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Lab Respiration - 7.1 Fermentation When you study the...

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Unformatted text preview: 7.1 Fermentation When you study the ability of yeast to ferment sugar, you will need to use a respirometer to measure the amount of carbon dioxide given off. Your first experimental procedure shows you how to prepare your respirometer. Experimental Procedure: Respirometer Practice 1. Completely fill a small tube (15 X 125 mm) with water (Fig. 7.2). 2. Invert a large tube (20 X 150 mm) over the small tube, and With your finger or a pencil, push the small tube up into the large tube until the upper lip of the small tube is in contact with the bottom of the large tube. 3. Quickly invert both tubes. Do not permit the small tube to slip away from the bottom of the large tube. A little water will leak out of the small tube and be replaced by an air bubble. 4. Practice this inversion until the bubble in the small tube is as small as you can make it. Figure 7.2 Respirometer for fermentation. Place a small tube inside a large tube. Hold the small tube in place as you rotate the entire apparatus, and an air bubble will form in the small tube. ' 76 Laboratory 7 Cellular Respiration yeast air bubble (height to be measured and recorded for each tube) filled and - ~ inverted little finger (Now, quickly respirometer holding invert tubes ready for use small tube while tightly against holding them large tube together.) 2 3 mark small tube (tube 1) 7—2 Ethanol Fermentation Yeast fermentation to produce ethanol and carbon dioxide has long been utilized by humans to produce wine and bread. During the production of wine, it is the ethanol that is desired while bread and other baked goods rise when yeast gives off carbon dioxide (Fig. 7.3). Recently, there has been a great deal of interest in using ethanol produced by yeast fermentation of corn as a substitute for gasoline in cars. Testing Sugars In the Experimental Procedure that follows, we are going to test which of several sugars is a better food source for yeast when they ferment. It will be assumed that the ease of sugar fermentation correlates with the amount of carbon dioxide Figure 7.3 Products of given off within a certain time limit. As background data, fermentation. observe the structure of the three sugars involved: H OH OH H glucose fructose sucrose State a hypothesis for your experiment in which you sequence the sugars according to how well you expect yeast to ferment them: Hypothesis: Experimental Procedure: Yeast Fermentation Have four large test tubes ready. With a wax pencil, label and mark off a small test tube at the 2/ 3-full level. Use this tube to mark off three other small tubes at the same level. 1. Label and fill the small tubes as directed, and record the contents in Table 7.1. Tube 1 Fill to the mark with glucose solution. Tube 2 Fill to the mark with fructose solution. Tube 3 Fill to the mark with sucrose solution. Tube 4 Fill to the mark with distilled water. 7—3 Laboratory 7 Cellular Respiration 77 2. Re-suspend a yeast solution each time, and fill all four tubes to the top with yeast suspension (Fig. 7.2). 3. Slide the large tubes over the small tubes, and invert them in the way you practiced. This will mix the yeast and sugar solutions. 4. Place the respirometers in a tube rack, and measure the initial height of the air space in the rounded bottom of the small tube. Record the height in Table 7.1. Q 5. Place the respirometers in an incubator or in a warm water bath maintained at 37°C. Note the time, and allow the respirometers to incubate about 20 minutes (incubator) or one hour (water bath). However, watch your respirometers and if they appear to be filling with gas quite rapidly, stop the incubation when appropriate. During the incubation period, begin the Experimental Procedure on cellular respiration (see page 79). 6. At the end of the incubation period, measure the final height of the gas bubble, and record it in Table 7.1. Calculate the net change, and record it in Table 7.1. Table 7.1 Fermentation by Yeast Initial Final Tube Sugar Gas Height Gas Height Net Change Ease of Fermentation ____—_____———_—————————-— 1 Conclusions: Yeast Fermentation 0 From your results, evaluate how the sugars tested compare as a food source for yeast fermentation. Enter your evaluation in Table 7.1. 0 Do your data support or fail to support your hypothesis? Explain. 0 Can your results be correlated with the comparative structure of the sugars? Explain. 0 Which respirometer was the control? 78 Laboratory 7 Cellular Respiration 7—4 ...
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Lab Respiration - 7.1 Fermentation When you study the...

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