OCR GCSE Biology A: Homeostasis, temperature control and blood glucose regulation (J247) – Revision Notes

These revision notes follow the OCR GCSE (9-1) Gateway Science Biology A (J247) specification, Version 4.0 (August 2026), for first assessment in 2018. They cover statements B3.3a to B3.3e of module B3.3. Only B3.3d (glucagon) is in bold in the specification, so it is Higher Tier only; everything else applies to both tiers. For full explanations and worked examples, use the study guide. When you can recall the notes, try the practice questions.

Course pages: OCR GCSE Biology hub and printable checklist. Not sure where to start? Take a free 10-minute diagnostic. Related topics: endocrine system and nervous system.

B3.3a: Why homeostasis matters

Homeostasis is keeping the internal environment constant despite internal and external change.

• Metabolic reactions are controlled by enzymes.
• Too cold: fewer successful collisions, so reactions are too slow.
• Too hot: enzymes denature (shape of the active site changes), so reactions slow sharply.
• Core body temperature is kept near 37 °C.
• Blood glucose too low: cells cannot respire fast enough. Too high for long periods: damage to the body.

Negative feedback in four steps

1. A receptor detects a change.
2. A control centre (brain or pancreas) processes it.
3. An effector responds.
4. The response reverses the change, and the level returns towards normal.

B3.3b: The skin and temperature

Skin receptors detect external temperature. The brain also monitors blood temperature. Impulses go to effectors.

Condition	Effectors	What happens	Result
Too hot	Sweat glands	Sweat released; evaporation transfers energy from skin	Body cools
Too hot	Arterioles to skin	Vasodilation: widen, more blood near the surface	More heat transferred to surroundings
Too cold	Skeletal muscles	Shivering: rapid contraction, respiration releases heat	Body warms
Too cold	Arterioles to skin	Vasoconstriction: narrow, less blood near the surface	Less heat transferred
Too cold	Sweat glands	Less sweat	Less evaporative cooling

Must-know distinctions

• Vasodilation (widen, hot) versus vasoconstriction (narrow, cold).
• Vessels do not move. Their diameter changes.
• Sweating cools only when sweat evaporates. Humid air slows evaporation.
• Shivering warms because muscle respiration releases heat.

Model answer frame: explain a temperature response

Use this chain: change detected, signal sent, effector, change in heat transfer or heat release, temperature returns towards 37 °C. For example, for a hot day: receptors detect the rise, the brain sends impulses to sweat glands and skin arterioles, sweat evaporates and vasodilation increases heat transfer, so the body cools.

Quick check on skin blood flow data

If a table shows skin blood flow of 30 units at 15 °C and 90 units at 35 °C, the increase is 60 units. As a percentage, 60 ÷ 30 × 100 = 200%. Explain it by vasodilation at the higher air temperature. If core temperature stays at 37 °C throughout, say that the response is keeping the internal environment constant.

B3.3c: Insulin and blood glucose

Method in steps (glucose too high, for example after a meal):

1. Glucose rises as digested carbohydrate is absorbed.
2. The pancreas detects the rise and secretes insulin into the blood.
3. Insulin acts on target cells, mainly in the liver and muscles.
4. Cells take up glucose from the blood.
5. The liver converts glucose to the storage carbohydrate glycogen.
6. Blood glucose falls. Insulin release falls as it does (negative feedback).

• Normal range is roughly 4 to 6 mmol/dm³ in a healthy person.
• Always say insulin is carried in the blood.

Reading a glucose and insulin graph

• Glucose rises first after a meal. Insulin rises a little later, because it is a response to the rise.
• Glucose peaks, then falls as insulin acts.
• Insulin falls back to its starting level once glucose is back near normal.
• Quote values and times from the axes, for example “glucose peaks at 7.4 mmol/dm³ at 30 minutes”.

B3.3d: Glucagon (Higher Tier only)

Glucagon is a second pancreatic hormone with the opposite effect to insulin.

	Insulin	Glucagon
Triggered by	High blood glucose	Low blood glucose
Acts on	Liver and muscle cells	Liver
Response	Glucose taken up; glucose converted to glycogen	Glycogen converted to glucose and released
Blood glucose	Falls	Rises

• Together they are an antagonistic pair and both are negative feedback.
• Glucose therefore oscillates around a set point.
• Glycogen is the store; glucagon is the hormone. Do not swap them.
• Typical situations that raise glucagon: skipping a meal, a long fast, or prolonged exercise using up glucose.
• A strong answer states the trigger, the target organ, the change in the liver and the effect on blood glucose.

