ABSTRACT
Living organisms are presented with numerous challenges by the physical and chemical principles of this world. This chapter discusses the observed correlations between cellular activities and energy state parameters in terms of their possible origin. The free energy of hydrolysis of adenosine triphosphate, the electrochemical potential difference for protons across the inner mitochondrial membrane and the electric potential difference across the plasma membrane are central free energies in cellular metabolism. An important step in exocytosis is the fusion of the intracellular storage vesicle with the plasma membrane of the secreting cell. Free-energy differences of reactions are potentials in the sense that they are defined as the change in free energy of the system when an infinitesimal amount of reaction is allowed to occur. Thermodynamics has been a significant help to biologists by defining a new type of energy that solely consists of the energy that can be applied to do work.
