Ecosystems, abiotic and biotic factorsEdexcel A-Level Biology A: Subtopic test

1. 1
   A school pond in a woodland contains common frogs, smooth newts, water beetles, dragonfly larvae, pondweed, algae and many microorganisms. The pond water has a pH of 6.8 and its temperature changes with the seasons.

   (a)

   Which term describes all the living organisms of all the different species in the pond?

   [1 mark]

   • AA population
   • BAn ecosystem
   • CA community
   • DA habitat

   (b)

   Which term describes all the smooth newts living in the pond at the same time?

   [1 mark]

   • AA population
   • BA community
   • CA habitat
   • DA niche

   (c)

   Explain why the pond is described as an ecosystem and not just as a community.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   On a rocky shore two species of barnacle form separate bands. Chthamalus lives high on the shore, which is covered by sea water only at the highest tides. Semibalanus lives lower on the shore, which is covered by sea water for most of the time. Ecologists removed Semibalanus from the lower shore, and Chthamalus then settled and grew there. Semibalanus grows faster than Chthamalus and covers the rock. When the ecologists removed Chthamalus from the upper shore, Semibalanus still failed to survive there.

   (a)

   Which term describes the effect of Semibalanus on Chthamalus on the lower shore?

   [1 mark]

   • AIntraspecific competition
   • BPredation
   • CMutualism
   • DInterspecific competition

   (b)

   Which factor best explains why Semibalanus is absent from the upper shore?

   [1 mark]

   • ACompetition for space with Chthamalus
   • BDrying out when it is exposed to air for long periods
   • CDisease caused by a parasite
   • DGrazing by limpets

   (c)

   Explain how both a biotic factor and an abiotic factor account for the distribution of the two species on the shore.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An ecologist is studying how the abundance of marram grass changes across a sand dune system, from the strand line (the top of the beach) to 200 m inland. She suspects that the water content and the salt content of the sand change across the dunes.

   (a)

   Describe how she could use quadrats and a transect to measure the distribution and abundance of marram grass.

   [3 marks]

   (b)

   Describe how she could collect and analyse data to decide whether the water content of the sand affects the abundance of marram grass, and explain one limitation of her conclusion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Red squirrels once lived throughout British woodland. Grey squirrels were introduced from North America in the nineteenth century. Both species feed mainly on tree seeds, but grey squirrels digest acorns and hazelnuts more efficiently, store more fat for the winter and so live at higher densities in broadleaved woodland. Grey squirrels are less efficient at feeding on the small seeds in conifer cones. Red squirrels now survive mainly in coniferous forests. Grey squirrels carry squirrelpox virus, which does not make them ill but usually kills red squirrels.

   (a)

   Using the concept of niche, explain why the numbers of red squirrels have fallen and why they now survive mainly in coniferous forests.

   [6 marks]

   (b)

   A forestry company proposes to plant 200 hectares of oak, a broadleaved tree with large acorns, next to a coniferous forest where red squirrels still live. Evaluate the likely effect on the abundance and distribution of the two species of squirrel, and suggest how the effect could be monitored.

   [6 marks]

   Total for question 4: 12 marks

End of questions