5.18 ADH and water balance
6 exam questions worth 17 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which gland releases ADH?
Choose one answer.
Correct Not quite: the answer is Pituitary gland
Mark scheme
C (pituitary gland)
Model answer
C: the pituitary gland.
A footballer loses a lot of water by sweating during a match.
Explain how ADH helps to return the water content of her blood to normal.
Mark scheme
- (low water content / concentrated blood) detected by the brain / hypothalamus (1)
- pituitary (gland) releases more ADH (1)
- (ADH) increases the permeability of the kidney tubules / collecting ducts (to water) (1)
- more water reabsorbed into the blood (1)
- small volume of concentrated urine (1)
- negative feedback (1)
Max 5
Model answer
Receptors in her brain detect that the water content of her blood is too low. Her pituitary gland releases more ADH into the blood. ADH makes the kidney tubules (collecting ducts) more permeable to water, so more water is reabsorbed into the blood. She produces a small volume of concentrated urine, and the water content of her blood returns to normal by negative feedback.
Describe the effect of ADH on the kidney tubules.
Mark scheme
- makes the tubules / collecting ducts more permeable to water (1)
- so more water is reabsorbed (into the blood) (1)
Model answer
ADH makes the kidney tubules more permeable to water, so more water is reabsorbed into the blood.
A person drinks 2 litres of water in a short time.
Describe the changes in ADH release and in the urine they produce.
Mark scheme
- less ADH released (1)
- tubules less permeable / less water reabsorbed (1)
- large volume of dilute urine (1)
Model answer
The pituitary releases less ADH, so the kidney tubules become less permeable and less water is reabsorbed. The person produces a large volume of dilute urine.
Explain how the body responds after a person eats a very salty meal.
Mark scheme
- blood becomes more concentrated / ion concentration rises (1)
- detected by the brain / hypothalamus (1)
- more ADH released, so more water reabsorbed by the kidneys (1)
- small volume of urine containing excess ions / kidneys remove excess ions in urine (1)
- person feels thirsty and drinks (1)
Max 4
Model answer
The salt makes the blood more concentrated, which is detected by the hypothalamus. The pituitary releases more ADH, so the kidneys reabsorb more water and produce a small volume of concentrated urine that removes the excess ions. The person also feels thirsty and drinks, which dilutes the blood back to normal.
Explain why the control of water content by ADH is an example of negative feedback.
Mark scheme
- a change in water content triggers a response that reverses the change (1)
- e.g. low water causes more ADH so more water is reabsorbed, raising the water content (back to normal) (1)
Model answer
Any change in the water content of the blood triggers a response that reverses it: for example, too little water causes more ADH to be released, so more water is reabsorbed and the water content rises back to normal.
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