# A student runs a 400 m race. During the race, their muscles begin to respire anaerobically as well as aerobically. After the race, the student continues to breathe heavily for several minutes. Explain why the student's muscles switch to anaerobic respiration during the race, and why the student continues to breathe heavily after finishing.

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

> During intense exercise, the body's demand for energy increases rapidly. Aerobic respiration requires a continuous supply of oxygen to release energy from glucose.

## Mark scheme (5 marks)

1. During intense exercise, oxygen cannot be delivered to the muscles fast enough / oxygen supply is insufficient to meet demand
2. Anaerobic respiration occurs so that muscles can continue to release energy (without oxygen)
3. Anaerobic respiration produces lactic acid (in the muscles)
4. The lactic acid produces an oxygen debt that must be repaid after exercise
5. The student continues to breathe heavily to take in extra oxygen to oxidise / break down the lactic acid (repaying the oxygen debt)

## Key terms

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

## 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)
- [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-student-runs-a-400-m-537b723f) · Published by Druglandscape Ltd.