OxfordAQA International GCSE Biology: Homeostasis, temperature control and blood glucose (9201) – Revision Notes

These revision notes are aligned to the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams from May/June 2018 onwards. They cover sections 3.4.2 (Homeostasis), 3.4.4 (Temperature control) and 3.4.5 (Control of blood glucose). The course is untiered. For full explanations, start with the study guide. Then test yourself with the practice questions.

Course pages: OxfordAQA IGCSE Biology hub, printable checklist and the free 10-minute diagnostics.

Key definitions

Term	Meaning
Homeostasis	Automatic control systems keep conditions inside the body relatively constant
Receptor	A cell that detects a stimulus (a change in the environment)
Coordination centre	Receives and processes information from receptors
Effector	Brings about a response; muscles and glands are effectors
Vasodilation	Blood vessels supplying skin capillaries widen, so more blood flows through them
Vasoconstriction	Blood vessels supplying skin capillaries narrow, so less blood flows through them
Glycogen	Storage form of glucose, held mainly in the liver and muscles
Insulin	Hormone from the pancreas that allows glucose to move from blood into cells
Glucagon	Hormone from the pancreas that makes stored glycogen change back into glucose, which enters the blood

3.4.2 Control systems at a glance

Order of events: stimulus, receptor, coordination centre, effector, response.

Organ	Receptors detect
Eyes	Light
Ears	Sound and changes in position (balance)
Tongue and nose	Chemicals (taste, smell)
Skin	Touch, pressure, pain, temperature changes
Brain	Blood temperature, water concentration of blood
Pancreas	Blood glucose concentration

• Coordination centres: brain, spinal cord, pancreas.
• Controlled conditions: temperature, water content, ion content, blood glucose.
• Structure of the eye and ear is not required.

3.4.4 Temperature control

Two sources of information go to the thermoregulatory centre in the brain:

1. Receptors in the centre itself, sensitive to the temperature of blood flowing through the brain (core temperature).
2. Impulses from temperature receptors in the skin (skin temperature).

	Core temperature too high	Core temperature too low
Skin blood vessels	Dilate, so more blood flows through skin capillaries	Constrict, so less blood flows through skin capillaries
Energy transfer from skin	More	Less
Sweat	More released; cools body as it evaporates	Not part of the response
Muscles	No change	May shiver; contraction needs respiration, which transfers some energy that warms the body
Fluid	Replace by drinking or eating	No extra need

The name “hypothalamus” is not required.

Method in steps: explain a temperature response

1. Say what changed (core temperature too high or too low).
2. Name the detector: receptors in the brain and temperature receptors in the skin.
3. Name the centre: the thermoregulatory centre.
4. Name the effector: skin blood vessels, sweat glands, muscles.
5. Say what each does, ending with the effect on energy transfer or temperature.

3.4.5 Blood glucose

Pancreas monitors glucose and releases both hormones.

Blood glucose	Hormone	Result
Too high	Insulin	Glucose moves from blood into cells; stored as glycogen in liver and muscles; when stores are full, excess stored as lipid
Too low	Glucagon	Stored glycogen changes back into glucose, which enters the blood

Diabetes

	Type 1	Type 2
Cause	Pancreas does not produce enough insulin	Body does not respond to its own insulin
Main factor	No factor stated in the specification	Obesity is a significant factor
Control	Careful diet, exercise, injecting insulin	Careful diet, exercise, drugs that help cells respond to insulin

Must-know distinctions

• Insulin and glucagon. Insulin: glucose out of the blood and into cells. Glucagon: glycogen to glucose, released into the blood.
• Vasodilation and vasoconstriction. Dilate means wider and more blood flow. Constrict means narrower and less blood flow.
• Type 1 and Type 2. Type 1: too little insulin is made. Type 2: cells respond poorly to the insulin.
• Receptor and effector. Receptors detect. Effectors respond.
• Sweat and cooling. The sweat itself does not cool you. Evaporation does.

Worked reminders

Percentage change. Blood glucose falls from 9.6 to 6.0 mmol/dm³. Change = 3.6. Percentage = 3.6 ÷ 9.6 × 100 = 37.5% fall. Always divide by the starting value.

Fluid lost. A person sweats 0.75 dm³ per hour for 4 hours. Loss = 0.75 × 4 = 3.0 dm³. If they drink 2.2 dm³, the shortfall is 3.0 − 2.2 = 0.8 dm³.

Rate. Glucose rises from 4.6 to 5.8 mmol/dm³ in 3 hours. Rate = 1.2 ÷ 3 = 0.4 mmol/dm³ per hour.

