# Describe how natural selection leads to a population of bacteria becoming resistant to an antibiotic over time.

> Cambridge International IGCSE Biology (0610) — 18.3 Selection · Describe · 4 marks

## Mark scheme (4 marks)

1. A mutation occurs in a bacterial cell that makes it resistant to the antibiotic
2. When the antibiotic is administered, non-resistant bacteria are killed but the resistant bacterium survives
3. The resistant bacterium reproduces, passing on the resistant allele to offspring
4. Over many generations the frequency of the resistant allele increases in the population so that most or all bacteria are resistant

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-natural-selection-leads-to-56ef2595) · Published by Druglandscape Ltd.