1[1 mark]
Respiration is an exothermic reaction. What does this mean?
- Energy is transferred to the surroundings
- Energy is taken in from the surroundings
- Oxygen is used up
- Carbon dioxide is produced
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Answer: A A (energy is transferred to the surroundings)
2[2 marks]
Write the word equation for aerobic respiration.
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- glucose + oxygen (1)
- → carbon dioxide + water (1) allow correct balanced symbol equation
3[4 marks]
Describe how a respirometer can be used to compare the rate of respiration of germinating seeds at two different temperatures.
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- place seeds in a tube with soda lime / carbon dioxide absorber, connected to a capillary tube with a drop of coloured liquid (1)
- place the tubes in water baths at the two temperatures (1)
- measure the distance the liquid moves in the same time (1)
- control variables, for example the same mass of seeds and the same time (1)
- repeat and calculate a mean (1)
- Max 4
4[3 marks]
In a respirometer experiment, the coloured liquid moved 12 mm in 4 minutes at 20 °C and 30 mm in 5 minutes at 30 °C. Calculate the rate of movement at each temperature in mm per minute and state how many times faster the rate of respiration was at 30 °C.
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- 20 °C: 12 ÷ 4 = 3 mm per minute (1)
- 30 °C: 30 ÷ 5 = 6 mm per minute (1)
- twice as fast / 2 times (1)
5[6 marks]
Compare the process of aerobic respiration with the process of anaerobic respiration.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A detailed comparison covering oxygen requirement, energy released and the products in animals and in plants or yeast. Similarities and differences are clearly linked. |
| 2 | 3–4 | Some similarities and differences are described, but the comparison is incomplete, for example products for only one type of organism. |
| 1 | 1–2 | Basic statements about one or both types of respiration, with little or no comparison. |
Indicative content
- both are exothermic reactions that release energy from glucose
- both happen in living cells to release energy for metabolic processes
- aerobic respiration needs oxygen, anaerobic respiration does not
- aerobic respiration breaks glucose down completely, anaerobic is an incomplete breakdown
- aerobic releases much more energy per glucose molecule
- aerobic products are carbon dioxide and water
- anaerobic products in animals: lactic acid
- anaerobic products in plants and yeast: ethanol and carbon dioxide