# A person has not drunk any water for several hours and their blood water concentration has dropped below the normal level. Explain how the body responds to restore normal blood water concentration.

> OCR GCSE Biology A: Gateway Science (J247) — B3.3 Maintaining internal environments · Explain · 4 marks

> The body constantly monitors and adjusts its internal conditions. Water balance is one of the key variables that must be kept within narrow limits.

## Mark scheme (4 marks)

1. The pituitary gland releases (more) ADH into the bloodstream
2. ADH increases water reabsorption in the kidney / makes kidney tubules more permeable to water
3. This raises/restores the blood water concentration back to normal / less water is lost in the urine (urine becomes more concentrated)
4. This is an example of negative feedback / once water concentration is restored, less ADH is released

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](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-person-has-not-drunk-any-121b7402) · Published by Druglandscape Ltd.