April 08, 2010
Background: 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:
+ CO2 + energy
Note that alcohol is a byproduct of this fermentation.
If yeast are given sugar in the absence of oxygen, they will produce
alcohol and carbon dioxide and capture 2 ATP of energy through the process of
anaerobic respiration (fermentation). To
measure the rate of fermentation, it is easier to measure the amount of carbon
dioxide released than to measure the amount of alcohol.
The biology gas pressure sensors and CBL’s will measure gas pressure
changes as carbon dioxide is released as a result of the process of anaerobic
respiration in yeast. Living things
use a sugar source, broken down into the form of glucose by enzymes, as a fuel to capture
enough energy to carry out essential life functions.
Sugars are classified as either monosaccharides or disaccharides.
Monosaccharides include fructose and glucose.
Disaccharides include sucrose, lactose, and maltose.
Brewers and vintners need to know what kind of sugar is the best sugar
for a yeast solution that yields the maximum amount of alcohol.
The source of this sugar is either a grain, vegetable, or fruit.
For instance, the beer making process uses barley and hops as a sugar
source, where as wines use grapes as a sugar source. Those sources consist of
different types of sugars (glucose, fructose, sucrose etc.) It is very
important that the correct sugar be matched with the yeast in order to produce
the beverage of choice. Your research team will design a controlled experiment to
determine what type of sugar will release the greatest amount of carbon dioxide
(thus yield the most alcohol) through the process yeast fermentation.
Assignment: You will conduct an experiment that tests the effect of sugar type on fermentation in yeast. You will use CBL's to measure changes in gas pressure as yeast metabolize these sugars. You will hand in a complete lab report on the experiment.
Before beginning: Visit the Yeast Fermentation Data 1999 - 2001 page in the data base to view data collected from past years. Write a hypothesis that states which type of sugar will yield the greatest amount of alcohol and release the most amount of carbon dioxide and is supported by background information regarding sugar, yeast, and the process of anaerobic respiration (fermentation).
Handouts for Fermentation of Yeast Experiment: