Light that falls onto a photosystem excites two electrons in a chlorophyll molecule, causing the electrons to leave the molecule by Photoionization. These two electrons are absorbed by the thylakoid membrane and are passed down a chain of electron carrier molecules via oxidation reduction reactions. The energy released by these oxidation reduction reactions actively transports H+ ions out of the thylakoid membrane into the stroma. The H+ ions then diffuse back in through ATP Synthase channels producing ATP molecules. Oxidative Phosphorylation is the process of producing ATP through the electron transport chain.