Cambridge O Level Biology 5090: Coordination and control (5090) – Revision Notes

For full explanations and worked examples, read the study guide first. These notes cover Topic 14, Coordination and control, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4): every learning outcome in sections 14.1 to 14.6. The syllabus is not tiered, so all of it applies to every candidate, and this topic lists no set practical.

When you are ready, test yourself with the practice questions. The course hub lists every topic, the printable checklist tracks outcomes, and the free 10-minute diagnostics show where to focus. Denaturation of enzymes, the reason body temperature must stay steady, is in the Enzymes revision notes.

Key definitions

Term	Definition
Nervous system	Brain, spinal cord and nerves; coordinates and regulates body functions
CNS	Brain and spinal cord
PNS	Nerves outside the brain and spinal cord
Reflex action	A rapid and automatic response to a stimulus
Synapse	A junction between two neurones
Sense organ	A group of receptor cells responding to a specific stimulus
Hormone	A chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
Homeostasis	The maintenance of a constant internal environment
Negative feedback	A change away from the set point triggers a response that returns the value towards the set point

14.1 Nervous system

Neurones. Electrical impulses travel along neurones.

• Sensory: receptor → CNS; cell body on a short side branch, outside the spinal cord.
• Relay: inside the CNS only; short, many branches.
• Motor: CNS → effector; cell body at the CNS end, long fibre to a muscle or gland.

Reflex arc (learn the order):

receptor → sensory neurone → relay neurone → motor neurone → effector (muscle or gland)

Synapse structure: vesicles containing neurotransmitter molecules in the first neurone; the synaptic gap; receptor proteins on the next neurone.

Synapse events (method in steps):

1. Impulse arrives → neurotransmitter released from vesicles into the gap.
2. Neurotransmitter diffuses across the gap → binds with receptor proteins.
3. An impulse is stimulated in the next neurone.

One way only: vesicles on one side, receptors on the other.

14.2 Sense organs and the eye

Stimuli: light, sound, touch, temperature, chemicals.

Part	Function
Cornea	Refracts light
Iris	Controls how much light enters the pupil
Lens	Focuses light onto the retina
Ciliary muscles + suspensory ligaments	Control lens shape
Retina	Light receptors, some sensitive to different colours
Fovea	Greatest density of light receptors
Optic nerve	Carries impulses to the brain
Blind spot	Optic nerve leaves; no receptors

Pupil reflex. Circular and radial muscles are antagonistic.

• Bright: circular contract, radial relax → pupil constricts.
• Dim: radial contract, circular relax → pupil dilates.

Memory hook: circular closes.

Accommodation.

	Near	Far
Ciliary muscles	Contract	Relax
Suspensory ligaments	Slack	Taut
Lens	Fat	Thin
Refraction	More	Less

Memory hook: near = contract = fat lens.

14.3 Hormones

Gland	Hormone(s)
Adrenal glands	Adrenaline
Pancreas	Insulin, glucagon
Pituitary gland	FSH, LH
Testes	Testosterone
Ovaries	Oestrogen, progesterone

Adrenaline: released in fear, stress or excitement (danger, competition, exams). Raises blood glucose concentration and heart rate → more glucose and oxygen to muscles for respiration.

Nervous vs hormonal:

	Speed of action	Duration of effect
Nervous	Fast	Short
Hormonal	Slower	Longer lasting

14.4 Homeostasis and negative feedback

set point → change detected → corrective response → back towards set point

Rise → response lowers it. Fall → response raises it.

14.5 Temperature control

Skin labels: hairs, hair erector muscles, sweat glands, receptors, sensory neurones, blood vessels, fatty tissue.

Control: skin temperature receptors → sensory neurones → hypothalamus (monitors blood temperature, compares with set point, coordinates responses).

Insulation: fatty tissue; trapped air between hairs or fur.

Too hot	Too cold
Sweating: water evaporates, transferring heat away	Shivering: muscle contractions, respiration releases heat
Hair erector muscles relax, hairs lie flat	Hair erector muscles contract, hairs trap air
Vasodilation: skin arterioles widen, more heat lost by radiation	Vasoconstriction: skin arterioles narrow, less heat lost

14.6 Blood glucose control

Why: steady glucose supply for respiration; too much lowers blood water potential.

Blood glucose	Hormone from pancreas	Liver does	Blood glucose then
High	Insulin	Glucose → glycogen (stored)	Falls
Low	Glucagon	Glycogen → glucose (released)	Rises

Type 1 diabetes: signs = increased blood glucose concentration, glucose in urine. Treatment = administration of insulin.

