HUMAN NUTRITION.
BALANCED DIET.
Balanced diet- is a diet which contains all nutrients in their correct amounts and
proportions needed to sustain the body and ensure good health and growth.
COMPONENTS OF A BALANCED DIET.
 Carbohydrates
 Fats
 Proteins
 vitamins, limited to C and D
 Mineral salts, eg calcium and iron
 Fibre (roughage)
 Water
The three basic functions of the components of the balanced diet.
1.To allow growth, replacement of cells and repair of worn and
damaged tissues.
 Food provides substance needed for making new cells and tissues e.g.
proteins.
 Proteins are needed for replacement of red blood cells, replacement of
skin cells.
2. To provide energy.
 This is the main role of carbohydrates and fats.
 Proteins are used for energy only if they are in excess of
requirements for growth, development, repair and replacement.
3. To regulate the body’s metabolism.
 Vitamins and minerals are needed in very small quantities in the diet
to help regulate metabolism.
1
How age, gender and activity affect dietary needs of humans.
 Dietary needs depend on age, sex and activity.
1.Children have a greater energy requirement than adults.
 As children grow, the energy requirements increase because of the
energy demands of the growth process.
 Energy is also needed to maintain body temperature; children have
higher basal metabolic rate (BMR)-the rate of energy expenditure
when one is at rest.
Children have larger surface area to volume ratio so they lose a lot of
heat energy to the environment as result their rate of metabolic
reactions increase in order to produce heat energy to replace the heat
lost to the environment.
 They require relatively larger amounts of Vit D and calcium for bone
development.
 Children also require more protein per kilogram of body weight than
adults for growth.
2.Females have lower energy requirements than males.
 On average females have lower body mass than males, which has a
lower demand on energy intake.
 Males are more masculine; muscle contraction require energy.
 There are also different physical demands made on boys than girls.
3.Energy requirements increases with increasing physical activity.
 The energy needs of occupations that involve physical activity
are greater than less active jobs that involve sitting at a desk.
 People who take part in vigorous physical sports also require
high energy and protein diets.
2
4.Pregnant women require a special diet.
 A pregnant woman needs extra food rich in protein, calcium, iron,
and vitamin D.
 These are needed by the growing baby.
 The baby needs proteins for making tissues, calcium and vit D for
bone development and ion to make haemoglobin in red blood
cells.
5. Lactating women needs a special diet.
 Lactation means the production of breast milk for feeding the
baby.
 Mother needs food rich in proteins, vitamins and calcium to
produce milk of adequate quantity and quality.
SAMPLE QUESTION.
N04 P3 Q2 Fig. 2.1 shows pie charts of the diets of two twelve-yearold girls, one from Europe and one from Africa.
Fig. 2.1
(a) Using information from Fig. 2.1, complete the table to compare the
African diet with that of the European diet.
In each box, write more or less or the same.
3
(b) The daily energy intake is provided mainly by carbohydrates and
fats.
Select one of the food groups from Fig. 2.1 that would provide a good
source of:
(i) carbohydrates;.
(ii) fats.
[2]
(c) With reference to the pie charts:
(i) suggest why the African girl may not grow as fast as the European
girl;
[1]
(ii) suggest why the European girl is more likely to suffer from scurvy
than the African girl;
[2]
(iii) suggest why the European girl is more likely to suffer from
constipation and colon cancer than the African girl. [2]
MARKING POINTS.
2 (a)
(b)
 cereals/sugar/sweets/vegetables/fruit;
 dairy products/meat/eggs/fish/sweet
[2]
(c) (i)
 less or not enough proteins in African diet
4
 less meat/eggs/fish
 less calcium in diet
 less dairy products
[1]
(ii)
 less or not enough vegetables/fruit;
 less vitamin C/ascorbic acid; ® less vitamins
unqualified. [2]
(iii)
 less or not enough vegetable/fruit/cereals;
less or not enough roughage/fibre/cellulose + present
 gives bulk to food passing through gut .
 to help with peristalsis;
 more meat + increases chance of colon cancer
5
[3]
SOURCES OF NUTRIENTS.
NAME
Carbohydrate
Fats
RICH FOOD
SOURCE
Rice, potato, yam,
cassava, bread,
millet, sugary foods.
Butter, milk, cheese,
egg-yolk, animal fat,
ground nuts.
USE IN THE BODY

Source of energy.



