Download Mucus is secreted by Peristalsis is carried out at

A.
Multiple-choice
1.
The diagram below shows the set-up of three test tubes.
Y
X
Z
meat extract +
boiled meat extract +
meat extract +
proteases +
proteases +
boiled proteases +
pH indicator
pH indicator
pH indicator
The pH of the contents of each test tube was recorded at the beginning and again
15 minutes later. How did the pH change?
A
B
C
D
2.
The pH increased in all test tubes.
The pH decreased in all test tubes.
The pH increased in tubes Y and Z and did not change in tube X.
The pH decreased in tubes X and Y and did not change in tube Z.
The table below shows the pH of the digestive juice in organs in the human
digestive system.
Organ
pH of the digestive juice
Salivary gland
7
Stomach
2
Pancreas
X
What is the value of X?
A
C
2
7
B
D
4
8
Directions: Questions 3 and 4 refer to the diagram below, which shows the structure
of a tooth.
P
Q
R
S
3.
Which of the following contain(s) living structures?
A
B
C
D
4.
Which of the following is not a correct match of the structure and its description?
A
B
C
D
5.
Structure
P
Description
It is the hardest part of the tooth.
Q
R
S
It supplies nutrients to the tooth.
It contains nerve fibres for sensations.
It attaches the tooth to the gum.
Which of the following is not a physical digestion?
A
B
C
D
6.
R only
P and Q only
Q and R only
R and S only
churning in the stomach
peristalsis
the breakdown of polypeptides into amino acids
chewing by teeth
Which of the following is/are present in pancreatic juice?
(1) bile salts
(2) proteases
(3) lipase
A
B
C
(3) only
(1) and (2) only
(1) and (3) only
D
7.
The digestion of fats and oils occur more quickly when they are emulsified.
Emulsifying fats and oils give them
A
B
C
D
8.
a lower temperature for the action of enzymes.
a greater surface area for the action of enzymes.
a smaller mass for the action of enzymes.
a higher pH for the action of enzymes.
Which of the following is a correct match of the type of tooth and its function?
A
B
C
D
9.
(2) and (3) only
Type of tooth
canine
incisor
premolar
Function
biting food
tearing flesh
cutting food
molar
grinding food
Food is chewed into smaller pieces for
A
B
C
D
faster chemical digestion.
direct absorption into the body.
assimilation.
egestion.
10. Which of the following is the hardest structure of a tooth?
A
gum
B
enamel
C
dentine
D
pulp cavity
11. The chemical digestion of rice starts in
A
the mouth.
B
the stomach.
C
the duodenum.
D
the ileum.
12. The role of cardiac sphincter is to
A
control the entry of food.
B
control the exit of food.
C
secrete gastric juice.
D
shape food into a bolus.
13. Which of the following digestive juices digests food physically?
A
saliva
B
gastric juice
C
pancreatic juice
D
bile
14. Which of the following help(s) move food in the alimentary canal?
A
B
C
D
water
mucus
peristalsis
all of the above
15. Which of the following shows the correct sequence of the different components
in the digestive system?
A
B
C
D
mouth, oesophagus, stomach, ileum, duodenum, colon, anus
mouth, oesophagus, duodenum, stomach, ileum, colon, anus
mouth, oesophagus, stomach, duodenum, ileum, colon, anus
mouth, stomach, oesophagus, ileum, duodenum, colon, anus
16. Digestion is complete at
A
the stomach.
B
C
D
the duodenum.
the ileum.
the colon.
17. Which of the following is the significance of villi in the small intestine?
A
B
C
The villi help push the food in the small intestine forwards.
The villi speed up blood circulation.
The villi increase the surface area for absorption.
D
The villi secrete bile which aids in the digestion of lipids.
18. Absorbed food is transported to the liver via
A
C
the hepatic portal vein.
the hepatic portal artery.
B
D
the hepatic vein.
the hepatic artery.
19. Which of the following is not a function of the liver?
A
regulation of blood glucose level B
storage of glycogen
C
storage of calcium and iron
breakdown of excess amino acids
D
Directions: Questions 20 and 21 refer to the diagram below, which shows the upper
part of the human alimentary canal.
(3)
(4)
(1)
(5)
(2)
(6)
20. Which structure is responsible for the physical breakdown of food?
A
(1)
B
(3)
C
(4)
D
(5)
21. Which of the following is a correct match?
Mucus is secreted by
Peristalsis is carried out at
A
(3)
(2)
B
(4)
(5)
C
(3)
(4)
D
(4)
(6)
22. Which of the following statements about the stomach and its contents is not
correct?
A
Acid is present to change pepsin to protease in the stomach.
B
Mucus is present to protect the stomach wall from damage by enzymes.
C
Pepsin in the stomach acts on proteins to form peptides.
D
Food is churned up by the strong movement of the stomach wall.
Directions: Questions 23 and 24 refer to the diagram below, which shows a model
demonstrating a part of the human alimentary canal.
dialysis tubing
distilled water
starch and glucose solution
23. The water outside the dialysis tubing represents
A
the water present in saliva.
