# Explain how the kidneys help to maintain water balance in the body when a person becomes dehydrated.

> Eduqas A-Level Biology — 3.7 Homeostasis and the kidney · Explain · 5 marks

> When a person does not drink enough water, the concentration of their blood plasma rises above normal levels.

## Mark scheme (5 marks)

1. The hypothalamus detects the increase in blood plasma concentration (water potential falls / blood becomes more concentrated)
2. The pituitary gland releases more ADH (antidiuretic hormone)
3. ADH travels in the blood to the kidneys
4. The kidney tubules become more permeable to water
5. A smaller volume of more concentrated urine is produced

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