Explain how the body responds to a sudden drop in core body temperature, such as when a person enters cold water.

IB DP Biology Standard 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 the fall in core body temperature.
The hypothalamus, acting as the control centre or thermostat, receives this information and initiates a response.
Effectors are activated:
• Vasoconstriction of skin arterioles reduces heat loss.
• Shivering causes rapid muscle contractions that generate heat.
These responses form a negative‑feedback loop – once core temperature has returned to the set point, the corrective actions are turned off.

Examiner tips

  • Mention the hypothalamus as the control centre; link receptors to effectors; describe both vasoconstriction and shivering; state that it is a negative‑feedback system.
  • Use the exact terms ‘thermoreceptors’, ‘vasoconstriction’, ‘shivering’, and ‘negative feedback’ as the mark scheme expects.

Common mistakes

  • Confusing the hypothalamus with the skin as the sole control centre; omitting either vasoconstriction or shivering; failing to identify the system as negative feedback.

Mark scheme (4 marks)

  1. Thermoreceptors in the skin / hypothalamus detect the fall in core body temperature
  2. The hypothalamus acts as the control centre / thermostat and coordinates the response
  3. Effectors are activated: vasoconstriction of skin arterioles reduces heat loss / shivering generates heat through muscle contraction
  4. This is an example of negative feedback — once core temperature returns to the set point, the corrective responses are switched off

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