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Science at key stage 3    (Year 8)

Unit 8A: Food and digestion
Section 11: b. What do digestive enzymes do?

QCA

Objectives
Children should learn:
  • to identify factors relevant to a particular context
  • to plan how to control variables
  • to explain their results using knowledge of the human digestive system
  • to show relationships between ideas by using links that show purpose and reservation

Activities

Outcomes
Children:
  • Remind pupils of the range of food types with large molecules and explain that in addition to enzymes the conditions inside the gut assist the breakdown of large molecules, eg body temperature. Ask the pupils to discuss what other substances are found in the stomach. After the discussion inform the pupils that hydrochloric acid is produced by the lining of the stomach.
  • Provide them with an opportunity to investigate the action of a particular enzyme, eg trypsin acting on the gelatine of exposed and developed black-and-white photographic film; protease acting on albumen.
  • Ask pupils to suggest what might affect how well the enzyme digests the food, eg pH, temperature, and help them to plan an investigation, identifying what they are going to measure and which variables they will need to control. Ask pupils to produce an account of their investigation, relating what they found out to the conditions in the gut.
  • suggest relevant variables, eg pH, temperature
  • identify a way to keep variables, eg temperature, constant
  • identify the conditions under which digestion occurs, eg at a temperature of 37?C, and relate these to their results

Points to note
  • At this stage, pupils do not need to know the names of specific digestive enzymes, although some pupils might find these out for themselves.
  • In unit 7E 'Acids and alkalis' pupils may have found out about the use of acid in the human digestive system.
  • The effect of pH changes on enzyme activity could be monitored using ICT.
  • Extension: pupils could find out which is the best washing powder for an egg yolk stain, eg biological or non-biological. Be aware that some pupils may be allergic to biological washing powders.

    • Safety

    • pupils' plans must be checked for health and safety before practical work begins. Remind pupils how to safely heat test tubes of acid and other substances

Sections in this unit

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This unit is divided into sections. Each section contains a sequence of activities with related objectives and outcomes. You can view this unit by moving through the sections or print/download the whole unit.
1. a. What's in food and why is it important?
2. b. What's in food and why is it important?
3. c. What's in food and why is it important?
4. a. Which foods provide a balanced diet?
5. b. Which foods provide a balanced diet?
6. c. Which foods provide a balanced diet?
7. Checking progress
8. a. What happens to food inside the digestive system?
9. b. What happens to food inside the digestive system?
10. a. What do digestive enzymes do?
11. b. What do digestive enzymes do?
12. Where are the products of digestion used?
13. Reviewing work