1. 9.1 Composition of Food
Today’s Learning Objectives:
 Name the five main food groups
 Name the main types of carbohydrate found in
food.
 Name the chemical elements present in
carbohydrate, protein and fat.
 Name the molecular units from which
carbohydrates are made up.
 Name the molecular units from which proteins are
made up.
 Name the molecular units from which fats are made
up.
 State how the units of carbohydrate, protein and
fat are joined together.

2. • The three main food groups are …?
Carbohydrates
Proteins
Fats

3. Carbohydrates
G G G G G G
Starch (insoluble)
G G GG
G
G
G
Maltose (soluble)
Glucose (soluble)

4. Fats and Oils
Fatty Acid
Fatty Acid
Fatty Acid
Glycerol
Fat Molecule

5. Proteins
Protein
(insoluble)
Peptides
Amino acids
(soluble)

6. nn
Food Groups
Growth and
repair
Energy
Energy/ stored
energy
Use
Diagram
Amino Acids
Fatty acids &
glycerol
Glucose/Maltose
molecules
Basic Units
Carbon
Hydrogen
Oxygen
Nitrogen
Carbon
Hydrogen
Oxygen
Carbon
Hydrogen
Oxygen
Elements
Present
ProteinsFatsCarbohydrates
nn

7. 9.2 Alimentary Canal
Today’s Learning Objectives:
 Identify the associated organs of the alimentary
canal.
 Describe the role of the mouth in the mechanical
breakdown of food.
 Describe the role of saliva in aiding swallowing.
 Describe peristalsis in the oesophagus and state its
role.
 Describe the action of the muscles of the stomach
and explain their function.

8. Mouth
Salivary Gland
Liver
Stomach
Large Intestine
Small Intestine
Anus
Rectum
Pancreas
Gall Bladder
Oesophagus
Tongue

9. Peristalsis
 Takes place along the whole length of the gut from
mouth to anus, to move food through the gut.
Layers of
muscle Contraction
of muscle
Relaxation
of muscle
Direction of movement

10. 9.3 Digestion Process
Today’s Learning Objectives:
 State the connection between molecular size and the
solubility of food.
 Explain the importance of solubility of food molecules.
 Define the term digestion in terms of food molecules.
 Describe where starch digestion takes place and what
happens to the starch molecules after they are
digested.
 Describe where protein digestion takes place and
what happens to the protein molecules after they are
digested.
 Describe where fat digestion takes place and what
happens to the fat molecules after they are digested.
 Name the different types of enzyme involved in
digestion of starch, protein and fat.

11. Digestion
 Digestion is the breakdown of large,
insoluble molecules into small, soluble
molecules by digestive juices.
 The digested food molecules can then be
absorbed through the wall of the small
intestine into the blood stream.

12. Digestive Enzymes
 Most digestive juices contain enzymes.
 There are groups of enzymes involved in
digestion.
 Each group acts on a different type of
food, called the substrate.
 The substrate gets broken down by
enzymes to substances called products.

13. Digestive Enzymes
PeptidesProteinPepsinProteases
Fatty acid
and glycerol
FatsLipaseLipases
MaltoseStarch
Salivary
amylase
Amylases
ProductsSubstrateEnzyme
Enzyme
Group

14. 9.4 Stomach and Digestion
Today’s Learning Objectives:
 Name three substances secreted by cells in the
stomach wall and name the structure these cells form
in the stomach wall.
 State the function of these three substances.
 State why pepsin is not produced in its active form.
 State the pH of the stomach contents.
 Explain why the pH of the stomach needs to be low.
 Name the substrate for the enzyme pepsin.
 Describe the effect of pH on the activity of pepsin.

15. Columnar cells secrete
mucus to protect stomach
lining from digestive
enzymes and stomach acid.
Inside the stomach…

16. Gastric glands in the folds of the stomach wall
contain cells which secrete:
mucus
digestive enzymes
acid
Enzyme producing cells secrete an inactive enzyme
which is activated after its release from the gland.
Pepsin (the activated enzyme) breaks down proteins
into peptides.
The enzyme cannot be active when it is secreted or
it would break down the cells!!

17. Acid secreting cells release hydrochloric acid.
- creates the conditions to activate pepsin
- provides optimum pH for digestion of protein (pH2).
Mucus secreting cells produce a slimy mucus to
protect stomach wall from damage.
All three of these cell types are in the gastric gland.

18. 9.5 Temperature and Protein Digestion
Today’s Learning Objectives:
 Explain why egg white suspension has a cloudy
appearance.
 Explain why egg white suspension clears when acted
on by pepsin.
 Describe an experiment to show the effect of
temperature on the activity of pepsin.
 State how experiments can be made more reliable.
 State why investigations should always be
evaluated.

19. 9.6 Absorption Process
Today’s Learning Objectives:
 Define the term ‘absorption’.
 Explain the importance of molecular size in the
absorption of food from the alimentary canal.
 Describe a visking tubing experiment to
demonstrate absorption.
 Describe the adaptations of the intestine for
absorption.
 Label a diagram of a villus.
 Describe how villi help to increase the surface area
and state which vessel absorbs glucose and amino
acids and which absorbs the products of fat
digestion.

20. The Small Intestine

21. Villi are finger like folds in the surface of the small
intestine

22. The Villi
Thin
epithelium
Blood
capillary
Tiny lymphatic
vessel (lacteal)
Enzyme
secreting gland
- Glucose and amino acids, transported in the blood stream.
- Fats transported in the lymphatic system.

23. 9.7 Where it all Goes
Today’s Learning Objectives:
 Name the organ in the body which regulates the
glucose and amino acids in the bloodstream.
 Describe the fates of excess glucose molecules and
amino acid molecules.
 Describe the fates of glucose molecules and amino
acid molecules when they are used in the body.
 Name the fluid which transports absorbed food
molecules from a lacteal.
 Describe three possible fates for the products of
digested fat molecules in the body.
 State what the main contents of the large intestine
are.
Describe absorption and elimination in the large
intestine.

24. The Liver
Hepatocytes, liver cells, process incoming nutrients and produce
bile, a fat emulsifier, as well as store vitamins and detoxify the
blood.

25. The liver…
- regulates glucose by allowing all that is required to
pass into the general bloodstream.
- excess glucose stored in the liver as glycogen and
released as the body needs it (large glucose
excesses are converted to fat and stored elsewhere
in the body.)
- allows as much amino acids as required to enter
blood stream. Excess molecules may be converted to
urea and later removed by kidneys.
- transports vitamins and minerals in bloodstream,
via liver cells. Excess vitamins or minerals are either
stored or excreted.

26. Large Intestine
By this point only indigestible
material and water remains.
The large intestine absorbs
water and remaining material
is excreted as faeces.

27. DigestiveSystem