Photosynthesis has two main stages: light reactions and dark reactions. The light processes the light from the sun, the dark is the internal process creating energy. It is also called the light reaction because direct sunlight is needed for solar energy to start the process. In the light reaction, chlorophyll absorbs the light and starts the chemical process that ends in creating oxygen. It is during this time that manganese is used in the reaction creating oxygen from water molecules.
Manganese basically uses its electrons to split the water. In what scientists call Photosystem II, this particular set up is the only time this biological enzyme is used to oxidize water. First manganese neutralizes the charge of the photon sent to it. This is the catalyst that then binds two water molecules together. From there it oxidizes molecules with an exchange of electrons. It is attributed to the fact that manganese can be found in multiple oxidation states, thus being able to hold electrons at different levels. This process is so complex that scientists have not been able to make a similar catalyst and be successful.
The dark reactions are done inside of the plant, and while often done during the day, it does not need direct light. During this reaction, the carbon dioxide is changed to sugar, which breaks down to glucose and fructose, and that is what the plant uses for energy. It is during the light reaction that manganese plays its most important role. The process of creating oxygen cannot be done without it, and we cannot live without oxygen. If photosynthesis did not use the water-to-oxygen process, the earth’s atmosphere would have a lot less oxygen for humans and animals.
It is in the basic process of collecting sunlight, and processing it for energy, that plants create life for us. As with most ecosystems, if one aspect changes, it can throw off the entire system. It’s the same at the cellular level as well: without manganese to oxidize the water, the world would be a different place. Edited from Manganese and Photosynthesis.