What you'll learn
This revision guide covers everything you need to know about diabetes for AQA GCSE Biology. You'll understand how the body normally controls blood glucose concentration, what goes wrong in Type 1 and Type 2 diabetes, and how each condition is managed. This topic links directly to homeostasis and the endocrine system, and is frequently examined through data interpretation and comparison questions.
Key terms and definitions
Diabetes — a disease where the body cannot properly control blood glucose concentration, leading to dangerously high levels
Insulin — a hormone produced by the pancreas that causes glucose to move from the blood into cells, reducing blood glucose concentration
Pancreas — the organ that monitors and controls blood glucose concentration by secreting hormones including insulin
Glucagon — a hormone produced by the pancreas that causes glucose to be released from glycogen stores in the liver, increasing blood glucose concentration
Type 1 diabetes — a disorder where the pancreas fails to produce sufficient insulin, usually developing in childhood
Type 2 diabetes — a disorder where the body cells no longer respond properly to insulin, strongly associated with obesity and poor diet
Blood glucose concentration — the amount of glucose dissolved in the blood, normally maintained between 4-6 mmol/dm³
Glycogen — a storage carbohydrate found in the liver and muscles, made from many glucose molecules joined together
Core concepts
Normal blood glucose regulation
The body maintains blood glucose concentration within a narrow range through negative feedback mechanisms. This is essential because:
- All cells require glucose for respiration to release energy
- Blood glucose that is too high damages blood vessels and organs
- Blood glucose that is too low means cells cannot respire properly, leading to unconsciousness
The pancreas constantly monitors blood glucose levels. When blood glucose rises (after eating), the pancreas detects this change and responds by:
- Secreting insulin into the bloodstream
- Insulin binds to receptors on liver and muscle cells
- These cells take up glucose from the blood
- Liver and muscle cells convert excess glucose into glycogen for storage
- Blood glucose concentration decreases back to normal
When blood glucose falls (during exercise or between meals), the pancreas responds by:
- Secreting glucagon into the bloodstream
- Glucagon causes liver cells to break down glycogen stores
- Glucose is released into the blood
- Blood glucose concentration increases back to normal
This system ensures blood glucose stays within the optimal range of approximately 4-6 mmol/dm³.
Type 1 diabetes: cause and mechanism
Type 1 diabetes develops when the pancreas produces little or no insulin. This occurs because:
- The immune system attacks and destroys the insulin-secreting cells in the pancreas
- This is an autoimmune disease — the body's immune system mistakenly targets its own cells
- The condition usually appears in childhood or adolescence
- Patients cannot produce enough insulin to control their blood glucose
Without sufficient insulin, the following problems occur:
- Blood glucose concentration rises to dangerous levels after eating
- Cells cannot take up enough glucose from the blood
- Cells lack glucose for respiration
- Excess glucose is excreted in urine (the kidneys cannot reabsorb it all)
- The person feels tired and fatigued due to insufficient cellular respiration
Type 1 diabetes is not caused by diet or lifestyle — it results from a malfunction of the immune system. Scientists do not fully understand why the immune system begins attacking pancreatic cells, though genetic and environmental factors may play a role.
Type 2 diabetes: cause and mechanism
Type 2 diabetes develops when body cells stop responding properly to insulin. Key characteristics include:
- The pancreas may still produce insulin (sometimes even more than normal)
- Liver and muscle cells become insulin-resistant — they no longer respond effectively to the hormone
- Blood glucose concentration remains too high because cells do not take up glucose efficiently
- The condition usually develops in adults, though increasingly affects younger people
- Strongly linked to obesity, poor diet, and lack of exercise
Risk factors for Type 2 diabetes:
- Obesity — particularly excess fat around the abdomen
- Poor diet — high in refined carbohydrates and sugars, low in fibre
- Lack of physical activity — sedentary lifestyle
- Age — risk increases with age
- Genetics — family history increases risk
- Ethnicity — higher rates in people of African-Caribbean, Black African, and South Asian descent
The global increase in Type 2 diabetes correlates with rising obesity rates. In the UK and Caribbean nations, Type 2 diabetes has become a major public health concern, with prevention campaigns focusing on healthy eating and regular exercise.