B
the water surrounding the villi.
C
the blood supplied to the small intestine.
D
the blood supplied to the oesophagus.
24. After one hour, the water outside the dialysis tubing would contain
A
glucose only.
B
starch only.
C
both glucose and starch.
D
neither glucose nor starch.
25. Which of the following statements about the enzymes in the human intestine
is/are not correct?
(1) The enzymes can synthesize essential amino acids.
(2) The enzymes can break down large food molecules into soluble products.
(3) The enzymes can convert excess food to useful products.
A
(1) only
B
(1) and (3) only
C
(2) and (3) only
D
(1), (2) and (3)
Directions: Questions 26 and 27 refer to the diagram below, which shows the
longitudinal section through a certain structure of the human small
intestine.
(1)
X
(2)
to venule
from arteriole
26. Structure X is
A
C
a villus.
an epithelium.
B
D
a lacteal.
a capillary.
27. The products from the digestion of lipids enter
A
the lymphatic system through route (1).
B
C
D
the blood circulatory system through route (2).
the blood circulatory system through route (1).
the lymphatic system through route (2).
Directions: Questions 28 and 29 refer to the diagram below, which shows the
longitudinal section of a tooth.
P
Q
R
S
28. What part is rich in calcium salts?
A
P
B
Q
C
R
D
S
29. We would feel pain from tooth decay when
A
B
C
D
a layer of plaque is formed on the surface of P.
P is dissolved by acid.
the bacteria reach Q.
R is damaged.
30. The table below shows the sites of the action and reaction carried out by three
different digestive juices. What are digestive juices X, Y and Z?
A
B
C
D
Digestive juice
Site of action
Reaction (substrate -> product)
X
mouth cavity
starch -> maltose
Y
stomach
protein -> peptide
Z
duodenum
starch -> maltose
X
gastric juice
bile
saliva
saliva
Y
saliva
gastric juice
gastric juice
bile
Z
pancreatic juice
pancreatic juice
pancreatic juice
intestinal juice
Directions: Questions 31 and 32 refer to the diagram below, which shows the
cross-section of a small intestine.
31. The epithelium of the small intestine is covered with structure X. What is X?
A
B
C
D
cilium
villus
hair
air sac
32. What are the function and structural adaptation of this structure?
A
B
C
Function
for digestion
for digestion
for absorption
Structural adaptation
It is a gland that secrete digestive juices.
It has a lacteal to produce lymph to help digestion.
It has a dense network of capillaries for efficient
absorption.
D
for absorption
Its epithelium contains several layers of cells to increase
the time for absorption
Conventional questions
1.
The diagram below shows part of the gut wall of a cow.
X
Y
a
b
i
Name the structure labelled X.
(1 mark)
ii Describe the function of the layer labelled Y.
(1 mark)
Describe and explain any two features shown in the diagram that facilitate
the absorption of digested food.
(4 marks)
2.
The diagram below shows the blood supply to part of the digestive system.
vein from heart
Z
X
liver
direction of blood
flow
intestine
Y
a
Name blood vessels X and Y.
(1 mark)
b
Which of the blood vessels above contains the highest concentration of
i
urea?
(1 mark)
ii
glucose after a heavy meal?
(1 mark)
c
Describe two ways in which the liver assimilates glucose.
(2 marks)
d
Explain why urea is an excretory product.
(2 marks)
3.
The diagram below shows the arrangement of teeth in the lower jaw of a human.
Q
R
S
P
a
Using the letters in the diagram, state which one is
i
a canine.
(1 mark)
ii
a molar.
(1 mark)
iii
an incisor.
(1 mark)
b
What is the function of a molar?
(1 mark)
c
Explain how canines and incisors are adapted to their functions in humans.
(2 marks)
4.
Ivy is having a meal. The dish contains mainly proteins and lipids.
Use the words from the box below to complete the following sentences.
glucose
stomach
mouth
amino acids
ileum
glycerol
large intestine
lipids
In Ivy’s digestive system, proteases will digest the proteins into
.
This takes place in her
. The food is then further digested in
her
, where lipases break down the
into fatty acids
and
.
(5 marks)
5.
The diagram below shows part of the human alimentary canal.
X
Y
Z
a
b
Name parts X, Y and Z.
On the diagram, label
i
‘P’ to show where ingestion occurs.
ii
(3 marks)
(1 mark)
‘Q’ to show where absorption of digested food occurs.
(1 mark)
The diagram below shows a bolus inside a section of the alimentary canal.
lumen
bolus
muscles
c
Describe how the bolus moves along the alimentary canal.
(2 marks)
6.
7.
a
State, with one example, what physical digestion is.
b
Using the digestion of lipids as an example, contrast physical and chemical
digestion.
(4 marks)
a
What is the purpose of mastication in digestion?
b
After masticating some rice for some time, a person finds that it tastes
sweet.
Account for the observation.
8.
(3 marks)
(2 marks)
(3 marks)
The diagram below shows the structure of a villus in the human small intestine.
capillaries
lacteal
a
State two adaptive features of the villus for the absorption of soluble
nutrients.
