A Simple Thermodynamic Analysis of Photosynthesis

Abstract

Abstract:In this paper we present a comparative study of nine photosynthetic pathways by means of their thermodynamic performance. The comparison is made by using the thermal efficiency of light-to-chemical energy conversion and the so-called ecological criterion arising from finite-time thermodynamics. The application of both criteria leads to photosynthesis made by metaphytes and non sulfur purple bacteria as those of best thermodynamic performance. In spite of the simplicity of our thermodynamic approach some insights over the low overall efficiency of photosynthesis is suggested.

Cyanobacteria and Microalgae: Thermoeconomic Considerations in Biofuel Production

“…Photosynthesis is a process that leads to complex organic molecules starting from simple molecules and by absorbing solar radiation [64,65] Now, it is fundamental to evaluate the entropy generation, to introduce the entropy generation principle in the thermodynamic analysis of photosynthesis. We consider the sun, the photosynthetic organism and the earth as different systems [64].…”

“…We consider the sun, the photosynthetic organism and the earth as different systems [64]. Fluxes occur among these.…”

Scientific Élan Vital: Entropy Deficit or Inhomogeneity as a Unified Concept of Driving Forces of Life in Hierarchical Biosphere Driven by Photosynthesis

“…The entropy deficit I = hȞ 0 /T s í hȞ 0 /T r = 590.6 í 149.2 = 441.4 J mol í1 K í1 per mole photon or 48 × 441.4/1,000 = 21.187 kJ mol í1 K í1 per glucose (in the steady-state) is the ultimate driving force of all other biochemical reaction leading to the synthesis of glucose. This is equivalent to the change in generalized entropy ¨S*° = -¨G°/T as defined in Equation (9). Many people vaguely think that 'energy' is introduced in the process of photosynthesis, but this is a misleading concept.…”

“…However, we can consider difference in free energy divided by temperature as a measure of inhomogeneity. Increment in Gibbs free energy ¨G is expressed by increment in enthalpy ¨H, increment in entropy ¨S and temperature T: (8) According to Atkins and de Paula [14], Equation (8) can be rewritten in the following form: (9) Here, í¨H/T represents 'entropy change in the environment' caused by the transfer of heat out of the system into the environment. In other words, this term represents dissipation of heat (if there is no pressure changes and no non-mechanical work), in which the heat localized within the system is now distributed in the whole universe.…”

“…Calculations of entropy in various processes of photosynthesis have been published [8] to give us some reliable hint on the entropy balance of the biosphere. A comparison of entropy balance in various types of photosystems was presented [9].…”