<P> Photosystems are functional and structural units of protein complexes involved in photosynthesis that together carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons . Photosystems are found in the thylakoid membranes of plants, algae and cyanobacteria (in plants and algae these are located in the chloroplasts), or in the cytoplasmic membrane of photosynthetic bacteria . There are two kinds of photosystems: II and I, respectively . </P> <P> At the heart of a photosystem lies the reaction center, which is an enzyme that uses light to reduce molecules (provide with electrons). This reaction center is surrounded by light - harvesting complexes that enhance the absorption of light . </P> <P> Two families of reaction centers in photosystems exist: type I reaction centers (such as photosystem I (P700) in chloroplasts and in green - sulphur bacteria and type II reaction centers (such as photosystem II (P680) in chloroplasts and in non-sulphur purple bacteria . </P>

Provide energy to photosystem i and photosystem ii