(2 marks)
b
Name two food substances that enter the capillaries.
(1 mark)
c
Name one food substance that enters the lacteal.
(1 mark)
d
After absorption, what will be the fate of the excess simple sugars?
(2 marks)
e
After absorption, what will be the fate of the excess amino acids?
(1 mark)
9.
Kelvin was given three digestive enzymes X, Y and Z. He was asked to find out
what types of enzymes they were. Kelvin did the investigation by adding equal
volumes of enzymes to different food substances. After 24 hours, he carried out
food tests to check if the food substances were still present. The table below
shows the results:
Key:
Enzyme
Proteins
Starch
Lipids
X
+
–
+
Y
+
+
–
Z
–
+
+
+
=
food substance(s) present
–
=
food substance(s) absent
a
i
ii
What types of enzymes were X, Y and Z?
(3 marks)
Write the word equations for the digestive actions of X, Y and Z
respectively.
(3 marks)
b
Where can X be found in our alimentary canal?
(1 mark)
10. The diagram below shows the longitudinal section of a villus of the small
intestine.
Y
X
a
Name structures X and Y.
(1 mark)
b
i
Which nutrient is absorbed into structure X?
(1 mark)
ii
What is the importance of the nutrient in b i to our body?
(1 mark)
c
With reference to the diagram, state and explain two features of the villi that
facilitate the absorption of digested food.
(2 marks)
d
What happens if excess amino acids are absorbed into structure Y?
(2 marks)
11. Some people continually overproduce acid in the stomach. During acid reflux,
the acidic contents of the stomach move up into the oesophagus, causing
irritation and damage to the cells lining the oesophagus. Acid reflux is one cause
of ‘heartburn’.
A pH probe was used to discover whether a patient’s ‘heartburn’ was caused by
acid reflux. This probe monitored the pH in the oesophagus from 8 a.m. to
midnight. The results are shown below.
a
Suggest how the stomach contents are normally prevented from moving up
into the oesophagus.
(1 mark)
b
State two functions of the acid secreted in the stomach.
c
Why are cells lining the stomach not affected by acid in the same way as the
cells lining the oesophagus?
(1 mark)
d
Suggest an explanation for the pH values observed in the oesophagus up to
an hour after a meal is eaten.
(3 marks)
(3 marks)
12. The diagram shows the processes that would take place in a simple tube gut.
a
b
i
Name the processes numbered 1–4 .
(2 marks)
ii
Define the process numbered 2.
(1 mark)
In mammals the gut is modified to form specialized organs with specific
roles. Complete the following table to show some of the enzymes secreted
by a mammalian gut, their action and the associated organs.
(4 marks)
Enzyme
Substrate
Pepsin
Peptidases
Products
Site of secretion
Peptides
Peptides
Lipids
Fatty acids and
glycerol
Maltose
Salivary gland
13. The drawing represents a section of the wall of the small intestine.
a
b
c
What is the role of the following structures in the function of the small
intestine?
i
Circular and longitudinal muscles
(1 mark)
ii
Lacteals
(1 mark)
i
Which vessel does the blood in vein X enter?
(1 mark)
ii
What is the name of the fluid in structure Y?
(1 mark)
Coeliac disease in humans is caused by chemicals in wheat, barley and rye
leading to a loss of villus height and a breakdown of microvilli.
i
Explain why people with coeliac disease sometimes suffer from
deficiency diseases.
(2 marks)
ii
How do you account for the reduced efficiency of digestive enzymes
such as those involved with the final breakdown of disaccharides and
dipeptides in people with coeliac disease?
(3 marks)
14. Physical or mechanical digestion is an important aspect of digestion as food
passes through the alimentary canal.
a
b
i
State the two main areas of the alimentary canal where mechanical
breakdown occurs.
(1 mark)
ii Why is mechanical breakdown important?
(1 mark)
Bile is released into the small intestine where it is mixed with the contents.
Bile contains bile salts.
In an experiment, lipase was added to a mixture of water and olive oil and
the pH of the mixture was monitored at regular intervals. The experiment
was repeated, under the same conditions, but with bile salts. The results are
shown in the table below.
Time (min)
i
ii
c
pH
Lipase
Lipase and bile salts
1
8.0
8.0
2
7.8
7.4
3
7.4
6.8
4
7.1
6.3
5
6.8
5.9
6
6.6
5.9
Explain why lipase causes a drop in pH.
(1 mark)
Explain the more rapid drop in pH when bile salts are present.
(2 marks)
iii State one other function of bile in the small intestine.
(1 mark)
Obesity is a major health concern, in the western world including Wales.
Explain how an excess of all the absorbed digested products can lead to an
increase in body mass.
(2 marks)
15. In 1833, Dr William Beaumont conducted experiments on a man who, having
recovered from a gunshot wound, was left with a small hole in his body leading
to the interior of his stomach.
a
Draw a circle round the letter that shows the most probable position of the
hole.
