# Explain why a population of bacteria can become resistant to an antibiotic through natural selection.

> AQA GCSE Biology (8461) — 4.6.2 Variation and evolution · Explain · 4 marks

> MRSA is a type of bacteria that is resistant to the antibiotic methicillin. It has become a serious problem in hospitals worldwide.

## Mark scheme (4 marks)

1. A mutation occurs (randomly) in the DNA of some bacteria
2. The mutation gives some bacteria an advantage / makes them resistant to the antibiotic
3. Resistant bacteria survive and reproduce / non-resistant bacteria are killed by the antibiotic
4. The allele / gene for resistance is passed on to offspring, so the frequency of resistance increases in the population over time

## Key terms

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

## Related

- [Revision notes for AQA GCSE Biology (8461)](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-why-a-population-of-bacteria-26b20298) · Published by Druglandscape Ltd.