OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What role does the iris play in vision?

It refracts light
It adjusts the size of the pupil
It focuses light on the retina
It aids in night vision

The correct answer is: It adjusts the size of the pupil

The iris plays a pivotal role in vision by adjusting the size of the pupil, which in turn regulates the amount of light that enters the eye. By contracting or relaxing, the iris can make the pupil smaller or larger, allowing the eye to adapt to varying levels of light. This function is essential for optimizing vision under different lighting conditions; for instance, in bright light, the pupil becomes smaller to reduce light intake and protect the retina, while in dim light, it enlarges to allow more light in for better visibility. While the iris is crucial for controlling light entry, it does not refract light, focus light on the retina, or directly aid in night vision on its own, although its size adjustment indirectly supports vision in low-light situations.