They are made of alternating layers of guanine crystals (n1.83) and cytoplasm (n.- 1.33). The thickness d, of the guanine layers is 98 nm.

Under what circumstances will there be constructive interference of visible wavelengths of light? That is, how must n, n, de the thickness d, of the cytoplasm layers, and λ be related in order for this to happen?

The wavelength of light that is most strongly reflected from the ventral scales of the sprat is 720 nm. What is the thickness of the cytoplasm layers?

When the salinity of the water in which the sprat swims is increased, the wavelength of maximum reflection for the fish's scales shifts to shorter wavelengths. The guanine crystals are not affected by the salt, and the change in the index of refraction of the water and of cytoplasm is negligible. What causes the shift (be specific)? This phenomenon means that sprat scales can be used as an osmomete