ABSTRACT
Photosynthesis, a major route for the uptake of energy, is the basis for all life functions. It appeared very early on earth through photosynthetic bacteria, since the atmosphere and water did not provide organic mol ecules or minerals yielding a large quantity of energy, or in sufficient concentrations, except in particular ecosystems. Photosynthesis may be considered to have developed in two major stages. First there was formation of a photochemical system with bacterial chlorophyll, which, when it absorbs light energy, can achieve a separation of charges that allows electron activation from substances (still sufficiently abundant in the terrestrial atmosphere) having Em7 values that could be considered averages, for example H2S (S/HS~ = -0.18 V), H2 (H2/2H + + 2e = -0.43 V (but in fact the values are closer to zero in the natural environment, because of pH and low concentration), succinic acid (close to -0.1 V), and fumaric acid (close to 0 V).
