Within the thyakoid membrane, electrons from water are "excited" by photons of light energy in Photosystem II. The excited electrons "fall" from Photosystem II, pass throu
…gh the electron transport chain (ETC) and flow into Photosystem I. As the electrons travel down the ETC, one molecole of hydrogen is pumped across the membrane from the stroma (fluid space inside the chloroplast) into the thylakoid where a higher gradient of H+. The ions pass onto the protien, ATP synthase which takes one H+ ion and pumps it through the membrane acting like a motor generating one molecule of ATP. The ATP is now located in the stroma and will be used shortly in the Calvin Cycle. (MORE) 
