Disease and response · GCSE Biology
Blood glucose and diabetes
Control blood glucose for GCSE Biology: pancreas, insulin, glycogen in liver and muscle, glucagon on Higher tier, and the Type 1 versus Type 2 diabetes treatments examiners split.
High glucose: insulin, glucose into cells, stored as glycogen, level falls. Low glucose (Higher): glucagon, glycogen to glucose, level rises. Type 1: no insulin, inject. Type 2: cells do not respond, diet and exercise first.
The important bits
What you need to know
- 1
Blood glucose must stay in a narrow range so cells have fuel for respiration without drawing water out of cells by osmosis (high glucose is osmotically active).
- 2
When blood glucose is too high (after a meal), the pancreas releases insulin. Insulin makes liver and muscle cells take up glucose and convert it to glycogen for storage. Blood glucose falls.
- 3
On Higher tier, when blood glucose is too low, the pancreas releases glucagon. Glucagon makes the liver break glycogen down to glucose, which is released into the blood. Blood glucose rises. This is negative feedback.
- 4
Type 1 diabetes: the pancreas (islet cells) makes little or no insulin, often from a young age. Treatment: insulin injections, monitoring carbohydrate intake. Not caused by a high-sugar diet in the GCSE story; it is a lack of the hormone.
- 5
Type 2 diabetes: cells do not respond properly to insulin (insulin resistance), often linked to obesity and age. Treatment: reduce carbohydrate and energy intake, exercise, then drugs; insulin is not the first-line story.
- 6
Glycogen is the storage carbohydrate in liver and muscle (animals). Starch is the plant equivalent. Do not say insulin “breaks down sugar”.
- 7
Exercise uses glucose in muscle respiration, so it can lower blood glucose — useful in Type 2 management. Adrenaline also raises glucose in an emergency, opposing insulin briefly.
- 8
Everyone has blood glucose. Diabetes is a failure of control, not the presence of sugar in blood as if healthy people had none.
Quotations worth analysing
Short evidence. Real method.
“Insulin causes glucose to be taken up by cells and stored as glycogen.”
Pancreas secretes it; liver and muscle are the targets. “Insulin eats sugar” will not score.
“Type 1 diabetes is treated with insulin; Type 2 is treated first with diet and exercise.”
Match type to treatment. Swapping them is a high-frequency error.
“Glucagon causes glycogen to be converted to glucose (Higher).”
Opposite of insulin. Together they are negative feedback. Foundation papers may omit glucagon.
Go deeper
How do I write the insulin story in four marks?
Blood glucose rises (meal). Pancreas detects the rise and secretes insulin into the blood. Insulin binds to liver and muscle cells. Those cells take in glucose and convert it to glycogen. Blood glucose returns to the set point. That is negative feedback. Do not send insulin to the kidney as the main story (the kidney does filter glucose, but insulin’s job is cellular uptake and storage). Do not say insulin turns glucose into energy — respiration transfers energy from glucose once it is in the cell. If the paper is Higher and glucose then falls too low, glucagon is released, glycogen → glucose, level rises. Drawing a simple up-and-down sketch in revision beats a paragraph that never names glycogen.
Go deeper
How do Type 1 and Type 2 differ in cause and treatment?
Type 1: immune system or other damage means islet cells cannot make insulin. Glucose stays in the blood, cells starve, urine may contain glucose, thirst and weight loss can follow. Inject insulin because the hormone is missing. Type 2: insulin is often still made, but target cells do not respond (receptor or pathway problem), commonly associated with obesity. Reducing energy intake and increasing exercise improves sensitivity and uses glucose. Drugs can help later; insulin is not the opening treatment. In data questions, a BMI correlation with Type 2 is not a Type 1 story. Never write that diabetics “have sugar in the blood” as if others do not. The issue is control around 4–7 mmol/dm³ in typical mark-scheme language, not the existence of glucose.
Go deeper
Where do osmosis and respiration hide in this topic?
High blood glucose lowers water potential, so water can leave cells by osmosis — one reason untreated diabetes causes dehydration and frequent urination as the kidney dumps glucose and water follows. Inside cells, glucose is the respiration fuel: no insulin in Type 1 means glucose cannot enter many cells efficiently, so the person is tired despite high blood glucose. Exercise increases glucose use in muscle (respiration) and can increase insulin sensitivity in Type 2. These links turn a hormone page into a whole-course answer. If a six-mark asks why insulin injections must be balanced with food and exercise, say: too much insulin plus little carbohydrate can drop glucose too far (hypoglycaemia); extra food without insulin raises it; exercise uses glucose so dose may need adjusting.
See the idea in action
After a carbohydrate meal, blood glucose rises. The pancreas releases insulin. Liver and muscle cells take up glucose and store it as glycogen, so blood glucose falls. A Type 1 patient cannot make insulin, so they inject it and still have to match dose to meals. A Type 2 patient may still make insulin, but their cells do not respond well; a doctor starts with diet and exercise, not with the Type 1 injection story. Glucagon (Higher) would be released if glucose then fell too low, converting glycogen back to glucose.
Exam technique
Turn knowledge into marks
Name pancreas, insulin, liver/muscle, glycogen. For diabetes, say Type 1 or Type 2 and match the treatment. On Higher, add glucagon as the opposite hormone. Never write that insulin breaks down sugar.
Common mistakes
Do not give these marks away
- 01
Saying insulin “breaks down sugar” instead of causing uptake and storage as glycogen.
- 02
Swapping Type 1 (no insulin, injections) with Type 2 (cells do not respond, lifestyle first).
- 03
Writing that healthy people have no glucose in the blood, or putting glucagon on a Foundation-only answer as if it replaced insulin.
What does insulin do when blood glucose is too high?
AIt causes glycogen to be broken down to glucose
BIt causes liver and muscle cells to take up glucose and store it as glycogen
CIt raises body temperature
DIt stimulates pain receptors
Show the answer
It causes liver and muscle cells to take up glucose and store it as glycogen. Insulin is released by the pancreas when glucose is high. Cells take up glucose and store it as glycogen, so blood glucose falls. Glucagon does the reverse on Higher tier.
Quick questions
If this is the bit you searched
How does insulin control blood glucose?
The pancreas releases insulin when glucose is high. Insulin makes liver and muscle take up glucose and store it as glycogen, so blood glucose falls.
What is the difference between Type 1 and Type 2 diabetes?
Type 1: little or no insulin, treated with insulin injections. Type 2: cells do not respond properly to insulin, often linked to obesity, treated first with diet and exercise.
What does glucagon do?
Higher tier: when blood glucose is low, glucagon from the pancreas makes the liver convert glycogen to glucose, raising blood glucose.
Where is glycogen stored?
In the liver and in muscles. It is the animal storage carbohydrate made from glucose. Plants store starch instead.