient of sodium ions created by
active transport
Glucose channels allow the glucose to move by
facilitated diffusion from the cytoplasm to the interstitial

spaces inside the villus and on into blood capillaries in the
villus
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Villi  finger like extensions that increase the surface
area of the ileum
Lacteal  used to transport and absorbs dietary fats in
the villi-it is part of the lymph system that eventually
joins up to the capillaries
Circular muscle to longitudinal muscle