What is the Pasteur effect?
Pastuer found that in the absence of O2, yeast would use the sugars in the medium to produce ATP through fermentation. However, when they were exposed to O2, they switched to aerobic respiration and less sugar is used as food. If there is no sugar available, the yeast will go through aerobic respiration. Yeast is a facultative aerobe and needs less sugar in the presence of O2