Differentiation of photoreceptor cells and morphogenetic function of biomembranes

Photoreceptor cells of eyes in vertebrate animals have been chosen as an example to illustrate the morphogenetic function of biomembranes in differentiation of the eye outer segments -- rods and cones. Morphogenetic function of biomembranes in photoreceptor cells involves an insertion of the heterogeneous molecule of visual pigment into the original plasma membrane. Depending on some features of visual pigment in one case cones may be produced or rods as more complicated structures may be differentiated in the other one. Some evolution aspects of photoreceptor cell differentiation have also been under discussion.