Ecosystems, populations and nichesAQA A-Level Biology: Subtopic test

1. 1
   A woodland contains oak trees, caterpillars, blackbirds, mites that live on the blackbirds, and fungi and bacteria in the soil. The woodland also has non-living components such as soil pH, light intensity and temperature.

   (a)

   Which is an example of a population?

   [1 mark]

   • AAll the organisms living in the woodland
   • BAll the blackbirds living in the woodland
   • CAll the blackbirds and caterpillars in the woodland
   • DThe oak trees and the soil in the woodland

   (b)

   Which is an abiotic factor in the woodland ecosystem?

   [1 mark]

   • ASoil pH
   • BCompetition for light between oak seedlings
   • CPredation of caterpillars by blackbirds
   • DParasitism of blackbirds by mites

   (c)

   Explain the difference between a community and an ecosystem.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two species of barnacle live on a rocky shore. Species X is found on the upper shore, where it is exposed to air and drying out for long periods. Species Y is found on the lower shore, which is covered by the sea for most of the time. When species Y was removed from an area of the lower shore, species X spread into that area and survived there. When species X was removed from the upper shore, species Y still did not survive there.

   (a)

   Which statement best describes the niche of species X?

   [1 mark]

   • AThe place where species X lives on the shore
   • BThe number of individuals of species X on the shore
   • CThe organisms that species X feeds on
   • DThe role of species X in the ecosystem, governed by its adaptation to abiotic and biotic conditions

   (b)

   Which is the biotic factor that limits species X on the lower shore?

   [1 mark]

   • AExposure to air
   • BWave action
   • CCompetition from species Y
   • DSalinity of the sea water

   (c)

   Explain why species X is found only on the upper shore.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a northern forest, the population of snowshoe hares rises and falls in a cycle. The population of lynx, which prey on the hares, follows the same cycle about a year later. The hares feed on young plant shoots and twigs.

   (a)

   Explain how an increase in the hare population leads to changes in the lynx population and then in the hare population.

   [3 marks]

   (b)

   A winter of unusually deep snow covers much of the plant food. Suggest how this abiotic factor could affect both populations.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Beavers build dams across a woodland stream. Behind each dam a pond forms. Trees in the flooded area die, so more light reaches the water. The water flow slows, the water temperature rises and the oxygen concentration falls. Some invertebrate species increase in number in the pond. Trout, which need cool, fast-flowing, oxygen-rich water, decrease in number.

   (a)

   Explain how the beaver population and the abiotic factors in the stream affect each other.

   [6 marks]

   (b)

   Explain, in terms of niche, why the trout population decreased and some invertebrate populations increased after the dams were built.

   [6 marks]

   Total for question 4: 12 marks

End of questions