(1 mark)
b
Dr Beaumont described one of his experiments as follows: ‘Juice was
extracted from the stomach and placed in a small tube. A solid piece of
boiled, recently salted beef was added. The tube was then corked and kept
under controlled conditions. A similar piece of beef was suspended on a
string into the man’s stomach’.
i
c
Suggest one condition which he might have controlled in the tube.
(1 mark)
ii State the importance of using ‘boiled, recently salted beef’. (1 mark)
After two hours, Dr Beaumont recorded the following results:
‘Beef in tube – the cellular texture seems to be entirely destroyed, leaving
the muscle fibres loose and unconnected, floating about in fine, small shreds,
very tender and soft.’
‘Beef in stomach – I drew out the string, but the meat was completely
digested and gone.’
Use your knowledge of the process of digestion to account for the
difference between the changes in the tube and in the stomach. (3 marks)
d
After digestion in the stomach, the contents passes into the duodenum.
i
Explain why proteases are usually secreted in an inactive form.
(2 marks)
ii
Some of the absorbed end products of digested beef may undergo
deamination. Explain the purpose of this process.
(1 mark)
16. Below is a diagram of the human digestive system.
a
Label parts A and B in the diagram.
(2 marks)
b
An experiment was set up to investigate the digestion of starch by enzymes.
Five test tubes were set up as follows and kept in a water bath at 35oC.
After 2 minutes a drop was taken from each tube and added to iodine
solution on a white tile. This was repeated after 60 minutes. Iodine is a
brown solution which changes colour in the presence of starch. The results
are shown below:
Tube number
Colour after 2 minutes
Colour after 60 minutes
1
Blue-black
Blue-black
2
Brown
Brown
3
Blue-black
Brown
4
Blue-black
Blue-black
5
Blue-black
Blue-black
i
Explain why a colour change occurs in tube 3 but not in tube 4.
(3 marks)
ii
Explain why tubes 1 and 2 were included in the experiment.
(2 marks)
iii
Explain the results in tube 5.
iv
On the diagram of the digestive system in a, mark with the letter X
where you could expect the reaction in tube 3 to take place. (1 mark)
v
Describe the test for simple sugars and the expected colour change.
(3 marks)
(1 mark)
17. In our mouth we produce an enzyme which digests starch. A scientist measured
the amount of this enzyme in three groups of people who eat different foods. The
results are shown in the table:
Group
Food eaten
Amount of enzyme in
mouth (units per cm3)
A
Mixed diet of meat,
vegetables, fruit and
starchy cereals
101
B
Mainly meat
22
C
Mainly starchy cereals
248
a
How does the type of food eaten affect the amount of the enzyme produced?
(1 mark)
b
The graph shows the effect of temperature on the digestion of starch by this
enzyme.
i
c
Describe the effect of temperature on the action of this enzyme.
(2 marks)
ii Explain the results obtained between 35–65°C.
(2 marks)
Complete the table below to show the action of enzymes in different regions
of the digestive system.
(3 marks)
Region of digestive system
Enzyme
Stomach
Protease
Small intestine
Action of enzyme
Digests starch to glucose
Lipase
Digests fats to fatty acids
and glycerol
18. a
i
By means of a simple labelled diagram indicate the structure of a
triglyceride molecule. (Detailed biochemical structure is not expected.)
(2 marks)
ii
Give two differences between the structure you have drawn and a
phospholipid.
(2 marks)
b
Suggest one reason why animals tend to store energy in the form of fat
rather than carbohydrate.
(1 mark)
c
What is the difference between a saturated and an unsaturated fat?
(1 mark)
d
An experiment was carried out to find the effect of the enzyme lipase on the
fat in milk. 10 cm3 of full cream milk was mixed with 0.5 cm3 of sodium
carbonate solution and three drops of universal (pH) indicator. Universal
indicator changes colour as shown below.
pH 4
pH 7
pH 10
red
green
blue
1 cm3 of unboiled enzyme was added to one tube (A). Then, 1 cm3 of lipase
was boiled, cooled and added to a second tube (B). The milk, sodium
carbonate and indicator solution were divided between the two test tubes.
Tubes A and B were then incubated at 35°C for 3 hours.
i
Suggest why sodium carbonate was added to the tubes.
(1 mark)
ii
What colour would you expect in tube A after 3 hours of incubation?
(1 mark)
iii
Briefly explain your answer to d ii.
iv
Explain why no appreciable change in colour was observed in tube B.
(2 marks)
(2 marks)
19. a
b
The diagram below shows the digestive system.
Name the parts labelled A–D.
(4 marks)
In the experiment below a length of visking tubing was used to act as a
model gut. The visking tubing was filled with a starch and protein solution.
A sample of the water surrounding the visking tube was taken every 15
minutes and tested for starch, protein, amino acids and glucose.
After 45 minutes a protease enzyme was added to the contents of the
visking tube. The results are shown below.
