During an eye examination, a person sits in dim light for two minutes. An examination lamp is then switched on near the person's face.
| condition | pupil diameter / mm |
|---|---|
| before the lamp is switched on | 6.4 |
| 5 seconds after the lamp is switched on | 2.3 |
Calculate the percentage decrease in pupil diameter after the lamp is switched on.
Explain how the muscles in the iris cause the measured change and why this response is useful.
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.