Food chains and food websIB MYP Sciences: Subtopic test

1. 1
   On a grassland in Kenya, grass is eaten by grasshoppers. The grasshoppers are eaten by lizards, and the lizards are eaten by eagles. Ecologists draw this as a food chain with arrows between the organisms.

   (a)

   Which organism is the secondary consumer in this food chain?

   [1 mark]

   • AGrass
   • BGrasshopper
   • CLizard
   • DEagle

   (b)

   What does each arrow in a food chain show?

   [1 mark]

   • AThe direction in which energy flows, from the organism eaten to the one that eats it
   • BThe organism that eats the other one, pointing from predator to prey
   • CThe number of organisms at each level
   • DThe area of land each organism needs

   (c)

   Explain why the grass is called the producer in this food chain.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A freshwater pond in Hungary contains algae, snails, tadpoles, dragonfly larvae, sticklebacks (small fish), a heron, bacteria and fungi. Snails and tadpoles feed on the algae. Dragonfly larvae eat tadpoles. Sticklebacks eat both snails and dragonfly larvae. The heron eats the sticklebacks. Bacteria and fungi live on the dead remains and waste of all the other organisms.

   (a)

   Which organisms in the pond are the decomposers?

   [1 mark]

   • AAlgae and snails
   • BSticklebacks and the heron
   • CDragonfly larvae and tadpoles
   • DBacteria and fungi

   (b)

   Which organism is both a secondary consumer and a tertiary consumer in the pond food web?

   [1 mark]

   • ATadpole
   • BStickleback
   • CDragonfly larva
   • DHeron

   (c)

   Explain why the decomposers are important in the pond.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Ecologists in a national park in Canada counted the snowshoe hares and the lynxes (large wild cats that hunt hares) in the same forest for seven years. The hare population was 40 000, 80 000, 120 000, 70 000, 30 000, 25 000 and 60 000 in years 1 to 7. The lynx population was 10 000, 12 000, 25 000, 50 000, 60 000, 35 000 and 15 000 in the same years.

   (a)

   Describe the pattern shown by the hare and lynx populations.

   [3 marks]

   (b)

   A student's hypothesis is that the number of lynxes depends only on the number of hares. Use the data to evaluate this hypothesis.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Sea otters live in the kelp forests off the Californian coast. Kelp is a large seaweed that makes its own food and gives shelter to fish and many other animals. Sea urchins graze on kelp, and sea otters eat sea urchins. In the 1800s sea otters were hunted for their fur until almost none were left. The urchins then multiplied and destroyed most of the kelp, leaving bare rocky areas called urchin barrens. Today otters are protected and some groups have been reintroduced. Otters also eat abalone and crabs, which fishing communities collect and sell.

   (a)

   Explain how the removal of the sea otters affected the other organisms in the kelp forest.

   [6 marks]

   (b)

   Discuss and evaluate the decision to protect sea otters and to reintroduce them to new areas.

   [6 marks]

   Total for question 4: 12 marks

End of questions