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

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What do rods in the retina primarily respond to?

Bright light
Colors
Dim light
Movement

The correct answer is: Dim light

Rods in the retina are specialized photoreceptor cells that are highly sensitive to light. They play a crucial role in vision under low-light conditions, allowing us to see in dimly lit environments. Unlike cones, which are responsible for color vision and work best in bright light, rods are more concentrated around the periphery of the retina and are optimized for detecting light intensity rather than color. Rods contain a photopigment called rhodopsin, which is effective at capturing photons even in low light. This makes them essential for night vision and for detecting shades of gray in varying light conditions. Therefore, the primary response of rods is to dim light, allowing us to perceive our surroundings even when illumination is minimal.