Chapter 10 · Question 1

Describe the function of the iris and pupil in the human eye.

Answer Revealed

Direct Answer:

The iris controls the size of the pupil, which regulates the amount of light entering the eye.

Simple Explanation

The iris is the coloured ring around the pupil that works like a camera aperture — it expands and contracts to let more or less light into the eye through the pupil, which is the small opening in the centre.

Exam-Ready Structure

The iris and pupil work together to control light entry into the eye: 1. The iris is a muscular diaphragm behind the cornea that gives the eye its colour. 2. The pupil is the central circular opening in the iris through which light enters the eye. 3. In bright light, the iris contracts to shrink the pupil, reducing light entry and protecting the retina. 4. In dim light, the iris expands to dilate the pupil, allowing more light to enter for better vision. 5. This automatic adjustment protects the sensitive retina from damage due to excessive light while also enabling vision across a wide range of brightness conditions.

Key Points

Iris is a muscular diaphragm that controls pupil size
Pupil is the opening through which light enters the eye
In bright light, pupil constricts to reduce light entry
In dim light, pupil dilates to allow more light in
Together they regulate light reaching the retina

Common Mistakes

Confusing the function of iris with that of the cornea or lens
Saying the pupil itself expands or contracts (the iris muscles cause this)

Describe the function of the iris and pupil in the human eye.