The eye, rods and pupil responsesEdexcel A-Level Biology A: Mind map

Exam questions on The eye, rods and pupil responses

1. An ophthalmologist shines a bright light into one eye of each of two patients and watches the pupil. In the first patient the pupil constricts quickly. In the second patient, the motor neurones that supply the iris muscles have been damaged by a head injury, and the pupil does not constrict.
   Explain why the pupil of the second patient does not constrict.2 marks
2. A driver leaves a brightly lit petrol station and pulls onto an unlit country road at night. For the first few minutes she cannot see the road edge clearly, but her vision gradually improves.
   Explain why the driver cannot see clearly at first on the dark road.2 marks
3. Vitamin A is needed to make retinal. A man whose diet is deficient in vitamin A has difficulty seeing in dim light, a condition called night blindness. His rod cells contain less rhodopsin than normal.
   Explain why the man's lack of vitamin A makes it difficult to detect dim light.3 marks