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Junior Certificate Biology
Chapter 2 – The Digestive System
The digestive system in humans is group
of organs working together to break
down food.
Liver
Produces bile to break
down fats.
Small
intestine
Produces enzymes and
carries out the final
breakdown of the food.
Food is absorbed into the
bloodstream here.
Large
intestine
Water passes back into
the bloodstream from
here producing solid
waste.
Anus
Waste food is released
through here.
Mouth
oesophagus
Liver
Small
intestine
Stomach
Large
intestine
Anus
Organ
Function
Mouth
Food is mixed with saliva
and chewed. Amylase
enzyme breaks down the
starch.
Oesophagus
A tube which brings the
food from the mouth to
the stomach by muscular
action.
Stomach
Churns the food and
mixes it with digestive
juices and acid. Acid kills
bacteria.
Pancreas
The five stages of Nutrition
1. Ingestion – taking in food.
2. Digestion – breaking down the
food by chewing and churning or
by enzyme.
3. Absorption – passing of food into
the blood stream.
4. Assimilation – this is where body
cells use the food for energy,
growth and repair.
5. Egestion – getting rid of waste
food through the anus.
Physical digestion of food
The physical digestion of food is carried
out by (i) muscle action, the stomach and
intestinal walls crush the food by
squashing it, or (ii) crushing, using teeth
to cut and grind the food.
Produces digestive
enzymes.
1
G. Nugent
Junior Certificate Biology
There are four types of teeth.
Incisors
A second enzyme called maltase then
breaks down the maltose into glucose.
Sharp flat front teeth used
to cut food.
Canines
Pointed teeth for tearing
food.
Premolars
Flat back teeth for grinding
food
Mandatory experiment; To show the
action of amylase enzyme on starch.
A
B
water at 37oC
Molars
Larger flat back teeth for
grinding food.
Chemical digestion
Chemical digestion involves the use of
special chemicals, called enzymes, to
breakdown the large food molecules
(proteins, fats and carbohydrates) into
smaller ones.
An enzyme can be defined as a
biological catalyst. A catalyst is a
chemical which speeds up a chemical
reaction without itself being used up.
Starch only
Starch and amylase
enzyme
1. In test tube A put starch only.
2. In test tube B put some starch
and a few drops of amylase
enzyme solution.
3. Place both in a beaker of warm
water. The enzyme works best in
warm conditions.
4. After 10 minutes, take out a small
amount of A and B and test them
with iodine solution.
5. ‘A’ will turn blue/ black due to the
presence of starch.
6. ‘B’ will not change the colour of
the iodine because the enzyme has
converted all of the starch to
maltose.
7. Test both test tubes with
Benedict’s solution.
8. A shows no reaction to it.
9. B changes the blue benedict’s
solution to brick red. This shows
that test tube B now contains
sugar. This must be due to the
presence of the enzyme.
How enzymes work
 The substance acted-on by the
enzyme is called the substrate.
 The substance formed by the
enzyme action is called the
product.
 The enzyme works by grabbing a
substrate molecule, breaking it
down and then releasing the
products when they are formed.
An example of this is amylase enzyme. It
grabs starch molecules, breaks them
down into maltose molecules and then
releases them.
2
G. Nugent