Energy store.
Insulation.
Synthesis of
hormones.
Cell membrane
formation.
Protection of
delicate organs.
Growth
Repair of tissues
Synthesis of
enzymes.
Synthesis of
hormones.
Synthesis of body
structures e.g
nails.
Synthesis of
haemoglbin.
Tissues repair.
Resistance to
diseases.
Strengthens bones
and teeth.
Formation
haemoglobin in
red blood cells.


Proteins.
Meat, fish, eggs,
soya, groundnuts,
milk, cowpeas.






Vitamin C
Vitamin D
Iron.
Calcium.
Oranges, Lemons
and other citrus
fruits.
Fish oil, milk,
butter.
Liver, meat, cocoa,
eggs.
Milk, fish,
green
vegetables.
Fibre.
Plant material.




 Strengthens
bones.
 Adds bulk to
the content
food and assist
in peristalsis.
 Helps to retain
water .
6
DEFICIENCY
SYMPTOM
 Fatigue
 Dizziness
 Constipation
 Mental fatigue
 Constantly feeling
cold
 Dry and scaly skin
 Dry hair
 Dry eyes

Kwashiorkor and
marasmus.

Bleeding of
gums(scurvy)




Soft bones in adults.
Rickets in children
Tiredness.
Lack of
energy(anaemia).
 Weak brittle
bones.
 Muscle
weakness and
cramps.
 Constipation.
WATER.
About 70% of most tissues consist of water, it is an essential part of cytoplasm.
The body fluids, blood, lymph and tissue fluid are composed of mainly water.
Role of water.
 Formation of blood and cytoplasm.
 Solvent for transport of nutrients and removal of wastes.
 For hydrolysis reactions.
SAMPLE QUESTION.
N09 P2 Q3 (a) Micronutrients are food materials that are only needed
in very small quantities in the
human diet.Draw one straight line from each micronutrient to its
deficiency symptom.
(b) Explain how iron, in the diet of humans, is used in the body.
Marking points.
(a) micronutrient deficiency symptom
7
[3]
(b) 1 (iron) used to make / part of haemoglobin;
2 present in red blood cells;
3 used to carry / transport / hold oxygen;
4 component of myoglobin / some enzymes /
electron carriers;
5 (myoglobin) present in muscle cells
MALNUTRITION.
Malnutrition is the result of not eating a balanced diet. There may be:
 Wrong amount of food: too little or too much
 Incorrect proportion of main nutrients
 Lacking in one or more key nutrients
Effects of malnutrition.
A. Obesity - Too much food (carbohydrate, fat or protein).
Obesity and overweight results from taking more carbohydrates, fats and
proteins than the body needs for growth, energy and replacement.
Major causes of obesity.
 Excess carbohydrates are converted to fats and stored in fat deposits
under the skin or in the abdomen.
 Too little exercise also contributes to obesity.
 Social and emotional stress, leads to comfort eating which also
contribute to obesity.
 Obesity is calculated using the body mass index (BMI).
8
BMI =
𝑀𝑎𝑠𝑠(𝐾𝑔)
[𝐻𝑒𝑖𝑔ℎ𝑡]2
A person with BMI of less than 20 is underweight
BMI between 25 and 30 is overweight.
BMI over 30 is obese.
BMI between 20 and 24 is acceptable.
Symptoms and consequences of obesity.
 Heart disease.
 Stroke.
 Diabetes.
 Overweight can cause problems with joints.
SAMPLE QUESTION.
J04 P3 Q2.
2.Coronary heart diseases.


Too much saturated/animal fat in the diet results in high cholesterol levels.
Cholesterol can stick to the walls of arteries supplying heart muscles with blood
gradually blocking them.
 If coronary arteries become blocked, the results can be a coronary heart disease.
 Blockage of coronary arteries reduces blood flow increasing risk of blood clotting.
9
Effects of accumulation of cholesterol.