Time (minute)
Starch
Protein
Amino acid
Glucose
0
-
-
-
-
15
-
-
-
-
30
-
-
-
-
45
-
-
-
-
60
-
-
+
-
75
-
-
+
-
90
-
-
+
-
Key: + = substance present, - = substance absent.
i
After the protease enzyme was added, amino acids were present in the
sampled water. Explain this result.
(2 marks)
ii
Explain why protein is not found in the sampled water.
iii
1
Name an enzyme that you would add to the contents of the
visking tubing so that glucose was present in the sampled water.
(1 mark)
2
State where in the digestive system this enzyme is made.
(1 mark)
(1 mark)
20. The diagram below shows the absorption of glucose into a surface of ileum and
then to the blood vessel towards the liver.
glucose
X
Y
a
b
Name structure X and blood vessel Y.
Explain how they can facilitate glucose absorption.
(2 marks)
(4 marks)
c
A piece of the ileum wall was placed in a solution of glucose. The
concentration of glucose in the solution was lower than that inside the cells.
The graph below shows the concentration of glucose in the cells over 40
minutes.
concentration of glucose
in the epithelial cells
12
(arbitary unit)
10
8
6
4
2
0
10
20
30
time (minute)
40
With the help of the graph, explain how glucose is absorbed into the
epithelial cells.
(4 marks)
21.
To study the effects of digestive enzymes on food substances, a student extracted
digestive juices from three regions of the alimentary canal of a mammal. Each
digestive juice was incubated with a mixture of starch, proteins and lipids in a
test tube. The changes in the composition of the food substances were examined
after an hour. The results are summarized in the following table.
Digestive juice
Result after incubation
X
Peptides and amino acids formed
Y
Reducing sugars, peptides, amino acids and
fatty acids formed
Z
Reducing sugars formed
a
From the results, deduce the organs from which the different digestive
juices were extracted. Explain your answer.
(7 marks)
b
Biological washing powders can remove food stains from clothes more
effectively than ordinary washing powders.
i
What extra substances do you think biological washing powders
contain?
(1 mark)
ii
What are the effects of these extra substances?
iii
Some precautions on the temperature of water are taken. State and
explain the precautions.
(2 marks)
(1 mark)
22. The diagram below shows the longitudinal section of a human tooth.
P
Q
R
S
U
V
T
a
Name the type of tooth shown in the diagram. What is the function of this
particular type of tooth in humans?
(2 marks)
b
Using the letters in the diagram, state the hardest part of the tooth. What is
the major composition of this part?
(2 marks)
c
Using the letters in the diagram, state the parts that attach the tooth to the
jaw bone.
(2 marks)
d
Using the letters in the diagram, state the part that causes the painful
feeling in tooth decay.
(1 mark)
e
Why leaving the decayed tooth untreated can be detrimental to health?
(2 marks)
f
Give one practice that helps prevent tooth decay.
(1 mark)
23. The table below shows the time taken for the complete breakdown of a sample of
starch suspension in the presence of an enzyme at different pH.
pH
Time (min)
5
6
5.5
4.5
6
3
6.5
2
7
1.25
7.5
1.25
8
3
8.5
5
a
What can be done to prevent the results from being affected by any change
in the temperature of different solutions?
(1 mark)
b
How can the complete breakdown of starch be detected?
(1 mark)
c
Plot the results on a graph.
(4 marks)
d
What is the optimum pH for this enzyme?
(1 mark)
e
Name the enzyme. Where does it work in the alimentary canal? (2 marks)
f
Name one region of the alimentary canal where the function of this enzyme
would be stopped.
(1 mark)
24. The diagram below shows the changes in the amounts of different food
substances as they pass along the human alimentary canal. The band width
represents the amount of food substance.
Food
substance
Mouth cavity
X
Small
intestine
Fat
Lipids
Starch
Starch
Vitamins
Dietary
fibre
Proteins
Proteins
a
i
Which food substance remains undigested as it passes along the
alimentary canal?
(1 mark)
ii
Suggest one food that is rich in the food substance you answered in a i.
(1 mark)
b
c
Identify X. Explain your answer.
(2 marks)
What happens to vitamins and minerals in our alimentary canal once they
have been ingested? Explain your answer.
(2 marks)
d
Describe what happens to the lipids, starch and proteins in the small
intestine.
(4 marks)
25. The following set-up of dialysis tubing demonstrates the need of digestion for
absorption in the mammalian alimentary canal. The tubing allows only glucose
and fructose but not sucrose to pass through. After an hour, the distilled water
was tested for reducing sugars and the result was positive.
a
What does distilled water represent in the process of food absorption?
(1 mark)
b
How does the set-up explain the need of digestion of food substances?
(2 marks)
c
In which part of the alimentary canal does most of the absorption take
place?
Name two adaptive features of the part.
(3 marks)
d
Consider a person eating a cheese sandwich. Name the nutrients other than
vitamins and minerals which can pass through the alimentary canal wall
after digestion.
(2 marks)
26. Digestion is completed in the small intestine. Give an account of the uptake of
the products of digestion. Describe what happens to each product once it has
entered the body.
