A student regularly trains by cycling long distances. During a training session, the student's muscles use glucose for respiration. Explain how blood glucose concentration is maintained during a long training session when glucose is being used rapidly by muscles.

Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 7 Run for your Life · Explain · 5 marks · View as Markdown

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

During prolonged exercise, muscles respire continuously, consuming large amounts of glucose. The body must respond to prevent blood glucose levels from falling dangerously low.

Model answer (5 marks)

During exercise blood glucose falls as muscles consume it.
1. The pancreas senses the low glucose level.
2. It secretes glucagon.
3. Glucagon stimulates hepatic glycogenolysis.
4. Glucose is released into the blood.
5. Blood glucose rises back to normal – a negative‑feedback homeostatic response.

Examiner tips

  • Use the exact sequence of events; include pancreas, glucagon, glycogenolysis, liver, blood glucose rise.
  • Show the process as a negative‑feedback loop – this is what the scheme rewards.
  • Keep each point short but complete – 5 marks total.

Mark scheme (5 marks)

  1. Blood glucose concentration falls / decreases during exercise
  2. The pancreas detects the low blood glucose concentration and secretes glucagon
  3. Glucagon causes glycogen to be broken down to glucose in the liver
  4. Glucose is released into the bloodstream, raising blood glucose concentration back to normal
  5. This is an example of homeostasis / negative feedback, maintaining a stable internal environment

Key terms in this question

blood glucose concentration

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