2. Digestion is the process by
which
insoluble food, consisting of large molecules is
broken down into soluble compounds
3. What are starch, proteins & fats
broken down into?
enzyme
STARCH
Glucose
enzyme
PROTEIN
Amino acids
enzyme
FAT
Fatty acids &
glycerol
4. Why must food be digested?
1
Food in
intestine
2
Blood
Food in
intestine
enzyme
Blood
Wall of
intestine
3 Food in
intestine
Blood
To be small enough
to be absorbed
through the wall of
intestine.
6. Food is broken down by two actions:
1. PHYSICAL
/MECHANICAL
2. CHEMICAL
7. 1. PHYSICAL DIGESTION by:
teeth
peristalsis of the alimentary
canal
Chewing (mastication)
8. Why is it important to break down
food physically?
To increase the surface area for enzyme action.
9. Question: SEP, 2009
Give TWO reasons why food must be masticated
before swallowed. (4)
1. Increased surface area for enzymes to act
quickly.
2. Easier to manipulate by tongue to form a
bolus.
10. 2. CHEMICAL DIGESTION by:
enzymes
Digestive enzymes are the chemicals that break
large insoluble food molecules into smaller soluble
molecules.
11. Four stages in feeding & digestion:
2. Digestion
3. Absorption into
the bloodstream
4. Egestion
1. Ingestion
12. Digested food is absorbed & then
assimilated by the cells
Absorption
Assimilation
Digestive
system
Body
cell
Circulatory
system
26. Peristalsis:
wave-like motions of the alimentary
canal which move the food forwards
Digestive tract
Bolus
1
Wave of
relaxation
Bolus
moves
2
2
Wave of
contraction
31. The stomach stores
food for some time &
releases it slowly
Food stays for 2-6 hours in the
stomach
Chyme:
creamy liquid leaving
the stomach
32. Food remains inside stomach due to
contraction of two sphincters
Oesophagus
Cardiac sphincter
Pyloric sphincter
Lining of
mucus
Duodenum
Churning due to:
Layers of muscle
33. Which sphincter is contracted?
Cardiac sphincter:
Pyloric sphincter:
relaxes to let chyme
into the duodenum
contracted
37. Functions of hydrochloric acid:
1. creates the optimum pH for pepsin
HCl
Pepsinogen
2.
(inactive form)
Pepsin
(active enzyme)
3. kills bacteria taken in
with the food
43. Pepsin is a protease:
breaks:
Proteins
Polypeptides
44. Which conditions are needed for a
piece of meat to be digested?
Pepsin in acidic conditions
45. Question: MAY,2009
The following diagram represents the protein found
in egg white. Each circle represents an amino acid.
Complete the diagram below to show how pepsin
breaks down the protein found in egg white.
[Idea is that short chains representing polypeptides are
made.]
(Do NOT accept individual amino acids represented as single
circles or dipeptides represented as a pair of circles)
46. Question: MAY, 2012
List TWO reasons why amylase does not act on
starch in the stomach. (2)
i. pH in stomach is not optimum for amylase
ii. there is no enzyme in the stomach to break
starch
47. Some substances that are absorbed
by the stomach:
ethanol
vitamins
certain salts and drugs
some water
glucose
How did I
get drunk so
quickly?
48. Rennin
is an enzyme found in the stomach of young
children
Function:
Pepsin then acts
on the insoluble
protein
Soluble protein
in milk
Changes into
insoluble protein
58. Bile:
has no enzymes
consists of:
water
sodium chloride
bile salts
bile pigments
pH = 8
59. Functions of Bile:
dilutes contents from stomach
creates optimum pH for pancreatic enzymes
to work in duodenum
contains bile salts which emulsify fats
Bile salts
60. Bile salts emulsify fats i.e.:
break large fat globules into smaller globules
What is the benefit of emulsification?
The surface area where lipase can act is increased.
Emulsification
of fats
61. A person had his gall bladder removed.
Explain why the doctor told him to limit
fats in the diet.
Fats cannot be emulsified;
difficult to digest fats by lipase.
