1. 1
   A group of students investigated two characteristics in a population of pea plants growing in a school garden: plant height, which ranged smoothly from short to tall, and seed shape, which was either clearly round or clearly wrinkled with no intermediate forms.

   (a)

   A class of students measured the heights of 100 pea plants and found a smooth range of heights from short to tall, with no distinct groups. What type of variation does this describe?

   [1 mark]

   • ADiscontinuous variation
   • BContinuous variation
   • CSex-linked variation
   • DMutation

   (b)

   The students also recorded seed shape, finding that every seed was either clearly round or clearly wrinkled, with no intermediate forms. What is the most likely cause of this type of variation?

   [1 mark]

   • ABoth genes and environment equally
   • BEnvironment only
   • CGenes only
   • DRandom chance with no genetic basis

   (c)

   Explain why plant height shows continuous variation but seed shape shows discontinuous variation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Scientists studying a population of bacteria in a laboratory exposed a culture to X-rays, which are a form of ionising radiation. After exposure, a small number of bacteria showed a new, heritable characteristic that had not been observed in the population before the treatment.

   (a)

   A population of bacteria was exposed to X-rays in a laboratory. Some bacteria in the population subsequently showed a new, heritable characteristic not seen before. What process most likely caused this new characteristic to appear?

   [1 mark]

   • AMitosis
   • BMutation
   • CDiffusion
   • DActive transport

   (b)

   Which statement correctly describes the effect of ionising radiation on this bacterial population?

   [1 mark]

   • AIt has no effect on genetic material
   • BIt increases the rate of mutation
   • CIt only affects the phenotype, not the genotype
   • DIt prevents all further reproduction

   (c)

   Define the term mutation, and state two other sources of genetic variation in populations besides mutation.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A hospital microbiology team is monitoring two different populations of organisms affected by variation and selection. The first is a population of Staphylococcus bacteria on a hospital ward, some of which have become resistant to a commonly prescribed antibiotic. The second is a population of desert lizards living near the hospital's research station, which shows a wide range of skin colours from pale sandy brown to dark brown.

   (a)

   A hospital ward keeps a careful record of hand hygiene compliance among staff, since some pathogens found in hospitals have become resistant to commonly used antibiotics. Explain, in terms of natural selection, how a population of bacteria in a hospital could become resistant to an antibiotic over time.

   [3 marks]

   (b)

   The research station also studies a population of desert lizards that shows a wide range of skin colours, from pale sandy brown to dark brown, living on rocky and sandy ground of varying colour. Explain how natural selection could result in lizards with skin colour that matches their local ground colour becoming more common over many generations.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A moth species living near an industrial town exists in two forms, pale and dark, whose relative numbers changed dramatically as industrial pollution blackened tree bark with soot over several decades. A separate population of desert plants in the same region shows adaptive features, including some species with thick, water-storing stems and no visible leaves, which are studied by the same research team to compare different examples of adaptation.

   (a)

   Explain this change in the population using the theory of natural selection, referring to genetic variation, the struggle for survival, and differential reproduction.

   [6 marks]

   (b)

   Some desert plants studied by the same research team have very thick, fleshy stems that store water and greatly reduced or absent leaves, unlike most plants found in wetter environments. Explain how these features are adaptive for survival in a hot, dry desert environment, and explain how such adaptations would have arisen through natural selection over many generations.

   [6 marks]

   Total for question 4: 12 marks

End of questions