Insulin vs Glucagon

Insulin vs Glucagon

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

The key difference

Insulin lowers blood glucose by stimulating cells to take up glucose and the liver to convert glucose into glycogen. Glucagon raises blood glucose by stimulating the liver to convert glycogen back into glucose. Together they maintain blood glucose homeostasis.

Insulin and glucagon are two pancreatic hormones that work antagonistically to keep blood glucose concentration within a narrow, safe range. This is a classic example of negative feedback: a concept that examiners test frequently at both Core and Extended level.

Feature	Insulin	Glucagon
Source	Beta (β) cells of the islets of Langerhans in the pancreas	Alpha (α) cells of the islets of Langerhans in the pancreas
Released when	Blood glucose concentration is too high (e.g. After a meal)	Blood glucose concentration is too low (e.g. Between meals or during exercise)
Effect on blood glucose	Decreases blood glucose	Increases blood glucose
Mechanism	Stimulates body cells to take up glucose; stimulates liver to convert glucose → glycogen (glycogenesis)	Stimulates liver to convert glycogen → glucose (glycogenolysis) and release it into the blood
Target organ	Liver and body cells (especially muscle cells)	Liver
Type of feedback	Negative feedback: rising glucose triggers insulin, which lowers glucose, which reduces insulin secretion	Negative feedback: falling glucose triggers glucagon, which raises glucose, which reduces glucagon secretion

Negative Feedback Explained

Both insulin and glucagon operate through negative feedback. This means that the response (change in blood glucose) acts to cancel out the original stimulus:

Blood glucose rises → pancreas detects the rise → beta cells release insulin → glucose is taken up and converted to glycogen → blood glucose falls back to normal → insulin secretion reduces
Blood glucose falls → pancreas detects the fall → alpha cells release glucagon → glycogen is converted to glucose → blood glucose rises back to normal → glucagon secretion reduces

The result is that blood glucose oscillates around a set point, never going dangerously high or low in a healthy person.

What Happens in Type 1 Diabetes

In Type 1 diabetes, the beta cells of the pancreas are destroyed by the immune system, so the person cannot produce insulin. Without insulin, body cells cannot take up glucose effectively, and the liver cannot convert glucose to glycogen. Blood glucose remains dangerously high after eating (hyperglycaemia). Treatment requires regular insulin injections and careful monitoring of blood glucose levels.

In Type 2 diabetes, the body still produces insulin but the cells become resistant to it: they do not respond properly. This is often linked to obesity, lack of exercise, and genetic factors. Treatment involves diet, exercise, and sometimes medication.

Try a comparison question (4 marks)

After eating a meal, a person's blood glucose concentration rises. Describe how the body returns blood glucose to its normal level. [4]

Show the answer and marking guidance

The pancreas detects the rise in blood glucose concentration
Beta cells in the islets of Langerhans release insulin into the blood
Insulin stimulates body cells to take up glucose from the blood and stimulates the liver to convert glucose into glycogen
Blood glucose concentration decreases back to the normal level (negative feedback)

Original Cambridge-style practice written for this site.

Common comparison mistakes

When answering a compare question, write matched pairs rather than two separate descriptions.

Confusing insulin and glucagon: insulin LOWERS blood glucose, glucagon RAISES it
Saying insulin "breaks down glucose": insulin promotes glucose uptake and conversion to glycogen, not breakdown
Confusing glycogen with glucagon: glycogen is a storage polysaccharide, glucagon is a hormone
Forgetting to mention the pancreas as the organ that detects blood glucose changes and secretes both hormones

Negative Feedback Explained

What Happens in Type 1 Diabetes

Try a comparison question (4 marks)

Common comparison mistakes

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