Exam questions · Biology · Human Impact on Ecosystems
The Benefits of Maintaining Biodiversity
- 8 exam questions
- 25 marks
- 8 quick checks
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1 State [1 mark]
State what is meant by biodiversity.
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Model answer
The variety of different species of organisms (in an ecosystem or on Earth).
Mark scheme
- The variety of different species of organisms — 1 mark
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2 Give [2 marks]
Give two benefits to people of maintaining the biodiversity of rainforests.
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Model answer
Any two of: the rainforest plants may provide new medicines, there are wild relatives of crops with useful alleles, the forest provides timber and other materials, the trees absorb carbon dioxide and help to stabilise the climate, and it gives jobs in tourism.
Mark scheme
- First benefit — 1 mark
- Second benefit — 1 mark
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3 Explain [3 marks]
Explain why a woodland containing many species is more stable than a field containing only one crop.
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Model answer
In the woodland there are many food chains linked in a food web, so if one species declines the animals that fed on it can eat something else. A disease or pest that attacks one species cannot destroy the whole woodland. In the field, a single disease or pest could wipe out the only crop, and there are very few other species.
Mark scheme
- Many species means many food chains (more than one food source) — 1 mark
- If one species declines others can fill the gap, so the ecosystem keeps working — 1 mark
- A single pest or disease could destroy a monoculture — 1 mark
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4 Describe [4 marks]
Describe two ways in which an endangered animal species can be conserved.
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Model answer
One way is to make a nature reserve or national park, which protects the animal's habitat from development, farming and hunting. Another is captive breeding, in which zoos breed the animals and release the young back into the wild, which increases numbers. Other acceptable ways are laws that ban hunting and the trade in the animal, or restoring its habitat.
Mark scheme
- First method named (such as protected area, laws, captive breeding or habitat restoration) — 1 mark
- A description of how it helps the species — 1 mark
- Second method named — 1 mark
- A description of how it helps the species — 1 mark
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5 Explain [4 marks]
The diagram shows a hillside before and after trees were planted. Explain how planting trees on the hillside can reduce flooding and increase biodiversity.
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Model answer
The roots of the trees hold the soil together, so less soil is washed into the river, and the trees take up water from the soil, so less rain runs off quickly into the river, which reduces the risk of flooding. The trees also provide food and shelter, so animals and other plants can live there and the number of species increases.
Mark scheme
- Roots hold the soil (less erosion) — 1 mark
- Trees take up water, so less runs off into the river (lower flood risk) — 1 mark
- Trees provide food and shelter (habitat) — 1 mark
- So more species can live there, which increases biodiversity — 1 mark
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6 Calculate [2 marks]
A captive breeding programme was started for an endangered species. In 1995 there were 250 animals in the wild. By 2015 there were 700. Calculate the percentage increase in the wild population.
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Model answer
Change = \(700 - 250 = 450\). Percentage increase = \(450 \div 250 \times 100 = 180\%\).
Mark scheme
- \(450 \div 250\) — 1 mark
- 180% — 1 mark
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7 Explain [3 marks]
A company wants to clear part of a rainforest that scientists have not yet studied in detail. Explain why scientists want to protect the biodiversity of the forest.
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Model answer
The forest may contain species that provide new medicines or other useful chemicals, which would be lost if the species became extinct. It may have wild plants with alleles that could be bred into crops, so the gene pool is a resource for the future. The trees also take carbon dioxide from the air, and the forest holds the soil and water, so clearing it could affect the climate and cause floods.
Mark scheme
- There may be unknown species that could provide medicines or materials — 1 mark
- A large gene pool is a resource for future crops and for adapting to change — 1 mark
- Forests help to stabilise the climate and to protect the soil and water — 1 mark
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8 Evaluate [6 marks]
A government plans to replant a large area of cleared rainforest with a single fast-growing species of tree, to be cut for timber. Evaluate this plan as a way of increasing the biodiversity of the area.
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Model answer
Planting trees will help the area in some ways. The trees will take in carbon dioxide, hold the soil and reduce erosion and flooding, and the timber will provide jobs and income, which gives local people a reason to look after the forest. However, a plantation of one species is not a forest, and it will provide food and shelter for far fewer species than the original rainforest, so the biodiversity will be lower. A single species is also at risk of being wiped out by one disease. Cutting the trees for timber will remove the habitat again. A better plan would be to replant a mixture of native species and to cut only a few trees at a time, so that the habitat is kept. Overall, the plan would help the climate and the economy but would not fully restore biodiversity.
Mark scheme
- Benefit: trees take in carbon dioxide or reduce erosion and flooding — 1 mark
- Benefit: timber and jobs give local people an income — 1 mark
- A single species supports far fewer species than a natural forest, so biodiversity stays low — 1 mark
- A monoculture is at risk from a single disease — 1 mark
- Cutting the trees removes the habitat again, or a mix of native trees would be better — 1 mark
- A clear judgement that follows from the points — 1 mark
Quick check
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1
Which of these best describes global biodiversity?
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C: The variety of all the species on Earth
Global biodiversity is the variety of all the species on the whole Earth.
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2
Why is a habitat with many species usually more stable?
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A: There are many food chains, so it can cope if one species declines
There are many food chains, so if one species declines others can take its place and the system keeps working.
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3
Which medicine was first made from a chemical in willow bark?
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D: Aspirin
Aspirin was first made from a chemical found in willow bark.
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4
What is captive breeding?
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B: Breeding endangered animals in zoos or centres
Captive breeding means breeding endangered animals in zoos or centres, so that young can be released into the wild.
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5
How does reforestation help to reduce flooding?
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C: Trees take up water and their roots hold the soil
Roots hold the soil and trees take up water, so less rain runs quickly into rivers.
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6
A population grows from 50 to 200 animals. What is the percentage increase?
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A: 300%
The change is 150, and 150 divided by 50 is 3, which is 300%.
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7
Why might a plantation of one tree species not restore biodiversity?
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D: It supports far fewer species than a mixed forest
A single species provides food and shelter for far fewer species than a mixed native forest does.
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8
Which of these is a reason for keeping a large gene pool in wild crop relatives?
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B: They may carry useful alleles for breeding into crops
Wild relatives of crops may carry alleles, such as for disease resistance, that can be bred into the crops.