Question

Why do the standards need to have their transmittance values measured at 600 nm? Why is 600 nm an appropriate wavelength for this experiment (a UV-visible spectrum may help answer that question)?

Answer 1

The absorbance or the OD of any solution is taken at a particular wavelength which depends on the color of the solution. protein absorbance at 280 is the absorbance of uv light by aromatic amino acids and all other absorbance at different wavelengths are after some tests like biuret test 540 nm. and 620 nm for albumin test by some kits. here the concentration of protein is dependent on the amount of color developed due to presence of protein or peptide bond. hope this is clear now. now OD due to turbidity is actually due to scattering of light and what you have heard about 600nm is for bacterial cells.

That's why the standards need to have their transmittance values measured at 600 nm