Maintaining a constant internal environmentSpec 7.9
In short
Homeostasis is maintaining a constant internal environment in response to internal and external change. The body keeps blood glucose concentration, body temperature and the water content of the blood within narrow limits. This matters because enzymes and cells work best in a narrow range of conditions. Many of these controls use negative feedback.
- Homeostasis
- Maintaining a constant internal environment in response to internal and external change.
Conditions inside the body change. Eating a meal changes blood glucose. Exercise raises body temperature. A hot or cold day changes the temperature outside. The body responds to keep the conditions inside constant.
| Condition | Example of a change |
|---|---|
| Blood glucose concentration | A meal raises it, exercise lowers it |
| Body temperature | Hot or cold surroundings, or exercise |
| Water content of the blood | Sweating, or drinking a lot |
This matters because enzymes and cells work best in a narrow range of conditions. If conditions drift too far, reactions in cells slow down or stop. Many of these controls use negative feedback.
Constant does not mean the level never changes. It means the body brings it back to a set level, so say ‘kept within narrow limits’.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026