THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -Photoreceptors are the cells in the retina that respond to light. Their distinguishing feature is the presence of large amounts of tightly packed membrane that contains the photopigment rhodopsin or a related molecule.

Detailed explanation-2: -Light causes cGMP to fall by activating PDE via the enzymatic cascade including photoactivated rhodopsin, the G-protein called transducin, and the effector enzyme PDE. The reduction in the cGMP concentration results in channel closure and photoreceptor hyperpolarization.

Detailed explanation-3: -Vertebrate photoreceptors can respond to light by virtue of their containing a visual pigment embedded in the bilipid membranous discs that make up the outer segment. The visual pigment consists of a protein called opsin and a chromophore derived from vitamin A known as retinal.