Increased risk of blood clotting.
Reduced blood flow.
Less blood is supplied with oxygen and glucose is supplied to the heart muscles
Reduced blood supply to heart muscles results in chest pains when exercising.
Muscles respire anaerobically.
Heart muscle deprived of oxygen die.
When a major coronary artery is blocked, this may result in heart failure
Other Risk factors of coronary heart diseases.
(a) Stress.
 Emotional stress often leads to raised blood pressure.
 High blood pressure may increase the rate at which atheroma is formed.
 Prevention:Avoid severe or long term stress
(b).Smoking.
10
 Statistical studies suggest that smokers are more two to three times more
likely to die from a heart attack.
 The carbon monoxide and other chemicals in cigarette smoke may damage
the lining of the arteries, allowing atheroma to form.
 Nicotine cause an increase in the heart rate and cause clumping together of of
platelets leading to clotting.
 Prevention: stop smoking.
(c). Genetic predispotion.
 Coronary heart disease appears to be passed from generation to generation in
some families.
(d).Age.
 Risk of developing CHD increases with age.
 Arteries lose their elasticity with age.
(e).Gender.
 Males are more at risk of a heart attack than females ,this is likely because of
the less healthy life style they live than females.
(f). Lack of exercise.
 Heart muscles lose their tone and become less efficient at pumping blood
when exercise is not taken.
 Slow flow of blood from lack of exercise may allow atheroma to form in the
arterial lining.
11
Treatment of CHD.
1.Coronary bypass.
 A blood vessel is taken from another part of the body, usually the leg or the
arm and is attached to the coronary artery above and below the narrowed and
blocked area .
 The blocked area is bypassed.
2. Angioplasty and stent.
 This is a less complex operation, angioplasty involves the insertion of a long,
thin tube called a catheter into the blocked or narrowed blood vessels.
 A wire is attached to a deflated balloon is then fed through the catheter to the
damaged area.
 Once in place it is inflated to widen the artery wall.
 Sometimes a mesh wire called a stent is applied and is left in place to keep
the artery open.
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3.Antiplatelets medicines.
 Asprin is an example of an antiplatelet drug.
It prevents blood clots forming in the arteries.
SAMPLE QUESTION.
J17 P41 Q1 (e)One possible effect of too much fat in the diet is coronary heart disease.
Describe how too much fat in the diet may cause coronary heart disease.
[3]
(f) Describe and explain how coronary heart disease can be treated.
[6]
Marking points.
(e)
 fat is deposited in (walls of) arteries ;
 coronary arteries arteries are blocked ;
 less blood flow to, heart muscle
 less / no, / glucose / oxygen, reaches heart, muscle
cells
(f)
 drug treatment ;
13
 aspirin is used to, reduce risk of / prevent,
blood clotting ;
surgery / operation ;
 (coronary) by-pass ;
 piece of blood vessel attached to carry blood
around the blocked artery .
 angioplasty ;
 balloon inserted into artery and inflated to
widen artery ;
 stent(s) is inserted to keep the artery open.
 blood supply (to heart muscle) I s restored.;
B.Starvation.
 It is caused by taking too little food ( e.g. intense fear of gaining weight).
 Extreme slimming diets, such as those that avoid carbohydrates foods,
can result in the disease called anorexia nervosa.
Effects of starvation.
 Weight loss.
 In fertility in females.
 Organ damage.
 Death.
C. CONSTIPATION.
Lack of roughage or fibre cause constipation.
Roughage provides bulk to food and stimulates peristalsis.
Roughage also reduces chance of developing colon cancer.
Effects of constipation.
 Unable to defecate.
14
D. KWASHIORKOR AND MARASMUS.
 These conditions are a result of protein energy malnutrition (PEM)
Kwashiokor.- Caused by too much carbohydrates and lack of protein
Symptoms of Kwashiokor.
 Oedema ( swelling of the abdomen and legs)
 Sparse dry hair.
 Fat accumulation in the liver.
15
Marasmus.- Caused by lack of proteins and carbohydrates
.
Symptoms of marasmus.
 Very low body mass.
 Thin arms and legs.
 Old looking face.
 fatigue ;
 muscle wasting ;
 more prone to, infections
16
SAMPLE QUESTION.
J17 P42 Q4 A balanced diet is required to ensure healthy weight gain as children grow.
(a) Explain the term balanced diet.
[3]
(b) A doctor diagnosed a young child with marasmus.
Describe the symptoms of marasmus.
.[3]
(c) The child with marasmus was put on a special diet.
He was given fortified milk, which is milk that has extra nutrients added to it.
The child was encouraged to drink as much fortified milk as he wanted over a period of
seven months.
Table 4.1 shows the composition of the fortified milk given to the child and the
composition of cow’s milk for comparison.
Table 4.1
The body mass of the child who had marasmus and the mean body mass of healthy children
of the same age were recorded. The data is shown in Fig. 4.1.
Using the information in Table 4.1 and Fig. 4.1, describe and explain the importance of diet
when treating children affected by marasmus.
[6]
17
MARKING POINTS.
4(a)
 all, nutrients / components ;
 nutrients in correct, proportions / amounts ;
.e.g carbohydrates, proteins, fats, vitamins mineral ions, water and fibre;
 to maintain health ;
 energy requirments vary according to, age / sex / lifestyle /
pregnancy ;
4(b)






