# A drug is defined as a substance that alters the body's chemical reactions when introduced into the body. Describe how antibiotics work against bacterial infections and explain why a doctor would not prescribe antibiotics to treat a viral infection such as influenza.

> Cambridge International IGCSE Biology (0610) — 15.1 Drugs · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. Antibiotics kill bacteria OR prevent/inhibit the growth of bacteria
2. Some antibiotics work by destroying the bacterial cell wall, causing the cell to burst
3. Viruses do not have a cell wall (or the same cellular structure as bacteria)
4. Viruses do not reproduce/grow in the same way as bacteria, so antibiotics have no effect on them

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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/a-drug-is-defined-as-a-a5d93554) · Published by Druglandscape Ltd.