A researcher tests two observers in a darkened room. Each observer looks continuously at a small central marker. A faint spot of light is flashed either on the marker or to one side.
One observer has damaged rod cells. The other observer has no damaged receptor cells. Neither observer has damaged cone cells or focusing structures.
| Position of faint spot | Correct detections by observer R, out of 20 | Correct detections by observer S, out of 20 |
|---|---|---|
| on the central marker | 3 | 3 |
| to one side of the marker | 17 | 4 |
Explain which observer has damaged rod cells. Use the results in your answer.
The researcher then asks both observers to identify small coloured letters shown at the central marker in bright light.
Suggest how the performance of the observer with damaged rod cells would compare with the performance of the other observer. Justify your answer.
102 exam-style questions on Edexcel GCSE Biology 2.4 The eye, covering 2.4.1 Structure and function of the eye and 2.4.2 Eye defects and their correction. Each one has a worked solution and a mark scheme showing where the marks go.