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

What adjustment does the eye make for focusing on close objects?

1. The lens flattens

2. The ciliary muscles relax

3. The lens becomes more rounded

4. The pupil constricts

The correct answer is: The lens becomes more rounded

When focusing on close objects, the eye adjusts by making the lens more rounded. This change occurs because the ciliary muscles contract, which relieves tension on the zonular fibers connected to the lens. As a result, the lens' natural elasticity causes it to bulge, allowing it to increase its curvature. A more rounded lens is effective for refracting light rays that come from nearby objects, enabling clear visual perception. In contrast, when focusing on distant objects, the lens flattens, and the ciliary muscles relax to allow the eye to adapt accordingly. The pupil may constrict for better depth of field or to improve sharpness in certain lighting conditions, but this adjustment is secondary to the lens's role in focusing. Thus, becoming more rounded is essential for clear vision of close-up tasks, such as reading or examining details closely.