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GCSE Biology · key term
The coloured ring of muscle that controls how much light enters the eye by changing the diameter of the pupil.
Used by AQA, Edexcel and OCR
Specification 4.5.2.3 · Paper 2
The coloured ring of muscle that changes pupil size to control how much light enters the eye.
Revise: Structure and Function of the EyeBehind the cornea is the coloured iris. The opening in its centre is the pupil, through which light enters. Behind the pupil, the transparent lens changes shape to bring light into focus on the retina.
Specification 2.15B · Paper 1
Revise: Structure and Function of the EyeThe cornea and lens focus the light, the iris controls how much enters, and rod and cone cells in the retina detect it.
Specification B3.1d · Paper 1 (Foundation), Paper 3 (Higher)
The coloured ring of tissue that controls the diameter of the pupil and therefore the amount of light entering the eye.
Revise: The eyeBehind the cornea is the iris, the coloured part of the eye. At its centre is the pupil. The pupil is not a piece of tissue: it is a hole through which light passes.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
The coloured ring of muscle that controls the size of the pupil.
Revise: The EyeThe cornea bends, or refracts, the light. It then passes through the pupil, an opening in the coloured iris, and through the transparent lens. The cornea and lens bring rays from each point on the object together on the retina at the back of the eye.
Describe the iris as controlling pupil size: the pupil widens in dim light and narrows in bright light.
Do not say that the pupil changes size by itself. The pupil is an opening; muscles in the iris alter its diameter.
The pupil is an opening in the iris, not a muscle. The iris changes the pupil's diameter.
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