At an indoor climbing centre, a climber moves from a shaded wall to a wall lit by bright floodlights. The climber's pupils become smaller. The iris contains circular muscles and radial muscles.
Which explanation best accounts for this change?
The circular muscles relax while the radial muscles contract, reducing the amount of light reaching the retina.
The circular muscles contract while the radial muscles relax, reducing the amount of light reaching the retina.
The lens becomes thicker and pulls the pupil smaller, reducing the amount of light reaching the retina.
The circular and radial muscles both contract, reducing the amount of light reaching the retina.
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.