AQA Biology 4.5.2.3

The eye

Every part of the eye has a shape that suits its job. Find each part, then watch the lens change for near and far.

Triple Science · Higher tier

Start here

Lights off.

You walk from a bright kitchen into a dark bedroom. At first you can see almost nothing.

If you had to guess, do your pupils get bigger or smaller?

Structure and function

Parts of the eye.

The eye is a sense organ containing receptors sensitive to light intensity and colour. Tap each part to find it and see how its structure suits its job.

Tap a part.

Accommodation

Near and far, light and dark.

Accommodation is the process of changing the shape of the lens to focus on near or distant objects. Switch between them.

Distant object: the ciliary muscles relax, the suspensory ligaments are pulled tight, and the lens is pulled thin. It refracts light only slightly. The light focuses on the retina.

The pupil changes size by reflex. The iris has two sets of muscles: when one set contracts, the other relaxes.

Dim light: the radial muscles contract and the circular muscles relax. The pupil gets bigger, letting more light in.

When the eyeball or lens can’t focus light on the retina: Defects of the eye. Reflexes in general: Reflex actions.

Think again · relax to see close?

“To see close up, the ciliary muscles relax.”

Your call

Choose

You stop looking at the far side of a field and look at a book in your hands. What do the ciliary muscles do?

Sort

Near or far?

Place each change.

Tap a card, then tap the box it belongs in. Tap a placed card to take it back.

Command words in this lesson

Identify: Each structure on a diagram of the eye.
Explain: How each structure’s shape suits its function.
Describe: What happens to the lens for a near or a distant object.

Key fact

Near object: ciliary muscles contract, suspensory ligaments loosen, lens thicker. Distant object: ciliary muscles relax, ligaments pulled tight, lens thinner.

Key note · AQA 4.5.2.3 (Triple)

The eye

The eye is a sense organ with receptors sensitive to light intensity and colour, in the retina.
Cornea refracts; iris controls the pupil; lens focuses; optic nerve carries impulses to the brain; sclera protects and keeps the shape.
Near: ciliary muscles contract, ligaments loosen, lens thicker. Distant: muscles relax, ligaments tight, lens thin.
Dim light: pupil bigger. Bright light: pupil smaller. One set of iris muscles contracts while the other relaxes.

Photograph this card. Tomorrow, cover it and say each line first.

Previous and next

Connects to

Reflex actions

Ask MrBadmus

Getting contract and relax the wrong way round?

The eye diagrams are schematic and not to scale.