<P> The photosystem I was named "I" since it was discovered before photosystem II, but this does not represent the order of the electron flow . </P> <P> When photosystem II absorbs light, electrons in the reaction - center chlorophyll are excited to a higher energy level and are trapped by the primary electron acceptors . To replenish the deficit of electrons thus created, electrons are extracted from water by a cluster of four Manganese ions in photosystem II and supplied to the chlorophyll via a redox - active tyrosine . </P> <P> Photoexcited electrons travel through the cytochrome b6f complex to photosystem I via an electron transport chain set in the thylakoid membrane . This energy fall is harnessed, (the whole process termed chemiosmosis), to transport hydrogen (H) through the membrane, into the thylakoid lumen, to provide a potential energy difference between the thylakoid lumen space and the chloroplast stroma, which amounts to a proton - motive force that can be used to generate ATP . The protons are transported by the plastoquinone . If electrons only pass through once, the process is termed noncyclic photophosphorylation . </P> <P> When the electron reaches photosystem I, it fills the electron deficit of the reaction - center chlorophyll of photosystem I . The deficit is due to photo - excitation of electrons that are again trapped in an electron acceptor molecule, this time that of photosystem I . </P>

Where do electrons get their energy in photosystem i
find me the text answering this question