The human body constantly monitors and adjusts its internal conditions. Describe how the body detects and responds to a rise in core body temperature, and explain why maintaining a stable internal temperature is necessary for enzyme-controlled reactions.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Body temperature in a healthy adult is maintained at approximately 37 °C. When core temperature rises above this level, several automatic responses are triggered.
Model answer (5 marks)
Receptors (thermoreceptors) in the skin and in the hypothalamus sense the rise in core temperature.
The hypothalamus sends signals to the sweat glands, causing them to secrete more sweat. The increased sweat evaporates from the skin, removing heat.
At the same time, the hypothalamus induces vasodilation of blood vessels close to the skin surface. Wider vessels allow more blood to reach the skin, where heat is lost to the environment.
Enzymes work best at an optimum temperature (≈37 °C). If the body temperature rises above this, the enzyme’s three‑dimensional shape, especially the active site, changes.
A changed active site no longer fits the substrate; enzyme–substrate complexes cannot form, so metabolic reactions slow or stop.
The hypothalamus sends signals to the sweat glands, causing them to secrete more sweat. The increased sweat evaporates from the skin, removing heat.
At the same time, the hypothalamus induces vasodilation of blood vessels close to the skin surface. Wider vessels allow more blood to reach the skin, where heat is lost to the environment.
Enzymes work best at an optimum temperature (≈37 °C). If the body temperature rises above this, the enzyme’s three‑dimensional shape, especially the active site, changes.
A changed active site no longer fits the substrate; enzyme–substrate complexes cannot form, so metabolic reactions slow or stop.
Examiner tips
- Use the word "thermoreceptors" and mention both skin and hypothalamus. Include "sweat glands" and "vasodilation" as the two main responses. Explain the enzyme effect by linking temperature to shape change and loss of substrate binding. Keep each point concise to fit the 5‑mark structure.
Common mistakes
- Failing to name both skin and hypothalamic receptors. Omitting the link between enzyme shape change and loss of substrate binding. Using vague terms like "heat loss" without specifying sweating or vasodilation.
Mark scheme (5 marks)
- Receptors / thermoreceptors in the skin and/or hypothalamus detect the rise in temperature
- Sweat glands produce more sweat / sweating increases
- Vasodilation occurs — blood vessels near the skin surface widen / more blood flows to the skin, increasing heat loss
- Enzymes have an optimum temperature; if temperature rises too far above 37 °C, the enzyme's shape / active site changes
- If the active site changes shape, the substrate can no longer fit / enzyme–substrate complexes cannot form, so metabolic reactions slow or stop
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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