A runner finishes a long-distance race on a hot day. Their body temperature rises above the normal level. Describe how the body uses a negative feedback system to restore normal body temperature.

OCR GCSE Biology A: Gateway Science (J247) — B3.3 Maintaining internal environments · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

During intense exercise in warm conditions, the body produces large amounts of heat, causing core body temperature to rise above its set point of approximately 37 °C.

Model answer (4 marks)

The rise in body temperature is detected by temperature receptors in the hypothalamus.
The hypothalamus activates effectors such as sweat glands to produce sweat and causes vasodilation of blood vessels near the skin.
Sweat evaporates and the dilated vessels allow heat to be lost to the environment, reducing core temperature.
This response is a negative feedback system because it opposes the initial rise in temperature, restoring it to about 37 °C.

Examiner tips

  • Use the word ‘receptor’ and ‘hypothalamus’ for detection. Mention both sweat glands and vasodilation as effectors. Explain that heat loss brings temperature back to the set point. Show the feedback loop by stating the response opposes the change.

Common mistakes

  • Confusing the hypothalamus with the skin as the detector. Omitting one of the effectors (sweat or vasodilation). Failing to state that the system restores temperature to the set point. Not explicitly linking the response to negative feedback.

Mark scheme (4 marks)

  1. The rise in body temperature is detected (by a receptor / the hypothalamus)
  2. Effectors are activated to reduce body temperature (e.g. sweat glands produce sweat / vasodilation of blood vessels near the skin surface)
  3. Heat is lost from the body so body temperature decreases / returns towards normal (37 °C)
  4. This is a negative feedback system because the response reverses / opposes the original change (rise in temperature)

Key terms in this question

negative feedback system

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