# A marathon runner is able to complete a 26-mile race using aerobic respiration. However, in the final sprint to the finish line, the runner's muscles switch to anaerobic respiration. Explain why the muscles switch to anaerobic respiration during the sprint and describe the consequences for the runner after the race has finished.

> AQA A-Level Biology (7402) — 3.5.2 Respiration · Explain · 5 marks

## Mark scheme (5 marks)

1. During the sprint, muscles require energy (ATP) more quickly than aerobic respiration can supply it
2. Oxygen cannot be delivered to the muscles fast enough / oxygen supply is insufficient
3. Anaerobic respiration in muscles produces lactic acid
4. Lactic acid causes muscle fatigue / pain / cramp in the muscles
5. After the race, the runner continues to breathe deeply / takes in extra oxygen to oxidise / break down the lactic acid (to repay the oxygen debt)

## Key terms

- [anaerobic respiration](https://www.gradenine.co.uk/glossary/anaerobic-respiration)
- [aerobic respiration](https://www.gradenine.co.uk/glossary/aerobic-respiration)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-marathon-runner-is-able-to-8e4ac2c7) · Published by Druglandscape Ltd.