1. 1
   An ecologist describes a food chain found in a meadow: grass is eaten by a grasshopper, the grasshopper is eaten by a frog, and the frog is eaten by a snake. The ecologist also records that the same meadow contains several other feeding relationships, which together form a food web.

   (a)

   In a food chain described as: grass, then grasshopper, then frog, then snake, which organism is the producer?

   [1 mark]

   • AGrass
   • BGrasshopper
   • CFrog
   • DSnake

   (b)

   In the food chain grass, grasshopper, frog, snake, what is the frog classed as?

   [1 mark]

   • AProducer
   • BPrimary consumer
   • CSecondary consumer
   • DDecomposer

   (c)

   The ecologist finds that the meadow also contains several other feeding relationships in addition to the grass–grasshopper–frog–snake food chain, together forming a food web. Explain what is meant by a food web, and explain one advantage of representing feeding relationships as a food web rather than as a single food chain.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Fishermen in a coastal region have been overharvesting a species of small fish that forms a central part of the local marine food web, being eaten by seabirds, larger predatory fish, and marine mammals. In a separate part of the same region, a foreign species of crab has recently been introduced to the coastal habitat by cargo ships.

   (a)

   Populations of seabirds and larger predatory fish that feed on this small fish have subsequently declined sharply. What term describes an organism, like the small fish, that many other organisms in a food web feed on?

   [1 mark]

   • AAn apex predator
   • BA key prey species within the food web
   • CA decomposer
   • DA producer

   (b)

   A foreign species of crab has recently been introduced to the same coastal habitat by cargo ships, and has begun competing with native crab species for food and space. What is the most likely long-term effect of introducing this foreign species on the existing food web?

   [1 mark]

   • AIt will have no effect on the food web, since only native species can interact within a food web
   • BIt will only affect producers, since only producers form the base of a food web
   • CIt will automatically increase biodiversity with no negative consequences
   • DIt could disrupt the food web by outcompeting native species, altering the balance of existing feeding relationships

   (c)

   Using the food web described, explain the impact that overharvesting the small fish species is likely to have on the populations of seabirds and larger predatory fish in the region.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A conservation group is studying a woodland food web with the following feeding relationships: oak trees are eaten by caterpillars and by squirrels; caterpillars are eaten by blue tits; squirrels and blue tits are both eaten by hawks. A serious outbreak of disease has recently killed off almost all of the caterpillars in this woodland.

   (a)

   A woodland food web includes the following feeding relationships: oak trees are eaten by caterpillars and by squirrels; caterpillars are eaten by blue tits; squirrels and blue tits are both eaten by hawks. Draw out (in words) the separate food chains that make up this food web, and identify the producer and all consumers, stating whether each consumer is a primary, secondary or tertiary consumer.

   [3 marks]

   (b)

   A serious outbreak of disease has recently killed off almost all of the caterpillars in this woodland. Using the food web described, explain the likely knock-on effects of this disease outbreak on the populations of blue tits, squirrels and hawks in the woodland.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An ecology textbook compares two very different feeding communities to illustrate the concept of food webs. The first is a savannah food web in which grass is eaten by zebras, wildebeest and gazelles, which are all eaten by lions, with decomposers breaking down dead remains. The second is a rocky shore food web in which seaweed is eaten by limpets and periwinkles, which are eaten by crabs and shorebirds, with several introduced non-native species recently observed feeding on the limpets.

   (a)

   A savannah food web includes: grass is eaten by zebras, wildebeest and gazelles; zebras, wildebeest and gazelles are all eaten by lions; and dead remains of all these animals are broken down by decomposers such as bacteria and fungi. Explain fully how energy and matter flow through this food web, describing the roles of the producer, consumers and decomposers, and explain why a food web gives a more accurate representation of feeding relationships in this savannah ecosystem than a single food chain would.

   [6 marks]

   (b)

   On a rocky shore, seaweed is eaten by limpets and periwinkles, which are in turn eaten by crabs and shorebirds. Marine biologists have recently observed a non-native species of predatory snail, introduced accidentally via ship ballast water, feeding heavily on the limpet population. Explain, using the food web described, the possible knock-on effects that this introduced species could have on the seaweed, periwinkles, crabs and shorebirds, and explain why introducing a foreign species to a habitat is generally considered a negative impact of human activity on an ecosystem.

   [6 marks]

   Total for question 4: 12 marks

End of questions