Explain how the structure of the eye allows a person to see an object that is close to them and then to see a distant object clearly.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The eye contains several structures that work together to focus light onto the retina. The lens and ciliary muscles play a key role in this process.
Model answer (5 marks)
1. Light from a close object must be bent more strongly to focus on the retina.
2. The ciliary muscles contract.
3. The suspensory ligaments loosen, allowing the lens to become more curved (fatter).
4. For a distant object the ciliary muscles relax and the suspensory ligaments tighten, making the lens thinner and less curved.
5. This change in lens shape is called accommodation and it ensures a focused image falls on the retina/fovea.
2. The ciliary muscles contract.
3. The suspensory ligaments loosen, allowing the lens to become more curved (fatter).
4. For a distant object the ciliary muscles relax and the suspensory ligaments tighten, making the lens thinner and less curved.
5. This change in lens shape is called accommodation and it ensures a focused image falls on the retina/fovea.
Examiner tips
- Use the word "accommodation" to link the process. Show the sequence: close → ciliary contraction + ligament slack → thicker lens; distant → ciliary relaxation + ligament tension → thinner lens.
- Mention that the image must fall on the fovea for clear vision.
Mark scheme (5 marks)
- Light from a close object requires greater refraction / bending to focus on the retina
- Ciliary muscles contract (when viewing a close object)
- Suspensory ligaments loosen / slacken (when viewing a close object), allowing the lens to become more curved / fatter
- For a distant object, ciliary muscles relax and suspensory ligaments pull tight, making the lens thinner / less curved
- This process (changing lens shape) is called accommodation and ensures a focused image falls on the retina / fovea
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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