Exam questions · Biology
Human Impact on Ecosystems
- 16 exam questions
- 51 marks
- 16 quick checks
Fish Farming, Introduced Species and Eutrophication
Just this lesson-
1 State [1 mark]
State what is meant by a non-indigenous species.
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Model answer
A species that has been introduced into an area where it does not naturally live (is not native).
Mark scheme
- A species introduced to an area where it is not naturally found — 1 mark
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2 Give [2 marks]
Fish farming has some benefits and some problems. Give one benefit and one problem of fish farming.
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Model answer
Benefit: a reliable source of protein, or it reduces overfishing of wild fish. Problem: waste pollutes the water, or parasites and disease spread to wild fish, or escaped fish breed with wild fish.
Mark scheme
- A benefit, such as protein supply or less overfishing — 1 mark
- A problem, such as pollution, disease spread or escapes — 1 mark
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3 Explain [3 marks]
Explain how fish farming can reduce the biodiversity of the sea around the farm.
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Model answer
Uneaten food and faeces from the farm add nutrients to the water, which can cause eutrophication and use up the oxygen, so organisms in the water and on the seabed die. Parasites and diseases spread from the crowded farmed fish to wild fish and may kill them. Farmed fish that escape can compete with wild fish and breed with them, which reduces their genetic variation.
Mark scheme
- Waste adds nutrients and causes eutrophication or pollution — 1 mark
- Parasites or disease spread to wild fish — 1 mark
- Escaped fish compete or breed with wild fish — 1 mark
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4 Explain [3 marks]
The graph shows the numbers of red squirrels and grey squirrels in Britain. Grey squirrels were introduced from North America. Explain why the number of red squirrels fell after the grey squirrels were introduced.
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Model answer
Grey squirrels and red squirrels compete for the same food, and the grey squirrels, which are bigger, are better at getting it, so the red squirrels have less to eat and fewer survive. Grey squirrels also carry squirrelpox virus, which does not harm them but kills red squirrels.
Mark scheme
- The two species compete for the same food (resources) — 1 mark
- The grey squirrels are better competitors, so the red squirrels get less food and decline — 1 mark
- Grey squirrels carry a disease (squirrelpox) that kills red squirrels — 1 mark
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5 Complete [2 marks]
The sentences below describe the stages of eutrophication, but they are in the wrong order. A: Fish die. B: Bacteria use up the oxygen in the water. C: Fertiliser is washed into a pond. D: Plants die because light is blocked. E: Algae grow quickly and form a bloom. Write the letters in the correct order, starting with C.
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Model answer
C, E, D, B, A.
Mark scheme
- C, E, D in the correct order — 1 mark
- B, A at the end, in that order — 1 mark
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6 Explain [5 marks]
Explain how the use of fertiliser on a farm can lead to the death of fish in a nearby pond.
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Model answer
Rain washes nitrates and phosphates from the fertiliser into the pond. The extra minerals make the algae grow and reproduce quickly, which forms an algal bloom on the surface. The algae block the light, so plants beneath them cannot photosynthesise and die. Bacteria decompose the dead plants and algae, and use up the oxygen in the water as they respire. The fish do not get enough oxygen for respiration, so they die.
Mark scheme
- Fertiliser (nitrates or phosphates) is washed into the pond — 1 mark
- Algae grow quickly (algal bloom) — 1 mark
- Light is blocked, so plants die — 1 mark
- Bacteria decompose the dead material and use up oxygen — 1 mark
- Fish die from lack of oxygen — 1 mark
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7 Describe and explain [4 marks]
Source: Data from a lake over one year. March: algae 20 units, dissolved oxygen 11 mg per dm\(^3\). May: algae 85 units, oxygen 10 mg per dm\(^3\). July: algae 150 units, oxygen 8 mg per dm\(^3\). September: algae 40 units, oxygen 3 mg per dm\(^3\). Fertiliser was washed into the lake in April. Use the data to describe the changes in the lake and explain why the oxygen level was lowest in September.
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Model answer
The amount of algae rose from 20 units in March to a peak of 150 units in July, and then fell to 40 units in September, while the oxygen level fell steadily from 11 to 3 mg per dm\(^3\). The fertiliser made the algae grow quickly. The algae then died in late summer, and bacteria decomposed them, using up oxygen in respiration, so the oxygen level was lowest in September.
Mark scheme
- Algae increased to 150 units in July, then fell to 40 units — 1 mark
- Oxygen decreased from 11 to 3 mg per dm\(^3\) — 1 mark
- Fertiliser made the algae grow quickly, then they died — 1 mark
- Bacteria decomposed the dead algae and used up oxygen, so oxygen was lowest in September — 1 mark
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8 Evaluate [6 marks]
A company wants to set up a large salmon farm in a sea loch where many wild fish live. Evaluate the positive and negative effects of fish farming on the ecosystem and on people.
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Model answer
The farm would provide a lot of protein for people and reduce the pressure of overfishing on wild salmon, so wild stocks could recover. It would also provide jobs in the area. However, the waste from the farm, uneaten food and faeces, would fall to the seabed and could cause eutrophication and harm the organisms on the seabed. The crowded farmed fish could spread parasites such as sea lice and disease to the wild fish, and any that escape could breed with wild salmon and reduce their genetic variation. Wild fish are also caught to make feed. Overall, a farm could be a good way to feed people if it is carefully managed, with a good flow of water to remove waste and nets that stop escapes, but in a loch with many wild fish the harm to biodiversity could outweigh the benefits.
Mark scheme
- A positive effect on people: protein supply or jobs — 1 mark
- A positive effect on the ecosystem: less overfishing of wild fish — 1 mark
- A negative effect: waste causing pollution or eutrophication — 1 mark
- A negative effect: parasites or disease spread to wild fish — 1 mark
- A negative effect: escapes breeding with wild fish, or wild fish caught for feed — 1 mark
- A reasoned judgement, such as it depends on how well the farm is managed — 1 mark
Quick check
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1
Which of these is an example of a non-indigenous species in Britain?
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C: The grey squirrel
The grey squirrel was introduced from North America in the 1870s, whereas the red squirrel, badger and fox are native.
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2
What is the first stage in eutrophication?
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A: Nitrates and phosphates enter the water
Fertiliser or sewage enters the water first, which provides the extra minerals for the algae.
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3
Why do plants beneath an algal bloom die?
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D: Light cannot reach them for photosynthesis
The algae block the light, so the plants beneath cannot photosynthesise.
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4
What uses up the oxygen in a eutrophic pond?
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B: The bacteria decomposing dead material
Bacteria that decompose the dead plants and algae respire and use up the oxygen.
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5
Which is a benefit of fish farming?
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A: It reduces pressure on wild fish stocks
Farming fish gives a reliable food supply and means fewer wild fish need to be caught.
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6
Why might escaped farmed salmon harm a wild salmon population?
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C: They breed with and compete with wild fish
Escaped fish can breed with wild fish and compete with them, which can reduce the wild population's genetic variation.
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7
Why can a non-indigenous species spread quickly in a new place?
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D: It may have no natural predators or diseases
It often has no natural predators or diseases in its new home, so its population can grow fast.
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8
Cane toads were introduced to Australia to control beetles. Why was this a problem?
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B: They poisoned native predators and did not control the beetle
The toads did not control the beetles, and their poisonous skin killed native animals that ate them.
The Benefits of Maintaining Biodiversity
Just this lesson-
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.