Evolution of Photosynthesis

Evolution of Photosynthesis

	Evolution of Photosynthesis - On the basis of fossil evidence there are indications that biochemically advanced microbial life, existed on the earth more than 3, billion years ago. The precursors of prokaryotic cells must have existed even earlier and have been called progenotes or protocells. The evolution of progenotes into prokaryotes is believed to have occurred 3 to 4 billion years ago. Broda (1975) has presented the following sequence for the appearance of metabolic activities, in prokaryotes during the course of evolution:
Anaerobic fermentation Primitive bacterial photosynthesis Complex plant type photosynthesis, as in Cyanobacteria Aerobic respiration The earliest prokaryote cells were presumably fermenting bacteria They lived in an environment in which organic compounds were freely available, and in which the atmosphere was reducing. The bacteria were anaerobic scavengers which broke down compounds with a high free energy content.
The organic compounds were thus used as sources of energy, which was utilized by the organisms. The molecules with the lower freeenergy content were released as waste products. This process of fermentation is still used as a source of energy by such anaerobic bacteria as Clostridium.
The next step was the development of photosynthesis in which solar energy was trapped to synthesize molecules with a high free energy content. Photosynthesis is essentially a process in which electro magnetic energy is converted to chemical energy, which is easily convertible to ATP. The energy stored in the high free energy content molecules can be used in later activities according to Dickerson (1980), sulphate respiration (e.g. Desulfovibrio) evolved in response to sulphate-releasing photosynthesis (Chlorobiaceae green sulphur bacteria; Chloroflexaceae green filamentous bacteria;Chromtiaceae purple sulphur bacteria and Rhodosplrillaceae purple nonsulphur bacteria) early on the primitive earth.
	Oxygen respiration (e.g. Pseudomonas. Paracocus and mitochondrial respiration) evolved later in response to oxygen releasing photosynthesis (Cyanobacteria blue green bacteria and chloroplasts).

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