Populations in ecosystemsAQA A-Level Biology: Topic test

20 questions, 54 marks

AQA A-Level Biology

Populations in ecosystems topic test

Total 54 marks

Name

Class

Date

1
A freshwater pond contains pondweed, water snails, sticklebacks, dragonfly larvae and bacteria in the mud. The water has a mean temperature of 14 °C and a pH of 7.2.
(a)
Which of the following is an abiotic factor in this pond?
[1 mark]
ADragonfly larvae
BWater pH
CPondweed
DBacteria in the mud
(b)
Which term describes all of the living organisms in the pond together?
[1 mark]
APopulation
BHabitat
CEcosystem
DCommunity
(c)
Explain the difference between a community and an ecosystem.
[2 marks]
Total for question 1: 4 marks
2
In an oak woodland about 60 pairs of great tits breed each year, although each pair lays about nine eggs. The number of breeding pairs varies little from year to year. Great tits nest in holes in trees, and the number of suitable holes is limited. Blue tits also nest in these holes and eat the same caterpillars.
(a)
Which term describes the stable population size of great tits that the woodland can support?
[1 mark]
ACarrying capacity
BNiche
CBiodiversity
DClimax community
(b)
Which statement about competition for the nest holes is correct?
[1 mark]
ACompetition between great tits is interspecific, and between great tits and blue tits is intraspecific
BCompetition between great tits is intraspecific, and between great tits and blue tits is intraspecific
CCompetition between great tits is intraspecific, and between great tits and blue tits is interspecific
DCompetition between great tits is interspecific, and between great tits and blue tits is interspecific
(c)
Explain why the number of breeding pairs stays about the same each year even though each pair lays about nine eggs.
[2 marks]
Total for question 2: 4 marks
3
An ecologist estimates the number of garden snails living in a walled garden. She collects 64 snails, marks the shell of each with a small spot of paint and releases them where they were found. The next day she collects 58 snails, of which 16 are marked.
(a)
Calculate the ecologist's estimate of the number of snails in the garden.
[3 marks]
(b)
State two assumptions made when using this method. Explain how the estimate would change if the paint made marked snails more likely to be eaten by thrushes overnight.
[4 marks]
Total for question 3: 7 marks
4
A shallow lake in lowland England is slowly filling with silt and dead plant material. Moving from the lake centre to the drier edge there is open water with submerged pondweed, then water lilies, then reed swamp, then willow and alder woodland (carr), then oak woodland. A nature reserve manager wants to keep the reed bed because it is the only breeding site in the region for the bittern, a rare bird. Each winter a third of the reeds are cut and every ten years willow saplings are removed. Without this management, willow carr would replace the reed bed within about 30 years. Since management began 15 years ago, the number of breeding pairs of bittern has risen from 2 to 9. Reed bed has 14 plant species per 100 m² and willow carr has 21. Local thatchers buy the cut reeds, raising £18 000 a year, which pays for two wardens. Willow carr is common elsewhere in the region, but reed beds are rare.
(a)
Explain how the changes in the lake over time are an example of succession.
[6 marks]
(b)
Evaluate the manager's decision to manage succession in order to conserve the reed bed.
[6 marks]
Total for question 4: 12 marks
5
Common shrews and pygmy shrews live in the same area of grassland. Both eat invertebrates. Common shrews hunt mainly on the surface among leaf litter and take larger prey such as earthworms. Pygmy shrews hunt mainly in thicker vegetation and take smaller prey such as insects and spiders.
(a)
Which statement best describes the niche of a species?
[1 mark]
AThe area in which the species lives
BAll of the species living in one area
CThe role of the species in an ecosystem, determined by its adaptations to abiotic and biotic conditions
DThe number of individuals of the species that an area can support
(b)
Which statement about the two species of shrew is correct?
[1 mark]
AThey occupy different niches, because they differ in where they hunt and in the prey they take
BThey occupy the same niche, because they live in the same habitat
CThey form one population, because they live in the same grassland
DThey are in different communities, because they take different prey
(c)
Explain how the differences in their feeding allow both species to live together in the same grassland.
[2 marks]
Total for question 5: 4 marks
6
On a rose bush, the number of aphids rises rapidly in spring. A few weeks later the number of ladybirds, which eat aphids, rises. The number of aphids then falls, and some weeks after that the number of ladybirds falls.
(a)
What is the most likely reason that the number of ladybirds rises after the number of aphids?
[1 mark]
ALadybirds reproduce faster than aphids
BThe number of aphids is not affected by ladybirds
CLadybirds are not limited by any factor
DThe increased food supply lets ladybirds survive and breed, which takes time
(b)
A cold spell in June kills many aphids. This is an example of
[1 mark]
Aa biotic factor reducing population size by predation
Ban abiotic factor reducing population size
Cintraspecific competition
Dinterspecific competition
(c)
Explain why the number of aphids falls after the number of ladybirds rises, and why the number of ladybirds then falls.
[2 marks]
Total for question 6: 4 marks
7
A student thinks that wood sorrel, a woodland plant, grows best in shade. She studies an area of woodland of 600 m². She places twenty 0.5 m × 0.5 m quadrats at random positions in the area and counts the wood sorrel plants in each. She counts 46 plants in total. She then plans to investigate whether the distribution of wood sorrel is affected by light intensity, which decreases from the open edge of the wood to its dense, shaded interior.
(a)
Calculate an estimate of the total number of wood sorrel plants in the 600 m² area.
[3 marks]
(b)
Describe how the student could investigate the effect of light intensity on the distribution of wood sorrel.
[4 marks]
Total for question 7: 7 marks
8
The white-clawed crayfish is native to a chalk river in southern England. In the 1970s signal crayfish from North America were introduced to the river. Both species shelter under stones and in bank burrows and eat invertebrates, plants and dead material. Signal crayfish grow larger, are more aggressive and produce more young each year. They also carry a disease-causing organism that rarely harms them but kills white-clawed crayfish. In 1990 there were about 120 white-clawed crayfish per 100 m of bank and no signal crayfish. By 2020 there were about 4 white-clawed and 310 signal crayfish per 100 m. Burrowing by signal crayfish erodes the banks and damages a farmer's field. Restaurants buy signal crayfish from licensed trappers. Conservationists have moved 800 white-clawed crayfish to 12 isolated ponds and trap 40 000 signal crayfish a year from the river, but signal crayfish numbers recover within two years.
(a)
Explain why the population of white-clawed crayfish fell and the population of signal crayfish rose.
[6 marks]
(b)
Evaluate the conservation measures used on this river, taking account of the needs of local people.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).