4.5 Homeostasis and response

Unit Summary

This unit introduces homeostasis -how the body maintains stable internal conditions so cells can function within narrow limits and is fully aligned with the AQA GCSE Biology specification. It builds on prior knowledge of cells and enzymes, and prepares students for later topics such as inheritance and ecology.

Students first establish the general principle of homeostasis: that control systems made up of receptors, coordination centres and effectors work together to keep conditions such as blood glucose concentration, body temperature and water levels within optimal limits. They then study the human nervous system, learning how information passes from receptors along neurones to the central nervous system, which coordinates a response through effectors. The reflex arc (sensory neurone, synapse, relay neurone, motor neurone) is taught in detail, with reflex actions explained as rapid, automatic responses that do not involve conscious thought.

Students study the nervous system through the reflex arc (sensory neurone, synapse, relay neurone, motor neurone), then the brain (cerebral cortex, cerebellum, medulla, with coverage of how brain function is investigated), the eye (structure, accommodation, and correction of myopia/hyperopia), and control of body temperature via vasodilation, vasoconstriction, sweating and shivering.

Hormonal coordination covers the endocrine system and blood glucose control through insulin, with Type 1/Type 2 diabetes, plus glucagon and the insulin-glucagon negative feedback cycle. Students also study water and nitrogen balance and kidney function, extending to deamination, ADH control, and dialysis/transplant as treatments for kidney failure.

Reproduction is a key focus, covering oestrogen, testosterone, FSH and LH in the menstrual cycle, with their detailed interactions, contraception methods, and infertility treatment including IVF. Negative feedback is studied further through adrenaline and thyroxine.

The unit closes with plant hormones: auxin in phototropism/gravitropism, plus gibberellins, ethene and their agricultural uses.

Required practicals cover human reaction time and the effect of light or gravity on seedling growth. Real-world links include diabetes, contraception, vision correction and kidney treatment, with HT content extending into infertility, the stress response and plant hormone applications.

To promote deep and long-term learning, a variety of Assessment for Learning (AfL) strategies are woven into lessons, including retrieval practice, diagnostic questioning, model evaluation, and structured discussion. These approaches reinforce conceptual understanding, promote metacognition, and encourage students to connect ideas across the curriculum.