# A sprinter trains daily to improve their performance. During intense sprint sessions, their leg muscles respire anaerobically. After each sprint, the athlete breathes heavily for several minutes before their breathing rate returns to normal. Explain why the athlete's muscles respire anaerobically during a sprint and why the athlete continues to breathe heavily after the sprint has finished.

> Pearson Edexcel A-Level Biology A (9BI0) — 4.1 Cellular respiration · Explain · 5 marks

> A sprinter trains daily to improve their performance. During intense sprint sessions, their leg muscles respire anaerobically. After each sprint, the athlete breathes heavily for several minutes before their breathing rate returns to normal.

## Mark scheme (5 marks)

1. During a sprint, oxygen is delivered to the muscles too slowly / oxygen demand exceeds oxygen supply
2. Anaerobic respiration does not require oxygen and so allows energy / ATP to be released when oxygen is limited
3. Anaerobic respiration in (human) muscle cells produces lactic acid
4. After the sprint, the athlete must continue to breathe heavily to take in extra oxygen to break down / oxidise the lactic acid
5. The oxygen debt / the amount of extra oxygen required must be repaid before breathing rate returns to normal

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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