NEGATIVE ENTROPY CHANGE IN LIVING SYSTEMS 



187 



TABLE 7-6. Membrane Potentials, E, Observed, and Calculated from Measured 

 Concentration Ratios Across Cell Walls. 



Actually, any activity difference between two solutions separated by a mem- 

 brane is a sufficient condition for a membrane potential to exist. Three 

 cases will give rise to a potential difference: 



( 1 ) Two concentrations of the same salt (restricted flow). 



(2) The same (or different) concentrations of two different salts. Even 

 though the concentrations are the same, the effective concentrations 

 or activities differ because of different interactions with the solvent 

 and with each other. 



(3) Free flow through the membrane, except for one macromolecular ion. 

 This is a rather famous equilibrium, exemplified across living cell 

 walls, and described quantitatively by Donnan. 



To sort out these possibilities on living membranes is one of the hardest 

 tasks in biophysics today. The subject will be considered one step further: 

 the time-variation of the potential across nerve-cell membrane (Chapter 10). 



NEGATIVE ENTROPY CHANGE IN LIVING SYSTEMS 



The concept and the quantity entropy has been very carefully introduced 

 in a simple manner, as a specific heat — a very special specific heat, to be 

 sure — and this idea of entropy is sufficient for many considerations. But the 

 implications are more far-reaching than at first suspected. Thus, an increase 

 in entropy during the course of a reaction was described as meaning that 

 the modes of rotation, etc., of the products were more numerous than those 

 of the reactants. This interpretation means that the amount of complexity 

 in the system has increased with reaction, and could be rather loosely ex- 

 tended to mean that the amount of disorder in the system has increased. Thus 

 the extra heat, q', lost during a process done in a nonreversible manner con- 

 tributes quantitatively to the disorder of the system and its environment. 



The idea of entropy being associated with disorder or randomness can be 

 introduced systematically and logically through statistics. Briefly, the 



