# A person has been exercising vigorously in hot weather and has not drunk any water for several hours. Explain what happens in the body to reduce the amount of water lost in urine.

> WJEC A-Level Biology (Wales) — 3.7 Homeostasis and the kidney · Explain · 5 marks

> When the body loses more water than it takes in, the concentration of the blood plasma rises above normal levels.

## Mark scheme (5 marks)

1. The rise in blood plasma concentration / increased solute concentration is detected by osmoreceptors in the hypothalamus
2. The pituitary gland releases more ADH (anti-diuretic hormone)
3. ADH travels in the blood to the kidneys
4. The collecting duct / tubules become more permeable to water
5. A smaller volume of more concentrated urine is produced

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-person-has-been-exercising-vigorously-0083cde2) · Published by Druglandscape Ltd.