(10 marks)
27. Describe how lipids are digested in our body and the fate of the absorbed
products of lipid digestion.
(10 marks)
Answers
1.
D
21.
D
2.
D
22.
A
3.
C
23.
C
4.
B
24.
A
5.
C
25.
B
6.
D
26.
B
7.
B
27.
D
8.
D
28.
A
9.
A
29.
D
10.
B
30.
C
11.
A
31.
B
12.
A
32.
C
13.
D
33.
14.
D
34.
15.
C
35.
16.
C
36.
17.
C
37.
18.
A
38.
19.
C
39.
20.
A
40.
1.
a
b
i
Villus
1m
ii
It contracts to move food along the gut.
1m
Any two from:
2m x 2
There are many finger-like villi.
Villi increase the surface area for absorption.
OR
There is a network of capillaries in the villi.
This allows the absorbed food molecules to be carried away rapidly.
OR
Villi have a thin epithelium (which is only one-cell thick).
This allows rapid absorption due to the short distance for diffusion of food molecules
into the blood.
2.
a
b
c
X: hepatic artery
0.5m
Y: hepatic portal vein
0.5m
i
Z
1m
ii
Y
1m
Liver cells use glucose for respiration to release energy. /
Liver converts the excess glucose into glycogen. /
d
Liver stores the glycogen. (any 2)
1m x 2
Urea is harmful to the body.
1m
It is produced as a by-product of metabolism.
1m
i
Q
1m
ii
S
1m
iii
P
1m
3.
a
b
Crushing / grinding of food
1m
c
Canines are pointed and curved for tearing flesh.
1m
Incisors are chisel-shaped / have flat sharp edges for biting and cutting food.
1m
4.
amino acids
1m
stomach
1m
ileum
1m
lipids
1m
glycerol
1m
5.
a
b
c
X: oesophagus
1m
Y: stomach
1m
Z: colon / large intestine
1m
i
Mouth
1m
ii
Ileum
1m
The circular muscles behind the bolus contract while those in front of it relax. The
longitudinal muscles behind the bolus relax while those in front of it contract. The
lumen behind the bolus becomes smaller and the food is squeezed forwards.
1m
The rhythmic contraction and relaxation of the muscles result in peristalsis. 1m
6.
a
Physical digestion is the breaking down of food into smaller pieces by physical
actions.
1m
Examples include chewing by teeth, churning in the stomach, peristalsis along the
alimentary canal and emulsification by bile salts.
1m
The food is broken down into pieces so as to increase the surface area for chemical
digestion.
b
1m
Physical digestion of lipids is emulsification. The bile salts emulsify lipids into small
droplets.
1m
It involves no enzymes and the chemical structure of lipids does not change.
1m
Chemical digestion of lipids involves lipases.
1m
Under the actions of lipases, lipids are changed to fatty acids and glycerol.
1m
7.
a
Mastication mechanically breaks down large food masses into smaller pieces.
1m
b
This increases the surface area for the food to be mixed with saliva.
1m
Rice contains starch
1m
which is digested by amylase in saliva.
1m
Starch is hydrolysed to soluble sugars that taste sweet.
1m
8.
a
It is finger-like in shape to increase the surface area for absorption. /
Its thin epithelium is only one-cell thick so as to shorten the distance for diffusion of
food molecules into the blood or lymph. /
It has a lacteal and a dense network of capillaries for efficient absorption. (any 2)
1m x 2
b
Simple sugars, amino acids
0.5m x 2
c
Lipid molecules
1m
d
Excess simple sugars will be converted to glycogen in the liver.
1m
The glycogen will be stored in the liver and muscles.
1m
e
Excess amino acids will be deaminated in the liver to form urea and glucose.
1m
9.
a
i
ii
X: amylase
1m
Y: lipase
1m
Z: protease
1m
X: starch -> maltose
1m
Y: lipid -> fatty acid + glycerol
1m
Z: protein -> peptide
1m
b
Mouth cavity, duodenum
1m
a
X: lacteal
0.5m
Y: capillary
0.5m
i
Lipids
1m
ii
They are used to form cell membranes. /
10.
b
They may be deposited around the internal organs to protect them. /
They may build up under the skin to reduce heat loss. (any 1)
c
Any two from:
1m
1m x 2
The villi are finger-like.
This greatly increases the surface area for absorption.
OR
The epithelium is only one-cell thick.
This allows rapid absorption because the distance for absorption of digested food into
the bloodstream is very small.
OR
Each villus has a dense network of capillaries.
This allows absorbed food to be carried away rapidly.
d
Excess amino acids will be deaminated in the liver.
1m
The urea formed will be excreted in urine.
1m
11.
a
Contraction of the cardiac sphincter closes the entrance to the stomach.
1m
b
To kill bacteria.
1m
To provide optimum pH / correct pH
1m
for the activation / action of enzymes / proteases.
1m
c
The cells lining the stomach are covered with mucus.
