A athlete is preparing for a marathon. During training, their blood glucose levels drop significantly. Explain how the body responds to low blood glucose levels to restore them to normal, and describe why this method of communication is suited to coordinating a whole-body response.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
During prolonged exercise, muscles use glucose rapidly as a respiratory substrate. The blood glucose concentration can fall well below the normal range. The body must detect this change and respond to restore balance.
Model answer (5 marks)
The pancreas senses the fall in blood glucose.
The pancreas releases glucagon into the bloodstream.
Glucagon circulates to the liver, the target organ.
In the liver, glucagon stimulates glycogenolysis, converting glycogen back into glucose.
Glucagon raises blood glucose to normal.
Hormones are suited to a whole‑body response because they travel in the blood, can reach all organs, act on multiple target organs simultaneously and sustain the response over a longer period than nervous signalling.
The pancreas releases glucagon into the bloodstream.
Glucagon circulates to the liver, the target organ.
In the liver, glucagon stimulates glycogenolysis, converting glycogen back into glucose.
Glucagon raises blood glucose to normal.
Hormones are suited to a whole‑body response because they travel in the blood, can reach all organs, act on multiple target organs simultaneously and sustain the response over a longer period than nervous signalling.
Examiner tips
- Use the exact terms – pancreas, glucagon, liver, glycogenolysis. Show the sequence of events. Explain why hormones can coordinate a whole‑body response (blood circulation, multiple organs, sustained effect).
Common mistakes
- Confusing insulin with glucagon. Forgetting to mention the liver as the target organ. Saying hormones act only on one organ or that they are fast like nerves.
Mark scheme (5 marks)
- The pancreas detects the fall in blood glucose concentration
- The pancreas releases glucagon (a hormone) into the blood
- Glucagon travels in the blood to the liver (target organ)
- The liver converts glycogen back into glucose (glycogen is broken down), raising blood glucose back to normal
- Hormones are suited to a whole-body response because they travel in the blood and can reach all organs / act on multiple target organs simultaneously / the response is sustained over a longer period compared to nervous communication
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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