How does the body keep blood glucose steady, and what goes wrong in diabetes?
The control of blood glucose concentration by insulin and glucagon, the roles of the pancreas and liver, negative feedback, and the causes and treatment of type 1 and type 2 diabetes.
A focused answer to the OCR Gateway GCSE Biology A topic B3 on the control of blood glucose, covering insulin and glucagon, the pancreas and liver, negative feedback, and the causes and treatment of type 1 and type 2 diabetes.
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What this dot point is asking
OCR wants you to explain how blood glucose is controlled by insulin and glucagon through negative feedback, describe the roles of the pancreas and liver, and compare the causes and treatments of type 1 and type 2 diabetes.
Why blood glucose must be controlled
Glucose is the fuel for respiration, so every cell needs a steady supply. But too much or too little glucose in the blood is harmful, so the body keeps the concentration within a narrow range. This is part of homeostasis, the maintenance of a constant internal environment.
The control system uses negative feedback: when the level moves away from normal, the body acts to bring it back, and when it returns to normal, the correction stops.
Lowering blood glucose: insulin
When blood glucose is too high (for example after a meal high in carbohydrate):
- The pancreas detects the high glucose.
- The pancreas releases the hormone insulin into the blood.
- Insulin causes body cells, especially in the liver and muscles, to take up glucose.
- The liver converts the excess glucose into glycogen, an insoluble store.
This lowers the blood glucose back towards normal.
Raising blood glucose: glucagon
When blood glucose is too low:
- The pancreas detects the low glucose.
- The pancreas releases the hormone glucagon into the blood.
- Glucagon causes the liver to convert stored glycogen back into glucose.
- The glucose is released into the blood.
This raises the blood glucose back towards normal.
Type 1 diabetes
Type 1 diabetes is a condition in which the pancreas produces little or no insulin. It often begins in childhood. Without insulin, blood glucose can rise to dangerously high levels after eating.
It is treated with insulin injections (the dose matched to meals and activity), together with a controlled diet and regular monitoring of blood glucose.
Type 2 diabetes
Type 2 diabetes is a condition in which the body cells stop responding properly to insulin (insulin resistance), so glucose is not taken up effectively even though insulin is present. It is linked to risk factors such as obesity, a poor diet and inactivity, and is more common in later life.
It is usually managed first by a controlled diet, losing weight and taking exercise, and sometimes by medication. You meet type 2 diabetes again as a non-communicable disease in topic B6.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20196 marksExplain how the body returns blood glucose concentration to normal after a meal high in sugar, and how it responds when blood glucose falls too low. Use the terms insulin, glucagon and glycogen.Show worked answer →
A 6-mark extended response using negative feedback. Mark it for both directions.
Blood glucose too high (after a meal): the pancreas detects the high glucose and releases insulin into the blood. Insulin causes body cells (especially in the liver and muscles) to take up glucose, and causes the liver to convert excess glucose into glycogen for storage. This lowers the blood glucose back to normal.
Blood glucose too low: the pancreas detects the low glucose and releases glucagon. Glucagon causes the liver to convert stored glycogen back into glucose, which is released into the blood. This raises the blood glucose back to normal.
Markers reward both responses with the correct hormones (insulin lowers, glucagon raises), the conversion to and from glycogen in the liver, and the idea that this keeps blood glucose within a narrow range (negative feedback).
OCR 20214 marksCompare the causes and the usual treatments of type 1 and type 2 diabetes.Show worked answer →
A 4-mark Compare question.
Type 1: caused by the pancreas producing little or no insulin (often starting in childhood). It is treated with insulin injections, along with controlling diet and monitoring blood glucose.
Type 2: the body cells stop responding properly to insulin (insulin resistance), and it is linked to risk factors such as obesity and inactivity. It is usually managed first by a controlled diet, weight loss and exercise, and sometimes medication.
Markers reward the paired contrasts: type 1 is too little insulin treated by injections; type 2 is cells not responding to insulin, managed mainly by diet and lifestyle. A strong answer notes type 2 is associated with obesity as a risk factor.
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