Explain why a great biodiversity helps to keep an ecosystem stable.
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- reduces the dependence of one species on another (1)
- for food, shelter and the maintenance of the physical environment (1)
- so if one species is lost, others still have food and shelter / the community is less affected (1)
- Max 2
(a) Give one cause of pollution in water, one in air and one on land. (2) (b) Explain how pollution can reduce biodiversity. (1)
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- (a) all three correct (2); two correct (1):
- water: sewage / fertiliser / toxic chemicals
- air: smoke / acidic gases
- land: landfill / toxic chemicals
- (b) pollution kills plants and animals, so the number of species falls (1)
Peat bogs are destroyed to make garden compost. Explain the effects of this on biodiversity and on the atmosphere.
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- habitat area is reduced (1)
- so fewer species / less variety of plants, animals and microorganisms live there (1)
- decay or burning of peat releases carbon dioxide (into the atmosphere) (1)
(a) Name two gases in the atmosphere that are increasing and contribute to global warming. (2) (b) Describe one biological consequence of global warming. (1)
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- (a) carbon dioxide (1)
- methane (1)
- (b) loss of habitat / change in distribution of species / change in migration patterns (1)
Which is a positive human interaction in an ecosystem?
- Dumping waste in landfill
- A breeding programme for an endangered species
- Quarrying for stone
- Burning peat
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Answer: B B (1)
A government in a tropical country is deciding whether to allow a large area of rainforest to be cleared for cattle farms and crops for biofuels. Evaluate the environmental implications of deforestation and the conflicting pressures on maintaining biodiversity.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A balanced evaluation with both the benefits and the environmental costs explained, links made to biodiversity and carbon dioxide, and a justified conclusion. |
| 2 | 3–4 | Some benefits and some environmental costs given, with an attempt at explanation, but the evaluation is limited or has no conclusion. |
| 1 | 1–2 | Simple points about benefits or harm, without explanation. |
Indicative content
- benefits: land for cattle, rice and biofuel crops, which provides food, fuel and income
- habitat loss, so species lose food and shelter and biodiversity decreases
- fewer trees, so less carbon dioxide is removed by photosynthesis
- burning and decay of trees releases carbon dioxide, which contributes to global warming
- conflicting pressures: need for food, jobs and money versus protecting habitats and slowing global warming
- possible compromises: reducing deforestation, protecting rare habitats, using land already cleared
- a justified conclusion