Explain blood-glucose negative feedback
Compare insulin and glucagon effects in muscle and liver cells.
Section 14.1 · Homeostasis in mammals
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not a practical skills certification.
Before you begin
- A control system detects a change, communicates information and changes an effector response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which hormone lowers high blood glucose?
What you will learn
- Explain how insulin lowers elevated blood glucose
- Explain how glucagon raises low blood glucose through liver-cell responses
Build the explanation
When blood glucose is high, pancreatic beta cells release insulin. Insulin increases glucose uptake by muscle cells and promotes glucose storage as glycogen in liver and muscle, lowering blood glucose. When blood glucose is low, pancreatic alpha cells release glucagon. Glucagon acts mainly on liver cells, stimulating glycogen breakdown and glucose release into blood. Each response opposes the initial deviation; this is negative feedback.
Apply the limits
Insulin acts on muscle and liver cells; glucagon's stated target in this outcome is liver cells. Do not claim muscle releases glucose into blood in response to glucagon or confuse glycogen synthesis with glycogen breakdown.
Pause and explain
During fasting, a student says glucagon lowers blood glucose by moving it into liver glycogen. Correct the direction.
Worked example
Which hormone is released when blood glucose is low, and what does it do in liver cells?
Show the worked solution
- Low blood glucose stimulates glucagon release.
- Glucagon promotes glycogen breakdown and glucose release.
Answer Glucagon raises blood glucose by acting on liver cells.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare insulin and glucagon responses to opposite blood-glucose changes.
Give me a hint
Name the relevant structure or signal, then state its effect.
Compare my reasoning
- Insulin is released when glucose is high and promotes uptake or storage.
- Glucagon is released when glucose is low and promotes liver glycogen breakdown and glucose release.
Insulin lowers raised blood glucose through uptake and storage in muscle and liver. Glucagon raises low blood glucose by promoting glycogen breakdown in liver cells and glucose release.
Look for these in your work
- Correct mechanism
- Direction of response explained
After a carbohydrate-rich meal, blood glucose rises. Predict the hormone response and one target-tissue effect.
Give me a hint
Separate the observed change from the body's response.
Compare my reasoning
- Insulin secretion increases.
- Muscle cells take up more glucose and liver cells store more as glycogen.
Insulin release increases. It promotes glucose uptake by muscle cells and storage as glycogen in liver and muscle, helping return blood glucose toward its range.
Look for these in your work
- Evidence interpreted
- Control step identified
During fasting, a student says glucagon lowers blood glucose by moving it into liver glycogen. Correct the direction.
Give me a hint
Apply the mechanism to the new context without claiming more than the evidence shows.
Compare my reasoning
- Glucagon is associated with low blood glucose.
- It stimulates liver glycogen breakdown and glucose release into blood.
Glucagon raises blood glucose. It promotes breakdown of liver glycogen and release of glucose into the blood; insulin promotes storage when blood glucose is high.
Look for these in your work
- New context applied
- Limits preserved
Common mistakes
- Saying glucagon lowers blood glucose
- Giving glucagon a muscle-cell role in blood glucose release
What can you explain now?
Which hormone lowers high blood glucose?
Compare with the explanation
Insulin
Insulin increases glucose uptake and storage.
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Make it stick
How do insulin and glucagon oppose changes in blood glucose?
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