# A student goes for a brisk walk up a steep hill. During the walk, the student's muscles are supplied with enough oxygen to meet the demand for energy. Explain how the student's muscle cells release energy during the walk, and describe what would happen to the process of respiration in the muscles if the student began to run up the hill and oxygen supply to the muscles became insufficient.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.1 Cellular respiration · Explain · 5 marks

> During moderate exercise, muscles rely on aerobic respiration. During intense exercise, the oxygen supply to muscles may not meet the demand.

## Mark scheme (5 marks)

1. During the walk, glucose is broken down by aerobic respiration
2. Aerobic respiration produces ATP / energy, carbon dioxide and water
3. When running, oxygen supply is insufficient so anaerobic respiration occurs
4. During anaerobic respiration, glucose is converted to lactic acid
5. Lactic acid builds up in the muscles, causing fatigue / muscle ache / cramp

## 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)
- [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-goes-for-a-brisk-54439b2f) · Published by Druglandscape Ltd.