Cambridge IGCSE Biology 0610 · Topic 14
Coordination and Response
This is the largest chapter in the syllabus, and it can feel like five unrelated topics stitched together — nerves, the eye, hormones, blood glucose, plants bending towards light. It isn’t. Every one of those ideas runs on the same underlying logic: a stimulus is detected by a receptor, and a coordination system produces a response that is specific and traceable back to that stimulus. Once you hold onto that spine, the chapter stops being five topics and becomes one idea applied five times.
Living organisms have to detect changes around them and respond appropriately, and Cambridge splits the machinery that does this into two coordination systems. The nervous system uses electrical impulses travelling along neurones for a fast, short-lived response. Hormones travel as chemical messengers in the blood, acting more slowly but for longer. The same two systems also keep the body’s internal conditions stable through homeostasis, most visibly in the control of blood glucose concentration and body temperature. Plants, without a nervous system of their own, achieve something comparable through directional growth — tropic responses — that turn light and gravity into a bending shoot or root.
The single most exam-critical pathway in the whole chapter is the reflex arc: receptor → sensory neurone → relay neurone → motor neurone → effector. Almost every other idea in this chapter is a variation on that same shape — something detects a change, and something else, further along a defined pathway, produces the response. Where students lose marks is less often a knowledge gap and more often a precision gap: reversing which iris muscle contracts in bright light, describing a reflex as voluntary, or claiming a blood vessel physically moves towards the skin surface. The pages below are built around exactly these traps, because that is where Cambridge marking actually happens.
What’s in this chapter
| Page | Level | What it covers |
|---|---|---|
| The nervous system: CNS, PNS and neurones | Core | The headquarters-and-field-agents structure behind every nervous pathway, and why a neurone is identified by its direction, never its drawn shape. |
| Reflex actions and the reflex arc | Core | The exact five-stage pathway examiners expect, and why leaving out the relay neurone costs the mark even when everything else is right. |
| Synapses | Core + Supplement | Why two neurones never actually touch, and the one-way chemical sequence that crosses the gap between them. |
| Sense organs and receptors | Core | What makes something a sense organ at all, and why each one only ever answers to its own stimulus. |
| The eye: structure, pupil reflex, accommodation, rods and cones | Core + Supplement | Every required eye structure, why bright light shrinks the pupil, how the lens refocuses itself, and why rods and cones are not spread evenly across the retina. |
| Hormones and endocrine glands | Core + Supplement | The gland-hormone pairings Cambridge actually tests, adrenaline’s fight-or-flight effects, and how hormonal control differs from nervous control in speed and duration. |
| Homeostasis and negative feedback | Core + Supplement | What “constant internal environment” actually means, and how a set point turns a deviation into a corrective response. |
| Blood glucose control and Type 1 diabetes | Supplement | Insulin and glucagon acting as exact opposites on the liver, and why Type 1 diabetes is treated by replacing the hormone the body can no longer make enough of. |
| Body temperature control | Supplement | Sweating, shivering, vasodilation and vasoconstriction — and the trap that catches almost everyone: blood vessels never actually move towards the skin surface. |
| Gravitropism and phototropism | Core | Why shoots and roots read the same stimulus in opposite directions, and how to design an investigation that actually proves it. |
| Auxin and the chemical control of shoot growth | Supplement | How an unequal spread of one hormone, acting only through cell elongation, is enough to bend an entire shoot. |
Core or Supplement?
Four of the eleven pages here are Core throughout — the nervous system, the reflex arc, sense organs, and gravitropism and phototropism — so every candidate needs them regardless of tier. Two more, the eye and hormones, mix Core recall (structures, gland-hormone pairings, the required list of adrenaline’s effects) with Supplement mechanism (antagonistic iris muscles, accommodation, rods and cones, adrenaline and blood glucose), so read the whole page but pay attention to which parts are marked which way. The remaining five — synapses, homeostasis, blood glucose control, body temperature control, and auxin and shoot growth — lean heavily or entirely on Supplement content required only for the Extended paper. If you’re not sure which tier you’re sitting, it’s worth checking before investing time in the Supplement-only pages, since no Core content depends on them.