Thermodynamics living systems

In considering thermodynamic parameters, e.g., heat and work, we do not need to know the exact chemical pathway taken by the reactants in conversion to products. Using thermodynamics, we can obtain information about reactions that cannot be studied directly in living systems. Thermodynamics predicts, on the basis of the known energy levels of reactants and products, whether a reaction can be expected to occur spontaneously or how much energy must be supplied to drive the reaction in one direction or another. Such information is crucial in establishing reaction routes in metabolic pathways. Thermodynamics explains how equilibrium constants are related to changes in temperature. Thermodynamics also explains the basis for enzyme catalysis. 

In living systems, thermodynamically favorable reactions provide the flee energy needed to drive necessary but thermodynamically unfavorable reactions. 

A final observation is in order the quantitative application of the equilibrium thermodynamical formalism to living systems and especially to ecosystems is generally inadequate since they are complex in their organisation, involving many interactions and feedback loops, several hierarchical levels may have to be considered, and the sources and types of energy involved can be multiple. Furthermore, they are out-of-equilibrium open flow systems and need to be maintained in such condition since equilibrium is death. Leaving aside very simple cases, in the present state of the art we are, therefore, limited to general semiquantitative statements or descriptions (e.g. ecosystem narratives ). 

The kinetic and thermodynamic structure of a pathway or process in a cell or a tissue can only be maintained because living systems are open that is, they exchange matter and energy with the environment (Chapter 2). 

Fitness of adaptation to the environment means that biochemical correlates of physical or chemical characteristics of the environment must exist.1 Therefore, adaptive processes are always optimization processes be it that of metabolic sequences or of molecular properties.2-3 To recognize that a living system is adapted to a given environment is simply to recognize its finality4 or teleonomic characteristics.5 Optimization being a consequence of the second law of thermodynamics, it seems to me that what Jacob or Monod call finality or teleonomy is simply the finality of the second law. 

Lems, S. Thermodynamic explorations into sustainable energy conversion. Learning from living systems. PhD thesis, Delft University of Technology, Delft, the Netherlands, March, 2009. 

These thermodynamic efficiencies may be considered to be on the low side, particularly for land plants. But then it must be noted that this photosynthesis is an activity of a living system for which photosynthesis, or rather the capture of solar energy and its transformation into chemical energy, is only one aspect of life. Supply may exceed demand. Therefore, it may well be that if the only purpose of photosynthesis is the capture of light as an energy source, the efficiencies would have been higher. Support for this conjecture can be found in a calculation by Lehninger [12], who shows that under certain laboratory... 

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