Edexcel IGCSE Biology 2.92 Eye Focusing and Light Responses Questions

Adjusting focus changes lens shape; changing light activates iris muscles. Study accommodation, pupil data, and how eye conditions affect vision.

Exam points

Explain near and distant accommodation using ciliary muscles, suspensory ligaments, lens shape and refraction.
Explain pupil responses to bright or dim light using circular and radial iris muscle actions.
Describe how increasing light intensity changes pupil diameter using table data, including where the trend levels off.
Explain how absent iris pigment affects light entry and vision.
Explain how cataracts affect vision when the lens becomes cloudy and less light reaches the retina.
Suggest treatment needed after cataract lens removal, such as glasses, contact lenses or a replacement lens.

[Maximum number: 3]

Fur colour in rats is controlled by a gene with two alleles.

One allele codes for black fur colour. The other allele codes for agouti fur colour.
Several female rats with agouti coloured fur are mated with several male rats with black coloured fur.

All of the offspring have agouti coloured fur.

Some rats with white fur also have pink eyes.

These rats have pink eyes because they do not have pigment in their irises.
This means that their irises let light pass through, unlike the coloured irises found in other rats.

Explain how this difference in the iris affects vision in the rats with pink eyes.

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Edexcel IGCSE Biology 2.92 Eye Focusing and Light Responses Questions question 1