# A population of peppered moths (Biston betularia) lives in a woodland area. Before industrialisation, most moths had pale, speckled wings, with very few having dark wings. After industrialisation, dark-winged moths became much more common in the population. Explain why the proportion of dark-winged moths increased in this population after industrialisation.

> Pearson Edexcel A-Level Biology A (9BI0) — Topic 7 Genetics, Populations, Evolution and Ecosystems · Explain · 5 marks

> Before industrialisation, tree bark in the woodland was pale and covered with lichens. After industrialisation, soot from factories killed the lichens and darkened the tree bark.

## Mark scheme (5 marks)

1. Before industrialisation, pale moths were better camouflaged on pale, lichen-covered bark and so were less likely to be eaten by predators / survived in greater numbers
2. After industrialisation, the bark became dark / soot darkened the bark, so dark-winged moths were better camouflaged and pale moths were easier for predators to spot and eat
3. Dark-winged moths were more likely to survive and reproduce / had greater reproductive success
4. The allele(s) / genes for dark wing colour were passed on to offspring in greater numbers / frequency of the dark wing allele increased in the population
5. Over many generations, natural selection resulted in a higher proportion of dark-winged moths in the population

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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