In 1861 Louis Pasteur observed that when yeast grows in a flask with sugar and protein medium completely free of air they ferment vigorously and for every gram of yeast that forms 60 to 80 grams of sugar are consumed If the experiment is carried out in a flask in the presence of air for every gram of yeast that forms only 4 to 10 grams of sugar are consumed If the yeast is transferred to a sugar containing medium without air the yeast reverts to consuming 60 to 80 grams of sugar for each gram of yeast produced When the experiment is carried out in a protein based medium yeast grows only in the presence of oxygen Pasteur concluded that yeast can extract oxygen from air and in the absence of air the yeast derives oxygen from the sugar Pasteur applied quantitative methods to his studies of fermentation and was the first to report on organisms that could live and reproduce in the absence of oxygen His basic conclusion was however incorrect Even so the different behaviors of yeast in these experiments are now known as the Pasteur effect 1 Explain the three yeast behaviors based on modern concepts of microbial metabolism 2 Which metabolic processes occur in each of the experiments 3 What was incorrect about Pasteur s conclusion