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 the aerobic fermentation of sugars is much more efficient, in this experiment
we will have yeast ferment the 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 fermentation rate and metabolic activity of the
organism