Does the response function is the similar concept with spectral sensitivity which as a function of frequency or wavelength of the signal.

Why is S so much lower than the other two? Is this somehow biologically advantageous?

@Jeyla probably because it is not necessary to detect these colors strongly. Also, lower wavelength colors carry more energy (they are higher frequency), so probably a "weaker" receptor is more optimal to prevent "saturation" of those cones (and allow higher dynamic range, essentially).

do rod cells also have LMS response functions?