Niche, adaptation and natural selectionEdexcel A-Level Biology A: Subtopic test

1. 1
   Marram grass grows on exposed sand dunes, where water drains away quickly and strong winds dry the air. Its leaves are rolled lengthways, with the stomata on the inner surface in pits lined with hairs. It also has long roots that reach deep into the sand.

   (a)

   Which type of adaptation is the rolling of the leaves?

   [1 mark]

   • ABehavioural
   • BPhysiological
   • CGenetic
   • DAnatomical

   (b)

   Which statement best describes the niche of marram grass?

   [1 mark]

   • AIts role in the ecosystem, including its habitat, its interactions with other species and the abiotic conditions it tolerates
   • BThe sand dunes in which it grows
   • CThe number of marram plants in a given area of dune
   • DThe geographical area over which the species is found

   (c)

   Explain how the rolled leaves and stomata in hair-lined pits help marram grass to survive on the dunes.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Male emperor penguins incubate their eggs through the Antarctic winter. The males huddle tightly together and take turns to stand at the cold outer edge of the huddle. Each penguin has densely packed, overlapping feathers and a thick layer of fat under the skin. During incubation the males fast and lower their metabolic rate.

   (a)

   The huddling of the males is an example of which type of adaptation?

   [1 mark]

   • AAnatomical
   • BBehavioural
   • CPhysiological
   • DBiochemical

   (b)

   Which of these is an anatomical adaptation of the penguins?

   [1 mark]

   • AHuddling tightly together
   • BTaking turns to stand at the outer edge
   • CA thick layer of fat under the skin
   • DLowering the metabolic rate during incubation

   (c)

   Explain how huddling increases the chance of a male penguin surviving the winter and breeding successfully.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In the 1950s warfarin, a poison that causes fatal internal bleeding, was used to kill brown rats on farms in Britain. Within a few years warfarin-resistant rats were found in some areas. Resistance is caused by an allele of one gene that arose by mutation and is inherited. Before warfarin was used, the allele was very rare in the rat population.

   (a)

   Explain how the frequency of the resistance allele in the rat population increased.

   [3 marks]

   (b)

   A farmer says that the rats became resistant because they were exposed to warfarin. Use ideas about evolution to explain why this is incorrect.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   On a Galapagos island the medium ground finch feeds mainly on seeds. During a severe drought the plants produced few seeds; the small, soft seeds were eaten first, leaving mostly large, hard seeds, and most of the finches died. Birds with deeper beaks, which could crack the large seeds, were more likely to survive. Beak depth is inherited, and the mean beak depth of the next generation was about 0.5 mm greater than before the drought. On the same island the small ground finch has a narrow, pointed beak and feeds on small seeds and insects, mostly on the ground and in low shrubs, while the cactus finch feeds on cactus flowers and pulp.

   (a)

   Explain how the drought led to an increase in the mean beak depth of the next generation of medium ground finches.

   [6 marks]

   (b)

   Using the concept of niche, explain how the three finch species can live on the same island, and discuss how anatomical, behavioural and physiological adaptations may contribute.

   [6 marks]

   Total for question 4: 12 marks

End of questions