Sugar Fermentation in Yeast

Yeast are able to metabolize some foods, but not others. In order for an organism to make use of a potential source of food, it must be capable of transporting the food into its cells. It must also have the proper enzymes capable of breaking the food’s chemical bonds in a useful way. Sugars are vital to all living organisms. Yeast are capable of using some, but not all sugars as a food source. Yeast can metabolize sugar in two ways, aerobically, with the aid of oxygen, or anaerobically, without oxygen.

In this lab, you will try to determine whether yeast are capable of metabolizing a variety of sugars. Although aerobic fermentation of sugar is much more efficient, in this experiment we will have yeast ferment sugars anaerobically. When the yeast respire aerobically, oxygen gas is consumed at the same rate that CO2 is produced—there would be no change in the gas pressure in the test tube. When yeast ferment the sugars anaerobically, however, CO2 production will cause a change in the pressure of a closed test tube, since no oxygen is being consumed. We can use this pressure change to monitor the respiration rate and metabolic activity of the organism. A Gas Pressure Sensor will be used to monitor the fermentation of sugar.

The fermentation of glucose can be described by the following equation:

C6H12O6 [pic] 2 CH3CH2OH + 2 CO2 + energy glucose ethanol carbon dioxide

Note that alcohol is a byproduct of this fermentation.

[pic]

Figure 1

MATERIALS

|LABPRO OR CBL 2 INTERFACE |18 X 150 MM TEST TUBE |
|TI GRAPHING CALCULATOR |1-L BEAKER (FOR WATER BATH) |
|DATAMATE PROGRAM |BASTING BULB OR BERAL PIPETTE |
|VERNIER GAS PRESSURE SENSOR |HOT AND COLD WATER |
|GRAPHICAL ANALYSIS (OPTIONAL) |TEST TUBE RACK |
|RING STAND |UTILITY CLAMP |
|RUBBER-STOPPER ASSEMBLY |THERMOMETER |
|5% GLUCOSE, SUCROSE, LACTOSE, AND ONE OTHER SUGAR SOLUTION |YEAST SUSPENSION |
| |VEGETABLE OIL IN DROPPER BOTTLE |

PROCEDURE

[pic]

Figure 2
1. Connect the plastic tubing to the valve on the Gas Pressure Sensor. If your sensor has a blue plastic valve on it, place the valve in the position shown in Figure 2.

2. Plug the Gas Pressure Sensor into Channel 1 of the LabPro or CBL 2 interface. Use the link cable to connect the TI Graphing Calculator to the interface. Firmly press in the cable ends.

3. Turn on the calculator and start the DATAMATE program. Press [pic] to reset the program.

4. Set up the calculator and interface for a Gas Pressure Sensor.

a. If the calculator displays PRESS(KPA) in CH 1, proceed directly to Step 5. If it does not, continue with this step to set up your sensor manually. b. Select SETUP from the main screen. c. Press [pic] to select CH 1. d. Select PRESSURE from the SELECT SENSOR menu. e. Select the correct pressure sensor from the PRESSURE menu. f. Select the calibration listing for (KPA). g. Select OK to return to the main screen.

5. Prepare a water bath for the yeast. A water bath is simply a large beaker of water at a certain temperature. This ensures that the yeast will