Cellular respiration involves three main stages: glycolysis, the Krebs cycle, and the electron transport chain. [1] Glycolysis takes place in the cytosol and involves the breakdown of glucose into pyruvate, producing a small amount of ATP. [2] Pyruvate then enters the mitochondrion, where it is further oxidized in the Krebs cycle. [3] Electrons are transferred in the electron transport chain to produce most of the cell's ATP through oxidative phosphorylation.