weight loss ;
space hair ;
diarrhoea
fatigue ;
muscle wasting ;
more prone to, infections
4(c) description
1 marasmus child lower mass than healthy child, initially / AW ;
2 initial (rapid) increase in mass of child with marasmus ;
3 then trend almost follows increase of healthy children ;
4 later / AW, marasmus child is similar to / heavier than, healthy child ;
5 comparative data in children’s mass with units stated at least once ;
6&7&8 comparative data of milk with units stated at least once ;;;
explanation
9 protein required for, new cells / muscle / repair ;
10 carbohydrates / fats, required for, energy / respiration ;
11 fats required for, insulation / cell membranes / protecting organs /
neurones ;
12 treatment for marasmus / AW, has more, (named) nutrients / energy ;
13 marasmus child encouraged to drink as much as possible ;
14 nutrients are required (for children) for, growth ;
18
ALIMENTARY CANAL.
Definition of Key terms.
Ingestion is the taking of substances, e.g. food and drink, into the body through the
mouth.
Mechanical digestion is the breakdown of food into smaller pieces without
chemical change to the food molecules.
 It starts in the mouth where chewing breaks down food into smaller
pieces that can be swallowed.
 Muscular contractions of the stomach continue.
 In small intestines, large globules of fat are broken into smaller globules
by emulsification by bile.
NB: Mechanical digestion gives a larger surface area for the enzymes to work on.
Chemical digestion is the breakdown of large, insoluble molecules into small,
soluble molecules by action of enzymes.
Absorption is the movement of small food molecules and ions through the wall of
the intestine into the blood.
Assimilation is the movement of digested food molecules into the cells of the
body where they are used, becoming part of the cells.
Egestion is the passing out of food that has not been digested or absorbed, as
faeces, through the anus
19
REGIONS OF THE ALIMENTARY CANAL.
 The human digestive system consist of the alimentary canal and its
associated organs the liver, pancreas and the salivary gland.
20
 Food passes from the mouth to the stomach down a tube called the
oesophagus.
 Food leaves the stomach and enters the duodenum, the first part of the
small intestine.
 The second and longer part of the small intestine is called the ileum.
 The rest of the alimentary canal is made up of the large intestines which
end up with the rectum and the anus.
SAMPLE QUESTION
M16 P32 Q33 (a) Define the term enzyme.
[2]
(b) (i) Fig. 3.1 shows a diagram of part of the human alimentary canal and associated
organs.
Name the structures labelled A, B, C and D.
[4]
(ii) On Fig. 3.1, draw label lines with letters to show:
E where hydrochloric acid is made
F where bile is made
G where amylase is made
H where egestion occurs.
[4]
MECHANICAL DIGESTION.
21
Mechanical digestion is the breakdown of food into smaller pieces without
chemical change to the food molecules.
 It starts in the mouth where chewing breaks down food into smaller
pieces that can be swallowed.
 Muscular contractions of the stomach continue.
 In small intestines, large globules of fat are broken into smaller globules
by emulsification by bile.
Mechanical digestion in the mouth involves chewing of ingested food to make it
 easier to swallow and to
 Increase surface area for enzyme action.
SAMPLE QUESTION.
J16P41Q6(b) Explain the role of mechanical digestion.
Marking points.
breaks up food into small(er) pieces ;
without chemical change ;
by teeth / muscles ;
to mix (with digestive juice) ;
increases surface area for enzyme action ;
 speeds up chemical digestion and to make it easier to swallow ;





