Energy, activation photosynthetic

Chemical models of photosynthesis have been used to investigate two types of reactions photosynthesis and photocatalysis. In photosynthetic processes the standard Gibbs free energy of the reaction is positive, and solar energy is utilized to perform work. In photocatalytic processes the free energy is negative and solar energy is used to overcome the activation barrier. 

Figure 12.1. Schematic diagram of a photosynthesis reaction center. Light is absorbed by pigments in the light-gathering antenna and absorbed energy is transferred to a photochemically active site P, where it is utilized to initiate photosynthetic reactions.

Uncoupling is a specific toxic effect that takes place in energy-transducing membranes (photosynthetically active membranes, inner mitochondrial... 

Explosive research activity is going on in micellar photochemistry. This is related to the development of artificial photosynthetic systems, and the anisotropic nature of globular micelles and bilayer membranes is used for conservation of excitation energy. The subject has been recently reviewed (Kalyanasundaram, 1978). 

There are reports of algae releasing as much as 90t of their total photosynthetic product into the water (3-8). A great deal of energy is invested in those complex molecules. If these were of no value, such incredibly inefficient organisms could not dominate a community. Since they do, there is a value and the trait is fixed in evolutionary terms. This is the basis for primary allelochemical activity. 

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