In 1861 Louis Pasteur observed that yeasts, a facultative anaerobe, grow in a sugar and protein broth completely free of air, i. e. oxygen, and for every gram of yeast that forms 60-80 grams of sugar disappear from the broth. If the experiment is performed with air, i. e. oxygen, for one gram of yeast formed, 4 to 10 grams of sugar is removed from the broth. When this experiment was performed with only protein in the broth, the yeasts only grew in the presence of oxygen. 1. Explain the three different outcomes of the experiments on yeasts based on your knowledge of microbial metabolism.
2. Pasteur concluded that yeast take oxygen from the air and in the absence of air take oxygen from the sugar. Why is this incorrect?