Question 1
Describe the effects of untreated sewage on a river.
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- contains nitrates / ions so algae and plants grow quickly (1)
- contains organic matter so decomposers / bacteria use oxygen (1)
- less oxygen so fish and other animals die (1)
- may contain disease-causing microorganisms / pathogens (1)
- Max 3
- ignore 'pollutes the river' unqualified
Question 2
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanExcess fertiliser from fields is washed into a lake. Explain how this can cause the death of fish in the lake.
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- increased nitrate / ion availability (1)
- producers / algae grow faster (1)
- algal bloom blocks light so plants below die (1)
- increased decomposition (of dead producers) (1)
- increased aerobic respiration by decomposers / bacteria (1)
- dissolved oxygen falls (1)
- fish die as they need dissolved oxygen (1)
- Max 5
- reject algae use up the oxygen
Question 3
Plastic waste is non-biodegradable. (a) State what is meant by non-biodegradable. [1] (b) Describe two effects of plastic waste on aquatic ecosystems. [2]
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- (a) cannot be broken down by microorganisms / decomposers (1)
- (b) animals swallow plastic, which blocks the gut / they starve (1)
- animals become tangled and drown / cannot move or feed (1)
- plastic breaks into small pieces that enter food chains (1)
- Max 2 for part (b)
Question 4
Describe two effects of non-biodegradable plastics on land.
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- landfill sites fill up as plastic does not rot (1)
- animals eat plastic or become trapped (1)
- builds up in soil / releases harmful chemicals (1)
- Max 2
Question 5
Which activity releases methane into the atmosphere?
- Burning petrol in cars
- Cattle digesting food
- Photosynthesis in forests
- Making cement
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Answer: B (1)
Question 6
Describe the sources of carbon dioxide and methane, and explain how they cause the enhanced greenhouse effect and climate change.
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- carbon dioxide from burning fossil fuels / burning forests (1)
- methane from cattle / rice paddies / landfill (1)
- Earth re-radiates energy as infrared radiation (1)
- gases trap this heat in the atmosphere; more gases means more heat trapped (1)
- average temperature rises, causing climate change (1)
- reject reference to the ozone layer