Between anaerobic and aerobic respiration a ratio of 1:3 is maintained in release of carbon dioxide. Pasteur noticed that the supply of O2 to an anaerobic system does not increase the output of CO2. These means that in anaerobic respiration the ratio of 1:3 is not maintained always these is due the presence of excess of O2 in the system. The decrease rate of glucose breakdown in anaerobic systems caused by the presence of O2 is called Pasteur’s effect.