Evolution, speciation and conservation conflictsEdexcel International A Level Biology: Subtopic test

1. 1
   A population of beetles lives on a recently formed island of dark volcanic rock. Beetle colour is controlled by one gene with a dominant allele B for dark colour and a recessive allele b for pale colour. Birds feed on the beetles and find pale beetles easier to see against the rock. The frequency of allele B was 0.30 in the first generation studied and 0.55 five generations later.

   (a)

   Which of the following is the best definition of evolution?

   [1 mark]

   • AChanges in the characteristics of individual beetles during their lives
   • BA change in the total number of beetles in a population
   • CThe appearance of new alleles by mutation only
   • DA change in allele frequencies in a population over successive generations

   (b)

   Which process is the original source of a completely new allele?

   [1 mark]

   • ANatural selection
   • BMutation
   • CPredation by birds
   • DCompetition for food

   (c)

   Explain why the frequency of allele B increased over the five generations.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A river changed course and split a large population of ground squirrels into two populations living on opposite banks. The squirrels cannot swim the river, and the habitat on one bank is dry grassland while on the other bank it is wet woodland. After several thousand years, scientists have found that the two populations differ in body size, in alleles at several genes and in the calls used in courtship.

   (a)

   Which term describes the way in which the two squirrel populations have diverged?

   [1 mark]

   • ASympatric speciation
   • BStabilising selection
   • CAllopatric speciation
   • DGenetic bottleneck

   (b)

   The two populations are now considered to be separate species. Which observation would be the best evidence of this?

   [1 mark]

   • AIf individuals from the two populations are brought together they do not interbreed to produce fertile offspring
   • BThe two populations live on opposite banks of the river
   • CThe populations differ in the colour of their fur
   • DIndividuals of the two populations are different sizes

   (c)

   Explain how the geographical separation of the squirrel populations led to the formation of new species.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Apple maggot flies lay their eggs on fruit, and the larvae feed in the fruit. Originally the flies fed only on hawthorn fruit. After apple trees were introduced to the same area, some flies began to lay eggs on apples, which ripen earlier than hawthorn fruit. The flies mate on the fruit on which they developed. Both groups of flies live in the same orchards. A scientist genotyped 100 flies from each group for one gene. Of the 200 alleles in the hawthorn flies, 124 were allele A, and of the 200 alleles in the apple flies, 70 were allele A.

   (a)

   Explain how the two groups of flies living in the same orchards could become separate species by sympatric speciation.

   [3 marks]

   (b)

   Calculate the frequency of allele A in each group of flies and evaluate whether the data show that two species have formed.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The government of a tropical country plans to reduce its net carbon dioxide emissions. The proposals are to replant (reforest) areas of forest cleared for cattle farming, and to replace part of its petrol with ethanol made by fermenting sugar cane, which is to be grown on land that is currently degraded grassland. A study funded by an oil company concludes that biofuels give no climate benefit, a study by a sugar cane growers' association concludes that they give a very large benefit, and a university team has published a peer-reviewed analysis giving an intermediate result.

   (a)

   Evaluate the claim that reforestation and the use of biofuels are sustainable ways of reducing the net concentration of carbon dioxide in the atmosphere.

   [6 marks]

   (b)

   Explain why conclusions about controversial issues such as the benefit of biofuels may depend on who reaches them, and suggest how the reliability of the three studies could be judged.

   [6 marks]

   Total for question 4: 12 marks

End of questions