22
THE HUMAN TEETH.
Mammals have four different types of teeth which perform different roles.
Types of Human teeth.
1. Incisors are chisel shaped for biting and cutting.
2. Canines are pointed in many carnivores for piercing and tearing .In humans
their role is like that of canines.
3. Premolars have uneven cusps for grinding and chewing and also have 1-2 roots.
4. Molars have 4-5 cusps and have 2-3 roots. , they are for chewing and grinding.
NB : Human adult has 32 teeth, 4 incisors on each jaw,2 canines in ach jaw, 4
premolars in each jaw and 6 Molars in each jaw.
23
SAMPLE QUESTION.
N18 P31 Q4 (a) Fig. 4.1 shows the four different types of human teeth.
Fig. 4.1
Fig. 4.2 shows a diagram of the position of the different types of teeth in the mouth.
Fig. 4.2
Complete Table 4.1 by writing the names, positions and functions of the different types of
teeth in the mouth shown in Fig. 4.2.
24
Structure of human teeth.
25
 The teeth is made up of the root, which is embedded in the jaw and the
visible crown.
 The harder outer layer of the crown is made up of enamel which forms the
biting surface.
 The enamel covers the softer bone-like layer called the dentine which acts
as a shock absorber.
 The dentine surrounds the pulp cavity contains blood capillaries; tooth cells
and neurones.The blood vessels supply cells with glucose oxygen. The tooth
cells divide to form the dentine.
26
 The dentine of the root is kept firmly in place in the jaw by a layer of
cement with fibbers growing out of it which attach the tooth to the jawbone,
but allow slight movement when biting or chewing.
SAMPLE QUESTION.
N06 P3 Q2 A human tooth was suspended in hydrochloric acid and left for 24 hours, as
shown in Fig. 2.1. When the tooth was removed and washed, the lower part, to which the
cotton was attached, was no longer hard, but soft and rubbery. After replacing the tooth
in the acid for another 24 hours, the rest of the tooth was also soft.
Fig. 2.1
(a) (i) Name the part of the tooth to which the cotton was attached.
[1]
(ii) Name the type of human tooth used in this experiment. State two reasons for your
answer
[3]
(iii) With reference to tooth structure, suggest and explain why the lower part of the
tooth became soft before the upper part.
[3]
TOOTH DECAY.
How tooth decay is brought about.
 Bacteria are present on the surface of teeth.
27





