Homeostasis is the maintenance of a steady internal environment in the body, despite changes outside. Examples include keeping blood glucose, body temperature and water content within narrow limits. A steady internal environment lets the cells and enzymes work properly.

How is blood glucose controlled?

When blood glucose rises after a meal, the pancreas releases insulin, which makes the liver take up glucose and store it as glycogen, so the level falls back to normal. This is an example of negative feedback, where a change triggers a response that reverses the change. In diabetes the control fails, so blood glucose stays too high.

What is a reflex arc?

A reflex arc is the pathway of a fast, automatic response that protects the body: a receptor detects the stimulus, a sensory neurone carries the impulse to the spinal cord, a relay neurone passes it on, a motor neurone carries it to the effector, and the effector (a muscle or gland) responds. It is fast because it does not wait for the brain to decide.

How does the eye respond to bright and dim light?

In bright light, the circular muscles of the iris contract and the radial muscles relax, so the pupil gets smaller and less light enters, protecting the retina. In dim light the opposite happens: the radial muscles contract and the circular muscles relax, so the pupil gets larger to let more light in. This is the pupil reflex.

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Homeostasis and coordination for N(A)-Level Science (Biology): homeostasis and the control of blood glucose, the nervous system and the reflex arc, and the structure and response of the human eye

An N(A)-Level Science (Biology) module overview of homeostasis and coordination. What homeostasis is and how insulin controls blood glucose by negative feedback, the nervous system and the reflex arc as a fast automatic response, and the structure of the eye and how it responds to light, with links to every dot point.

Generated by Claude Opus 4.85 min readSEAB-5106/5107 Science (Biology component)Updated 2026-06-13

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this module covers
Homeostasis and blood glucose
The nervous system and the reflex arc
The human eye
How this module is examined
Check your knowledge

What this module covers

Homeostasis and coordination is about how the body keeps itself steady and responds to its surroundings. You need to define homeostasis and explain how insulin controls blood glucose by negative feedback, describe the nervous system and the reflex arc, and describe the eye and how it adjusts to changes in light.

This overview links every dot point in the module. Work through them in order, then check yourself with the questions at the end. See the full set at /sg-n-level/biology/syllabus.

Homeostasis and blood glucose

Start with the principle of keeping things steady. The page on homeostasis and blood glucose defines homeostasis, explains how the pancreas releases insulin to lower blood glucose by making the liver store it as glycogen, introduces negative feedback, and outlines what goes wrong in diabetes.

The nervous system and the reflex arc

Next, fast communication. The page on the nervous system and the reflex arc describes the central and peripheral nervous systems and the three types of neurone, and explains the reflex arc as a fast, automatic response that protects the body.

The human eye

Finally, a sense organ in detail. The page on the human eye describes the main parts of the eye and their jobs, how an image is formed on the retina, and the pupil reflex that changes the size of the pupil in bright and dim light.

How this module is examined

At N(A) level there is no standalone pure Biology paper. Biology is taken as part of a combined Science subject, either Science (Physics, Biology) syllabus 5106 or Science (Chemistry, Biology) syllabus 5107, so this module is examined within whichever combination your school offers.

Complete the feedback loop. Blood glucose answers reward naming insulin, the liver, glycogen and negative feedback.
Order the reflex arc. Reflex questions reward the correct sequence: receptor, sensory neurone, relay neurone, motor neurone, effector.
Name the iris muscles. Pupil reflex answers reward stating which muscles contract and relax in bright and dim light.

Check your knowledge

A mix of recall, sequencing and explanation questions. Attempt them, then check against the solutions.

Define homeostasis. (1 mark)
Explain how the body lowers blood glucose after a meal. (3 marks)
List, in order, the parts of a reflex arc. (2 marks)
Describe what happens to the pupil in bright light and explain why. (2 marks)

Sources & how we know this

Singapore-Cambridge GCE N(A)-Level Science (Physics, Biology) Syllabus 5106 — Singapore Examinations and Assessment Board (2026)
Singapore-Cambridge GCE N(A)-Level Science (Chemistry, Biology) Syllabus 5107 — Singapore Examinations and Assessment Board (2026)