1. 1
   An agricultural researcher is studying a large field of wheat plants. She records the height of every plant, finding a smooth range of values from very short to very tall, and she also records the blood group of each farm worker helping with the harvest, which falls into a small number of distinct categories (A, B, AB or O). She wants to compare the causes and patterns of these two types of variation.

   (a)

   An agricultural researcher measures the height of every wheat plant in a large field and plots the results, finding a smooth range of heights from very short to very tall with many values in between. What type of variation does plant height show in this study?

   [1 mark]

   • ADiscontinuous variation
   • BContinuous variation
   • CNo variation
   • DSex-linked variation

   (b)

   The researcher notes that wheat plant height is affected by both the genes each plant inherits and by growing conditions such as soil quality and rainfall, whereas the farm workers' blood groups are determined only by the alleles they inherited from their parents. What best describes the cause of variation in blood group compared with plant height?

   [1 mark]

   • ABlood group variation is caused only by genetic factors, while plant height variation is caused by both genetic and environmental factors
   • BBlood group variation is caused only by environmental factors, while plant height variation is caused only by genetic factors
   • CBoth blood group and plant height variation are caused only by environmental factors
   • DBoth blood group and plant height variation are caused only by genetic factors

   (c)

   Explain why plant height in the wheat field shows continuous variation while blood group in the farm workers shows discontinuous variation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a hospital, a small number of bacteria causing an infection happen to carry a mutation that makes them resistant to a commonly used antibiotic. When patients are treated with this antibiotic, the non-resistant bacteria in the population are killed, but the resistant bacteria survive, reproduce rapidly, and pass the resistance allele on to their offspring, so that over time a much larger proportion of the bacterial population becomes resistant.

   (a)

   In a hospital, a small number of bacteria in an infection happen to carry a mutation that makes them resistant to a commonly used antibiotic. When patients are treated with this antibiotic, the non-resistant bacteria are killed, but the resistant bacteria survive and reproduce, passing the resistance allele to their offspring. What term describes the antibiotic acting on the bacterial population in this scenario?

   [1 mark]

   • AMutation
   • BSpeciation
   • CSelection pressure
   • DFertilisation

   (b)

   Over repeated rounds of antibiotic treatment in the hospital, the proportion of resistant bacteria in the population steadily increases while non-resistant bacteria become rare. What is this increase in resistant bacteria over successive generations an example of?

   [1 mark]

   • ACloning
   • BGenetic engineering
   • CSelective breeding
   • DEvolution by natural selection

   (c)

   Using the stages of natural selection, explain how repeated use of the antibiotic in the hospital leads to a bacterial population that is mostly resistant, starting from the original mutation.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A palaeontologist examines the layers of rock exposed in a cliff face. In the deepest, oldest layers she finds only simple, single-celled fossil organisms; in progressively younger, shallower layers she finds increasingly complex fossil organisms; and in the most recent layers near the surface she finds fossils that closely resemble species living today. She wants to use this pattern to explain the evidence for evolution to her students, and also to discuss how such evidence was received historically.

   (a)

   A palaeontologist examines rock layers in a cliff face and finds simple, single-celled fossil organisms in the deepest, oldest layers, and progressively more complex fossil organisms in shallower, younger layers, with fossils closely resembling modern species found only near the surface. Explain how this pattern of fossils found in rock layers provides evidence to support the theory of evolution.

   [3 marks]

   (b)

   When Charles Darwin first proposed his theory of evolution by natural selection based on evidence including fossils and observations from his voyages, the theory was controversial and faced strong opposition from some scientists and religious leaders at the time. Explain why Darwin's theory was controversial when first proposed, and describe why it later became widely accepted by the scientific community.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A crop science company wants to produce a variety of maize that is resistant to a common insect pest without waiting for the many generations that traditional selective breeding would require. Scientists identify a gene from a soil bacterium that produces a protein toxic to the pest insect but harmless to humans, and use genetic engineering to insert this gene into maize plants, creating a genetically modified (GM) pest-resistant crop that the company plans to sell to farmers.

   (a)

   Explain the process by which this gene is transferred into the maize plants, including the roles of restriction enzymes, a vector and ligase, and describe why this genetic engineering approach can achieve the desired characteristic much more quickly than traditional selective breeding.

   [6 marks]

   (b)

   Before the GM pest-resistant maize can be sold to farmers, regulators must weigh up its potential benefits against possible risks. Discuss one benefit and one risk of growing genetically modified crops such as this pest-resistant maize, and evaluate whether, overall, the use of genetic engineering in agriculture is likely to be beneficial for food production.

   [6 marks]

   Total for question 4: 12 marks

End of questions