Food deposits and bacteria form a layer called plaque.
Bacteria on the plaque feed on sugars, producing acid.
The acid dissolves the enamel, forming a hole.
The dentine is softer so it dissolves more rapidly.
If the hole reaches the pulp cavity, bacterial infection can get to the nerves
resulting in toothache.
Stages of tooth decay.
Proper care of teeth.-(How to avoid tooth decay)
 Avoid sugary foods, especially between meals, so bacteria cannot
make acids.
 Clean teeth regularly to remove plaque ( a fluoride tooth paste hardens
tooth enamel).
 Use dental floss or toothpick to remove pieces of food and plaque
trapped between teeth.
 Visit the dentist regularly so any tooth decay is treated early and any
stubborn plaque is removed.
 Use antibacterial mouthwash.
 Eat food containing calcium.
 Rinse mouth with water after eating.
SAMPLE QUESTION.
N18 P31Q4(b) Teeth can develop dental decay.
(i) Explain how dental decay is caused.
(ii) Describe two ways to avoid dental decay.
28
[4]
[2]
CHEMICAL DIGESTION IN THE MOUTH.
Chemical digestion is the breakdown of large, insoluble molecules into small,
soluble molecules by action of enzymes.
 Chewing by the teeth increases surface area for enzyme action.
 Salivary glands secrete saliva.
Saliva contain the foollowing substances:
 Salivary amylase , which hydrolyses starch to maltose
 Mineral ions, maily sodium hydrogen carbonate , which help to keep
the Ph in the mouth at about 6.5-7.5 and chloride ions which activate
salivary amylase.
 Mucus, a slimy substance that lubricates the passage of the food bolus
along the oesophagus.
SAMPLE QUESTION.
N07 P3 Q2 Teeth and salivary glands associated with the digestion of food in the mouth.
(a) (i) Describe the role of the salivary glands in the digestion of food in the mouth.[3]
(ii) Describe the physical changes to food that are brought about by the action of the
molar teeth.Explain how these changes help digestion.
[3]
PERISTALSIS.
 The alimentary canal has two of muscles in its wall.
 The fibers of one layer muscles run around the canal (circular muscles) and
the other run along its length ( longitudinal muscle).
29
Peristalsis in the oesophagus.
Peristalsis is the wave of muscular contraction.
 Circular muscles contract and longitudinal muscles relax behind the
food bolus to push it along.
 In front of the bolus, circular muscles relax and longitudinal muscle
contract to widen the oesophagus to allow the bolus of food to move
along.
 Movement of food in small and large intestines is by peristalsis.
30
 Peristalsis is an involuntary action, it does not require thinking.
31
CHEMICAL DIGESTION IN THE STOMACH.
 The stomach walls secrete gastric juice.
The gastric juice contains the following.
 Hydrochloric acid which carries out two main important functions
due to its low pH.
1. It kills bacteria in food. The low pH denatures enzymes in any
harmful microorganism in the food.
2. The acid pH gives the optimum pH for the action of the
protease enzyme pepsin.
NB: Muscular wall of the stomach churn up food making sure it is
mixed well with the juice. Muscular action is a type of mechanical
digestion. The mixture of food, gastric juice and hydrochloric acid
is called chyme.
M15 P42 Q5(d) Mechanically digested food travels from the mouth to the stomach. The
gastric juice in the stomach contains hydrochloric acid, giving a low pH environment.
Explain why it is important to have a low pH in the stomach.
[3]
 Pespsin activated by HCl starts the breaking down of proteins
into smaller polypeptides.
 Mucus secreted by goblet cells protects the stomach walls from the
digestive actions of pepsin and HCl.
32
CHEMICAL DIGESTION IN THE SMALL INTESTINES.
Most of the digestive activities of the small intestine takes place in the
duodenum.The role of the small intestine are mainly absorption.
Role of Bile.
Bile is made in the liver and stored in the gall bladder.
 Bile is alkaline, it neutralizes the acidic chyme, and this gives the best Ph for
the enzymes in the small intestines.
 Bile emulsifies fats by breaking them into smaller droplets to increase
surface area for lipase that breaks down lipids to give glycerol and fatty
acids.
33
Role of the pancreatic juice.
The pancreas secretes pancreatic juice containing the following enzymes:
 Amylase- breaks down starch to maltose.
 Lipase – breaks down lipids to fatty acids and glycerol.
 Trypsin – breaks down proteins and polypeptides to peptides.
SAMPLE QUESTION.
N18 P42 Q6(b) Galapagos iguanas feed on seaweed which contains starch and other
carbohydrates.
(i) State the name of the enzyme that digests starch.
[1]
(ii) State the names of two parts of the alimentary canal where starch is digested. [2]
Role of enzymes on cell- surface membrane of the small intestines.
Cells lining the small intestines have membrane -bound enzymes which complete
digestion.
Examples of enzymes;
 Maltase- breaks down maltose to glucose.
 Sucrase- breaks down sucrose to glucose and fructose.
 Lactase- breaks down lactose to galactose and glucose.
ABSORPTION IN THE SMALL INTESTINES.
Absorption is the movement of small food molecules and ions through the wall of
the intestine into the blood.
Digested food molecules include simple sugars, amino acids, fatty acids and
