# During intense exercise, the muscles of an athlete may switch from aerobic respiration to anaerobic respiration. Explain why anaerobic respiration is less suitable for sustaining prolonged exercise compared with aerobic respiration, and describe what happens in the body after exercise stops to deal with the products of anaerobic respiration.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 8 Grey Matter · Explain · 5 marks

> An athlete completes a 400 m sprint and immediately feels muscle fatigue and cramp. After the race, the athlete continues to breathe heavily for several minutes.

## Mark scheme (5 marks)

1. Anaerobic respiration produces lactic acid (in animal/muscle cells)
2. Lactic acid build-up inhibits anaerobic respiration / causes cramp and fatigue, so exercise cannot be sustained
3. Anaerobic respiration releases less energy than aerobic respiration (from the same amount of glucose)
4. After exercise, lactic acid is transported (in the blood plasma) to the liver
5. Oxygen is used to oxidise / break down the lactic acid (in the liver), which is why the athlete continues to breathe heavily / an oxygen debt is repaid

## 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 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/during-intense-exercise-the-muscles-of-ac479215) · Published by Druglandscape Ltd.