Photosynthesis traps

A.QUATIC oxidation-reduction (redox) processes control the distribution of many major and minor elements in natural environments (1). Equilibrium redox calculations can be used to indicate the boundary conditions toward which a natural system must be proceeding. Real systems are frequently far from equilibrium because photosynthesis traps the energy of the sun in the form of energy-rich chemical bonds and thus creates nonequilibrium chemical species. The return to equilibrium (even when mediated by bacteria)... 

The maximum efficiency with which photosynthesis can occur has been estimated by several methods. The upper limit has been projected to range from about 8 to 15%, depending on the assumptions made ie, the maximum amount of solar energy trapped as chemical energy in the biomass is 8 to 15% of the energy of the incident solar radiation. The rationale in support of this efficiency limitation helps to point out some aspects of biomass production as they relate to energy appHcations. 

The value of these molecules in synthesis and energy capture, photosynthesis and oxidative phosphorylation, together makes the production of organic molecules, which are energy traps, more rapid and hence the total biomass survival is increased. Overall energy retention is also increased. The particular value of Mg2+ in chlorin is described in Section 5.7. 

These bacteria cannot in general oxidize water and must live on more readily oxidizable substrates such as hydrogen sulfide. The reaction centre for photosynthesis is a vesicle of some 600 A diameter, called the chromato-phore . This vesicle contains a protein of molecular weight around 70 kDa, four molecules of bacteriochlorophyll and two molecules of bacteriopheophy-tin (replacing the central Mg2+ atom by two H+ atoms), an atom Fe2+ in the form of ferrocytochrome, plus two quinones as electron acceptors, one of which may also be associated with an Fe2+. Two of the bacteriochlorophylls form a dimer which acts as the energy trap (this is similar to excimer formation). A molecule of bacteriopheophytin acts as the primary electron acceptor, then the electron is handed over in turn to the two quinones while the positive hole migrates to the ferrocytochrome, as shown in Figure 5.7. The detailed description of this simple photosynthetic system by means of X-ray diffraction has been a landmark in this field in recent years. 

Pairwise distribution can occur, for example, in the case of recombination of the trapped electrons with the parent counterions or with the products of their transformation provided that the two reagents are produced in sufficiently low concentration (see Chap. 6). The pairwise distribution is also characteristic of the recombination processes in the reaction centre of photosynthesis (see Chap. 8). 

Photosynthesis is a major cause of nonequilibrium conditions in natural waters. By trapping light energy and converting it to chemical... 

Several approaches to artificial photosynthesis involve the mimicking of membranes to effect charge separation. An easy extension of the micellar effects described above to systems amenable to study as photosynthetic models can be encountered in the charge separation derived on synthetic vesicles or membranes (275). Sonic dispersal of long chain ammonium halides, phosphates, sulfonate, or carboxylates produces prolate ellipsoidal vesicles with long term stabilities which can entrain and trap molecules in their compartments. With donor-acceptor photosystems, four physical arrangements about the vesicle are important, Fig. 6. 

Photosynthesis occurs in green plants, algae and photosynthetic bacteria. Its role is to trap solar energy and use this to drive the synthesis of carbohydrate from carbon dioxide and water. Using (CH20) to represent carbohydrate, the overall reaction is ... 

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