1. 1
   Cytochrome c is a protein of 104 amino acids found in the mitochondria of all eukaryotes. Researchers compared its amino acid sequence in humans with the sequence in other species. The number of amino acid positions that differ from the human sequence was: chimpanzee 0, rhesus monkey 1, horse 12, chicken 13, tuna 21 and baker's yeast 45.

   (a)

   Which conclusion is best supported by these data?

   [1 mark]

   • AHumans evolved from chimpanzees
   • BHumans share a more recent common ancestor with the horse than with the tuna
   • CBaker's yeast is not related to humans
   • DThe chicken and the horse must be each other's closest relatives, because they differ from humans by similar numbers of amino acids

   (b)

   The cytochrome c amino acid sequences of humans and chimpanzees are identical. Which statement about the genes coding for this protein in the two species is correct?

   [1 mark]

   • AThe base sequences of the two genes must be identical
   • BIdentical sequences show that humans and chimpanzees are the same species
   • CNo mutations can have occurred in either gene since the two lineages separated
   • DThe base sequences could differ, because more than one codon can code for the same amino acid

   (c)

   Explain how these data provide evidence for evolution from a common ancestor.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Wild cabbage (Brassica oleracea) is a small, leafy plant that grows on sea cliffs in western Europe. Over roughly the last 2500 years, farmers have produced from it cabbage (a large terminal bud), kale (large leaves), broccoli and cauliflower (enlarged flower heads), Brussels sprouts (large side buds) and kohlrabi (a swollen stem). All these varieties can still be crossed with each other and with wild cabbage to produce fertile offspring.

   (a)

   Which process produced these varieties of Brassica oleracea?

   [1 mark]

   • APlants developed larger parts during their lifetime through use and passed these to their offspring
   • BPlants in different habitats were selected by the environment for survival
   • CFarmers repeatedly chose plants with desired characteristics as parents for the next generation
   • DPopulations were geographically isolated until they became separate species

   (b)

   A gardener removes every flower bud from a kale plant each year for 20 years and saves the seeds from other, untouched plants. The plants grown from these seeds still produce flower buds normally. Which statement correctly interprets this observation?

   [1 mark]

   • ARemoving the buds is an acquired change that is not genetic, so it is not evolution
   • BThe kale population has evolved, because the gardener's plants changed
   • CLamarck's theory is supported, because the buds were removed for many generations
   • DThe experiment shows that flower-bud production cannot be inherited

   (c)

   Explain how the varieties of Brassica oleracea provide evidence of how rapidly evolutionary change can occur.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Common chimpanzees (Pan troglodytes) live north and east of the Congo River in central Africa, while bonobos (Pan paniscus) live only in the forests to the south of it. Neither species can swim. Genetic evidence suggests the two populations separated roughly 1–2 million years ago, around the time the river formed. North of the river, chimpanzees share their forests with gorillas, which eat large amounts of ground herbs; chimpanzees forage in small, shifting parties and males are often aggressive. South of the river there are no gorillas, ground herbs are abundant, and bonobos travel in larger, more stable groups with much less aggression between individuals.

   (a)

   Explain how the formation of the Congo River could have led to reproductive isolation of the two ape populations.

   [3 marks]

   (b)

   Suggest how differential selection could explain the differences in social behaviour between bonobos and chimpanzees.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student writes in a revision summary: "Evolution is only a theory, so it has not been proved. One piece of evidence for it is that bats and birds both have wings, which shows they evolved from a common winged ancestor."

   (a)

   Discuss the student's statement that evolution is "only a theory" and has not been proved.

   [6 marks]

   (b)

   Evaluate the student's use of bat and bird wings as evidence that the two groups evolved from a common winged ancestor.

   [6 marks]

   Total for question 4: 12 marks

End of questions