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Science at key stage 3    (Year 8)

Unit 8B: Respiration
Section 10: How are inhaled and exhaled air different?

QCA

Objectives
Children should learn:
  • to make comparisons between the composition of inhaled and exhaled air
  • to present findings in a suitable format
  • to discuss and respond to initial ideas and information, carry out the task and then review and refine ideas

Activities

Outcomes
Children:
  • Ask pupils to use what they know about respiration to predict the differences between inhaled and exhaled air.
  • Show pupils how to demonstrate changes in oxygen concentration, eg length of time a candle burns in exhaled air compared to normal air, volume changes when oxygen is absorbed by alkaline pyrogallate. Ask pupils to investigate other changes in the air as they breathe in and out, eg presence of more carbon dioxide in expired air, pupils breathe onto cold mirrors or glass and test the moisture with cobalt chloride paper. Discuss the results with the pupils. Ask pupils to use reference sources to present their findings, including a table of changes in composition of air when it is breathed. Relate this to knowledge of respiration, deciding whether their predictions were correct.
  • While the pupils are waiting for results, ask them to use reference sources to find out how aquatic animals and plants obtain oxygen from water.
  • describe the differences in the concentrations of oxygen, water vapour and carbon dioxide in inhaled and exhaled air
  • present their results in a table which relates their findings to other data about the composition of the air and their knowledge of respiration

Points to note
  • Pupils will have used the lime water test for carbon dioxide in unit 7E 'Acids and alkalis' and unit 7F 'Simple chemical reactions', and hydrogencarbonate indicator earlier in this unit.

    • Safety

    • pyrogallic acid (benzene 1,2,3 triol) can be dissolved in saturated sodium hydrogencarbonate to produce a less hazardous solution, with a lower pH than that commonly used. Pupils require eye protection during use. If pupils breathe into lime water, eye protection and sterilised mouthpieces are required

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. 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