Cambridge IGCSE Biology 0610: Coordination and response – Study Guide

This study guide teaches topic 14, Coordination and response, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. It covers sections 14.1 to 14.5: the nervous system, sense organs, hormones, homeostasis and tropic responses. Core outcomes are for every candidate. Supplement outcomes are labelled Extended only; they are examined on Papers 2 and 4 but not on the Core Papers 1 and 3.

Other pages for this topic: revision notes and an existing practice set on 14.1 and 14.2. Course links: Cambridge IGCSE Biology hub, printable checklist, free Core diagnostic and Extended diagnostic.

What this topic covers

Section	What you must be able to do	Extended only
14.1	Nervous system (CNS, PNS), neurone types, reflex arc, reflex action, synapse as a junction	Synapse structure and events; one-way transmission
14.2	Sense organs; parts of the eye and their functions; pupil reflex	Iris muscles; accommodation; rods, cones, fovea
14.3	Hormones; four glands and hormones; adrenaline effects; nervous vs hormonal	Glucagon; adrenaline and blood glucose and heart rate
14.4	Homeostasis; insulin lowers blood glucose	Negative feedback; glucose control; Type 1 diabetes; skin; temperature control
14.5	Gravitropism and phototropism; investigating them	Auxin and shoot growth

14.1 The nervous system

Electrical impulses travel along neurones. The mammalian nervous system has two parts:

• the central nervous system (CNS): the brain and the spinal cord
• the peripheral nervous system (PNS): the nerves outside the brain and spinal cord.

Its role is the coordination and regulation of body functions.

Three types of neurone

Neurone	Carries impulses	How to identify it in a diagram
Sensory	From a receptor to the CNS	Cell body on a short branch part-way along the fibre
Relay	Within the CNS, from sensory to motor neurone	Short, found inside the spinal cord or brain
Motor	From the CNS to an effector	Cell body at one end, inside the CNS, with a long fibre to the effector

Reflex arcs and reflex actions

A simple reflex arc is: receptor → sensory neurone → relay neurone → motor neurone → effector. A reflex action is a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands).

Worked example. You step on a drawing pin and lift your foot before you feel pain. Pain receptors in the skin of the foot detect the stimulus. A sensory neurone carries impulses to the spinal cord. A relay neurone passes them to a motor neurone. The motor neurone carries impulses to leg muscles (the effector), which contract and lift the foot. No conscious thought is involved, which is why it is fast.

Synapses

A synapse is a junction between two neurones.

Extended only. A synapse contains vesicles holding neurotransmitter molecules, a synaptic gap, and receptor proteins on the next neurone. The events are:

1. An impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap.
2. The neurotransmitter molecules diffuse across the gap.
3. They bind with receptor proteins on the next neurone.
4. An impulse is then stimulated in the next neurone.

Synapses ensure that impulses travel in one direction only: only one side releases neurotransmitter and only the other side has receptor proteins.

14.2 Sense organs

Sense organs are groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals.

The eye

Part	Function
Cornea	Refracts light
Iris	Controls how much light enters the pupil
Pupil	Hole through which light enters
Lens	Focuses light on to the retina
Retina	Contains light receptors, some sensitive to light of different colours
Optic nerve	Carries impulses to the brain
Blind spot	Where the optic nerve leaves; no receptors, so no image is detected

Pupil reflex

In bright light the pupil narrows, so less light enters and the retina is protected. In dim light the pupil widens, so more light enters and you can see.

Extended only. The iris has two antagonistic muscle sets. In bright light the circular muscles contract and the radial muscles relax, so the pupil constricts. In dim light the radial muscles contract and the circular muscles relax, so the pupil dilates.

Accommodation (Extended only)

	Near object	Distant object
Ciliary muscles	Contract	Relax
Suspensory ligaments	Slacken (less tension)	Pulled tight (more tension)
Lens shape	Fatter, more convex	Thinner, less convex
Refraction of light	More	Less

Worked example. You look up from your phone to read the number on a distant bus. Your ciliary muscles relax, the suspensory ligaments are pulled tight, the lens becomes thinner, and light is refracted less, so the image of the bus is focused on the retina.

Rods, cones and the fovea (Extended only)

• Rods are spread across most of the retina. They are more sensitive to light, so they give night vision.
• Cones are concentrated in the fovea. There are three different kinds of cone, absorbing light of different colours, which gives colour vision.
• The fovea is the part of the retina directly opposite the lens. Its function is to give the most detailed, sharpest image, in colour.

14.3 Hormones

A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.

