Populations, habitats and ecological studyEdexcel International A Level Biology: Subtopic test

1. 1
   A coastal sand dune system contains marram grass, rabbits, beetles, bacteria and many other species. The sand is salty, dry and low in nutrients, and the wind speed is high.

   (a)

   Which term describes all of the populations of the different species living and interacting in the sand dune system?

   [1 mark]

   • APopulation
   • BCommunity
   • CEcosystem
   • DHabitat

   (b)

   Which is an abiotic factor that affects the distribution of marram grass in the dunes?

   [1 mark]

   • ASalinity of the sand
   • BGrazing by rabbits
   • CPredation by beetles
   • DCompetition with other grasses

   (c)

   Distinguish between the habitat and the niche of marram grass in the dune system.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student estimates the population of daisies in a rectangular field measuring 40 m by 25 m. She places 20 quadrats, each 0.5 m by 0.5 m, at positions chosen using random coordinates. She counts a total of 85 daisies in the 20 quadrats.

   (a)

   Calculate the estimated population of daisies in the field.

   [1 mark]

   • A17 000
   • B4 250
   • C85 000
   • D1 700

   (b)

   Why did the student choose the positions of the quadrats using random coordinates?

   [1 mark]

   • ATo ensure that the quadrats are evenly spaced across the field
   • BSo that only the areas with the most daisies are sampled
   • CTo avoid bias in the positioning of the quadrats
   • DSo that the counts do not need to be repeated

   (c)

   Suggest two ways in which the student could make her estimate of the population more reliable.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student lays a 30 m line transect running from the lower shore to the upper shore of a rocky beach and places a quadrat at 2 m intervals along it. The percentage cover of the seaweed Fucus falls from 90% at the lowest position to 5% at the highest position. Going up the shore, the length of time each position is covered by seawater each day falls and the temperature of the rock surface on sunny days rises.

   (a)

   Explain why a line transect is more suitable than random sampling for this investigation.

   [3 marks]

   (b)

   Suggest how abiotic factors could explain the decrease in the cover of Fucus up the shore, and describe how the student should measure one abiotic factor at each quadrat to make the data valid.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   On a rocky shore, two species of barnacle live in different zones: Chthamalus on the upper shore and Semibalanus on the lower shore. When Semibalanus is removed from the lower shore, Chthamalus survives there. When Chthamalus is removed from the upper shore, Semibalanus does not colonise it, and individuals of Semibalanus placed there die because they cannot tolerate being out of the water for long periods.

   (a)

   Use the information to explain how both abiotic factors and interactions with other species determine the distribution of the two species of barnacle.

   [6 marks]

   (b)

   Describe how a student could investigate the distribution and abundance of the two species of barnacle across the shore and relate them to abiotic factors.

   [6 marks]

   Total for question 4: 12 marks

End of questions