The appearance of oxygen on our globe induced profound changes in the nature of living systems which started to differentiate and build complex structures with complex functions. Oxidation was added to fermentation and unbridled proliferation was subjected to regulation. Fermentation demanded no structure, being the result of the action of a series of single molecules. Oxidation, with its electron flow, demanded structure and electronic mobility. To produce meaningful structures and complex functions the action of the single molecules had to be integrated. The question is: how could oxygen bring about these transformations? These changes are not limited to the distant past because in every division the cell has to revert, to some extent, to the undifferentiated, fermentative, proliferative state of ist earlier anaerobic period. After having completed its division, it has to find its way back to its oxidative resting state. If this road of return is deranged the cell has to go on dividing as it does in cancer. By elucidating the details of these processes we can hope to be able to control them. We can control only what we understand (Bernal). That oxygen can induce profound changes in cell life can be demonstrated even in the acute experiment. L. Pasteur showed that fermentation is inhibited by the admission of oxygen (“Pasteur Reaction”), and H. G. Crabtree demonstrated the opposite effect. The intimate relation of cancer and oxygen was made evident by H. Goldblatt and G. Cameron who provoked malignant transformation in their tissue culture by periodically limiting their oxygen supply. O. Warburg attributed the changes, induced by O2, to a wealth of energy it produced. Undoubtedly, without a new and rich source of energy these changes could not have occurred. Energy made them possible, but energy offers no mechanism. The chemical mechanism underlying these transformations will be the main topic of this paper and it will be shown that charge transfer is one of the central biological reactions. A biologist trying to understand life without electronic mobility is comparable to a Martian trying to understand our civilization without knowing about electricity. This paper will chiefly be concerned with principles. The chemical methods employed will be discussed in a subsequent paper by Dr. L. Egyud.