AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
This is controlled by negative feedback.
Full specification wording
Maintaining water and nitrogen balance in the body (biology only): This is controlled by negative feedback.
Negative feedback keeps internal conditions within a narrow range.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 16 of 17
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Negative feedback keeps internal conditions within a narrow range. A receptor detects a change from the normal level, a coordination centre processes this, and an effector responds to reverse the change. For example, if blood becomes too concentrated, receptors detect this and stimulate the pituitary gland to release more ADH. ADH travels to the kidney tubules, making them more permeable. More water is reabsorbed into the blood, producing a smaller volume of concentrated urine. If blood becomes too dilute, less ADH is released, less water is reabsorbed, and a larger volume of dilute urine is produced. This reverses the original change, restoring normal blood concentration.
What earns the marks
- Negative feedback reverses a change away from a normal level, returning the internal environment to its set point.
- A receptor detects the stimulus, a coordination centre processes the information, and an effector produces the response.
- In water balance, changes in blood concentration are detected and the pituitary gland releases ADH.
- ADH increases the permeability of the kidney tubules to water, increasing water reabsorption when blood is too concentrated.
- When blood is too dilute, less ADH is released, so less water is reabsorbed and a larger volume of dilute urine is produced.
- The response counteracts the original change, which is why the mechanism is described as negative feedback.
Common mistakes and how to put them right
Thinking that negative feedback amplifies a change.
Put it right: It reverses the change, returning conditions towards the normal level.
Using A-level terminology like 'collecting duct' or 'water potential'.
Put it right: Stick to the GCSE terms 'kidney tubules' and 'blood concentration'.
Stating that ADH is released when blood is too dilute.
Put it right: ADH release increases when blood is too concentrated and decreases when blood is too dilute.
Exam tips
- Use the sequence stimulus, receptor, coordination centre, effector and response when explaining negative feedback.
- Link each change in ADH concentration to a change in the permeability of the kidney tubules and the resulting volume of urine.
- Practise explaining both directions of the feedback loop, not only the response to dehydration.
Try the lesson
The start of the Maintaining water and nitrogen balance in the body (biology only): This is controlled by negative feedback. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement describes negative feedback in the control of water balance in the human body?
Listen
Negative feedback keeps internal conditions within a narrow range. A receptor detects a change from the normal level, a coordination centre processes this, and an effector responds to reverse the change. For example, if blood becomes too concentrated, receptors detect this and stimulate the pituitary gland to release more ADH. ADH travels to the kidney tubules, making them more permeable. More water is reabsorbed into the blood, producing a smaller volume of concentrated urine. If blood becomes too dilute, less ADH is released, less water is reabsorbed, and a larger volume of dilute urine is produced. This reverses the original change, restoring normal blood concentration. A strong answer earns marks for these points. Negative feedback reverses a change away from a normal level, returning the internal environment to its set point. A receptor detects the stimulus, a coordination centre processes the information, and an effector produces the response. In water balance, changes in blood concentration are detected and the pituitary gland releases ADH. ADH increases the permeability of the kidney tubules to water, increasing water reabsorption when blood is too concentrated. Exam tip: Use the sequence stimulus, receptor, coordination centre, effector and response when explaining negative feedback.
Key words
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Negative feedback
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Receptor
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Coordination centre
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Effector
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See every definition
- Negative feedback
- A mechanism in which the response counteracts the original change, reversing a change away from a normal level and returning the internal environment to its set point.
- Receptor
- Detects the stimulus, such as a change in blood concentration.
- Coordination centre
- Processes the information during a negative feedback pathway.
- Effector
- Produces the response that reverses the change.
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