A pilot looks away from an illuminated instrument panel towards the night sky. The pilot's pupil diameter increases.
The iris contains circular muscles and radial muscles.
Which statement correctly describes the activity of these muscles?
The radial muscles relax and the circular muscles also relax.
The circular muscles contract and the radial muscles relax.
The circular muscles contract and the radial muscles also contract.
The radial muscles contract and the circular muscles relax.
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.