1. 1
   A dairy farmer wants to increase the average milk yield of his herd of cows. Each generation, he selects the cows that produce the most milk and breeds them together, repeating this process over many generations. He compares his approach with the process of natural selection that occurs in wild cattle populations.

   (a)

   A dairy farmer repeatedly chooses the highest milk-yielding cows in his herd and breeds them together over many generations, gradually increasing average milk yield. What is this process called?

   [1 mark]

   • ANatural selection
   • BSelective breeding
   • CGenetic modification
   • DMutation

   (b)

   Which of the following best distinguishes selective breeding from natural selection?

   [1 mark]

   • AIn selective breeding, humans choose which individuals reproduce; in natural selection, the environment determines which individuals survive and reproduce
   • BSelective breeding does not involve genetic variation, whereas natural selection does
   • CNatural selection only occurs in plants, while selective breeding only occurs in animals
   • DThere is no meaningful difference between the two processes

   (c)

   Describe the steps involved in the farmer's selective breeding programme to increase milk yield in his herd.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A plant breeder is developing a new variety of wheat by crossing a variety with unusually large grains with a different variety that shows strong resistance to a fungal disease. The breeder selects and crosses offspring over several generations to try to combine both desirable features in a single new variety.

   (a)

   A plant breeder wants to produce a new variety of wheat with larger grains than any existing variety. Which method would allow the breeder to combine larger grain size with disease resistance from a different wheat variety over several generations?

   [1 mark]

   • AOsmosis
   • BDiffusion
   • CSelective breeding
   • DActive transport

   (b)

   After several generations of selective breeding, the new wheat variety consistently produces large grains and is disease-resistant. What must the breeder have done at each generation to achieve this outcome?

   [1 mark]

   • APrevented all reproduction to avoid genetic variation
   • BAllowed all offspring to breed randomly regardless of their features
   • CExposed all plants to ionising radiation to increase mutation rate
   • DSelected and crossed only the offspring showing both desirable features

   (c)

   Explain one advantage and one disadvantage of using selective breeding to improve crop plants such as this wheat variety.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer notices that an insecticide, which used to control an insect pest effectively, is becoming less effective on his crop after several years of repeated use. He consults an agricultural scientist, who explains that the pest population has evolved resistance to the insecticide through natural selection, and recommends comparing this with an artificial selection programme being used at a nearby research station to breed insect-resistant maize plants.

   (a)

   A population of insects living on the leaves of a crop plant is treated with an insecticide. Most of the insects are killed, but a very small number survive and reproduce, and their offspring show much greater resistance to the insecticide. Explain, in terms of natural selection, how this insecticide-resistant population arose.

   [3 marks]

   (b)

   At the research station, scientists are using artificial selection to breed a new variety of maize that is naturally resistant to the insect pest, rather than relying on insecticide. Explain the differences between the natural selection process described in your previous answer and this artificial selection (selective breeding) programme, referring to who or what determines which individuals reproduce.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A conservation biologist is studying two contrasting examples of selection. The first is a population of wild rabbits on an island, which diverged into two locally adapted forms after being separated into a cold northern habitat and a warm southern habitat over many generations. The second is a breeding programme run by a livestock company, which has selectively bred a strain of sheep that consistently produces unusually fine, soft wool by selecting and breeding only the finest-wool sheep in each generation.

   (a)

   A population of rabbits was introduced to an island with two distinct habitats: a cold, exposed northern area and a warmer, sheltered southern area. Over many generations, rabbits living in the northern area developed noticeably thicker fur and smaller ears than rabbits living in the southern area, even though they belong to the same species. Explain, using the theory of natural selection, how this difference between the two rabbit populations could have arisen.

   [6 marks]

   (b)

   The livestock company's breeding programme has, over 40 years of selective breeding, produced a strain of sheep with unusually fine, soft wool compared with the original wild sheep population, but this strain also shows reduced resistance to a common parasitic disease compared with the original population. Explain how the selective breeding process produced sheep with finer wool, and explain why this same process may have led to reduced disease resistance in the strain.

   [6 marks]

   Total for question 4: 12 marks

End of questions