A person is involved in a road accident and suffers damage to the retina of one eye. Explain how damage to the retina would affect the person's ability to see, referring to the roles of the rod cells and cone cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The retina contains two types of photoreceptor cells: rod cells and cone cells. Rod cells are sensitive to low light intensities but cannot distinguish colour. Cone cells require bright light and are responsible for colour vision and fine detail.
Model answer (5 marks)
The retina contains photoreceptor cells – rod cells and cone cells – that detect light and convert it into electrical impulses.
Damage to the retina prevents light from being converted into nerve impulses.
Rod cells are responsible for vision in dim or low light conditions; therefore damage would impair the person’s ability to see in the dark or at night.
Cone cells are responsible for colour vision and for detecting fine detail; damage would impair colour vision and the ability to see detail clearly.
Because impulses are not sent along the optic nerve, the brain cannot receive or process visual information, so no image is perceived.
Damage to the retina prevents light from being converted into nerve impulses.
Rod cells are responsible for vision in dim or low light conditions; therefore damage would impair the person’s ability to see in the dark or at night.
Cone cells are responsible for colour vision and for detecting fine detail; damage would impair colour vision and the ability to see detail clearly.
Because impulses are not sent along the optic nerve, the brain cannot receive or process visual information, so no image is perceived.
Examiner tips
- Use the exact terms ‘rod cells’ and ‘cone cells’ and link each to its function. Explain the consequence of loss of electrical impulses. Show the chain: retina → optic nerve → brain. Keep the answer concise and structured into clear points.
Common mistakes
- Confusing rods with cones or vice‑versa. Failing to mention the loss of electrical impulses. Writing overly long, unfocused explanations that miss one of the required points.
Mark scheme (5 marks)
- The retina contains photoreceptor cells / rod cells and cone cells that detect light
- Damage to the retina means light cannot be converted into electrical impulses / nerve impulses
- Rod cells are responsible for vision in dim / low light conditions, so damage would impair ability to see in the dark / at night
- Cone cells are responsible for colour vision and detecting fine detail, so damage would impair colour vision or ability to see detail clearly
- Impulses would not be sent along the optic nerve to the brain, so no image is perceived / the brain cannot process the visual information
Key terms in this question
retina · rod cells · cone cells
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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