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

Why can't rods detect color?

1. They are not located in the fovea

2. They are only active in bright light

3. They do not contain photopigments for color detection

4. They are only found in peripheral vision

The correct answer is: They do not contain photopigments for color detection

Rods are specialized photoreceptor cells in the retina that are highly sensitive to light, allowing us to see in low-light conditions. However, they do not play a role in color vision. This is because rods contain a type of photopigment called rhodopsin, which is sensitive to light intensity but not to different wavelengths associated with colors. This limitation means that rods can detect shades of gray but cannot differentiate between colors, which is the role of cone cells in the retina. The other choices highlight related aspects of rod function without accurately addressing their inability to detect color. Rods are indeed found throughout the retina but are most concentrated in the peripheral areas and not in the fovea, where cones are concentrated. Additionally, rods function best in dim light rather than bright light, which is when cones dominate. Finally, while rods are more prevalent in peripheral vision, that does not directly correlate to their color detection capabilities. Hence, the correct answer regarding why rods cannot detect color centers on the absence of photopigments responsible for color identification.