Photosynthesis is a process where by energy from light is harvested and used to drive synthesis of carbohydrates from carbon dioxide and water. Photophosphorylation is a process where the light energy captured by the photosynthetic organisms is transformed into the phosphate bond energy of ATP. Components of photosystem I and II transfer the electrons from water to NADP. Second step of photosynthesis is called Calvin’s cycle and it is a dark reaction. There are two stages here, I and II. Stage I is carbon dioxide fixation and stage II is the regeneration phase. Photorespiration is the process wherein oxygen consumption occurs in illuminated temperature zone of plants under high oxygen and low carbon dioxide. C4 cycle is the pathway adopted by C4 plants to conserve the carbon dioxide released via photorespiration. It occurs in mesophyll cells.
While photosynthesis is highly-evolved in the procaryotes, itapparentlyoriginated in the Bacteria and did not spread or evolve in Archaea.But the Archaea, in keeping with their unique ways, are not withoutrepresentativeswhich can conduct a type of light-driven photophosphorylation. The extremehalophiles, archaea that live in natural environments such as theDeadSea and the Great Salt Lake at very high salt concentration (as high as25 percent NaCl) adapt to the high-salt environment by the developmentof "purple membrane", actually patches of light-harvestingpigmentin the plasma membrane. The pigment is a type of rhodopsin called bacteriorhodopsinwhich reacts with light in a way that forms a proton gradient on themembraneallowing the synthesis of ATP. This is the only example in nature of nonphotosynthetic photophosphorylation. These organisms areheterotrophsthat normally respire by aerobic means. The high concentration of NaClin their environment limits the availability of O2 forrespirationso they are able to supplement their ATP-producing capacity byconvertinglight energy into ATP using bacteriorhodopsin.
The Discovery of Oxygen - Julian Rubin
All phototrophic bacteria are capable of performing cyclicphotophosphorylationas described above and in Figure 16 and below in Figure 18. Thisuniversalmechanism of cyclic photophosphorylation is referred to as PhotosystemI. Bacterial photosynthesis uses only Photosystem I (PSI), but themore evolved cyanobacteria, as well as algae and plants, have anadditionallight-harvesting system called Photosystem II (PSII). Photosystem IIis used to reduce Photosystem I when electrons are withdrawn from PSIforCO2 fixation. PSII transfers electrons from H2Oandproduces O2, as shown in Figure 20.
Light-dependent reactions of photosynthesis - BioTopics
The most common light-dependent reaction in photosynthesis is called noncyclic photophosphorylation. Noncyclic photophosphorylation involves both Photosystem I and Photosystem II and produces ATP and NADPH. During noncyclic photophosphorylation, the generation of ATP is coupled to a one-way flow of electrons from H2O to NADP+.
Plant Energy Transformations-Photosynthesis - …
ATP can also be made by a special series of light reactions, referred to as cyclic photophosphorylation, which occurs in the thylakoid membranes of the chloroplast .Algae are capable of photosynthetic generation of energy.