Explain how the body responds to a sustained drop in core body temperature, such as during prolonged exposure to a cold environment, to restore normal temperature.

IB DP Biology Higher Level (2023 syllabus) — D3.3 Homeostasis · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Thermoreceptors in the skin and in the hypothalamus detect a fall in core body temperature.
The hypothalamus, acting as the thermoregulatory centre, integrates the signal and sends nerve impulses to effectors.
It triggers shivering – rapid involuntary skeletal‑muscle contractions that increase cellular respiration and generate heat.
It also causes vasoconstriction of skin arterioles, reducing blood flow to the skin and thereby decreasing heat loss by radiation, conduction and convection.

Examiner tips

  • Mention both skin and hypothalamic thermoreceptors first. State the hypothalamus as the integration centre. Include both shivering and vasoconstriction as the two main responses. Use the exact terms ‘shivering’ and ‘vasoconstriction’ to match the mark scheme.

Common mistakes

  • Forgetting to name the hypothalamus as the thermoregulatory centre. Describing vasodilation instead of vasoconstriction. Using vague phrases like ‘body tries to warm up’ instead of specific mechanisms.

Mark scheme (4 marks)

  1. Thermoreceptors in the skin and/or hypothalamus detect a fall in core body temperature
  2. The hypothalamus acts as a thermoregulatory centre / integration centre and sends nerve impulses to effectors
  3. Shivering occurs — rapid involuntary skeletal muscle contractions generate heat through increased cellular respiration
  4. Vasoconstriction of skin arterioles reduces blood flow to the skin surface, reducing heat loss by radiation/conduction/convection

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