# A species of peppered moth exists in two forms: a pale speckled form and a dark form. In an unpolluted woodland, pale speckled moths are more common. After industrial pollution kills the pale lichens on tree bark, turning the bark dark, the dark form of the moth becomes more common over many generations. Explain how the dark form became more common in the population after the bark became darker.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 2.6 Adaptation and natural selection · Explain · 5 marks

> Peppered moths rest on tree bark during the day. Birds are predators of peppered moths and hunt by sight. Before pollution, pale speckled moths were well camouflaged against lichen-covered bark. After pollution, the bark became dark and the lichens died.

## Mark scheme (5 marks)

1. There is variation in colour/form within the moth population (pale and dark individuals exist)
2. Dark moths are better camouflaged / better adapted on the dark bark, so they are less likely to be seen and eaten by birds
3. Pale moths are easier for birds to see on dark bark and are more likely to be eaten / have a lower chance of survival
4. Dark moths are more likely to survive and reproduce, passing on the allele/characteristic for dark colouring to their offspring
5. Over many generations, the proportion of dark moths in the population increases (because more dark offspring survive to reproduce)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-species-of-peppered-moth-exists-f3ad73d9) · Published by Druglandscape Ltd.