1m
d
Food remains in stomach for 2–4 hours. /
The acid is mixed with the food in stomach. /
More acid production is stimulated once food arrives at the stomach. /
The pH falls as more acid moves up into oesophagus. (any 3)
1m x 3
12.
a
i
ii
1: ingestion
0.5m
2: digestion
0.5m
3: absorption
0.5m
4: egestion
0.5m
It is the breakdown of large, insoluble molecules into small soluble ones.
1m
b
Enzyme
Substrate
Products
Site of
secretion
Pepsin
Protein /
Peptides
Polypeptide
Peptidases
Peptides
Stomach /
Gastric pits
Amino acids
Pancreas / Small
intestine
Lipase
Lipids
Fatty acids and
Pancreas
glycerol
Salivary amylase
Starch / Amylose
Maltose
Salivary gland
0.5m x 8
13.
a
b
c
i
For peristalsis
1m
ii
To absorb lipids.
1m
i
Hepatic portal vein
1m
ii
Lymph
1m
i
The surface area is reduced.
1m
They cannot absorb substances efficiently.
1m
The intestine has no / fewer microvilli.
1m
ii
Many enzymes involved with digestion are adsorbed onto the membranes of
microvilli / components of the membrane.
1m
Catalytic surface is reduced for enzyme action.
1m
14.
a
i
Mouth / mouth cavity and stomach
1m
ii
To increase the surface area of food for enzyme action / chemical digestion.
1m
b
i
Lipids are converted to fatty acids.
1m
ii
Bile salts emulsify lipid droplets into smaller droplets.
1m
This increases the surface area of lipid for the activity of lipase.
1m
It neutralizes stomach acid.
1m
iii
c
Excess lipids and carbohydrates are stored as lipids in adipose tissue.
2m
a
B circled on drawing
1m
b
i
Temperature / acidic condition
1m
ii
To ensure no microorganisms or other enzymes in beef.
1m
15.
c
d
In stomach, churning breaks the beef tissue into smaller pieces.
1m
There is a large surface area for enzymes to act upon.
1m
The continuous enzyme production speeds up the digestion.
1m
i
The gut wall is made of proteins.
1m
Therefore, the active enzyme would digest the wall / organ / cells.
1m
To remove excess amino acids digested.
1m
ii
16.
a
b
A: oesophagus
1m
B: gall bladder
1m
i
Tube 3: The carbohydrase digests all starch.
1m
Tube 4: Boiling denatures the enzyme,
1m
so starch remains.
1m
To show that both starch and enzyme are required for the reaction.
1m
They are controls.
1m
iii
Tube 5: Protease does not digest starch.
1m
iv
X in mouth cavity or small intestine
1m
v
Benedict’s test for simple sugars
1m
The Benedict’s solution and a sample are heated strongly.
1m
If simple sugars are present, the colour changes from blue to red.
1m
ii
17.
a
The more starch is present, the more enzyme is produced.
1m
b
i
As temperature increases, the enzyme works faster up to 35°C,
1m
after which the action of the enzyme decreases.
1m
ii
The higher the temperature / at high temperatures, the more enzymes
become denatured.
1m
There is less activity of the enzyme. / The digestion of starch slows down or
decreases.
c
1m
Digests proteins to amino acids
1m
Carbohydrase / Amylase
1m
Small intestine
1m
i
Glycerol
1m
3 fatty acids
1m
18.
a
ii
Phospholipids have the phosphoric acid. /
A phospholipid contains 2 fatty acids. /
Phospholipids contain hydrophobic tails and hydrophilic head / are polar
molecules. (any 2)
b
Fat has a higher energy value.
1m x 2
1m
c
Saturated fats have more hydrogen. /
Saturated fats are solid at room temperature and unsaturated fats are liquid. /
Unsaturated fats contain double bonds and saturated fats contain single bonds only.
d
(any 1)
1m
i
To make the contents of the tubes alkaline / raise pH.
1m
ii
Red / green
1m
iii
Lipase / enzyme hydrolyses / splits the fat.
1m
Fatty acids make the contents acidic / lower the pH.
1m
iv
Heating changed the shape of the active site. /
Heating denatured the enzyme / broke the bond. /
The substrate no longer fitted / was no longer complementary to the enzyme. /
No enzyme-substrate complex formed. /
No fatty acids were produced. (any 2)
1m x 2
19.
a
b
A: mouth
1m
B: pancreas
1m
C: small intestine / ileum
1m
D: anus
1m
i
Protease digests / breaks down protein to amino acids.
1m
Amino acids pass through visking tube wall.
1m
ii
Protein molecules are too large to pass through the pores in the visking tube.
1m
iii
1
Carbohydrase / amylase
1m
2
Salivary glands / mouth / pancreas
1m
20.
a
b
c
X: villus
1m
Y: hepatic portal vein
1m
X increases the surface area
1m
for uptake of digested food substances.
1m
The wall of Y is one-cell thick.
1m
This shortens the diffusion distance of the nutrients.
1m
Glucose is absorbed into the cells by active transport.
1m
The concentration of glucose inside the cells increases.
1m
The rate of uptake is constant.
1m
Glucose can be absorbed against the concentration gradient.
