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

Which type of photoreceptor is responsible for color vision?

1. Rods

2. Cones

3. Melanopsin

4. Phototransductors

The correct answer is: Cones

The type of photoreceptor responsible for color vision is cones. Cones are specialized cells in the retina of the eye that are sensitive to different wavelengths of light, allowing humans to perceive a broad spectrum of colors. They come in three varieties, each sensitive to different segments of the light spectrum: short (blue), medium (green), and long (red) wavelengths. This trichromatic nature of cones is fundamental for distinguishing between the various colors we see. Rods, on the other hand, are more sensitive to light and are primarily responsible for vision in low-light conditions, but they do not contribute to color vision. Melanopsin is a type of photopigment found in certain retinal neurons, playing a role mostly in regulating circadian rhythms and responding to ambient light rather than contributing to the color vision process. Phototransductors refer broadly to any molecules or structures involved in the conversion of light into electrical signals in the visual system but do not specify the type of photoreceptor necessary for color vision. Therefore, the role of cones in color perception distinguishes them clearly as the correct choice in relation to this question.