1. 1
   A population of moths in a polluted woodland contains both pale and dark forms. Over several decades, soot from nearby factories darkened the tree bark. Bird predators hunt the moths by sight. Records show the proportion of dark moths rose from 2% to 95% of the population over this period.

   (a)

   Which statement best explains why the dark moths increased in proportion?

   [1 mark]

   • ADark moths were better camouflaged against the sooty bark, so fewer were eaten by birds
   • BDark moths mutated more often than pale moths
   • CPale moths deliberately changed colour to survive
   • DBirds preferred to eat dark moths, reducing pale moth numbers

   (b)

   Which term describes the dark colouring of the moths in this scenario, which gave them a survival advantage once the bark darkened?

   [1 mark]

   • AA learned behaviour
   • BAn advantageous variation
   • CAn acquired characteristic passed on by practice
   • DA vestigial structure

   (c)

   Using Darwin's theory of evolution by natural selection, explain how the proportion of dark moths increased from 2% to 95% over several decades.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hospital ward treated patients with the antibiotic methicillin for many years. Over time, doctors noticed that infections caused by the bacterium *Staphylococcus aureus* became increasingly difficult to treat with this antibiotic, and a resistant strain (MRSA) became common in the ward.

   (a)

   What is the most likely explanation for the rise of MRSA in the ward?

   [1 mark]

   • AThe resistant bacteria copied resistance genes from the patients' cells
   • BMethicillin caused the bacteria to develop resistance in response to treatment
   • CA few bacteria already had a mutation giving resistance, and methicillin killed the non-resistant bacteria, leaving resistant ones to multiply
   • DAll bacteria in the ward became resistant at the same time by chance

   (b)

   Which of the following would most effectively reduce the further spread of antibiotic-resistant bacteria such as MRSA in the ward?

   [1 mark]

   • AStopping antibiotic courses as soon as symptoms improve
   • BIncreasing the dose of methicillin given to every patient
   • CUsing methicillin to treat viral infections as well as bacterial ones
   • DPrescribing antibiotics only when necessary and completing the full course each time

   (c)

   Explain, in terms of natural selection, how the use of methicillin in the ward led to the emergence of MRSA as a common resistant strain.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Palaeontologists compared three human-relative fossils: Ardi, dated to 4.4 million years ago, with a mixture of climbing and upright-walking features; Lucy, dated to 3.2 million years ago, with a pelvis and leg bones more suited to upright walking than Ardi's; and a set of fossils found by Richard Leakey, dated to 1.6 million years ago, with a skeleton very similar to modern humans.

   (a)

   Explain how these three fossils, considered together, provide evidence for human evolution.

   [3 marks]

   (b)

   Alongside these fossils, archaeologists found stone tools buried in the same rock layers, close to each set of remains. The tools found near the oldest fossils were simple, roughly-shaped flakes, while the tools found near the youngest fossils were more finely shaped and symmetrical.
   
   Explain how dating the rock layers and stone tools alongside the fossils strengthens the evidence for human evolution, and describe what the change in tool design over time suggests about human ancestors.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student compares the forelimb bones of a human, a bat, a whale and a dog. Despite these animals living in very different environments and using their forelimbs for very different purposes (grasping, flying, swimming and walking), the student notices that all four forelimbs are built from the same basic arrangement of one upper bone, two lower bones, a set of wrist bones, and five digits (the pentadactyl limb).

   (a)

   Describe what the pentadactyl limb is, and evaluate why its presence across such different animals is considered strong evidence for the theory of evolution rather than being explained by chance or by each animal separately being designed for its own function.

   [6 marks]

   (b)

   New genetic analysis techniques allow scientists to compare DNA sequences between organisms far more precisely than earlier methods based only on visible physical features. Using this genetic evidence, scientists proposed replacing the traditional five-kingdom classification system (which grouped organisms mainly by visible characteristics) with a three-domain system based on genetic differences.
   
   Evaluate why genetic analysis led scientists to suggest the three-domain classification system instead of continuing to use the five-kingdom system, and discuss what this change reveals about how scientific classification can develop over time.

   [6 marks]

   Total for question 4: 12 marks

End of questions