A harbour worker needs to identify a yellow buoy as daylight fades.
After an injury to the worker's left eye, four observations are recorded.
| Test location | Observation |
|---|---|
| Light rays after passing through the cornea and lens | brought to a sharp focus on the retina |
| Receptor cells in the retina | electrical impulses produced |
| Start of the optic nerve at the back of the eye | electrical impulses recorded |
| End of the optic nerve next to the brain | no electrical impulses recorded |
Describe how the observations identify the stage of the pathway that has been disrupted and the effect of this disruption on vision in the left eye.
In a separate test using a healthy eye, the responses of two types of receptor cell, P and Q, are recorded.
| Light intensity / lux | Number of electrical impulses recorded in 10 s from cell type P | Number of electrical impulses recorded in 10 s from cell type Q |
|---|---|---|
| 500 | 38 | 44 |
| 50 | 29 | 11 |
| 5 | 12 | 0 |
State which cell type, P or Q, is a rod cell.
Using the data, describe how the results support your answer to part (b). Describe the colour and the level of detail with which the buoy is likely to be seen at a light intensity of 5 lux.
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.