When light hits a rod, what substance absorbs the photons?

When light hits a rod, what substance absorbs the photons?

• A. Photopsin
• B. Rhodopsin
• C. Retinal
• D. Opsin

Answer: (B)

Rods detect light using a single photopigment called rhodopsin. This pigment sits in the outer segment of the rod and is a complex of the protein opsin bound to a light-sensitive molecule called retinal. When a photon enters, retinal absorbs the light and changes shape, which activates opsin and kickstarts the phototransduction cascade. Because rhodopsin is the light-absorbing pigment in rods, it is the substance that directly absorbs the photons. (Retinal is the part of rhodopsin that actually absorbs the light, but the overall absorber in the rod is rhodopsin.) Photopsin is the pigment used by cones, and opsin is just the protein component of rhodopsin.

Rods detect light using a single photopigment called rhodopsin. This pigment sits in the outer segment of the rod and is a complex of the protein opsin bound to a light-sensitive molecule called retinal. When a photon enters, retinal absorbs the light and changes shape, which activates opsin and kickstarts the phototransduction cascade. Because rhodopsin is the light-absorbing pigment in rods, it is the substance that directly absorbs the photons. (Retinal is the part of rhodopsin that actually absorbs the light, but the overall absorber in the rod is rhodopsin.) Photopsin is the pigment used by cones, and opsin is just the protein component of rhodopsin.