the oxygenic, or oxygen-releasing, photosynthesis that occurs in plants, algae,and cyanobacteria is the dominant type on the earth.
Other phtosynthesizers such as green and purple bacteria possess bacteriochlorophyll, which is more versatile in capturing light.
They have only a cyclic photosystem I,which routes the electrons from the photocenter to the electrons carriers and back to the photosystem again.
This pathway generates a relatively small amount of ATP, and it may not produce NADPH.
As photolithotrophs, these bacteria use H2,H2s, or elemental sulfur rather than H2O as a source of electrons and reducing power.
As a consequence,they are anoxygenic, and many are strict anaerobes.