Homeostasis: keeping conditions constant

Your cells only work well if conditions inside the body stay within narrow limits. Keeping them steady is called homeostasis.

Practise this lesson free (6 questions)

What is homeostasis?

Homeostasis is keeping the internal environment of the body constant, even when conditions outside change.
Important examples: body temperature (about 37 °C), blood glucose concentration, and water levels in the body (osmoregulation).

Why it matters

Enzymes work best at their optimum temperature and pH. Too hot and they denature; too cold and reactions are too slow.
Water and ion levels: if the blood is too dilute or too concentrated, water moves into or out of cells by osmosis. Animal cells can swell and burst, or shrink.
Glucose: cells need a steady supply for respiration, but too much glucose in the blood damages tissues.

How control works

Receptors detect a change. A coordination centre (such as the brain or the pancreas) processes the information. Effectors (muscles or glands) respond to bring conditions back.
This is negative feedback: a change away from normal causes a response that reverses the change.
Control uses nerves (fast, short-lived) or hormones (slower, longer-lasting).
Worked example

After a sugary drink, blood glucose rises. Describe how negative feedback returns it to normal.

  1. Cells in the pancreas detect the rise.
  2. The pancreas releases insulin.
  3. Insulin makes cells take in glucose and the liver store it as glycogen, so the level falls back to normal.

Answer: The rise is detected, insulin is released and glucose is removed from the blood, reversing the change.

Key idea

Homeostasis keeps temperature, blood glucose and water levels constant so enzymes and cells work properly. Receptors detect changes, coordination centres process them and effectors respond, using negative feedback.

Key words
Homeostasis
Keeping the internal conditions of the body constant, such as temperature, water content and blood glucose.
Negative feedback
A control mechanism that reverses a change, bringing a level back towards normal.
Osmosis
The net movement of water molecules from a dilute solution to a more concentrated solution across a partially permeable membrane.
Respiration
An exothermic reaction in all living cells that releases energy from glucose.

All GCSE and International GCSE Biology key terms and definitions →

Quick check

Try two quick questions

See if it has sunk in. Answers are marked straight away.

Extra practice

2 more questions

Try each one, then tap to check.

  1. Which is an example of homeostasis?

    1. Digesting food
    2. Making new cells
    3. Controlling body temperature
    4. Fighting infection
    Show the answer

    Answer: Controlling body temperature

    Homeostasis keeps internal conditions steady.

  2. What happens to enzymes if body temperature rises too high?

    1. They become denatured
    2. They change into hormones
    3. They work faster for ever
    4. They are made faster
    Show the answer

    Answer: They become denatured

    The active site changes shape.

Check you have got it

Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.

Practise this lesson free (6 questions)All GCSE and International GCSE Biology lessons

Video for this lesson coming soon. Subscribe on YouTube

Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

What do exam command words like explain and evaluate mean? →

Related lessons