Respiration aids in replenishing O2 and decrease the CO2 level in the cell. O2 is an important receiver in the oxidative respiration chain in the mitochondria, which is responsible for producing ATP for the cell. ATP can be considered as the “energy currency” of the cell. Many biochemical reactions in the cell requires ATP, including the operations of ion channels, buffer systems, transportation via vesicles, etc. Therefore if there is no O2, the cell cannot produce ATP and will die.