A person drinks a large amount of water on a hot day. Describe the changes that occur in the body to return blood water potential to normal.

WJEC A-Level Biology (Wales) — 3.7 Homeostasis and the kidney · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

After drinking a large volume of water, the water potential of the blood rises above normal. The body must respond to restore the correct water potential.

Model answer (5 marks)

The hypothalamus senses the rise in blood water potential via osmoreceptors.
The pituitary gland releases less ADH.
The collecting ducts of the kidneys become less permeable to water.
More water is excreted in the urine.
Blood water potential is restored to normal by negative feedback.

Examiner tips

  • Use the word ‘hypothalamus’ and ‘osmoreceptors’ to show detection. Mention ‘less ADH’ and ‘less permeability’ to link to kidney action. Show the sequence: detection → hormone change → kidney response → outcome. Use ‘negative feedback’ to explain the regulation.
  • common_mistakes
  • :
  • Confusing ADH with vasopressin or omitting the pituitary. Saying ‘more ADH’ instead of ‘less ADH’. Failing to mention the change in kidney permeability or the negative feedback loop.

Mark scheme (5 marks)

  1. The change in blood water potential is detected by the hypothalamus (or osmoreceptors in the hypothalamus)
  2. Less ADH (anti-diuretic hormone) is released / secreted from the pituitary gland
  3. The kidneys / collecting duct / tubules become less permeable to water
  4. More water is excreted / lost in the urine
  5. Blood water potential returns to / is restored to normal (negative feedback)

Key terms in this question

water potential

Related

More Homeostasis and the kidney questions

▶ Try answering this question with AI marking (free) →