The Carnot efficiency and plant photosystems

Abstract

The concept that the Carnot efficiency places an upper limit of 0.60–0.75 on the thermodynamic efficiency of photosynthetic primary photochemistry is examined using a PSI-LHCI preparation. The maximal quantum efficiency was determined ≈0.99 which yielded a thermodynamic efficiency of at least 0.96, a value far above that predicted on the basis of the Carnot efficiency. The commonly presented reasoning leading to the Carnot efficiency idea was therefore critically examined. It is concluded that the conventional assumption that the excited/ground state pigments are ergodic is incorrect, as is the assumption that the pigment system, under illumination, is in equilibrium with the incident light field, at a black body temperature of T r. It is concluded that the classical reasoning used to describe the thermodynamics of heat systems is not applicable to “photonic” systems such as plant photosystems.