Evolution, speciation and scientific validationEdexcel A-Level Biology A: Subtopic test

1. 1
   A hospital ward is treated repeatedly with an antibiotic to control a population of Staphylococcus bacteria. Before the treatment began, about 1 in 10 000 of the bacteria carried an allele that made them resistant to the antibiotic. After two weeks of repeated treatment, most of the bacteria on the ward carried the resistance allele.

   (a)

   Which is the best definition of evolution?

   [1 mark]

   • AA change in allele frequency in a population over generations
   • BA change in the phenotype of an individual in response to its environment
   • CA mutation in the DNA of a single organism
   • DThe improvement of individuals through use of their features during their lifetime

   (b)

   What was the most likely origin of the resistance allele?

   [1 mark]

   • AThe bacteria produced it in response to exposure to the antibiotic.
   • BIt was transferred to the bacteria from the antibiotic.
   • CA random gene mutation that occurred before the antibiotic was used.
   • DNatural selection created the allele in the surviving bacteria.

   (c)

   Explain why the frequency of the resistance allele increased on the ward.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A research team compares the amino acid sequence of the beta chain of haemoglobin in four species of primate. Species A and B differ by 1 amino acid, species A and C differ by 6 amino acids and species A and D differ by 14 amino acids. The team concludes that the data support the theory that the four species evolved from a common ancestor. They submit their findings to a scientific journal and also present them at an international conference.

   (a)

   What is the main purpose of peer review before the findings are published in a journal?

   [1 mark]

   • ATo ensure the results are identical to those that have already been published
   • BTo allow independent experts to evaluate the methods, data and conclusions before publication
   • CTo patent the findings so that other scientists cannot use them
   • DTo make the findings available to the public without charge

   (b)

   Which conclusion about the primates is best supported by the data?

   [1 mark]

   • ASpecies D is the ancestor of species A.
   • BSpecies A and C share a more recent common ancestor than species A and B.
   • CSpecies A and D diverged more recently than species A and C.
   • DSpecies A and B diverged from a common ancestor more recently than species A and C or A and D.

   (c)

   Explain how presenting their findings at an international conference could help to validate the team's conclusion.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a woodland near an industrial city, the proportion of dark (melanic) peppered moths rose from 5% in 1850 to 95% in 1900. Soot had darkened the tree trunks on which the moths rest during the day, and birds found light moths easier to see. After clean air laws were introduced, the proportion of dark moths in the woodland fell from 95% in 1960 to 11% in 1990.

   (a)

   Explain how the proportion of dark moths increased between 1850 and 1900.

   [3 marks]

   (b)

   Calculate the percentage decrease in the proportion of dark moths between 1960 and 1990. Show your working. Explain why this explanation of the change should be peer reviewed before it is accepted by the scientific community.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Population 1: a ground beetle lived on a lowland plain. About 8000 years ago rising sea level flooded part of the plain, leaving beetles on two islands 20 km apart that they cannot cross. One island is dry grassland and the other is wet woodland.
   
   Population 2: in North America the apple maggot fly originally laid its eggs only on hawthorn fruit. About 170 years ago some flies began to lay eggs on apples, which had been introduced to the same area. Flies tend to mate on the type of fruit on which they developed, and apples ripen about three weeks earlier than hawthorn fruit, so the two groups of flies rarely meet to mate.

   (a)

   Explain how the island populations of beetles could eventually become separate species.

   [6 marks]

   (b)

   Compare allopatric speciation in the beetles with the speciation that may be happening in the apple maggot flies.

   [6 marks]

   Total for question 4: 12 marks

End of questions