The document provides information about the human digestive system and enzymes. It discusses how the digestive system breaks down large food molecules, the sites where digestive enzymes are produced, and the specific enzymes involved in digesting carbohydrates, proteins and lipids. It also addresses how enzymes work using the lock and key model, and factors that affect enzyme activity such as temperature and pH.

1. AQA 4.2
ORGANISATION
4.2.2
Animal tissues, organs and organ systems

2. 4.2.2.1 Human digestive
system- specification
• Cells are the basic building blocks of all living
organisms.
• A tissue is a group of cells with a similar structure
and function.
• Organs are aggregations of tissues performing
specific functions.
• Organs are organised into organ systems, which
work together to form organisms.

3. 4.2.2.1 The human digestive
system - specification
• This section assumes knowledge of the digestive system studied in Key
Stage 3 science.
• The digestive system is an example of an organ system in which several
organs work together to digest and absorb food.
• Students should be able to relate knowledge of enzymes to Metabolism.
• Students should be able to describe the nature of enzyme molecules and
relate their activity to temperature and pH changes.
• Students should be able to carry out rate calculations for chemical
reactions.
• Enzymes catalyse specific reactions in living organisms due to the shape of
their active site.

4. Digestive System LOs
• Recall the role of the digestive system, and the purpose of digesting
food
• State the sites of enzyme production for amylases, proteases and
lipases
• Know that amylase is a carbohydrase
• Construct simple word equations for the reactions of enzymes
• Link the products of digestion to their uses
• Know where bile is produced and stored
• Explain how bile is important for efficient digestion

5. STARTER: Place in order of smallest
to largest
organism
organ
system
tissues
cells
organssmallest
largest

6. organism
organ
system
tissues
cells
organs
smallest
largest

7. The role of the digestive
system
The job of the digestive system is the break
down large insoluble food molecules into
small soluble molecules.
These can then be absorbed through the
walls of the small intestine into the blood.

8. Digestion quiz

9. Complete sheet as we go through the next few slides

10. The digestive system organs

11. The digestive system organs

12. Sites of enzyme production

13. Enzyme reactions

14. Enzymes
Enzymes are chemicals which break the larger
molecules down into smaller molecules. There are three
types of enzymes that you need to know about.

15. Enzymes
• Carbohydrase chops carbohydrates into
smaller sugar molecules.
The three types of
enzymes are:
• Protease cuts proteins into the soluble amino
acids.
• Lipase breaks fats down into the smaller
fatty acids and glycerol.

16. Proteins are digested in the stomach by an enzyme
called Protease. This enzyme needs to work in an
acidic environment. Protease breaks proteins
(chains of different molecules) down into up to 20
different amino acids (four of which are shown).
Proteins digestion
Protease
Folded up protein
chain
Amino
acids

17. Carbohydrates are chains of identical sugar
molecules. The enzyme called Carbohydrase
breaks the chemical bonds between the individual
sugar molecules (called glucose) as part of
digestion.
Starch/ carbohydrates
Carbohydrase
Long
carbohydrate
Small
sugar

18. Fats are digested in two stages:
•Firstly bile (released by the gall bladder) allows
the fat to “mix” with water by breaking the fat up
into smaller droplets. This is called emulsification.
•Secondly, an enzyme called Lipase breaks the fats
down into the smaller fatty acid molecules and
glycerol.
Bile
Lipase
+
Fat
Fatty
acid
Glycerol
Fats

19. Enzymes of digestion

20. Word equations for the reactions of enzymes

22. • Challenge questions: If lipase is
added to some milk to digest the milk
fats, what will happen to the pH of the
milk? How would you test for this?
_________________________________________
_________________________________________
_________________________________________
_________________________________________
_________________________________________

23. Match the reactant

24. Enzymes; uses of products of
digestion; bile - specification
• Students should be able to use the ‘lock and key theory’ as a simplifed model to explain enzyme action.
• Students should be able to recall the sites of production and the action of amylase, proteases and lipases.
• Students should be able to understand simple word equations but no chemical symbol equations are
required.
• Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.
• Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down
starch.
• Proteases break down proteins to amino acids.
• Lipases break down lipids (fats) to glycerol and fatty acids.
• The products of digestion are used to build new carbohydrates, lipids and proteins. Some glucose is used in
respiration.
• Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the
stomach. It also emulsi es fat to form small droplets which increases the surface area. The alkaline
conditions and large surface area increase the rate of fat breakdown by lipase.

25. Enzymes LOs
• Recall the word equations for the reactions of enzymes
• Know that enzymes are proteins with a specific shaped
active site
• Use the 'lock and key' model to explain enzyme action
• Explain how the activity of enzymes are affected by
temperature and pH
• Investigate the effect of pH on the rate of reaction with
amylase.

26. Starter: write the correct enzyme name on the arrow for
each reaction
proteasecarbohydrase lipase
Lipids fatty acids + glycerol
starch simple sugars
proteins amino acids

27. Starter: write the correct enzyme name on the arrow for
each reaction
protease
carbohydrase
lipase
Lipids fatty acids + glycerol
starch simple sugars
proteins amino acids

28. Enzymes structure and function
• Enzymes are proteins
• They have a specific shaped active site
• A specific enzyme can only fit a specific molecule
into its active site
• So different enzymes will catalyse different
reactions

29. How enzymes work

30. What happens at the active site?
In the same way that a key fits into a lock, so a
substrate is thought to fit into an enzyme’s active site.
The enzyme is the lock, and the reactant is the key.
enzyme
reactant
+
enzyme-reactant
complex
↔
products
enzyme
+↔
+ ↔ ↔ +

31. The lock and key model

32. Lock and Key model
• We use the 'lock and key' model to explain
enzyme action

33. Name the structure

34. Enzymes: true or false?

35. Factors affecting enzymes
If the temperature and pH changes sufficiently beyond
an enzyme’s optimum, the shape of the enzyme
irreversibly changes.
normal denatured
heat
pH
This affects the shape of the active site and means that
the enzyme will no longer work.
When this happens the enzyme is denatured.

36. Enzymes and pH

37. Enzymes and temperature

38. Enzymes and temperature

39. Enzyme inhibitors

40. Identifying enzyme terms

41. • Required practical activity 3:
• use qualitative reagents to test for a range of
carbohydrates, lipids and proteins.
• To include: Benedict’s test for sugars; iodine test for
starch; and Biuret reagent for protein.
• AT skills covered by this practical activity: biology AT 2.
• This practical activity also provides opportunities to
develop WS and MS. Details of all skills are given in
Key opportunities for skills development.

42. • Required practical activity 4:
• investigate the effect of pH on the rate of reaction of amylase enzyme.
• Students should use a continuous sampling technique to determine the
time taken to completely digest a starch solution at a range of pH
values. Iodine reagent is to be used to test for starch every
• 30 seconds. Temperature must be controlled by use of a water bath or
electric heater.
• AT skills covered by this practical activity: biology AT 1, 2 and 5.
• This practical activity also provides opportunities to develop WS and
MS. Details of all skills are given in
• Key opportunities for skills development.

49. Did iodine go brown for the presence of starch? (Tick or cross)
after iodine stays orange-brown.
Time (s) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 260
pH
pH
pH
pH
pH

50. pH of solution Time taken for amylase to completely break down
the starch in seconds (s)