Explain how the eye is able to focus clearly on a nearby object, referring to the ciliary muscles, suspensory ligaments and lens.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
When a near object is viewed the ciliary muscles contract, causing the suspensory ligaments to relax and become slack. This releases the tension on the lens, allowing it to become thicker and more curved (more convex). The increased curvature raises the refractive power of the lens, bending light rays more strongly so that they converge on the retina, producing a clear image.
Examiner tips
- Use the correct sequence: ciliary muscles contract → ligaments relax → lens thickens → light refracts more.
- Mention the effect on the lens curvature and refractive power explicitly.
Common mistakes
- Confusing contraction of ciliary muscles with relaxation of the lens; or stating that the lens becomes thinner.
- Omitting the role of suspensory ligaments or the increase in refractive power.
Mark scheme (4 marks)
- The ciliary muscles contract when focusing on a near object.
- The suspensory ligaments relax / become slack.
- The lens becomes fatter / more curved / more convex.
- This causes light to be refracted more / focused onto the retina.
Key terms in this question
ciliary muscle · suspensory ligaments · lens
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →