Question

EXERCISE 5B CELLULAR RESPIRATION Alcoholic Fermentation by Yeast OBJECTIVES the completion of this exercise the student should be able to Upon 1 distinguish between the dependent and independent variables in a controlled experiment. . formulate a basic hypothesis. measure the volume of carbon dioxide generated by anacrobic fermentation in baker's 3. yeast. 4. express data in tabular form. 5, relate data generated in an experiment to a hypothesis previously formulated 6. graph data, calculate the slope of a line, and determine the rate of anaerobic fermentation. BAKER'S YEAST The model organism we will be using for this experiment is baker's yeast (Saccharomyces erevisiae). Baker's yeast is a haploid unicellular eukaryotic organism. In nature, yeast can be found growing on fruits, berries, and other plant parts that contain stores of carbohydrate molecules. The metabolism of yeast is very versatile and can operate under both acrobic and anaerobic conditions. In the presence of oxygen, electron transport is primarily used to make AIP. In the absence of oxygen, alcoholic fermentation is used to produce energy, though at a much lower and more inefficient rate. ERMENTATION nce of sugars but the absence of oxygen some organisms like baker's yeast can to make ATP by glycolysis alone, without subsequent pyruvate oxidation, Kreb's Cycle In the presence dorid, enyde. The conversion of pyruvate to acetaldehyde releases a molecule of carbon lo acetaldehyde. Acetaldehyde acts as the final electron acceptor for the high energy electrons harvested rn l ell as a sport. In fermentation, pyruvate, the end product of glycolysis is converted In accepting the electrons, acetaldehyde gets reduced to ethanol which is then colysis trom the cell as a waste product. 187 Lab Exercise 5B НН нон 2 NADH 2 NAD 2 ATP он 2 CO2 0 0 о- 2 ETHANOL 2 ACETALDEHYDE 2 PYRUVATE Note that fermentation is an anaerobic process. Glycolysis can function in the absence of oxygen. Under anaerobic conditions, yeast cells are able to "short circuit" catabolism bypassing pyruvate oxidation, Krebs Cycle and electron transport. Since glycolysis requires two ATP to make 4 ATP and harvest high energy electrons this process in very inefficient compared to electron transport but it is better than nothing and allows the organism to make energy and survive in the absence of oxygen. INDEPENDENTAND DEPENDENT YARIABLES n a controlled experiment some variables are controlled and some are measured. The independent variable is the one that is changed or controlled during the dependent variable is the one that is measured or calculated. When graphing results, independent variable is plotted on the X-axis and the dependent variable is plotted o Y-axis. The experiment. POSITIVEAND As part of any experiment, positive and conclusions about the results from additional experiments. give you infomation anetive controls must be established. Control ra information about what to expect in your experiment if the reacti hers compare the results obtained with the controls and this allows the controls must be esta ctions d this allows them to draw EXPERIMENTAL MOLECULES We will be measuring the ability of bakers yeast to ferment four different aefe glucose, sucrose, maltose, and starch, along with distilled water. Glucose is the Prbeun sourcefor baker's yeast. Distilled rboha fo water contains e. So our single experiment will have a positive and preferred food will be run at additional carbohydrates. no sugar. All five reaction tubes negative control and test the Lab Exercise 5B Instructor Sudent's Name Pre-lab Assignment ur lab manual and textbook to ansethe flowing questions. ibe the purpose of this laboratory exercise. 1. Describe 2. What type of organisms is yeast and where can it be found? 3. Consider alcoholic fermentation When would an organism use it? What final product is produced? What molecule is released during the process? How much ATP is produced? 4.Identify the independent variables in this experiment. and Identify the dependent variable in this experiment. 5. identify the positive control in this experiment. Why is it a positive control? wnali the negative control in this experiment. Why is it a negative control? 189 ab Exercise 5B addresses the rate of fermentation for all four carbohydrate expect the yeast to ferment rapidly, slowly, or not at all:?) (Be specific. Which do yOu 6. Using your knowledge of fermentation and carbohydrates, formulate 7. Explain why you would expect the yeast to metabolize (ferment) the carbohydrates at different rates. (Be specific.) 8. Consider data TABLE I. What kind of graph will you make? Explain why 9. Consider data TABLE 2. What kids of graph will you make? Explain why 190

Answer 1

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