Pearson Edexcel · GCSE · Biology
Course version: 1BI0 · Version from Sept 2016
7.20B Explain the effect of ADH on the permeability of the collecting duct…
Full specification wording
Topic 7 – Animal coordination, control and homeostasis: 7.20B Explain the effect of ADH on the permeability of the collecting duct in regulating the water content of the blood
ADH (antidiuretic hormone) controls how much water the collecting duct lets back into the blood.
Checked against the Pearson Edexcel 1BI0 specification (opens in a new tab) on .
- Point 17 of 19
Study notes
From the checked teaching notes for this specification point.
The idea
ADH (antidiuretic hormone) controls how much water the collecting duct lets back into the blood. When blood water content falls, the pituitary gland releases more ADH. ADH makes the collecting duct more permeable to water, so more water is reabsorbed by osmosis into the blood, and a smaller volume of more concentrated urine is produced. This raises the water content of the blood back towards normal. When blood water content is too high, less ADH is released, the collecting duct becomes less permeable, less water is reabsorbed, and a larger volume of dilute urine is produced. This negative feedback keeps blood water content steady.
What earns the marks
- ADH increases the permeability of the collecting duct to water.
- More ADH causes more water to be reabsorbed by osmosis into the blood.
- Increased reabsorption produces a smaller volume of more concentrated urine.
- Less ADH makes the collecting duct less permeable, so less water is reabsorbed and more dilute urine is produced.
- ADH is released by the pituitary gland and acts as part of negative feedback to regulate blood water content.
Common mistakes and how to put them right
Saying ADH makes the collecting duct less permeable.
Put it right: ADH increases permeability to water.
Confusing the direction of effect, claiming more ADH produces more dilute urine.
Put it right: More ADH gives more water reabsorption and more concentrated urine.
Stating ADH is released by the kidney.
Put it right: ADH is released by the pituitary gland and acts on the collecting duct.
Exam tips
- Link each change in ADH level to a change in permeability, then to water reabsorption, then to urine concentration.
- Use the term osmosis when describing water movement out of the collecting duct.
- Check the direction: more ADH means more reabsorption and less urine volume.
Try the lesson
The start of the Topic 7 – Animal coordination, control and homeostasis: 7.20B Explain the effect of ADH on the permeability of the collecting duct in regulating the water content of the blood lesson, made from checked teaching notes for this specification point.
Have a go first
When the water content of the blood falls, the pituitary gland releases more ADH. What effect does this increased ADH have on the collecting duct?
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