Worked reminders

Pupil reflex, model answer. You walk from a dark room into sunshine. Explain the change in your pupils. Light receptors in the retina detect the increase in light intensity. Impulses pass to the brain and out along motor neurones to the iris. The circular muscles contract and the radial muscles relax, so the pupil constricts. Less light enters, which protects the retina.

Negative feedback, model answer. Explain how blood glucose is kept steady during a long run. Muscles use glucose faster in respiration, so blood glucose falls below the set point. The pancreas detects the fall and releases glucagon. Glucagon causes the liver to convert glycogen into glucose and release it into the blood. Blood glucose rises back towards the set point, and glucagon release then falls.

Hot day, model answer. Explain two ways the body loses more heat on a hot day. Vasodilation: the arterioles supplying the skin surface capillaries widen, so more blood flows near the surface and more heat is lost by radiation. Sweating: sweat glands secrete more sweat, and as the water evaporates it transfers heat away from the skin.

Adrenaline, model answer. A sprinter waits for the starting gun. Suggest why her heart rate rises before she moves. The excitement causes the adrenal glands to release adrenaline. Adrenaline increases the heart rate, so more oxygen and glucose are delivered to the leg muscles for respiration once the race starts.

Choosing nervous or hormonal. Ask how fast and how long. Pulling your hand from a flame needs a response in a fraction of a second, so it is nervous. Keeping blood glucose steady through a day needs a long-lasting effect, so it is hormonal. Adrenaline is a hormone, so its effect lasts longer than a reflex response.

Command words for this topic

• State / Name: one word or phrase. “Pituitary gland” is enough.
• Describe: say what happens, in order. A reflex arc needs all five parts.
• Explain: give the reason. For accommodation, link muscle → ligament tension → lens shape → refraction.
• Identify (on a diagram): make each label line touch the structure clearly, so it cannot point to a neighbouring part.
• Suggest: apply the ideas to a new situation, such as a mammal in a cold climate. A thick layer of fatty tissue and dense fur are both insulation.
• Compare: give a point for each side, using comparative words: “nervous control is faster; hormonal control is slower”.

Must-know distinctions

• Glucagon (hormone) vs glycogen (stored carbohydrate in liver).
• Sensory (to CNS) vs motor (from CNS) neurone.
• Nerve (bundle of neurones) vs neurone (one cell).
• Vasodilation (widening, heat loss up) vs vasoconstriction (narrowing, heat loss down).
• Cornea refracts light; lens adjusts the focus.
• Fovea (most receptors) vs blind spot (no receptors).

Quick self-test

1. Name the two parts of the CNS.
2. Which neurone is found only inside the CNS?
3. What do the vesicles at a synapse contain?
4. By what process does neurotransmitter cross the synaptic gap?
5. Give the reason impulses cross a synapse in one direction only.
6. In dim light, which iris muscles contract?
7. State what happens to the suspensory ligaments when you focus on a near object.
8. Name the gland that produces FSH and LH.
9. A person’s heart rate rises from 60 to 84 beats per minute when adrenaline is released. Calculate the percentage increase.
10. Which part of the brain coordinates temperature control?
11. Explain why shivering warms the body.
12. State two signs of Type 1 diabetes.

Answers

1. Brain and spinal cord.
2. Relay neurone.
3. Neurotransmitter molecules.
4. Diffusion.
5. Vesicles are only on one side of the gap; receptor proteins are only on the other.
6. Radial muscles (circular muscles relax).
7. They slacken; tension decreases.
8. Pituitary gland.
9. (84 − 60) ÷ 60 × 100 = 40 %.
10. Hypothalamus.
11. Muscles contract rapidly; the extra respiration releases heat.
12. Increased blood glucose concentration; glucose in the urine.

Where marks are usually lost

• Leaving the relay neurone out of a reflex arc, or naming the five parts out of order.
• Calling the effector “the muscle” when the question needs “muscle or gland”, or not naming which muscle.
• Saying neurotransmitter is “pumped” or “conducted” across the gap instead of “diffuses”.
• Reversing the ciliary muscles in accommodation: near needs contraction.
• Writing “the pupil contracts”. The pupil is a hole; the circular muscles contract and the pupil constricts.
• Saying “capillaries dilate” or “capillaries move to the surface”. It is the arterioles supplying the skin capillaries that widen or narrow.
• Stating “insulin breaks down glucose”. Insulin causes the liver to convert glucose to glycogen.
• Writing “glucagon” and “glycogen” interchangeably, or spelling them so they could be either.
• Comparing nervous and hormonal control on anything other than speed of action and duration of effect when the question limits it.
• Giving “sweating cools the body” without saying the water evaporates.

Official syllabus

Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4), Topic 14: Coordination and control (14.1 to 14.6), published by Cambridge Assessment International Education.