1[1 mark]
Which is a negative effect of introducing a non-indigenous species to an area?
- It increases the number of native species
- It competes with native species so their numbers fall
- It always provides food for native species
- It increases biodiversity
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Answer: B it competes with native species so their numbers fall (1)
2[4 marks]
Fertiliser from a farm runs into a lake and the fish die. Explain how the fertiliser causes the fish to die.
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- fertiliser increases the nitrates in the water so algae grow rapidly / algal bloom (1)
- the algae block light so plants / algae below cannot photosynthesise and die (1)
- bacteria / decomposers feed on the dead material and increase in number, using up oxygen (1)
- fish die because there is not enough oxygen (1)
3[3 marks]
Explain how reforestation can benefit the environment.
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- restores habitats so biodiversity increases (1)
- trees absorb carbon dioxide by photosynthesis, reducing carbon dioxide in the atmosphere (1)
- tree roots hold soil so there is less soil erosion / flooding (1)
4
Triple only
[3 marks]Describe three biological factors that can reduce food security.
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- increasing human population needs more food (1)
- increasing animal farming / meat and fish consumption needs more land and resources because energy is lost between trophic levels (1)
- new pests and pathogens destroy crops / animals (1)
- environmental change caused by human activity reduces yields (1)
- sustainability issues such as land used for biofuels, or the cost of fertilisers, pesticides and feed (1)
- Max 3
5[6 marks]
Evaluate the positive and negative impacts of fish farming on biodiversity.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A balanced evaluation that gives several correct positive and negative impacts with explanations, and reaches a justified judgement. Scientific terms are used correctly. |
| 2 | 3–4 | Some positive and some negative impacts are given with some explanation, but the answer may be unbalanced or have no clear judgement. |
| 1 | 1–2 | One or two simple points are made, without explanation or balance. |
Indicative content
- positive: provides a food supply for a growing population
- positive: reduces overfishing so wild fish stocks and the species that feed on them are protected
- negative: waste and uneaten food pollute water and can cause eutrophication, so oxygen falls and organisms die
- negative: disease and parasites can spread from farmed fish to wild fish
- negative: escaped fish can compete or interbreed with wild fish, reducing genetic variety
- negative: fish may be fed on wild fish, and chemicals used can harm other organisms
- judgement: benefits depend on how well the farm is managed, for example controlling waste and preventing escapes