Explain how the structure of the eye allows a person to see an object clearly when light enters the eye.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The human eye contains several structures that work together to focus light onto the retina. When light from an object enters the eye, it must be refracted so that a sharp image is formed.
Model answer (5 marks)
Light enters the eye through the cornea, which refracts the light and gives the eye its first focusing power. The lens then further refracts the light, fine‑tuning the focus so that the image is sharp on the retina. The iris controls the size of the pupil, regulating how much light enters the eye and helping to maintain a clear image under different lighting conditions. The light is finally focused onto the retina at the back of the eye. The retina contains rod and cone receptor cells that detect the light and convert it into electrical impulses, which are carried by the optic nerve to the brain for visual perception.
Examiner tips
- Use the word ‘refract’ for both cornea and lens; mention the iris’s role in light regulation; state that the retina receives the focused image; include rods and cones and the optic nerve; keep answer concise and to the points.
Common mistakes
- Confusing the cornea with the lens or omitting the iris; failing to mention rods and cones; not specifying that the optic nerve transmits impulses to the brain.
Mark scheme (5 marks)
- Light enters the eye through the cornea, which refracts (bends) the light
- The lens also refracts the light / fine-tunes the focusing of light
- The iris controls the size of the pupil, regulating the amount of light entering the eye
- Light is focused onto the retina at the back of the eye
- The retina contains receptor cells (rods and cones) that detect light and send electrical impulses along the optic nerve to the brain
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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