# Explain how lactic acid is produced during vigorous exercise and describe what happens to the lactic acid after the exercise stops.

> AQA GCSE Biology (8461) — 4.4.2 Respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. During vigorous exercise, oxygen supply to muscles is insufficient / muscles cannot get enough oxygen
2. Anaerobic respiration occurs in the muscles, producing lactic acid
3. After exercise, extra oxygen is needed to break down / react with the accumulated lactic acid — this is the oxygen debt
4. Lactic acid is transported (in the blood) to the liver where it is converted back to glucose

## Key terms

- [lactic acid](https://www.gradenine.co.uk/glossary/lactic-acid)

## Related

- [Revision notes for AQA GCSE Biology (8461)](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/explain-how-lactic-acid-is-produced-4ca58336) · Published by Druglandscape Ltd.