Controlling water in the blood Edexcel International GCSE Biology revision
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In plain words
Drink a litre of water and you'll soon produce a lot of pale urine. Spend a hot day without drinking and you'll produce a little, dark urine. Your brain is measuring how watery your blood is and telling your kidneys what to do, using a hormone called ADH.
Three things to know
- The amount of water in the blood is kept steady. This is osmoregulation.
- If the blood has too little water, the pituitary gland releases more ADH. ADH makes the kidney's collecting ducts more permeable, so more water is reabsorbed, and a small volume of concentrated urine is made.
- If the blood has too much water, less ADH is released, less water is reabsorbed, and a large volume of dilute urine is made.
Tips and tricks
- More ADH, more water taken back, less urine. Think of ADH as the "anti-weeing" hormone.
- This is negative feedback: a change is detected and reversed, bringing the level back to normal.
It lands in your notebook with its questions as flashcards.
Controlling water in the blood: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which hormone controls the water content of the blood?
It is released by the pituitary gland.
What does ADH do to the kidney?
The collecting ducts become more permeable to water.
A person is dehydrated. What is their urine like?
More ADH means more water is taken back.
Where is ADH released from?
The brain detects the water content of the blood.
What is keeping the water content of the blood constant an example of?
It keeps conditions inside the body steady.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 6 marks. Write your answers on paper, then check them.
Controlling water in the blood
Edexcel International GCSE Biology 4BI1 · 6 marks · papermunch.org
Name ______________________________ Date ______________
Describe what happens when a person has not drunk enough water.[3]
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The water content of the blood falls. The pituitary gland releases more ADH. The kidneys reabsorb more water, so a small volume of concentrated urine is produced.
Name the gland that releases ADH.[1]
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The pituitary gland.
Explain why urine is pale and dilute after drinking a lot of water.[2]
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Less ADH is released, so the kidneys reabsorb less water and more is lost in the urine.
Answers: Controlling water in the blood
- 1. The water content of the blood falls. The pituitary gland releases more ADH. The kidneys reabsorb more water, so a small volume of concentrated urine is produced.
- 2. The pituitary gland.
- 3. Less ADH is released, so the kidneys reabsorb less water and more is lost in the urine.