A student is reading a book and then looks up to watch a bird flying in the distance. Describe how the structure of the eye allows a clear image to be formed on the retina in each situation, and name the part of the retina that produces the clearest image.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When focusing on a nearby object such as a book, and then a distant object such as a bird in the sky, different structures within the eye must adjust to ensure that a clear image is produced.
Model answer (5 marks)
The cornea refracts light as it enters the eye, giving most of the focusing power. The lens then changes shape to fine‑tune the focus onto the retina.
For a nearby object (the book) the lens becomes thicker and more curved, increasing its refractive power so that the image is focused on the retina.
For a distant object (the bird) the lens becomes thinner and flatter, decreasing its refractive power so that the image is again focused on the retina.
The clearest image is produced by the fovea, a small area of the retina that contains a high concentration of cone cells.
For a nearby object (the book) the lens becomes thicker and more curved, increasing its refractive power so that the image is focused on the retina.
For a distant object (the bird) the lens becomes thinner and flatter, decreasing its refractive power so that the image is again focused on the retina.
The clearest image is produced by the fovea, a small area of the retina that contains a high concentration of cone cells.
Examiner tips
- Use the word "refract" for the cornea and "change shape" for the lens; specify thicker/curved for near and thinner/flatter for far.
- Mention the fovea as the part of the retina that gives the clearest image.
- Keep the answer concise – 5 marks allow a short paragraph with 5 key points.
Common mistakes
- Confusing the cornea with the lens as the only focusing element.
- Forgetting to state that the lens changes shape (not just thickness).
- Not naming the fovea as the part of the retina that gives the clearest image.
Mark scheme (5 marks)
- The cornea refracts light as it enters the eye
- The lens changes shape to focus the image onto the retina
- For a nearby object (the book) the lens becomes thicker / more curved to refract light more strongly
- For a distant object (the bird) the lens becomes thinner / less curved / flatter to refract light less strongly
- The fovea produces the clearest image because it contains a high concentration of cone cells
Key terms in this question
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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