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Responses to heat and cold

Animal coordination, control and homeostasis · Homeostasis and temperature control · note 4 of 4

Spec 7.12B
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Responses to heat and coldSpec 7.12B

In short

When the body is too hot, sweat glands release sweat, which evaporates and takes heat from the skin. In vasodilation, the blood vessels supplying the skin widen, so more heat is lost. When the body is too cold, shivering muscles contract rapidly and respiration transfers energy as heat, sweating is reduced, and vasoconstriction narrows the vessels to reduce heat loss.

When the body is too hot

  • Sweat glands release sweat onto the skin. Sweat evaporates and takes heat from the skin, which cools the body.
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean
  • Vasodilation: the blood vessels supplying the skin surface widen. More blood flows near the surface, so more heat is lost to the surroundings.

When the body is too cold

  • Shivering: muscles contract rapidly. This needs more respiration in the muscle cells, which transfers energy as heat and warms the body.
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean
  • Vasoconstriction: the blood vessels supplying the skin surface narrow. Less blood flows near the surface, so less heat is lost.
  • Sweating is reduced when the body is cold.
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean
Common mistake:

Blood vessels do not move up or down in the skin. They get wider (vasodilation) or narrower (vasoconstriction).

Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean
Two skin cross-sections: on the left, too hot, the blood vessel below the surface is wide (vasodilation) and many heat arrows leave the skin; on the right, too cold, the vessel is narrow (vasoconstriction) and little heat is lost. (opens full size in a new tab)
Vasodilation brings more blood near the surface to lose heat; vasoconstriction reduces heat loss.

Quick check

  1. Define homeostasis.

    Show answer

    Maintaining a constant internal environment in response to internal and external change.

  2. 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.

  3. What happens to animal cells if the blood is too dilute? (Triple only)

    Show answer

    Water enters by osmosis. The cells swell and may burst.

  4. Which part of the brain coordinates temperature control? (Triple only)

    Show answer

    The hypothalamus.

  5. How does shivering warm the body? (Triple only)

    Show answer

    Muscles contract rapidly. Respiration in the muscle cells transfers energy as heat.

Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026

Frequently asked questions

Why is homeostasis important?

Homeostasis is important because enzymes and cells work best in a narrow range of conditions. If blood glucose concentration, body temperature or the water content of the blood drift too far, reactions in cells slow down or stop. The body responds to changes and brings each condition back to a set level, often using negative feedback.

How is body temperature regulated?

Triple only Body temperature is regulated by the hypothalamus in the brain, which monitors the temperature of the blood and receives impulses from temperature receptors in the skin. When the body is too hot, sweat glands release sweat, which evaporates and cools the skin. When it is too cold, muscles shiver, and the extra respiration transfers energy as heat.

What is the difference between vasodilation and vasoconstriction?

Triple onlyHigher tier Vasodilation is the widening of the blood vessels supplying the skin surface when the body is too hot, so more blood flows near the surface and more heat is lost. Vasoconstriction is the narrowing of these vessels when the body is too cold, so less blood flows near the surface and less heat is lost.

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