Symptoms of diabetes
Both types share common symptoms, though Type 1 symptoms typically appear more rapidly:
- Increased thirst and frequent urination (kidneys remove excess glucose in urine, drawing water with it)
- Extreme tiredness (cells cannot access glucose for respiration)
- Weight loss (particularly Type 1 — body breaks down fat and protein for energy)
- Blurred vision (high glucose levels affect the eye lens)
- Slow healing of wounds (high glucose damages blood vessels and immune function)
Type 1 symptoms often develop quickly over weeks. Type 2 symptoms may develop gradually over months or years, sometimes remaining undiagnosed for long periods.
Treatment and management of Type 1 diabetes
Type 1 diabetes is managed through insulin therapy:
- Patients inject insulin several times daily or use an insulin pump
- Insulin dose must match carbohydrate intake and activity levels
- Blood glucose must be monitored regularly using finger-prick tests or continuous monitors
- Patients learn to calculate appropriate insulin doses based on food and exercise
Modern insulin treatment approaches:
- Rapid-acting insulin injected before meals to deal with glucose from food
- Long-acting insulin provides background insulin throughout the day
- Insulin pumps deliver insulin continuously through a cannula under the skin
Patients must also:
- Follow a balanced diet with controlled carbohydrate portions
- Monitor blood glucose concentration multiple times daily
- Adjust insulin doses for exercise (physical activity reduces blood glucose)
- Recognise and treat hypoglycaemia (dangerously low blood glucose)
Without treatment, Type 1 diabetes is fatal. With proper management, patients can live full, active lives.
Treatment and management of Type 2 diabetes
Type 2 diabetes management focuses on lifestyle changes as the first approach:
Dietary modifications:
- Reduce intake of simple sugars and refined carbohydrates
- Increase fibre intake (slows glucose absorption)
- Control portion sizes to achieve weight loss
- Choose foods with a low glycaemic index (release glucose slowly)
Physical activity:
- Regular exercise improves insulin sensitivity
- Muscles take up glucose during activity, lowering blood glucose
- Exercise aids weight loss, further improving glucose control
- Aim for at least 150 minutes of moderate activity weekly
Weight management:
- Losing 5-10% of body weight significantly improves glucose control
- Reduces insulin resistance in many patients
- May reverse Type 2 diabetes in some cases if caught early
If lifestyle changes prove insufficient, medication may be prescribed:
- Metformin — reduces glucose production by the liver and improves insulin sensitivity
- Other medications that stimulate insulin production or improve cellular glucose uptake
- In advanced cases, insulin injections may be required
Early intervention through lifestyle modification can prevent or delay Type 2 diabetes in high-risk individuals. Prevention is far more effective than treatment.
Comparing Type 1 and Type 2 diabetes
| Feature | Type 1 | Type 2 |
|---|---|---|
| Cause | Pancreas cannot produce insulin | Body cells become insulin-resistant |
| Age of onset | Usually childhood/adolescence | Usually adulthood (increasingly younger) |
| Relationship to obesity | No link | Strong association |
| Preventable? | No | Often preventable through lifestyle |
| Treatment | Insulin injections essential | Lifestyle changes, sometimes medication |
| Speed of onset | Rapid (weeks) | Gradual (months to years) |
| Prevalence | Approximately 10% of diabetes cases | Approximately 90% of diabetes cases |
Both conditions result in high blood glucose concentration if untreated, leading to serious complications including:
- Cardiovascular disease
- Kidney damage
- Vision problems and blindness
- Nerve damage
- Poor circulation leading to amputation
Worked examples
Example 1: A student investigates how blood glucose changes after a meal in a person with and without diabetes. The graph shows blood glucose concentration over 3 hours.
Question: Explain why the blood glucose concentration in the person with Type 1 diabetes remains high after eating, while the healthy person's returns to normal. (3 marks)
Model answer:
- The person with Type 1 diabetes cannot produce (enough) insulin ✓
- So glucose is not taken up from the blood into cells / liver does not store glucose as glycogen ✓
- Therefore blood glucose concentration remains high / does not return to normal ✓
Examiner note: Notice each mark requires a separate point. Simply stating "they don't produce insulin" scores only 1 mark without explaining the consequence.
