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Photosynthesis occurs in two stages. In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the hydrogen carrier NADPH and the energy-storage molecule ATP. During the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide.
Free oxygen is produced in the biosphere through photolysis (light-driven oxidation and splitting) of water during photosynthesis in cyanobacteria, green algae, and plants. During oxidative phosphorylation in cellular respiration, oxygen is reduced to water, thus closing the biological water-oxygen redox cycle.
Light-dependent reactions of photosynthesis at the thylakoid membrane. Light-dependent reactions are certain photochemical reactions involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions: the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI).
The evolution of oxygen during the light-dependent steps in photosynthesis (Hill reaction) was proposed and proven by British biochemist Robin Hill. He demonstrated that isolated chloroplasts would make oxygen (O 2) but not fix carbon dioxide (CO 2). This is evidence that the light and dark reactions occur at different sites within the cell. [1 ...
Photosynthetic water splitting (or oxygen evolution) is one of the most important reactions on the planet, since it is the source of nearly all the atmosphere's oxygen. Moreover, artificial photosynthetic water-splitting may contribute to the effective use of sunlight as an alternative energy-source.
C 4 photosynthesis reduces photorespiration by concentrating CO 2 around RuBisCO. To enable RuBisCO to work in a cellular environment where there is a lot of carbon dioxide and very little oxygen, C 4 leaves generally contain two partially isolated compartments called mesophyll cells and bundle-sheath cells.
Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen (O 2) in the photosynthetic reaction center. The biochemical capacity for oxygenic photosynthesis evolved in a common ancestor of extant cyanobacteria. [11] The first appearance of free oxygen in the atmosphere is sometimes referred to as the oxygen ...
Oxygenic photosynthesis can be performed by plants and cyanobacteria; cyanobacteria are believed to be the progenitors of the photosystem-containing chloroplasts of eukaryotes. Photosynthetic bacteria that cannot produce oxygen have only one photosystem, which is similar to either PSI or PSII.