Homeostasis is the maintenance of a constant internal environment. Explain why it is important for the body to maintain a constant internal temperature and a constant blood glucose concentration.

Pearson Edexcel A-Level Biology A (9BI0) — 4.6 Homeostasis · Explain · 5 marks · View as Markdown

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

During exercise, a student notices they begin to sweat and feel hungry shortly afterwards.

Model answer (5 marks)

1. Enzymes in the body have an optimum temperature; if the body temperature rises above this, enzymes become denatured and lose activity.
2. If the body temperature falls below the optimum, enzyme‑controlled metabolic reactions slow down or stop, reducing the rate of energy production.
3. Glucose is the main fuel for cellular respiration, providing the ATP required for all cellular processes.
4. Low blood glucose means cells cannot respire adequately, so energy for cellular functions is insufficient.
5. High blood glucose draws water out of cells by osmosis, causing cells to shrink and become dehydrated, which impairs cell function.

Examiner tips

  • Use the exact phrases "optimum temperature" and "denatured" for enzymes. Mention both the consequences of too high and too low temperature. State that glucose is the main energy source for respiration. Explain both low and high glucose effects on cells. Keep each point concise to fit the 5‑mark structure.

Common mistakes

  • Confusing body temperature with ambient temperature. Forgetting that high glucose causes water loss from cells. Using vague terms like "heat" instead of "temperature". Failing to mention that enzymes are protein catalysts. Not linking glucose to ATP production.

Mark scheme (5 marks)

  1. Enzymes work best at an optimum temperature / enzymes are denatured if temperature is too high
  2. If body temperature is not maintained, metabolic reactions / enzyme-controlled reactions in cells will slow down or stop
  3. Glucose is needed as a source of energy / for respiration
  4. If blood glucose concentration is too low, cells cannot respire adequately / not enough energy is released for cellular processes
  5. If blood glucose concentration is too high, water moves out of cells by osmosis, causing cells to shrink / become dehydrated

Key terms in this question

homeostasis · internal environment · blood glucose concentration

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