B3.3e: Diabetes

	Type 1	Type 2
Cause	Too little insulin made (usually the immune system destroys the insulin-producing cells)	Cells respond poorly to insulin (insulin resistance)
Onset	Often childhood or early adult life	More often later in life
Risk factors	Not caused by diet	Obesity, inactivity, poor diet, age, family history
Treatment	Insulin injections or pump; monitor glucose; plan diet and exercise	Diet, exercise, weight loss; medicines (for example metformin); sometimes insulin

• Insulin is a protein, so it is injected. A tablet would be digested.
• Glucose in urine (test strips such as Clinistix) can indicate diabetes.
• A glucose tolerance test shows how fast glucose is removed. After a glucose drink, a healthy person’s level peaks and returns to normal within about 2 to 3 hours. In type 1 it starts high and stays very high. In type 2 it also starts raised and falls only slowly.
• Treatment comparison: type 1 needs insulin because the body makes too little. Type 2 is often managed first with lifestyle change, because cells can still respond to insulin if sensitivity improves.
• In both types, monitoring blood glucose helps people judge how well their treatment, diet and activity are working.

Maths and data reminders

Skill	Method
Percentage change	(new − old) ÷ old × 100
Rate	change ÷ time, with units
Reading tables and graphs	Quote values with units and times
Correlation	Describe the trend; a correlation does not prove cause

Small worked reminder

Blood glucose rises from 4.8 to 7.6 mmol/dm³. Change = 2.8; percentage = 2.8 ÷ 4.8 × 100 = 58% (58.3% before rounding).

Quick self-test

1. Name the organ that releases insulin.
2. State what happens to arterioles to the skin in cold conditions.
3. Blood glucose rises from 5.5 to 8.8 mmol/dm³ after a meal. Calculate the percentage increase.
4. Core temperature rises from 37.0 to 39.4 °C in 40 minutes. Calculate the mean rate in °C per hour.
5. Explain why sweating cools the body.
6. Explain why shivering warms the body.
7. Name the storage carbohydrate made from glucose in the liver.
8. Give two ways type 2 diabetes can be treated without insulin.
9. Explain why insulin is not given as a tablet.
10. (Higher Tier only) Describe what glucagon does when blood glucose is low.
11. Blood glucose falls from 9.0 to 6.3 mmol/dm³ after treatment. Calculate the percentage decrease.
12. Why can a high body mass index not prove that obesity causes type 2 diabetes?

Answers

1. The pancreas.
2. They narrow (vasoconstriction), so the skin capillaries receive less blood and less heat is lost.
3. Change = 3.3; 3.3 ÷ 5.5 × 100 = 60%.
4. Rise = 2.4 °C; 2.4 ÷ 40 = 0.06 °C per minute, so 3.6 °C per hour.
5. Sweat evaporates from the skin and transfers energy from the skin to the surroundings.
6. Muscles contract rapidly. This needs respiration, which releases heat.
7. Glycogen.
8. Any two of: a healthier diet, regular exercise, weight loss, medicines such as metformin.
9. Insulin is a protein, so it would be digested in the gut before reaching the blood.
10. It acts on the liver, which converts glycogen to glucose and releases it into the blood, so glucose rises.
11. Change = 2.7; 2.7 ÷ 9.0 × 100 = 30%.
12. A correlation shows an association only. Other factors, such as diet, age and inactivity, could also differ between the groups.

Where marks are usually lost

• Saying blood vessels move closer to the skin, rather than that arterioles widen or narrow.
• Writing “heat rises” or “cold air is let in” instead of heat transfer to the surroundings.
• Forgetting that sweat only cools as it evaporates.
• Saying insulin “turns glucose into glycogen” with no mention of the liver or of cells taking up glucose.
• Mixing up glycogen and glucagon.
• Stating that type 2 diabetes means no insulin at all.
• Missing the link between low temperature, slow enzymes and slow reactions.
• Calculating percentage change using the final value as the denominator.
• Giving a rate with no units, or a rate per minute when per hour was asked.

Official syllabus

OCR GCSE (9-1) Gateway Science Biology A (J247), specification Version 4.0 (August 2026), for first assessment in 2018, published by OCR. Module B3.3, statements B3.3a to B3.3e.