A student is reading a book held close to their face. They then look up and focus on a distant tree through the window. Explain the changes that occur in the eye to bring the distant tree into focus on the retina.

Pearson Edexcel A-Level Biology A (9BI0) — 4.4 Vision and hearing · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

The ciliary muscles relax, allowing the suspensory ligaments to become taut. This pulls the lens into a flatter shape, reducing its curvature. The flatter lens refracts light less, so light from the distant tree is bent by a smaller amount and is focused onto the retina, forming a sharp image.

Examiner tips

  • Use the exact terms: ciliary muscles, suspensory ligaments, lens curvature, refraction, retina.
  • Show the sequence of events in order.
  • Mention the effect on the image (sharp focus).

Common mistakes

  • Confusing relaxation with contraction of the ciliary muscles.
  • Saying the lens becomes more curved instead of flatter.
  • Failing to link the change in curvature to the amount of refraction.

Mark scheme (5 marks)

  1. The ciliary muscles relax when focusing on a distant object
  2. The suspensory ligaments become taut / tight / under tension
  3. The lens becomes less curved / thinner / flatter
  4. This refracts (bends) light less / by a smaller amount
  5. So that light from the distant tree is focused onto the retina / a sharp image forms on the retina

Key terms in this question

retina

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