GCSE Biology Homeostasis & Response Notes
Homeostasis keeps internal conditions constant. The nervous system responds quickly using electrical impulses; hormones give slower, longer-lasting control.
Key concepts
- Homeostasis
- Regulation of internal conditions (temperature, water, blood glucose) to keep them near an optimum for enzymes and cells.
- Reflex arc
- Stimulus → receptor → sensory neurone → relay neurone (spinal cord) → motor neurone → effector → response. Fast and automatic.
- Endocrine system
- Glands (e.g. pituitary, pancreas, thyroid, adrenal) that release hormones into the blood to target organs.
- Insulin lowers blood glucose (glucose → glycogen in the liver); glucagon raises it.
- Type 1 diabetes: pancreas fails to make insulin — treated with insulin injections. Type 2: cells no longer respond — controlled by diet and exercise.
- Reflex actions bypass the conscious brain to protect the body.
Worked example
Describe the pathway of a reflex when you touch a hot object.
- 1Receptor in skin detects heat (stimulus).
- 2Impulse travels along sensory neurone to spinal cord.
- 3Relay neurone passes it to a motor neurone.
- 4Motor neurone triggers muscle (effector) to contract and pull the hand away.
Answer: Stimulus → receptor → sensory → relay → motor → effector → response.
Common mistakes
✗ Confusing hormones and nerve impulses.
✓ Nerves: electrical, fast, short-lived, precise. Hormones: chemical, slower, longer-lasting, wider target.
✗ Saying insulin turns glycogen into glucose.
✓ Insulin does the reverse — glucose is stored as glycogen. Glucagon releases it.
✗ Missing 'relay neurone' in the reflex arc.
✓ Sensory → RELAY → motor. Missing the relay loses a mark.
Quick check
Try these, then reveal the answers.
Which organ produces insulin?Reveal answer
The pancreas.
Which system uses electrical impulses?Reveal answer
The nervous system.
State the order of neurones in a reflex arc.Reveal answer
Sensory → relay → motor.
Exam tips
- Use the word 'negative feedback' when describing how internal conditions are corrected.
- For diabetes, distinguish Type 1 (insulin missing) from Type 2 (cells insensitive).
- Learn the reflex arc pathway as an ordered list — several marks are awarded for the correct sequence.
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Frequently asked questions
Why is homeostasis important?+
It keeps enzymes and cells working at their optimum by regulating temperature, water and blood glucose within narrow ranges.
How is Type 2 diabetes usually controlled?+
Through diet (low sugar/carbohydrate), regular exercise and, if necessary, medication that improves the body's response to insulin.
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