# Farmers sometimes add antibiotics to animal feed to promote growth and prevent disease in healthy livestock. Scientists are concerned that this practice contributes to the spread of antibiotic-resistant bacteria. Explain how the widespread use of antibiotics in livestock farming could lead to the development of antibiotic-resistant bacteria, and explain why the presence of such bacteria is a serious concern for human health.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 5.4 Antibiotics and resistance · Explain · 5 marks

> Antibiotics are used routinely in livestock farming across many countries. A significant proportion of the total antibiotics produced globally are given to farm animals, not humans.

## Mark scheme (5 marks)

1. Antibiotics kill non-resistant bacteria / bacteria that are not resistant to the antibiotic are killed
2. Some bacteria have a random mutation that gives resistance / resistant bacteria naturally occur in the population by chance
3. Resistant bacteria survive and reproduce, passing on resistance to offspring / natural selection favours resistant bacteria
4. Over time / over many generations, the proportion of resistant bacteria in the population increases
5. Antibiotic-resistant bacteria could spread to humans and infections caused by these bacteria cannot be treated effectively with antibiotics / the antibiotic will no longer work against these bacteria in humans

## Key terms

- [antibiotic](https://www.gradenine.co.uk/glossary/antibiotic)
- [antibiotic-resistant bacteria](https://www.gradenine.co.uk/glossary/antibiotic-resistant-bacteria)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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/farmers-sometimes-add-antibiotics-to-animal-d1f915e1) · Published by Druglandscape Ltd.