Energy in Biology—Demand and Use

Abstract

From the point of view of energy management in biological systems, a fundamental requirement is to ensure spontaneity. Process spontaneity is necessary since in a thermodynamically open system—such as the living cell—only spontaneous reactions can be catalyzed by enzymes. Note that enzymes do not, by themselves, contribute additional energy. Spontaneity of biological processes may be expressed by the following correlation:

ΔG = ΔH − TΔS where ΔG means the change of free energy, ΔH—change of enthalpy, ΔS—change of entropy, T—temperature. Desirable processes which do not occur on their own must be coupled to other highly spontaneous mechanisms serving as energy sources. In biology, the fundamental sources of energy involve synthesis of water and photosynthesis. Since both processes are rather complex and cannot be exploited directly, they are used to synthesize ATP which acts as an energy carrier. Approaching biology from the point of view of elementary physics and chemistry reveals important mechanisms and enhances our understanding of various phenomena.

A coupled energy source is a prerequisite of sustained dynamics in thermodynamically open systems.