Chlorophyll's main functions in photosynthesis include the absorption of light energy (photons), initiation of the light-dependent reactions which include the splitting of water molecules (photolysis) to produce oxygen, protons, and electrons, and facilitating the conversion of light energy into chemical energy in the form of ATP and NADPH. The oxidation (breakdown) of carbohydrates, such as glucose, to release energy (ATP) is the process of cellular respiration, which occurs in mitochondria (or cytoplasm/cell membrane in some organisms) and is distinct from the function of chlorophyll and photosynthesis.