glycerol. These molecules pass through the wall of the small intestines either by
diffusion or by active transport.
34
Adaptations of the small intestines for absorption.
 The ileum is very long-about 6m in adult humans to increase surface area.
 Has a thin lining (one cell thick), so digested food can easily cross the wall
into the blood and lymph.
 It has a folded inner lining with millions of tiny, finger-like projections
called microvilli to increase surface area.
 The epithelial cells lining the villi have microscopic projections called
microvilli which further increase the surface area.
 The villi have good blood supply.
 Villi have also lacteal for fat absorption.
Detailed section of the ileum.
35
 Glucose and amino acids diffuse through the epithelial cells into the
blood capillaries.
 Fatty acids and glycerol from the epithelial cells they enter the
lacteal ( a lyphatic vessel).They travel via the lympatic system .The
lymph then empties them into the blood.
 Absorbed molecules are transported to the liver by the herpatic portal
vein.
How the villus is adapted for absorption.
 villi lining / epithelium, only one cell thick ;
 good blood supply / many capillaries ;
 microvilli to provide a large surface area ;
 lacteal for fats / fatty acid, absorption ;
 Epithelial cells have many carrier proteins for active transport and
diffusion of products of digestion;
 Mitochondria to provide energy for active transport ;
Detailed structure of the epithelial cells lining the small intestines.
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Adaptations of the cells for absorption.
 Cells have many microvilli to increase surface area for absorption.
 Have many mitochondria to provide energy for active transport of
substances.
 The cell membrane has many carrier proteins for active transport and
diffusion of products of digestion.
SAMPLE QUESTION.
M16 P42 Q5(e) Products of digestion are absorbed through the villi in the small intestine.
Explain how villi are adapted for absorption.[3]
(f) Coeliac disease is caused by a reaction to a protein called gluten. The villi become
damaged causing a reduction in the absorption of nutrients.
Suggest possible effects on the body of a reduction in the absorption of nutrients[3]
MARKING POINTS.
e)
 villi lining / epithelium, only one cell thick ;
 good blood supply / many capillaries ;
 microvilli to provide a large surface area ;
 lacteal for fats / fatty acid, absorption ;
 Epithelial cells have many carrier proteins for active
transport abd diffusion of products of digestion;
 Mitochondria to provide energy for active transport ;
(f)
 weight loss / poor growth / lack of energy / stomach
pain / abdominal pain /
cramps / diarrhoea / weaker immune system ;
 malnutrition / deficiency disease ;
 examples
 anaemia → iron / vitamin B12
 kwashiorkor → protein ;
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 marasmus → all nutrients
 scurvy → vitamin C
 night blindness →vitamin A / retinol
SAMPLE QUESTION.
J12 P32 Q1 Fig. 1.1 A shows a cell from the lining of the alimentary canal.
Fig. 1.1 B shows a cell from the lining of a kidney tubule.
Both cells absorb substances into the blood.
(a) Name the structures labelled C on the cells in Fig. 1.1.
[1]
(b) List three substances that are absorbed by both cells shown in Fig. 1.1.
[3]
(c) Explain how both cells shown in Fig. 1.1 are adapted for absorption of substances into
the blood.
[2]
(d) Name the part of the alimentary canal that is lined by the cells shown in Fig. 1.1 A. [1]
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SAMPLE QUESTION.
J17 P41 Q1 Fat is a necessary component of the human diet.
(a) State three ways in which the human body uses fat.
[3]
The arrows in Fig. 1.1 show the pathway of fat in part of the alimentary canal.
(b) State the name of
(i) the enzyme secreted by the pancreas that digests fat
[1]
(ii) the products of chemical digestion of fat
[1]
(iii) the liquid that is produced by the liver and stored by organ P in Fig. 1.1 [1]
(iv) organ P in Fig. 1.1.
[1]
(c) Explain what happens to ingested fat at R in Fig. 1.1 before chemical digestion occurs2
(d) Explain how the products of fat digestion are transported from Q to the rest of the
body.
[3]
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MARKING POINTS.
1(b)(i) lipase ;
(ii) fatty acids and glycerol ;
(iii) bile ;
(iv) gall bladder ;
(c) (bile) emulsifies fats ;
 breaks down into / changed into smaller, globules
 increases surface area (to volume ratio) ;
 for, enzyme(s) / lipase ;
(d)fatty acids / glycerol are the products of fat digestion.
 Pass through the (micro)villi into cells ;
 From the cells they into the lacteals / lymphatic capillary ;
 They travel in lymph vessels
 Lymph empties into blood ;
THE LARGE INTESTINE.
The large intestine is divided into caecum, colon and the rectum.
NB: Most of the water (5-10 dm3 per day) is absorbed in the small intestines.




The large intestine also absorbs water (0.3-.0.5dm3 per day).
Solid waste or faeces is stored in the rectum.
Eventually the faeces is egesteted through the anus.
The passing out of indigestible food through the anus is called egestion.
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