According to polarographically measured EOred of bacteriochlorophyll "a", chlorobium chlorophyll "660", "b" and "a" chlorophylls (-0.67 V, -0.73 V, -0.79 V, -0.86 V-n.h.e.) and literature data about Eoox of these pigments (+/-0.62 V, + 0.62 V, + 0.78 V, +0.77 V correspondingly) it has been shown that chemical energy stored in the singular photochemical set is increased in the evolution of the photosynthetic apparatus. It has apparently resulted in the possibility of evolutionary approach to utilization of more inert and more accessible (water) electron donors and favoured further development of photosynthesizing organisms.