The synthesis of the complex constituents of the cell from simple metabolism involves reactions which are accompanied by an increase in the free energy of the system. These, as has already been stated, require the simultaneous occurrence of several coupled reactions by which the necessary free energy liberated in one reaction is utilized for the performance of another. The availability of energy-rich compounds is thus necessary for many reactions which occur in the organism. These are formed as by products in the utilization of foodstuffs from which all the energy of the body must ultimately be obtained.

High-energy Phosphate Bonds A commonly occurring coupled reaction utilized in living systems in the high – energy phosphate bond. The term high energy refers to the fact that the hydrolysis of certain phosphoric acid esters goes nearly to completion with a large negative free energy change which can be utilized for others reactions. Adenosine tri phosphate is the most versatile of these high – energy phosphate bonds.

The manner in which the organism utilizes the energy of foodstuffs may be illustrated by a consideration of the metabolism of carbohydrate. The stored energy of this foodstuff released in the anaerobic oxidation of glucose to pyretic acid. Part of this released energy is dissipated as heat; the remainder is stored in the labile energy pool as high – energy phosphate formed by the combination of adenosinediphosphate (ADP) with inorganic phosphate to form adenosinetriphosphate (ATP).

The increase in entropy which accompanies the “activity of living” is avoided by the ingestion of foodstuffs of high negative free energy content. As it has been expressed by Schrodinger, the organism thermo dynamical speaking feeds “on negative entropy.”