Example 2: Scientists investigated the link between body mass index (BMI) and the development of Type 2 diabetes in 5000 adults over 10 years.
Question: Describe the relationship shown between BMI and Type 2 diabetes. Suggest why this relationship exists. (4 marks)
Model answer:
- As BMI increases, the percentage of people developing Type 2 diabetes increases ✓
- People with higher BMI are more likely to be obese / carry excess body fat ✓
- Obesity causes cells to become resistant to insulin ✓
- So cells do not respond to insulin / glucose is not taken into cells (so blood glucose remains high) ✓
Examiner note: "Describe" requires you to state the trend. "Suggest" means apply your knowledge to explain — you may not have learned this exact scenario but can use your understanding of diabetes.
Example 3: A person with Type 2 diabetes is given advice about managing their condition.
Question: Explain how each of the following helps control Type 2 diabetes: (a) Reducing the amount of sugar in the diet (2 marks) (b) Taking regular exercise (2 marks)
Model answer: (a)
- Less sugar in diet means less glucose absorbed into blood ✓
- So blood glucose concentration does not rise as high (after meals) / easier to control ✓
(b)
- Exercise causes muscles to take up more glucose (from the blood for respiration) ✓
- Exercise helps reduce body mass / fat, which improves the body's response to insulin / reduces insulin resistance ✓
Examiner note: With 2 marks available for each part, you need two distinct points. Make sure your second point adds new information rather than rewording the first.
Common mistakes and how to avoid them
Confusing which type is which — Remember: Type 1 = cannot produce insulin (usually young onset); Type 2 = cells do not respond to insulin (linked to obesity). Use "1" for "one problem = no insulin" as a memory aid.
Saying Type 1 is caused by diet — Type 1 is an autoimmune condition, not lifestyle-related. Only Type 2 has strong links to obesity and diet. Be precise about which type you're discussing.
Stating "insulin controls blood sugar" — Use correct terminology: insulin causes glucose to move from blood into cells, or causes liver to store glucose as glycogen. Avoid vague statements.
Writing that diabetics "lack glucose" — Diabetics have too much glucose in the blood because it cannot enter cells properly. Their cells may lack glucose, but blood glucose is high.
Forgetting the role of glucagon — Questions sometimes ask about the full control system. Remember glucagon is the opposite of insulin: it raises blood glucose by converting glycogen back to glucose.
Not using data from graphs or tables — In data questions, quote specific values and describe trends using the data provided. Don't make general statements without evidence from the source.
Exam technique for "Diabetes: Type 1 and Type 2"
"Explain" questions require cause and effect — State what happens AND why it happens. For example: "Insulin is not produced (what) so glucose remains in the blood / cells cannot take up glucose (why/consequence)." Each linked point typically earns one mark.
Compare/contrast questions need both types mentioned — If asked to compare Type 1 and Type 2, you must discuss both. Use comparative language: "whereas," "however," "in contrast." Tables can help structure your answer clearly.
Apply knowledge to unfamiliar contexts — You might see data about diabetes prevalence in Caribbean nations, new treatments, or prevention programmes. Use your core knowledge about causes and mechanisms to interpret new scenarios.
Practice calculations — Occasionally questions involve calculating percentage change in blood glucose or interpreting BMI data. Show your working: (change ÷ original) × 100 for percentage change.
Quick revision summary
Diabetes occurs when blood glucose concentration cannot be controlled properly. Type 1 diabetes results from the pancreas failing to produce sufficient insulin, usually due to autoimmune destruction of insulin-secreting cells. It requires insulin injection treatment. Type 2 diabetes develops when body cells become resistant to insulin, strongly linked to obesity and poor lifestyle. It is managed primarily through diet, exercise, and weight loss. Both types cause dangerously high blood glucose if untreated, but differ fundamentally in cause, prevention, and treatment approach.