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Comment on "Minimum entropy production in photosynthesis"

The law of minimum entropy production (Prigogine, I., 1967) is an important result from nonequilibrium thermodynamics. Its validity requires that the phenomenological coefficients are independent of the state variables such as the particle density n and temperature T. In its very simple derivation for the case of two flows and corresponding fluxes, one must assume linear phenomenological relations between forces and fluxes and reciprocal relations for cross-coefficients (Onsager, L. 1931) describing coupling between these two different irreversible processes. One process may be considered as the primary (driving), while the other may be secondary (driven by the primary process). Such a picture is apropriate for photosynthesis where everything is driven by the photon free energy (Meszena, G. and Westerhoff, H.V., 1999). The static head nonequilibrium steady state is established if the driving force is kept constant and the driven force left to adjust its value until the driven flux vanishes. The entropy production is then minimal with respect to the optimal (maximal) value of the secondary (driven) force. It is important to notice that minumum entropy production state, as defined by Prigogine (1967), is nonequilibrium steady state with constant non-zero entropy production due to the action of constant non-zero driving force and corresponding flux. Continous free-energy transduction serves only to maintain the maximal free-energy storage in the form of the secondary force in the static head state. In terms of efficieny in producing desired power (secondary flux and force) it is zero efficiency state due to vanishing secondary flux. This introduction serves to highlight the difference between minimal entropy production as described in the Andriesse & Hollestelle paper (2001) and standard derivation and application of that theorem. In that paper, which is using the results of an earlier paper by the same author, only the assumption of linear relationships between forces and flows is maintained. We shall not discuss how realistic is that assumption or their choice of driving and driven forces and flows in photosynthesis.We shall only show that minimal entropy production state, described in these two papers, is in reality an equilibrium state with zero entropy production.

entropy production; photosynthesis

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