1. 1
   A group of students studied an oak woodland ecosystem. They noticed that bluebells growing on the woodland floor flower and grow rapidly in early spring, before the oak trees are in full leaf. Grey squirrels in the woodland compete with red squirrels for food and nesting sites. Since grey squirrels were introduced, red squirrel numbers in many woodlands have declined sharply.

   (a)

   Which of the following best describes an ecosystem?

   [1 mark]

   • AA community of organisms of the same species living together
   • BThe interaction of a community of living organisms with the non-living parts of their environment
   • CA group of organisms belonging to the same species that can interbreed to produce fertile offspring
   • DThe physical location where organisms live, not including any living things

   (b)

   Bluebells growing and flowering rapidly before the oak canopy closes over is best explained as an adaptation that reduces competition with the oak trees for which resource?

   [1 mark]

   • ALight
   • BWater
   • CMineral ions
   • DSpace for root growth

   (c)

   Suggest two reasons why grey squirrels outcompeting red squirrels could reduce the population size of red squirrels in this woodland.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A garden pond contains pondweed, water fleas (small crustaceans), and goldfish. The pondweed produces glucose by photosynthesis. Water fleas feed on microscopic algae in the water, and goldfish feed on water fleas. One summer, a homeowner accidentally poured a small amount of garden fertiliser into the pond.

   (a)

   In this pond community, the pondweed is best classified as a...

   [1 mark]

   • APrimary consumer
   • BDecomposer
   • CPredator
   • DProducer

   (b)

   Which term describes the relationship whereby each species in the pond depends on other species for food or resources, so that removing one species could affect the whole community?

   [1 mark]

   • AAdaptation
   • BExtremophile
   • CInterdependence
   • DBiodiversity

   (c)

   Explain why accidentally adding fertiliser to the pond could affect the stability of this community.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of students investigated how the abundance of dandelion plants changed with distance from a hedge at the edge of a field. They placed a tape measure in a straight line from the hedge into the middle of the field. At intervals of 2 metres along the tape, they placed a 0.5 m × 0.5 m quadrat and counted the number of dandelion plants inside it. They found that dandelion numbers were low near the hedge and increased with distance from the hedge. In the same field, dandelions are eaten by rabbits, which are eaten by foxes.

   (a)

   Describe how the students could improve the reliability of their investigation into the distribution of dandelions in the field.

   [3 marks]

   (b)

   Using the information given, construct a food chain including dandelion, rabbit and fox, and use it to explain why a decrease in dandelion numbers close to the hedge could lead to a decrease in the number of foxes in that part of the field.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A grassland ecosystem contains grass, grasshoppers, small birds and a hawk that preys on the small birds. Ecologists measured the total dry biomass of organisms at each trophic level. They found that 100 000 kg of grass supported the community, and estimated that only around 10% of biomass is transferred from one trophic level to the next. When grass and other organisms die, decomposers break down the dead material.

   (a)

   Explain how the biomass of the grass is transferred to the hawk through the food chain, and explain why the biomass of organisms decreases at each successive trophic level.

   [6 marks]

   (b)

   Explain the role of decomposers in this grassland ecosystem, and explain how temperature and the availability of water and oxygen affect the rate at which dead grass and other organic material decay.

   [6 marks]

   Total for question 4: 12 marks

End of questions