1. 1
   On the African savanna, grass is eaten by zebras, which are in turn hunted and eaten by lions, forming the food chain: grass -> zebra -> lion.

   (a)

   In the food chain grass to zebra to lion, what trophic level does the zebra occupy?

   [1 mark]

   • AProducer
   • BPrimary consumer
   • CSecondary consumer
   • DDecomposer

   (b)

   Why is grass classified as a producer in this food chain?

   [1 mark]

   • AIt converts light energy into chemical energy by photosynthesis
   • BIt obtains energy by eating other organisms
   • CIt breaks down dead organic matter for energy
   • DIt transfers energy directly to the lion

   (c)

   Explain the role that decomposers play in this savanna ecosystem, and why this role is important.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Ecologists studying a pond record the following feeding relationships: algae are eaten by both tadpoles and water snails; tadpoles and water snails are both eaten by perch; and perch are eaten by herons. One year, a disease causes the perch population in the pond to crash dramatically.

   (a)

   In the pond food web, algae are eaten by tadpoles and by water snails; tadpoles and water snails are both eaten by perch (a fish); perch are eaten by herons. What trophic level is the perch?

   [1 mark]

   • AProducer
   • BPrimary consumer
   • CSecondary consumer
   • DTertiary consumer

   (b)

   Based on this food web, what would you expect to happen to the heron population immediately after the perch population crashes?

   [1 mark]

   • AThe heron population would decrease because algae numbers would fall
   • BThe heron population would increase, as competition for algae is reduced
   • CThe heron population would be unaffected, as herons do not rely on perch
   • DThe heron population would decrease, as its main food source has declined

   (c)

   Explain why this food web gives a more realistic picture of the pond's feeding relationships than a single food chain, such as algae -> tadpoles -> perch -> herons, would on its own.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer is deciding how to make the most efficient use of his cereal crop. He can either sell the cereal crop directly for people to eat, or use it as feed for cattle, which are later slaughtered and sold as beef for people to eat.

   (a)

   Explain why only about 10% of the energy taken in by the cattle is transferred to the next trophic level when the cattle are eaten.

   [3 marks]

   (b)

   Explain why it would provide more energy for the human population if people ate the cereal crop directly, rather than feeding it to cattle and then eating the beef.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Marine biologists study the food chain: phytoplankton -> zooplankton -> herring -> tuna. They construct a pyramid of biomass for this chain, which is a regular, upright pyramid shape. They compare this with a food chain involving a single large oak tree that supports thousands of caterpillars, for which a pyramid of numbers is constructed.

   (a)

   Explain why the transfer of energy along this marine food chain results in far less energy/biomass being available at the tuna's trophic level than at the phytoplankton's trophic level.

   [6 marks]

   (b)

   Explain why a pyramid of biomass for the phytoplankton to tuna food chain is a regular, upright pyramid shape, whereas a pyramid of numbers for the oak tree to caterpillars food chain might not be pyramid-shaped.

   [6 marks]

   Total for question 4: 12 marks

End of questions