ABSTRACT
This chapter begins by a recalling of the origin of biological energy, that is to say, the radiant energy coming from the sunlight. It provides an introduction of the photosynthesis, of the respiration and of the fermentation. Then, the chapter introduces the biological work. The flow of matter in the biological world is also briefly investigated. A large amount of energy input is necessary to the system in order for the “uphill” reaction to take place. It is supplied by the light energy which is captured by the chlorophyll. The oxidation of complex organic fuel molecules is the most important process yielding chemical energy in heterophic cells. In both aerobic and anaerobic cells, the energy coming from the oxidation of the foodstuff molecules is not conserved as heat but as chemical energy. Actually, it is essentially conserved in the compound named adenosine triphosphate (ATP). The chapter provides a brief overview of the part played by ATP.
