# A marathon runner finishes a long race on a hot day. During the race, their body temperature rose and they lost a large amount of water through sweating. Explain how the body detects and responds to maintain a stable internal environment after the race.

> OCR A-Level Biology B — Advancing Biology (H422) — 5.5 Communication and homeostasis · Explain · 5 marks

> Maintaining a stable internal environment is essential for the body's cells to function correctly. This is known as homeostasis, and it relies on communication between different parts of the body.

## Mark scheme (5 marks)

1. The body monitors internal conditions / receptors detect changes in temperature or water content
2. A message / signal is sent to a processing centre (the brain / hypothalamus)
3. The processing centre sends a signal to effectors to bring about a response
4. A named corrective response to high body temperature, e.g. sweating increases / vasodilation occurs to lose more heat
5. The response returns conditions to the normal level / maintains a stable internal environment (homeostasis)

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](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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