1
Triple onlyHigher tier
[2 marks]A river contains many bloodworms and sludgeworms but no stonefly nymphs or freshwater shrimps. What does this suggest about the water?
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- it is polluted (1)
- with low oxygen levels / for example sewage (1)
2
Triple onlyHigher tier
[4 marks]Evaluate the use of lichens as indicator species to assess air quality, compared with measuring the concentration of sulfur dioxide with a meter.
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- lichens are cheap / easy / need no special equipment (1)
- they show the effect of pollution over a long period of time (1)
- but other factors, such as habitat or temperature, may affect lichens (1)
- they do not give an accurate or quantitative measure of pollution, whereas a meter gives a precise value for sulfur dioxide (1)
3
Triple only
[4 marks]Explain how (a) vacuum packing and (b) adding salt each preserve food.
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- vacuum packing removes oxygen (1)
- microorganisms need oxygen for aerobic respiration, so decomposition is slower (1)
- salt removes water from the microorganisms by osmosis / reduces available water (1)
- microorganisms need water to grow and reproduce (1)
4
Triple only
[3 marks]A gardener turns the compost heap regularly and keeps it moist but not waterlogged. Explain why this speeds up decomposition.
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- turning adds oxygen to the heap (1)
- decomposers need oxygen for aerobic respiration (1)
- decomposers need water, but waterlogging fills the air spaces so there is less oxygen (1)
5
Triple only
[2 marks]A sample of leaves had a mass of 20.0 g. After 5 days its mass was 14.0 g. Calculate the mean rate of decay in g per day.
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- change in mass = 20.0 − 14.0 = 6.0 g (1)
- 6.0 ÷ 5 = 1.2 g per day (1) award 2 marks for a correct answer with no working