64. Question: MAY, 2012
Bile and pancreatic juice are involved in
digestion of fats.
a) Describe the role of both secretions in this
process. (4)
b) Explain why bile must be released before
pancreatic juice for the efficient digestion of
fats. (2)
69. Remember: Digestion of starch
Starch
Salivary Amylase
(In Mouth)
Maltose
No digestion of starch in
stomach (amylase is
denatured)
Maltose
(in ileum)
Maltase
Glucose
Pancreatic
Amylase
75. The ileum is adapted to absorb
digested food
by providing a LARGE surface area:
Folded walls
Has villi
Has microvilli
76. Ileum is adapted for absorption:
1. Ileum is long:
more time for digestion
a greater surface area for absorption
2. Villi:
increase surface area for absorption
3. Microvilli in epithelium:
increase surface area for absorption
4. Epithelium is very thin:
soluble products of digestion pass through quickly
5. Dense capillary network:
removes the digested food
78. The large intestine is composed of:
4. Colon
1.Caecum
2. Appendix
3. Rectum
Anus
79. Material in the large intestine
consists of:
water
mucus
dead cells
undigested matter
Most of the undigested matter is
cellulose. Why is this so?
83. I really have
to go to the
bathroom!
Egestion / Defaecation
the process of removing
faeces
84. Caecum & Appendix are
Vestigial in humans:
[small & no function]
Caecum
Appendix
Large in herbivores
85. Question: SEP, 2011
Explain why the caecum /
appendix in humans is small
and non-functional. (4)
Human
Rabbit
Humans are omnivores.
Do not depend only upon vegetation for
nutrients.
A large caecum is found in herbivores and is full
of bacteria that produce cellulase to digest
cellulose.
86. Ingestion
(2 L)
Salivary gland secretions
(1 L)
Gastric secretions
(2 L)
Bile
(0.7 L)
Small intestine
secretions
(2 L)
1% in
faeces
Pancreatic secretions
(1.2 L)
Although 8.9 L of
water are ingested
or secreted daily,
the faeces are dry.
Explain.
87. Ingestion
(2 L)
Salivary gland secretions
(1 L)
Gastric secretions
(2 L)
Bile
(0.7 L)
Small intestine
secretions
(2 L)
1% in
faeces
Pancreatic secretions
(1.2 L)
Absorbed in the
small intestine &
colon.
89. Deamination occurs in the liver
AMINO ACID
is broken into two:
Part with
nitrogen forms:
AMMONIA
UREA
The rest is
used for
energy
90. Question: MAY, 2007
Write the correct term for each of the following
processes:
i) the breakdown of excess amino acids
Deamination
ii) rhythmical muscular contractions that push
food along the digestive system
Peristalsis
91. iii) the elimination of indigestible food from
the body
Egestion / Defaecation
iv) the passage of digested food through the
gut wall in the blood stream.
Absorption
93. Blood supply to and away from the liver
HEART
HEPATIC VEIN
to heart
HEPATIC
PORTAL VEIN
Blood from
digestive system
LIVER
HEPATIC ARTERY
GUT
Oxygenated blood
from heart
94. Write an account of a controlled experiment
you would perform to show the action of the
enzyme amylase on starch. (6) [MAY, 1997]
1
Two spotting tiles are
prepared with a drop of
iodine solution in each
hole.
2
An equal volume of starch
is placed into two separate
test tubes, labelled A and B.
95. 3
An equal volume of amylase is placed
into two separate test tubes, labelled C
and D.
Test tube C is boiled for 5 minutes to
denature the enzyme and so act as a
control.
4
All four test tubes are
placed in a water bath at
37C for 5 minutes to
acclimatise.
96. Starch in test tube A is
poured into amylase in test
tube D, mixed and the stop
watch is started.
5
6
After 30 seconds, a drop of the
mixture is taken and added to one
of the drops of iodine solution on
the spotting tile. This is repeated
until a yellow colour appears.
97. 7
8
Starch in test tube B is poured
into amylase in test tube C,
mixed and the same method is
repeated.
Contents in test tube:
i) D give a yellow colour with
iodine solution after a few
minutes
ii) C continues to give a blueblack colour after 30 minutes.
98. 9
10
The results show that amylase breaks down
starch.
If Benedict’s solution is added to
the contents of test tubes C and D
and heated for a few minutes, a
brick red colour is obtained only
in test tube D [unboiled amylase].
This shows that when starch
breaks down, reducing sugars are
formed.
C
D
