Heterotrophic theory

On the abiotic synthesis of biochemical monomers and the heterotrophic theory on the origin of life... 

Cells are isothermal systems—they function at essentially constant temperature (they also function at constant pressure). Heat flow is not a source of energy for cells, because heat can do work only as it passes to a zone or object at a lower temperature. The energy that cells can and must use is free energy, described by the Gibbs free-energy function G, which allows prediction of the direction of chemical reactions, their exact equilibrium position, and the amount of work they can in theory perform at constant temperature and pressure. Heterotrophic cells acquire free energy from nutrient molecules, and photosynthetic cells acquire it from absorbed solar radiation. Both kinds of cells transform this... 

Thingstad, T. F. 1987. Utilization of N, P, and organic C by heterotrophic bacteria. I. Outline of a chemostat theory with a consistent concept of maintenance metabolism. Marine Ecology Progress Series 35 99-109. 

The endosymbiotic theory of the origin of eukaryotes states that eukaryotes arose from symbiotic groups of prokaryotic cells. According to this theory, smaller prokaryotes lived within larger prokaryotic cells, eventually evolving into chloroplasts and mitochondria. Chloroplasts are the descendant of photosynthetic prokaryotes and mitochondria are likely to be the descendants of bacteria that were aerobic heterotrophs. Serial endosymbiosis is a sequence of endosymbiotic events. Serial endosymbiosis may also play a role in the progression of life forms to become eukaryotes. 

Such a theory of metabolic and photosynthetic evolution goes far towards explaining the similarities and differences amongst the various metabolic processes as we know them today. The path of carbon reduction in photosynthesis employs many reactions which are similar to those employed by heterotrophic organisms in the oxidation of carbohydrates. The apparatus for transporting electrons from water to the point of reduction of carbon dioxide in photosynthesis is similar in many aspects to the apparatus used for the transport of electrons from the oxidation of carbohydrate to oxygen in respiration. 

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