The oxidation of glucose starts with glycolysis in cytoplasm which followed by Krebs' cycle and finally Electron transport Chain (ETC) in inner mitochondrial membrane. The end of $\mathrm{ETCO}_2$ is required.
Where, it acts as final hydrogen acceptor. $\mathrm{O}_2$ is responsible for removing electrons from the system. In the absence of oxygen, electrons could not be passed through the coenzymes, inturn proton pump will not be established and ATP will not be produced via oxidative phosphorylation. Thus oxygen plays an important role in aerobic respiration in mitochondrial matrix.