Model answers to learn

Explain how the body responds when core temperature falls. Receptors in the brain detect the cooler blood, and skin receptors send impulses to the thermoregulatory centre. The blood vessels supplying the skin capillaries constrict, so less blood flows through the capillaries and less energy is transferred to the environment. Muscles may shiver. Their contraction needs respiration, which transfers some energy to warm the body.

Explain how blood glucose is lowered after a meal. The pancreas detects the high glucose concentration and produces insulin. Insulin allows glucose to move from the blood into the cells. Much of it is stored as glycogen in the liver and muscles. When these stores are full, excess glucose is stored as lipid.

Explain how blood glucose is raised between meals. When blood glucose falls, the pancreas produces glucagon. Glucagon makes stored glycogen change back into glucose, and this glucose enters the blood.

Reading data on these topics

• Two lines moving in opposite directions. If one hormone rises as glucose falls, the hormone is probably glucagon. If one rises as glucose rises, it is probably insulin.
• A lag. A hormone peak that comes slightly after a glucose change fits a hormone released in response to that change.
• Flat core temperature with changing skin temperature. This shows the control system working: the effectors keep the core steady while the skin changes.
• A level that stays high. After a meal, a glucose level that rises and does not come down fits diabetes. Use the cause given (not enough insulin, or poor response to it) to decide the type.
• Compare using numbers. Quote values from the table and use units. Calculate a difference or a percentage if the command word asks for it.

Linking the three sections

All three sections follow one pattern. A condition changes. Receptors detect it. A coordination centre processes the information. Effectors reverse the change. For temperature the centre is in the brain. For blood glucose the pancreas both detects the change and releases the hormones. Learn the pattern once, then fill in the detail for each case.

Condition	Receptors	Centre	Effectors	Result
Core temperature high	Brain; skin	Thermoregulatory centre	Skin vessels, sweat glands	Cooler
Core temperature low	Brain; skin	Thermoregulatory centre	Skin vessels, muscles	Warmer
Blood glucose high	Pancreas	Pancreas	Cells and glycogen stores, with insulin	Glucose falls
Blood glucose low	Pancreas	Pancreas	Glycogen stores, with glucagon	Glucose rises

Mini-checks before the exam

• Can you draw the chain from stimulus to response for a hot day without looking?
• Can you say, in one line each, what insulin and glucagon do?
• Can you give two differences between Type 1 and Type 2 diabetes?
• Can you rearrange rate = change in glucose ÷ time to find the time?

Quick self-test

1. Name the part of the body that contains receptors sensitive to blood glucose concentration.
2. Name two coordination centres.
3. Which two types of information reach the thermoregulatory centre?
4. Describe what happens to skin blood vessels when core temperature is too high.
5. Explain why shivering warms the body.
6. Which hormone is released when blood glucose is too low?
7. What is stored as glycogen, and where?
8. Give two ways Type 1 diabetes may be controlled, other than diet.
9. Explain what is wrong in Type 2 diabetes.
10. Blood glucose rises from 5.6 to 8.4 mmol/dm³. Calculate the percentage rise.
11. A person sweats 0.9 dm³ per hour for 5 hours. Calculate the total volume.
12. A person gains 3.6 mmol/dm³ in 12 minutes. Calculate the rate per minute.

Answers

1. The pancreas.
2. Any two of: brain, spinal cord, pancreas.
3. Blood temperature (core temperature) from receptors in the centre, and skin temperature from skin receptors.
4. They dilate, so more blood flows through skin capillaries and more energy is transferred to the environment.
5. Muscle contractions need respiration, which transfers some energy that warms the body.
6. Glucagon.
7. Glucose, in the liver and muscles.
8. Exercise and injecting insulin.
9. The body does not respond to its own insulin.
10. 2.8 ÷ 5.6 × 100 = 50%.
11. 0.9 × 5 = 4.5 dm³.
12. 3.6 ÷ 12 = 0.3 mmol/dm³ per minute.

Where marks are usually lost

• Writing “insulin lowers sugar” without saying that glucose moves from the blood into cells.
• Forgetting that glucagon converts glycogen to glucose and that the glucose is released into the blood.
• Saying “more blood vessels” or “vessels move closer to the skin” instead of dilation and constriction.
• Saying sweating cools you without mentioning evaporation.
• Omitting the energy link in shivering: contraction needs respiration, which transfers energy.
• Describing Type 2 diabetes as a lack of insulin.
• Missing the units on a rate or the “per hour” in a rate.
• Naming the eye or ear structures. They are not required.

Official syllabus

The OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams May/June 2018 onwards, published by OxfordAQA.