# Antibiotic resistance in bacteria is an example of natural selection in action. A population of bacteria was treated with an antibiotic. After several generations, most of the bacteria in the population were resistant to the antibiotic. Explain how natural selection resulted in the majority of bacteria in the population becoming resistant to the antibiotic.

> Eduqas GCSE Biology — 2.4.2 Evolution and natural selection · Explain · 4 marks

> Antibiotic resistance is a major global health concern. When a population of bacteria is exposed to an antibiotic, some individuals may survive and reproduce whilst others die.

## Mark scheme (4 marks)

1. A random mutation occurred in some bacteria, producing a resistant allele / variant that gave resistance to the antibiotic
2. Bacteria without the resistant allele were killed by the antibiotic / were less well suited to the environment
3. The resistant bacteria survived and reproduced, passing the advantageous allele to their offspring
4. Over many generations the frequency of the resistant allele increased in the population, so most bacteria became resistant

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/antibiotic-resistance-in-bacteria-is-an-a1360138) · Published by Druglandscape Ltd.