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Material Type: Lab; Class: General Biology; Subject: Biology; University: Morehouse College; Term: Unknown 1989;
Typology: Lab Reports
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Objectives
oxygen (anaerobic environments), cells are limited to glycolysis alone, but must use alternative means of recycling NAD. This recycling is performed in one of two alternative processes in which the end product of glycolysis, pyruvate is used as an electron acceptor. These anaerobic processes are lactic fermentation and alcohol fermentation. Lactic fermentation occurs in animal muscle cells (including human skeletal muscles) during repeated muscle contraction. Many plant and fungal cells can perform both types of fermentation, but alcohol fermentation is particularly common in yeasts. Some bacteria use lactic fermentation under anaerobic conditions. Although the ATP yield from either fermentation pathway is a fraction of that possible under aerobic conditions, the ATP from fermentation can be used to sustain life processes in some cells. Many bacteria are obligate anaerobes and conduct all their life processes in the absence of oxygen often using fermentation metabolism. There are other anaerobic processes performed only by Bacteria and Archaea which we will not consider at this time. Some cells are obligate aerobes that either lack the enzymes for fermentation or have energy demands too great to tolerate the low energy conditions of fermentation (for example, brain cells). There are many facultative anaerobes that can survive periods of low oxygen conditions by means of fermentation. Anaerobic conditions are very common in liquid (water) environments in which the diffusion of oxygen is often much slower than in the air. In this study, you will be evaluating the rates of alcohol fermentation by live yeast cells. Materials and Methods Fermentation by Yeast Each group will conduct their study in the water bath at your bench. Start by conducting the fermentation experiment in which the main variable is yeast concentration in the reaction tube. After you conduct the initial study, you should conduct a second study in which 1% solutions of commonly used spices (naturally occurring materials that, in the days before refrigeration, were used to preserve foods and prevent spoilage) will be introduced to the reaction mixture. Your objective will be to determine which spices inhibit fermentation and therefore would be the best preservatives against yeasts. In this study, the rate of carbon dioxide production by fermenting yeast, Saccharomyces cerevisiae , will be used to measure the rate of fermentation. Carbon dioxide will be measured in a respirometer apparatus (Figure 1) in which the increasing volume of gas in the graduated pipette will be recorded during a 20 minute period. You will be able to evaluate a number of variables that might influence the rate of fermentation, concentration of yeast, and the presence of spices. What hypotheses will you be testing when you conduct this experiment with different yeast concentrations? What are the predicted results for each hypothesis? What hypotheses will you be testing when you conduct this experiment with different spices? What are the predicted results of each hypothesis?