In the year 1861, Louis Pasteur observed that when yeasts grow in a sugar and protein medium, completely free of air, they ferment vigorously; and for each and every gram of yeast which forms, 60 to 80 grams of sugar disappeared. If the experiment is taken out in the presence of air, for one gram of yeast that forms, only 4 to 10 grams of sugar are eliminated. The yeasts again ferment if transferred to a sugar-having medium absent air.
Whenever the experiment is repeated with a protein medium, the yeasts grow only in the presence of oxygen. Pasteur concluded that the yeasts can take oxygen from air, and in the absence of air, the yeasts take oxygen from sugar.
Pasteur applied quantitative techniques to his studies of fermentation and was the first to report on organisms which could live and reproduce in the absence of oxygen. His conclusions were, though, incorrect. These different behaviors of yeasts are known nowadays as the Pasteur Effect.
1) Describe the three yeast behaviors based on the modern concepts of microbial metabolism.
2) What was incorrect regarding the Pasteur's conclusion?