Explain how the body responds when blood glucose concentration falls below the optimum level. In your answer, name the hormone involved and describe the mechanism by which blood glucose concentration is returned to normal.

WJEC A-Level Biology (Wales) — 4.2 Inheritance · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

The pancreas senses a fall in blood glucose.
1. Low glucose triggers the alpha cells of the pancreas to secrete glucagon.
2. Glucagon enters the bloodstream and travels to the liver.
3. In the liver, glucagon activates glycogen phosphorylase, converting stored glycogen into glucose.
4. The released glucose enters the blood, raising glucose concentration back to the optimum level, completing the negative‑feedback loop.

Examiner tips

  • Use the word "pancreas" and "alpha cells" to show detection. Mention "glucagon" as the hormone. Explain the liver action: glycogen → glucose. Show the return to normal as negative feedback.

Common mistakes

  • Confusing insulin with glucagon. Forgetting to mention the liver as the site of glycogen breakdown. Omitting the negative‑feedback description.

Mark scheme (5 marks)

  1. The pancreas detects the fall in blood glucose concentration / low blood glucose is detected
  2. Glucagon is released / secreted by the pancreas
  3. Glucagon travels in the blood(stream) to the liver / glucagon is a chemical messenger carried in the blood
  4. Glycogen is converted into glucose in the liver / glucagon stimulates the conversion of glycogen to glucose
  5. Blood glucose concentration rises back to / returns to the optimum / normal level (negative feedback)

Key terms in this question

glucose · blood glucose concentration

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