# During a long-distance cycling race, a cyclist's muscles switch from aerobic to anaerobic respiration as they sprint uphill. Explain why this switch occurs and describe one consequence for the cyclist's muscles.

> Eduqas GCSE Biology — 1.2.1 Aerobic and anaerobic respiration · Explain · 4 marks

> During intense exercise, muscles may not receive oxygen fast enough to meet their energy demands.

## Mark scheme (4 marks)

1. During intense exercise, oxygen cannot be delivered to the muscles fast enough (to keep up with demand)
2. Anaerobic respiration occurs without oxygen / glucose is broken down without oxygen
3. Anaerobic respiration in muscle cells produces lactic acid (as well as energy)
4. Lactic acid build-up causes muscle fatigue / pain / cramp, meaning muscles cannot contract as effectively

## 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 Eduqas GCSE Biology](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-a-long-distance-cycling-race-a-c5bd83d8) · Published by Druglandscape Ltd.