# Explain how natural selection leads to a population of bacteria becoming resistant to an antibiotic over many generations.

> OCR GCSE Biology A: Gateway Science (J247) — B5.2 Natural selection and evolution · Explain · 4 marks

> A hospital notices that a species of bacteria that was once easily treated with a common antibiotic is no longer being killed by that antibiotic. Scientists suggest this change has come about through natural selection.

## Mark scheme (4 marks)

1. Random mutation occurs in some bacteria, producing an allele that gives antibiotic resistance
2. When the antibiotic is present, non-resistant bacteria are killed / resistant bacteria survive
3. Resistant bacteria reproduce and pass the advantageous allele to offspring
4. Over many generations the frequency of the resistant allele increases in the population

## Key terms

- [natural selection](https://www.gradenine.co.uk/glossary/natural-selection)

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](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/explain-how-natural-selection-leads-to-cb4f54bd) · Published by Druglandscape Ltd.