Students should be able to identify the following structures on a diagram…

The idea

The eye is a sense organ containing receptors sensitive to light intensity and colour. Light passes through the cornea, which is transparent and curved, so it refracts light strongly as it enters. The iris controls the pupil diameter, adjusting how much light reaches the retina. The lens fine-tunes focusing, while the ciliary muscles and suspensory ligaments alter lens shape. The retina lines the inside and contains rods and cones that convert light into electrical impulses. The optic nerve carries these impulses to the brain. The sclera is the tough, white outer coat that protects the eye and maintains its shape. When identifying structures, link each named part to its role: for example, the cornea's transparency and curvature allow refraction, and the optic nerve's bundle of neurones transmits impulses.

What earns the marks

• The retina contains light-sensitive receptor cells (rods and cones) that convert light energy into electrical impulses.
• The optic nerve is a bundle of neurones that carries electrical impulses from the retina to the brain.
• The sclera is a tough, white outer layer that protects the eye and helps maintain its shape.
• The cornea is a transparent, curved front layer that refracts light as it enters the eye.
• The iris contains muscles that adjust pupil diameter, controlling the amount of light entering the eye.
• The ciliary muscles contract or relax to change the shape of the lens during accommodation.
• The suspensory ligaments attach the ciliary muscles to the lens and transmit tension to change lens shape.

Common mistakes and how to put them right

• Confusing the cornea with the lens.

  Put it right by stating that the cornea provides most refraction but the lens fine-tunes focus.

• Thinking the iris is the black hole in the eye.

  Put it right by labelling the pupil as the gap and the iris as the surrounding tissue.

• Believing the optic nerve carries images rather than impulses.

  Put it right by describing the signal as electrical impulses, not a picture.

Exam tips

• Practise labelling a blank eye diagram from memory, then write one function beside each label to link structure and function.
• Use precise terms such as transparent, curved, tough and light-sensitive rather than vague words like clear or strong.
• When explaining a function, always name the structure and state what it does, for example 'the sclera protects the eye and maintains its shape'.