1. 1
   A student is studying a population of ladybirds in a school garden. Some ladybirds are red with black spots, while others are black with red spots. The student notes that offspring from the same two parent ladybirds can show slightly different numbers of spots from each other and from their parents.

   (a)

   Which of the following is the correct definition of a mutation?

   [1 mark]

   • AA change in the number of chromosomes in a gamete only
   • BA change in the sequence of bases in DNA
   • CA change in the environment that an organism lives in
   • DA change in the phenotype caused only by diet

   (b)

   The student concludes that the difference in the number of spots between siblings from the same two parents is most likely due to which cause of variation?

   [1 mark]

   • AGenetic causes only
   • BEnvironmental causes only
   • CA combination of genetic and environmental causes
   • DAsexual reproduction

   (c)

   The student finds that the overall colour pattern (red with black spots, or black with red spots) is inherited and does not change with environment, whereas the exact number of spots varies. Explain why extensive genetic variation exists within the ladybird population even though all the ladybirds belong to the same species.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener grows two rows of the same variety of tomato plant from seed. One row is grown in a greenhouse with controlled temperature and watering, and the other row is grown outdoors exposed to variable weather. The outdoor plants grow to different heights and produce fewer tomatoes than the greenhouse plants.

   (a)

   What is the most likely cause of the height difference between the two rows?

   [1 mark]

   • AA mutation that occurred in the outdoor seeds only
   • BAsexual reproduction in the outdoor row
   • CThe two rows being genetically different varieties
   • DEnvironmental conditions affecting the plants after germination

   (b)

   Within the greenhouse row alone, the plants are genetically identical because they were propagated by taking cuttings from a single parent plant. Which type of variation would you expect to see between these genetically identical greenhouse plants?

   [1 mark]

   • AEnvironmental variation only, since any genetic variation is ruled out
   • BGenetic variation only
   • CNo variation at all, since they are genetically identical
   • DVariation caused only by new mutations in every cutting

   (c)

   The gardener wants to compare the tomato yield of the greenhouse row and the outdoor row to work out how much of the difference in yield is due to the environment rather than genetics. Explain how the gardener could be confident that any yield difference observed is caused by the environment and not by genetic differences between the two rows.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Scientists studying a colony of bacteria in a laboratory notice that after several days of growth in a nutrient broth containing a low concentration of an antibiotic, a small number of bacterial cells survive and continue to reproduce, while the majority of the colony is killed.

   (a)

   Explain, in terms of mutation and variation, why a small number of bacteria are able to survive exposure to the antibiotic.

   [3 marks]

   (b)

   The scientists then take the surviving bacteria and grow them for many further generations in nutrient broth containing progressively higher concentrations of the same antibiotic. Explain what is likely to happen to the proportion of antibiotic-resistant bacteria in the population over these further generations, and why inappropriate use of antibiotics in general is a public health concern.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A conservation researcher is studying two isolated populations of the same species of fish that live in two lakes which used to be connected by a river. A landslide blocked the river many centuries ago, separating the two populations completely, and each lake has slightly different water temperature, food availability and predator species.

   (a)

   Explain, using ideas about genetic variation and natural selection, how these two populations of fish might change over many generations as a result of living in different environments.

   [6 marks]

   (b)

   The researcher proposes an alternative explanation based on Lamarck's theory: that fish in each lake develop new useful characteristics during their own lifetime in response to their environment, and then pass these acquired characteristics directly on to their offspring. Evaluate this explanation compared with Darwin's theory of evolution by natural selection, and explain why Darwin's theory, rather than Lamarck's, is accepted by scientists today as the correct explanation for how the two fish populations would change over time.

   [6 marks]

   Total for question 4: 12 marks

End of questions