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Science at key stage 3    (Year 8)

Unit 8B: Respiration
Section 3: c. How do cells use the food molecules absorbed after digestion?

QCA

Objectives
Children should learn:
  • that respiration is the sum of the chemical reactions which release energy from food molecules

Activities

Outcomes
Children:
  • Remind pupils of work they did in earlier units on fuels and, by questioning, establish that when fuels burn they react with oxygen and release energy. Demonstrate this using 2.5cm of icing sugar in a tin-can 'bomb', igniting the fine powder with the flame of a candle and showing that this type of dust explosion can blow off the can lid. Emphasise that the chemical reaction in cells is much more controlled than the dramatic demonstration. Explain that, although burning does not occur, a similar reaction takes place between glucose and oxygen in the cells of the body and that this is aerobic respiration.
  • recognise that oxygen is needed for aerobic respiration
  • state that glucose is used for energy release
  • identify differences between reactions in cells and burning, eg in the cell the release of energy is controlled

Points to note
  • Pupils will have explored burning fuels to release energy in unit 7I 'Energy resources'. In unit 7F 'Simple chemical reactions' they will also have explored the production of carbon dioxide and water during the combustion of fuels containing carbon and hydrogen.
  • The analogy with burning fuels is useful. However, pupils need to be aware that 'fuels' used by cells do not 'burn'.

    • Safety

    • screens and eye protection should be used and pupils should be seated 2-3 metres away

Sections in this unit

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1. a. How do cells use the food molecules absorbed after digestion?
2. b. How do cells use the food molecules absorbed after digestion?
3. c. How do cells use the food molecules absorbed after digestion?
4. d. How do cells use the food molecules absorbed after digestion?
5. a. How does the oxygen needed for respiration reach the tissues of the body?
6. b. How does the oxygen needed for respiration reach the tissues of the body?
7. What happens to the oxygen when it reaches the cells?
8. Checking progress
9. What is the role of the lungs?
10. How are inhaled and exhaled air different?
11. a. Do other organisms respire in a similar manner?
12. b. Do other organisms respire in a similar manner?
13. Reviewing work