What is the maximal absorption wavelength of rhodopsin?

• A. 507 nm
• B. 530 nm
• C. 557 nm
• D. 426 nm

Answer: (A)

Rhodopsin, the pigment in rods, has a distinct absorption spectrum with a peak in the blue‑green part of the spectrum. This maximum occurs because the retinal chromophore bound to the opsin absorbs photons most efficiently around that wavelength, triggering the phototransduction cascade when light hits it. In humans, the peak is typically cited near 507 nm, which is right in that blue-green region. Among the given options, 507 nm aligns with this peak, making it the best match for the maximal absorption of rhodopsin. The other values lie farther from the peak (violet, greener, and more yellow-green), where rhodopsin absorbs less efficiently.