1m
Digestive juice X was extracted from the stomach.
1m
It is because the digestive juice in the stomach contains proteases only.
0.5m
Proteases digests proteins into peptides and amino acids.
0.5m
Digestive juice Y was extracted from the pancreas.
1m
21.
a
It is because the digestive juice in the pancreas contains carbohydrases, proteases
and lipases.
0.5m
Carbohydrases digest starch into reducing sugars.
0.5m
Proteases digest proteins into peptides and amino acids.
0.5m
Lipases digest lipids into fatty acids.
0.5m
Digestive juice Z was extracted from the mouth cavity.
1m
It is because the digestive juice in the mouth cavity contains amylase only. 0.5m
b
Amylase digests starch into reducing sugars.
0.5m
i
The extra substances are proteases and lipases.
1m
ii
They digest the proteins and lipids in food stains into soluble forms which can
iii
be removed more easily by water.
1m
The water used should not be too hot or too cold.
1m
Otherwise the enzymes will be denatured and become inactive at high and
low temperature respectively.
1m
22.
a
Premolar / molar
1m
To chew, crush and grind the food into small pieces suitable for swallowing. 1m
b
P
1m
It is mainly made of calcium phosphate, calcium fluoride and a small amount of
organic matter.
1m
c
V, T
1m x 2
d
U
1m
e
Bacteria may enter the blood through the blood vessels
1m
and attack other important organs such as the brain.
1m
f
Brush the teeth at least twice a day. /
Brush the teeth in the correct way. /
Improve brushing style with the help of dental disclosing agents. /
Use toothpaste that contains fluoride. /
Use dental floss. /
Do not eat too many sweets or too much sugary food. /
Have a balanced diet with adequate calcium, phosphorus and vitamin D. /
Do not bite very hard materials. /
Go for a dental check-up at least twice a year. (any 1)
1m
23.
a
Place the reacting solutions in a water bath of about 37oC.
b
Perform iodine test on the solutions. When the iodine solution remains brown in colour,
starch is completely broken down.
1m
1m
time (min)
c
Correct title
0.5m
Correct labelling of axes
0.5m x 2
Correct scale of axes
0.5m x 2
Correct curve
1.5m
d
7.25
1m
e
Amylase
1m
Mouth / mouth cavity / duodenum
1m
Stomach
1m
f
24.
a
i
Dietary fibre
ii
Vegetables / fruits / cereals
1m
1m
b
c
Stomach
1m
It is because only proteins are digested in this part.
1m
Vitamins and minerals remain unchanged in the alimentary canal.
1m
They are small enough to be absorbed into the blood in the small intestine. 1m
d
Lipids are broken down into fatty acids and glycerol by the action of lipases. 1m
Starch is broken down into glucose by the action of amylase and other
carbohydrases.
1m
Proteins are broken down into amino acids by the action of proteases.
1m
The end-products will then be absorbed into the capillaries and lacteals in the
small intestine.
1m
a
Blood
1m
b
Only small molecules can pass through the wall of alimentary canal for absorption.
25.
1m
Food substances with large molecules have to be broken down into small
c
molecules.
1m
Ileum
1m
The presence of numerous villi increases the surface area of absorption. /
The villi have thin epithelia to facilitate the passage of food substances. /
The presence of lacteal and a network of capillaries carry away the absorbed food
molecules rapidly. /
The movement of the villi caused by peristalsis keeps a steep concentration
gradient of food molecules across the wall of the small intestine. (any 2)
1m
d
Monosaccharides, amino acids, fatty acids, glycerol
0.5m x 4
26.
Any ten from:
1m x 10
Absorption occurs in ileum with good capillary supply.
The surface area is increased by villi on the surface of the ileum.
Glucose is absorbed by diffusion / active transport.
Glucose diffuses down the concentration gradient into the blood vessels in the villus.
Amino acids are taken up by active transport.
Blood travels from the small intestine to the liver via the hepatic portal vein.
Fatty acids and glycerol are absorbed by diffusion across the cell membrane.
Lipids move into the lacteal and transported through the lymphatic system which rejoins
the bloodstream.
Glucose is used for respiration / stored as glycogen / lipids.
Amino acids are used for protein synthesis.
Excess amino acids are deaminated in the liver.
Lipids are used for making cell membranes / hormones / stored in adipose tissue.
27.
Any seven from:
1m x 7
Mechanical digestion such as chewing by teeth, churning in the stomach and peristalsis
along the alimentary canal breaks fatty food into small pieces.
Bile is secreted by the liver and stored by the gall bladder.
It contains bile salts which emulsify lipids into small droplets.
This facilitates lipid digestion by increasing the surface area for lipases to act on.
Lipases in pancreatic juice catalyse the metabolism of lipids into fatty acids and glycerol.
The products are transported by lacteal in ileum to all parts of the body.
The absorbed lipids act as the energy reserve of the body.
Lipids can be used by cells to make cell membranes.
Excess lipids are deposited around the internal organs or in adipose tissue under the
skin.
Effective communication
3m