5.8 Accommodation: focusing near and far
6 exam questions worth 12 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What happens to the lens when the eye focuses on a near object?
Choose one answer.
Correct Not quite: the answer is It becomes thicker and refracts light more
Mark scheme
B
Model answer
B: it becomes thicker and refracts light more strongly.
Define accommodation.
Mark scheme
(the process of) changing the shape of the lens to focus on near or distant objects
Model answer
Accommodation is changing the shape of the lens to focus on near or distant objects.
A student is reading a book. She looks up at a bird far away.
Describe the changes in her eye that keep the bird in focus.
Mark scheme
- ciliary muscles relax (1)
- suspensory ligaments are pulled tight (1)
- lens is pulled thin / becomes flatter (1)
- light is refracted less / only slightly (1)
- (so the light is) focused on the retina (1)
Max 4
Model answer
Her ciliary muscles relax, so the suspensory ligaments are pulled tight. This pulls the lens into a thinner shape, which refracts light only slightly, so the parallel light from the distant bird is focused on her retina.
Explain why the suspensory ligaments become slack when the ciliary muscles contract.
Mark scheme
- ciliary muscles form a ring (around the lens) (1)
- when they contract the ring gets smaller / moves closer to the lens, so there is less tension on the ligaments (1)
Model answer
The ciliary muscles form a ring around the lens. When they contract the ring gets smaller, moving closer to the lens, so the ligaments are no longer pulled tight.
Explain why a thin lens is needed to focus light from a distant object.
Mark scheme
- light from a distant object is (nearly) parallel / needs little refraction (1)
- a thin lens refracts light less, so it focuses the light on the retina (1)
Model answer
Light from a distant object arrives almost parallel, so it only needs a little refraction; a thin lens refracts light only slightly, so the image is focused on the retina rather than in front of it.
Many people over 50 find it hard to focus on near objects.
Suggest why.
Mark scheme
- lens becomes less elastic / stiffer with age (1)
- so it cannot become thick enough / round enough to refract light strongly (1)
Model answer
With age the lens becomes less elastic, so when the ligaments loosen it cannot become thick enough to refract light strongly, and near objects are focused behind the retina.
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