Gland	Hormone
Adrenal glands	Adrenaline
Pancreas	Insulin (and glucagon, Extended only)
Testes	Testosterone
Ovaries	Oestrogen

Adrenaline is secreted in “fight or flight” situations. Its Core effects are increased breathing rate, increased heart rate and increased pupil diameter. Extended only: adrenaline controls metabolic activity by increasing the blood glucose concentration and increasing heart rate, so more glucose and oxygen reach the muscles for respiration.

Nervous vs hormonal control

	Nervous	Hormonal
Speed of action	Very fast	Slower
Duration of effect	Short	Longer lasting

14.4 Homeostasis

Homeostasis is the maintenance of a constant internal environment. Insulin decreases blood glucose concentration.

Negative feedback (Extended only)

Each controlled factor has a set point. If the factor rises above the set point, the change is detected and a response brings it back down; if it falls below, a response brings it back up. The response always reverses the change, which is why it is called negative feedback.

Blood glucose control (Extended only)

• Blood glucose rises (after a meal): the pancreas secretes insulin. The liver takes up glucose and converts it to glycogen. Blood glucose falls.
• Blood glucose falls (between meals, exercise): the pancreas secretes glucagon. The liver converts glycogen to glucose and releases it. Blood glucose rises.

Worked example. After a glucose drink, a person’s blood glucose rises from 5.0 to 8.0 mmol per dm³ in 30 minutes. Percentage increase = (8.0 − 5.0) ÷ 5.0 × 100 = 60%. Over the next 90 minutes it falls to 5.2 mmol per dm³. Explanation: the rise is detected, the pancreas secretes insulin, and the liver converts glucose to glycogen, so the concentration returns towards the set point.

Type 1 diabetes (Extended only): the pancreas does not produce enough insulin. Treatment is outlined as injections of insulin, regular monitoring of blood glucose, and controlling diet, especially carbohydrate intake, and exercise.

Temperature control (Extended only)

You must identify in skin diagrams: hairs, hair erector muscles, sweat glands, receptors, sensory neurones, blood vessels and fatty tissue.

Temperature receptors in the skin send impulses along sensory neurones to the brain, which also detects blood temperature and coordinates the responses.

	Too hot	Too cold
Sweating	Sweat glands release sweat; evaporation removes heat	Little or no sweating
Arterioles to skin surface capillaries	Vasodilation: more blood near the surface, more heat lost	Vasoconstriction: less blood near the surface, less heat lost
Shivering	None	Muscles contract rapidly; respiration releases heat
Hairs	Hair erector muscles relax; hairs lie flat	Hair erector muscles contract; hairs trap a layer of insulating air
Fatty tissue	Insulation reduces heat loss at all times

Arterioles widen or narrow. Capillaries do not move up or down in the skin, and they do not dilate or constrict.

14.5 Tropic responses

• Gravitropism: parts of a plant grow towards or away from gravity. Roots grow towards gravity; shoots grow away from it.
• Phototropism: parts of a plant grow towards or away from the direction of the light source. Shoots grow towards light; roots grow away from it.

Investigating them. Place seedlings in a box with light entering through one slit and compare with seedlings in all-round light. For gravitropism, lay germinating seeds on their side on damp paper in the dark and observe root and shoot direction over several days. Keep other variables (temperature, water, seedling type) the same.

Auxin and shoot growth (Extended only)

Phototropism and gravitropism of a shoot are examples of the chemical control of plant growth:

1. Auxin is made in the shoot tip.
2. Auxin diffuses through the plant from the shoot tip.
3. Auxin is unequally distributed in response to light and gravity.
4. Auxin stimulates cell elongation.

With light from one side, more auxin collects on the shaded side. Those cells elongate more, so the shoot bends towards the light. In a shoot lying horizontally, more auxin collects on the lower side, which elongates more, so the shoot bends upwards.

Worked example. In a shoot lit from the left, cells on the shaded side are 0.15 mm long and cells on the lit side are 0.10 mm long. Shaded-side cells are (0.15 − 0.10) ÷ 0.10 × 100 = 50% longer, consistent with more auxin on the shaded side.

Common errors

• Saying ligaments contract. Only the ciliary muscles contract.
• Saying capillaries dilate or move towards the skin surface.
• Writing that auxin “moves towards the light”. It collects on the shaded side.
• Saying insulin converts glucose to glycogen. Insulin causes the liver to do it.
• Confusing glycogen, glucagon and glucose.
• Forgetting that effectors include glands as well as muscles.

Where to go next

Use the revision notes, then the 14.1–14.2 practice set. The previous topic is excretion in humans.

Official syllabus

Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 (Version 3), published by Cambridge University Press & Assessment (Cambridge International Education). Topic 14, sections 14.1 to 14.5 Coordination and response.