Which photopigment has a maximal absorption wavelength of 507 nm?

• A. Chlorolabe
• B. Erythrolabe
• C. Rhodopsin
• D. Cyanolabe

Answer: (C)

Photopigment sensitivity is defined by the wavelength at which the pigment absorbs light most efficiently. A peak around 507 nm sits in the blue-green portion of the spectrum and is characteristic of rhodopsin, the visual pigment in rods. Rods are responsible for vision in low light, and their peak sensitivity around this region explains why they respond best in dim, blue-green light. In contrast, cone pigments have distinct peaks: the blue-cone pigment peaks toward the blue end, green-cone toward the green-yellow, and red-cone toward the longer red wavelengths. Those peaks do not center at 507 nm, so the pigment with maximal absorption at 507 nm is rhodopsin.