Maintaining a constant internal environmentSpec 7.9
- 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.
Quick check
Define homeostasis.
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Maintaining a constant internal environment in response to internal and external change.
Why does a high body temperature stop reactions in cells? (Triple only)
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Enzymes are denatured, so substrates no longer fit the active site.
What happens to animal cells if the blood is too dilute? (Triple only)
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Water enters by osmosis. The cells swell and may burst.
Which part of the brain coordinates temperature control? (Triple only)
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The hypothalamus.
How does shivering warm the body? (Triple only)
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Muscles contract rapidly. Respiration in the muscle cells transfers energy as heat.