3.3.2Organism Level Systems

Insulin in Blood Sugar Control — OCR Gateway GCSE Combined Science A J250 - Biology Revision Notes & Topical Questions

5 min read 9 parts Lesson 11 of 13

📚 OCR Gateway GCSE Combined Science A J250 - Biology Hub / Topical Revision

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Part 1 of 7Why blood glucose must be controlled

Glucose is the main fuel for respiration.

Its concentration in the blood should stay at about 4 to 6 mmol per dm³.

After eating a meal containing carbohydrates, digestion produces glucose which is absorbed into the blood, raising the concentration.

If it stays high, the concentration of the blood changes, water moves out of cells by osmosis and tissues are damaged.

Between meals and during exercise, glucose is used and the level falls, so the body needs to be able to raise it again.

Pancreas

The pancreas monitors the glucose level and releases hormones to control it.

Part 2 of 7How insulin works

When the blood glucose concentration rises above the normal level, cells in the pancreas detect the change and release insulin into the blood. Insulin is carried by the blood to its target cells, mainly in the liver and muscles, where it:

makes the cells take up glucose from the blood;

Glycogen

stimulates the liver and muscles to convert glucose into glycogen, a storage carbohydrate;

increases the use of glucose in respiration in cells.

These actions reduce the blood glucose concentration back to normal. As the level falls, the pancreas secretes less insulin: negative feedback. The glycogen can be broken down again later (see the next lesson).

Part 3 of 7Type 1 diabetes

In type 1 diabetes the pancreas does not make enough insulin, usually because the immune system has destroyed the insulin-producing cells. Blood glucose rises to a dangerously high level after eating, and glucose is lost in the urine. Symptoms are thirst, frequent urination, tiredness and weight loss. It is controlled by:

Type 1 diabetes

Insulin injections

Insulin injections or an insulin pump, usually before meals, since insulin is a protein and would be digested if taken as a tablet.

Careful diet, with limited intake of simple carbohydrates, and regular meals.

Blood glucose monitoring using a small sensor or finger-prick test.

The dose has to match the food eaten and the exercise taken. Too much insulin causes the glucose level to fall too low (hypoglycaemia), causing shakiness, confusion or unconsciousness; eating sugar corrects it.

Part 4 of 7Type 2 diabetes

In type 2 diabetes the body cells stop responding properly to insulin (insulin resistance), or too little insulin is made.

Type 2 diabetes

It is linked to obesity, poor diet, inactivity, age and family history.

It is managed with a healthy diet that is low in refined carbohydrate, regular exercise and weight loss, and sometimes drugs or insulin.

The number of cases is rising with obesity.

Feature	Type 1	Type 2
Cause	No insulin made	Cells do not respond to insulin
Usual onset	Childhood or young age	Usually later in life
Treatment	Insulin injections plus diet	Diet, exercise, drugs; sometimes insulin

Part 5 of 7Interpreting glucose graphs

A graph of blood glucose after a meal in a healthy person shows a rise for about an hour, followed by a quick fall as insulin acts.

In a person with diabetes, the peak is higher and the level returns to normal slowly or not at all.

A glucose tolerance test records the glucose levels after a drink of glucose.

To answer questions, compare figures: the peak, the time taken to return to normal, and the values at the start.

Then explain: in diabetes insulin is missing or ineffective, so glucose is not taken up and converted to glycogen.

Part 6 of 7Using glucose data, calculations and monitoring

Questions often give a table of blood glucose concentration at times after a meal.

For a healthy person the concentration might rise from 5 to 8 mmol per dm³ and return to 5 within two hours.

For a person with diabetes it might rise from 9 to 16 and stay high.

Calculate the percentage increase using (increase / starting value) x 100, so 5 to 8 is a 60% rise.

Compare both sets of results and relate the difference to insulin.

Monitoring and treatment have improved in recent years.

Continuous glucose monitors under the skin send readings to a phone,

and insulin pumps give small amounts of insulin throughout the day with larger doses at meals.

Pancreas or islet cell transplants can free a patient from injections, but they need immunosuppressant drugs, and donor organs are scarce.

Genetic engineering is also relevant: human insulin is produced by bacteria,

which have been given the human insulin gene,
so it is cheaper and avoids using animal insulin that could cause reactions.

Long-term complications of poorly controlled diabetes include damage to the eyes, kidneys, nerves and blood vessels,

which explains why careful control matters even when the patient feels well.

Part 7 of 7Exam-style questions

Describe how the body responds when blood glucose concentration rises after a meal. [4]4 marks
Explain why a person with type 1 diabetes injects insulin rather than taking it as a tablet. [2]2 marks
Suggest why people with type 2 diabetes are advised to lose weight and take exercise. [2]2 marks

Key terms

Term	Meaning
Insulin	Hormone from the pancreas that lowers blood glucose.
Glycogen	A storage carbohydrate made from glucose in the liver and muscles.
Pancreas	Organ that makes insulin, glucagon and digestive enzymes.
Type 1 diabetes	Condition in which the pancreas fails to make enough insulin.
Type 2 diabetes	Condition in which cells respond poorly to insulin.
Hypoglycaemia	Blood glucose level that is too low.
Target cells	Cells that respond to a particular hormone.

Avoid these mistakes

Saying insulin converts glycogen to glucose; it does the opposite.

Writing that diabetes means there is no glucose in the blood.

Saying insulin is made in the liver; it is made in the pancreas.

Confusing type 1 (no insulin) and type 2 (insulin resistance).

Stating insulin is taken as a tablet.

Last updated: 20 October 2026