Photopigment rhodopsin in the dark and lightRetinal changes shapeFIGURE 6-35 Photoreceptors. (a) The three parts of the rods and cones, the eye’s photoreceptors. Note in the outer segment of the rod and cone the stacked, flattened, membranous discs, which contain an abundance of photopigment molecules. (b) A photopigment, such as rhodopsin, depicted here and found in rods, consists of opsin, a plasma-membrane protein, and retinal, a vitamin-A derivative. In the dark, 11-cis-retinal is bound within the interior of opsin and the photopigment is inactive. In the light, retinal changes to all-trans-retinal, activating the photopigment.