AQA GCSE Biology 4.5 Homeostasis and response: a complete overview of nerves, hormones and control
A deep-dive AQA GCSE Biology guide to module 4.5 Homeostasis and response. Covers the principles of homeostasis and control systems, the nervous system and reflexes, hormonal coordination and the endocrine system, the control of blood glucose and diabetes, and the hormones of human reproduction and fertility, with the required practical and exam patterns AQA repeats.
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What module 4.5 actually demands
Homeostasis and response is about control: how the body detects changes and responds to keep itself stable. The examiners reward a clear grasp of the receptor, coordinator, effector model, the nervous versus hormonal comparison, and the detailed feedback loops for blood glucose and the menstrual cycle. Several parts (glucagon, IVF detail) are higher tier.
This guide walks through the module and ties together the matching dot-point pages, each with its own practice questions.
Principles of homeostasis
Homeostasis keeps internal conditions (blood glucose, body temperature, water levels) within narrow limits so enzymes and cells work well. Every control system has receptors (detect a change), coordination centres (process information) and effectors (carry out the response), working by negative feedback.
The nervous system
The nervous system uses electrical impulses along neurones from receptors to the CNS (brain and spinal cord) and out to effectors. Signals cross synapses as chemicals. A reflex action is fast and automatic because it bypasses the conscious brain, passing through the reflex arc: receptor, sensory neurone, relay neurone, motor neurone, effector. The required practical measures reaction time.
Hormones and the endocrine system
Hormones are chemical messengers carried in the blood to target organs. Compared with nerves they are slower but longer lasting. The pituitary is the master gland. Key glands and hormones: thyroid (thyroxine, controls metabolic rate by negative feedback), adrenal (adrenaline, the fight-or-flight hormone), pancreas (insulin and glucagon), ovaries (oestrogen) and testes (testosterone).
Blood glucose and diabetes
The pancreas controls blood glucose: insulin lowers it (storing glucose as glycogen), and glucagon (higher tier) raises it. Type 1 diabetes is too little insulin (treated with injections); Type 2 is cells not responding to insulin (linked to obesity, managed by diet and exercise).
Hormones in reproduction
At puberty, testosterone and oestrogen drive development. The menstrual cycle uses FSH, oestrogen, LH and progesterone. Contraception can be hormonal (the pill inhibits FSH) or non-hormonal (barrier methods), and fertility treatments include FSH and LH drugs and IVF.
How module 4.5 is examined
- Pathways. The reflex arc and the receptor-coordinator-effector model.
- Comparison. Nervous versus hormonal coordination.
- Feedback loops. Blood glucose control and the menstrual cycle, often as graphs.
- Evaluation. Diabetes treatment, contraception choices and IVF.
Check your knowledge
A mix of recall and application questions covering module 4.5. Attempt them under timed conditions, then check against the solutions.
- Name three internal conditions controlled by homeostasis. (3 marks)
- State the three parts of a control system. (3 marks)
- List the structures of a reflex arc in order. (2 marks)
- Give two differences between nervous and hormonal responses. (2 marks)
- Name the gland that releases thyroxine and state what it controls. (2 marks)
- Explain what insulin does when blood glucose is too high. (2 marks)
- State the difference between Type 1 and Type 2 diabetes. (2 marks)
- Name the hormone that triggers ovulation. (1 mark)
Sources & how we know this
- AQA GCSE Biology (8461) specification — AQA (2016)