Thermodynamics and biology

Throughout this and the preceding chapter we have considered the thermodynamic aspects of a number of processes which occur in biological systems. Let us now summarize the main contributions that the study of thermodynamics makes to our understanding of the functioning of a living organism. 

Again it should be emphasized that there is no evidence to suggest that biological systems violate thie laws of thermodynamics in any way. Statements such as Life cheats in the game of entropy are misleading. A correct statement of the situation was made by Erwin Schrodinger, who said that 

Living systems live on negative entropy absorbed from their environment. 

In other words, they decrease their own entropy by increasing that of their surroundings. 

Consider, for example, the development and reproduction of bacterial cells. These are open systems in the thermodynamic sense the bacterial cell continuously acquires food from its environment and excretes waste products into its environment. If we were to consider the bacterial cells alone, without reference to the environment, we would find that the process was endergonic, largely as a result of the substantial decrease in entropy associated with the increase in order. Such an endergonic process would not be thermodynamically possible in itself. However, the metabolic reactions which are coupled with the development of cells are sufficiently exergonic to enable the development to occur, in full accord with the second law. 

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T. K. Dam and C. F. Brewer, Carbohydrate-lectin crosslinking interactions Structural, thermodynamic, and biological studies, Methods Enzymol., 362 (2003) 455—486. 

TNC. 24.1. Prigogine and R. Lefever, Termodinamica e Biologia (Thermodynamics and biology), in Enciclopedia della Scienza e della Tecnica, Mondadori, 1971. 

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