A student is studying how the eye and ear detect different stimuli. Describe how light entering the eye is focused onto the retina, and explain what happens after the retina detects the light stimulus.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The human eye and ear are both sense organs. The eye detects light stimuli, while the ear detects sound stimuli. Both organs send information to the brain via nerve impulses.
Model answer (5 marks)
Light enters the eye through the cornea, which refracts the light. The light then passes through the aqueous humour and the lens, which further refracts and focuses it onto the retina at the back of the eye. The retina contains photoreceptor cells – rods for low light and cones for colour and detail – that detect the light stimulus. These receptor cells convert the light into electrical signals and send nerve impulses via the optic nerve. The impulses travel to the brain where they are interpreted as visual images.
Examiner tips
- Use the word ‘refract’ for both cornea and lens; mention the retina and photoreceptors; state that impulses travel via the optic nerve to the brain.
- Show the sequence: cornea → lens → retina → optic nerve → brain.
- Include both rod and cone cells to cover the full answer.
Common mistakes
- Omitting the lens or the optic nerve; confusing cornea with lens; not naming rods and cones; writing that light is ‘absorbed’ instead of ‘focused’ onto the retina.
Mark scheme (5 marks)
- Light passes through the cornea, which refracts (bends) the light
- The lens also refracts light and focuses it onto the retina
- The retina contains receptor cells (rod and/or cone cells) that are sensitive to light
- The receptor cells generate / send nerve impulses
- Nerve impulses travel along the optic nerve to the brain, where they are interpreted as vision
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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