The production of ATP occurs through the process of photophosphorylation. When light energy hits the chlorophyll molecule, it is absorbed by photosystem I and photosystem II. This raises the energy levels of electrons within the photosystems, causing them to jump to higher energy levels. From here, the electrons are passed down a chain of electron carriers, each one at a successively lower energy level. Energy is released as the electrons moved down the chain, which is used to form ATP from ADP and P.