Which photoreactive protein is responsible for the sensitivity of rods to light?

Rhodopsin is the photoreactive protein that plays a crucial role in the sensitivity of rod cells to light, which is essential for vision in low-light conditions. Rhodopsin is a complex of a protein called opsin and a chromophore, retinal. When light enters the eye, it causes a conformational change in the retinal component of rhodopsin, leading to a series of biochemical events that create an electrical signal sent to the brain. This process is fundamental for the functioning of rod cells, which are highly sensitive to dim light compared to cone cells, aiding in night vision.

Chlorophyll is primarily involved in the photosynthesis process in plants and does not play a role in human vision. Although opsin is a part of rhodopsin, it is not solely responsible for light sensitivity; it requires retinal to function effectively. Therefore, recognizing rhodopsin as the integral protein that combines both components and directly mediates the response to light clarifies why it is the correct choice.