YEAST RESPIRATION AND FERMENTATION

Transcription

1 YEAST RESPIRATION AND FERMENTATION STUDENT HANDOUT...pages 1-6 TEACHER REFERENCE PAGES...pages 7-18 GAS CHROMATOGRAPH INSTRUCTIONS...pages 19-23

2 Yeast Respiration and Fermentation STUDENT HANDOUT Introduction Most organisms, including yeasts, use oxygen in a process called cellular respiration. Cellular respiration is the controlled breakdown of carbohydrate to carbon dioxide and water with capture of some of the energy in the form of ATP. In the absence of oxygen, fermentation partially breaks down carbohydrate and a small amount of energy is captured in the form of ATP. The products are different depending upon the organism involved; in the case of yeast the products are ethanol and carbon dioxide. This is inefficient compared to respiration, but enables the yeast to survive and grow where no oxygen is available. Purpose To identify the products of yeast cultures grown under varying conditions. Equipment Supplies Gas chromatograph, hot plates. 100 ml graduated cylinder, 125 ml Erlenmeyer flask, 2-hole stopper with glass tubing and thermometer, screw cap sample vial, ring stand, three-finger clamp, 16 oz plastic cups, paper towel. Procedure 1. Obtain 50 ml of one of the cultures, using your labeled graduated cylinder. Note which culture you have (A, B, or C). 2. Place the culture sample into a 125 ml Erlenmeyer flask and assemble the distillation apparatus (see Figure 1). 3. Turn on the hot plate (medium setting) and place the flask on it. 4. Use the thermometer to monitor the temperature of the vapor in the flask. When the temperature reaches 70 C, wrap the glass tube with a cool, wet paper towel to help condense the vapors (See Figure 1). A Pasteur pipet may be used to add additional water to the paper towel. Be sure no water drips from the Biology Yeast Lab, Page 1 4/26/01

3 paper towel into your collection vial. 5. Do not let the culture heat up beyond 90 C. It is best to maintain the temperature between C. Maintaining the temperature close to 85 C will give better results. 6. When distillate begins to drip into the vial, turn off the hot plate and continue collecting 10 more drops. 7. Take your sample (A, B, or C) to the appropriate gas chromatograph and with assistance from the instructor inject your sample for analysis. Biology Yeast Lab, Page 2 4/26/01

4 Data collection Record all data in the tables below. Parts I and III will be done by the instructor, or you will be given separate instructions for them. PART I: Demonstration- Test for Carbon Dioxide 1. Why are we using bromothymol blue solution to test for carbon dioxide? 2. Would you expect to find CO 2 in a yeast culture? Explain. 3. Would you expect to find CO 2 in a students' breath? Explain. 4. What did you observe? What does this mean? PART II: Distillation and Gas Chromatography 1. Why are we using GC standards? 2. Which gas chromatograph are you using? A or B 3. Using the data from the teacher demonstration and computer printouts from the standard sample injections, complete the following table: (Be sure to use the data from the same GC you plan to use for your injection). Ethanol standard: First peak Time Second peak Time Biology Yeast Lab, Page 3 4/26/01

5 Mixed standard: Name of compound, formula and formula weight, and time of peak appearance: First peak Second peak Third peak Fourth peak 4. Predict the product compounds you will find in the culture flasks listed below and the expected times of the peaks for each. (Hint: Reread introduction and look at times for standard compounds.) A. Aerobic (Red) B. Anaerobic (Blue) C. Control (Green) 5. Record the times of peaks and the identity of the compounds found in your own and in your classmates computer printouts - (remember to compare data from the same machine): A. Aerobic distillate (Red): Biology Yeast Lab, Page 4 4/26/01

6 B. Anaerobic distillate (Blue): C. Control distillate (Green): 6. Record the area percentage of the compounds found in the following: (from your own and your classmates' computer printout) A. Aerobic: Peak 1 Peak 2 B. Anaerobic: Peak 1 Peak 2 C. Control: Peak 1 Conclusions: 1. What are the products of cellular respiration? of fermentation? 2. Did you find the products you expected in the distillates for the three cultures? Explain. 3. Which culture (aerobic or anaerobic) produced more ethanol? Why? Biology Yeast Lab, Page 5 4/26/01

7 Part III: Wet weight of yeast cells NOTE: Directions will be provided by teacher if time permits. See page 18 in Teacher reference section. 1. What product of cellular respiration does yeast need to grow and reproduce? 2. Which culture (aerobic or anerobic) do you think should grow and reproduce more rapidly? Why? Data: (A) aerobic B) anaerobic Weight of pellet + tube Weight of centrifuge tube Weight of pellet Conclusion: Summary of experiment: What product(s) are being produced during yeast respiration and during yeast fermentation? What parts of your experiments support this conclusion? Explain what the control flask shows. Biology Yeast Lab, Page 6 4/26/01