Explain how the endocrine system uses negative feedback to return blood glucose concentration to its optimum level after a person goes for a long run.

OCR GCSE Biology A: Gateway Science (J247) — B3.2 Coordination and control — the endocrine system · Explain · 4 marks · View as Markdown

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

During a long run, muscles use glucose rapidly for respiration, causing blood glucose concentration to fall below its optimum level. The endocrine system detects this change and responds to restore balance.

Model answer (4 marks)

The pancreas senses the drop in blood glucose and releases glucagon into the bloodstream.
Glucagon stimulates the liver to convert stored glycogen into glucose.
The released glucose enters the blood, raising glucose concentration towards the optimum level.
This is negative feedback because the response (glucose rise) opposes the initial fall in glucose.

Examiner tips

  • Use the word ‘glucagon’ and ‘pancreas’ to show detection. Show the sequence: fall → glucagon → glycogen → glucose → rise. Explain that the rise opposes the fall to restore balance.

Common mistakes

  • Confusing insulin with glucagon. Failing to mention the liver as the site of glycogen breakdown. Not linking the rise in glucose back to the concept of negative feedback.

Mark scheme (4 marks)

  1. The pancreas detects the fall in blood glucose concentration and releases glucagon into the bloodstream.
  2. Glucagon causes glycogen to be converted into glucose (in the liver).
  3. This raises / increases blood glucose concentration back towards the optimum level.
  4. This is an example of negative feedback because the response reverses / opposes the original change (fall in blood glucose).

Key terms in this question

endocrine system

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