1. 1
   An ecologist is studying an African savanna grassland ecosystem. In this ecosystem, grass grows using energy from sunlight, zebras graze on the grass, and lions hunt and eat the zebras. The ecologist wants to describe the roles of each organism and how they are organised into a food chain.

   (a)

   An ecologist studies an African savanna grassland where grass is eaten by zebras, which are in turn hunted by lions. The grass makes its own food using sunlight, carbon dioxide and water. What term describes the role of the grass in this ecosystem?

   [1 mark]

   • AProducer
   • BPrimary consumer
   • CSecondary consumer
   • DDecomposer

   (b)

   In the savanna food chain grass to zebra to lion, what term describes the role of the lion?

   [1 mark]

   • AProducer
   • BPrimary consumer
   • CSecondary consumer
   • DDecomposer

   (c)

   Using the organisms described, write out the food chain for this savanna ecosystem and explain what the arrows between the organisms represent.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a freshwater pond ecosystem, pondweed is eaten by small insects, the insects are eaten by fish, and the fish are eaten by herons. Together, the pondweed, insects, fish, herons and decomposing bacteria in the pond form a community that is interdependent, meaning a change affecting one species can affect the others in the food web.

   (a)

   All of the pondweed, insects, fish and herons living in and around the pond, together with all of the other species present, make up what is described in ecology as the community. Which term describes just the pondweed population, the insect population, the fish population and the heron population considered separately from each other?

   [1 mark]

   • AHabitat
   • BPopulation
   • CNiche
   • DEcosystem

   (b)

   A local water company accidentally releases a pollutant that kills almost all of the small insects living in the pond, while leaving the pondweed, fish and herons directly unharmed. Based on the feeding relationships described, what is the most likely immediate effect on the fish population?

   [1 mark]

   • AThe fish population will increase because there is more pondweed available
   • BThe fish population will immediately become extinct
   • CThe fish population will be completely unaffected because fish do not depend on insects
   • DThe fish population will decrease because their main food source has been greatly reduced

   (c)

   Explain how the loss of most of the pond's insect population, caused by the pollutant, could also eventually affect the heron population and the pondweed population, even though herons and pondweed were not directly harmed by the pollutant.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In an Arctic ecosystem, scientists have recorded the population sizes of snowshoe hares and the Canada lynx that preys on them over many decades. The data show that hare numbers rise for several years and then fall sharply; lynx numbers also rise and fall repeatedly, but each lynx population peak occurs shortly after a hare population peak, and each lynx population low occurs shortly after a hare population low.

   (a)

   Describe the pattern shown by these predator-prey population changes over time.

   [3 marks]

   (b)

   Explain why the snowshoe hare and Canada lynx populations show this repeating, cyclical pattern, including why the lynx population changes occur slightly after the corresponding hare population changes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In a tropical rainforest ecosystem, a wide variety of trees, insects, birds and mammals depend on each other through a complex food web, and decomposer organisms such as fungi and bacteria break down dead leaves, fallen wood and animal remains, releasing nutrients back into the soil for the trees and other producers to absorb and reuse.

   (a)

   Explain the role of decomposers in this ecosystem and discuss what would be likely to happen to the rest of the food web if decomposer organisms were removed from the rainforest.

   [6 marks]

   (b)

   Conservationists are considering introducing a new predator species into the rainforest to control the population of a particular herbivorous mammal that has become unusually abundant. Discuss, using the concept of interdependence within a food web, the range of effects that introducing a new predator species could have on the rainforest ecosystem, and evaluate why such an introduction carries significant ecological risk even if the intended aim (controlling the herbivore population) is achieved.

   [6 marks]

   Total for question 4: 12 marks

End of questions