A person looks through an adjustable viewing filter. The filter is changed from its dark setting to its pale setting. The eye is allowed to adjust before each measurement.
| Filter setting | Light transmitted / % | Pupil diameter / mm |
|---|---|---|
| dark | 18 | 6.2 |
| pale | 72 | 2.8 |
The iris contains circular muscles and radial muscles.
Which statement explains the change when the pale filter is selected?
The circular muscles and the radial muscles both relax, decreasing the pupil diameter so less light enters.
The circular muscles contract and the radial muscles relax, decreasing the pupil diameter so less light enters.
The circular muscles and the radial muscles both contract, decreasing the pupil diameter so less light enters.
The circular muscles relax and the radial muscles contract, decreasing the pupil diameter so less light enters.
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.