Yeast Fermentation Lab Report

Ummatul B. Choudary
Dr. Gerard P. McNeil
Biology 202 Lab GGJ
4/21/2018
LAB REPORT Lab #9- Yeast Fermentation Dates of performed work: 3/26/18 Date submitted: 4/23/18

Abstract
Yeast are unicellular fungi which act as facultative anaerobes. This means that yeast is able to produce ATP by aerobic respiration while oxygen is present, but are also capable of anaerobic respiration if oxygen is not available. This is called fermentation. Fermentation allows glycolysis to continue in the absence of oxygen. The type of anaerobic respiration used is alcohol fermentation, which produces ethanol.
This differs from mammals, which utilize lactic acid fermentation.
Hypothesis
The purpose of this experiment is to measure the rate of CO2 production in yeast that is undergoing fermentation. The variables present in this experiment include different types of sugars, as well as temperature and the introduction of a glycolysis inhibitor. These variables are used because different sugars are metabolized differently and should result in various rates of CO2 production. Temperature and the presence of an inhibitor should also affect the rate of CO2 production.
Method
1) Seven test tubes were prepared with a constant amount of yeast in each (1mL). The first test tube did not include sugar and served as the control group.
2) This tube was given 1mL of yeast, and was then filled to the top with buffer.
3) Tubes 2 through 5 were given 1mL of yeast as well as 1mL of sugar (tube 2 contained glucose, tube 3 contained fructose, tube 4 contained sucrose, and tube 5 contained arabinose) before being filled to the top with buffer.
4) Tube 6 was given 1mL of yeast and 1mL of sucrose, as well as 1mL of Sodium Fluoride (NaF), which acts as a glycolysis inhibitor.
5) It was then filled to the top with buffer.
6) Finally, tube 7 was prepared the same way as tube 4; with 1mL yeast, 1mL sucrose, and then filled to the top with buffer.
7) After each tube was prepared, it was swirled to prevent settling. They were then carefully placed in fermentation chambers and inverted.
8) Fermentation chambers 1 through 6 were placed into the same candle jar. Fermentation chamber 7 was placed into a separate candle jar.
9) The candles inside both jars were lit, and then the jars were sealed. The purpose of the candles is to use up the remaining oxygen in the jar.
10) When the flame extinguishes, this indicates that there is no oxygen remaining in the jar, thus insuring aerobic respiration cannot take place and anaerobic respiration can begin.
11) Finally, once the flame is extinguished, the first jar, which contains fermentation chambers 1 through 6, was placed into a 37oC water bath, while the second jar, which contains only fermentation chamber 7, was left at room temperature (approximately 25oC).
12) Every ten minutes for an hour, the amount of CO2 in mL that had evolved was observed via the marks on the test tubes and recorded.
13) At the end of the hour, these results were plotted and compared.
Results

As hypothesized, the rate and amount of CO2 evolved varied with each test tube. Temperature, type of sugar, and the presence of NaF all affected the amount of CO2 evolved as well as the rate at which it evolved. The only test tube in which no CO2 evolved was tube 5, which contained arabinose.

The control group, tube 1, which contained no sugar, evolved very little CO2.
After 40 minutes, 0.25 mL of CO2 evolved. No more evolved after that. Tube 2, which contained glucose, and tube 4, which contained sucrose and was kept at 37oC evolved the most CO2 compared to the other tubes. Of the other tubes that contained sucrose; tube 6, which included NaF and was also kept at 37oC, evolved only 1.25 mL CO2 and tube 7, which was kept at room temperature, evolved 1.50 mL CO2. Tube 3, which contained fructose, also evolved as much CO2 as tube 6, but at a different rate. Finally, tube 5, which contained arabinose, evolved no CO2 at
all. With sucrose kept at 37oC, CO2 evolved at the fastest rate. Glucose evolved at a slower rate on average, starting slowly and experiencing a spike at 40 minutes. The tube containing fructose and the tube containing sucrose and NaF caused CO2 to evolve at similar rates, with fructose being slightly faster. The sucrose kept at 25oC caused CO2 to evolve at a slower rate than the tube with sucrose and NaF. Finally, only the tube containing arabinose, in which no CO2 evolved at all, was slower than the tube containing no sugar.
Conclusion
Based on these results, we can conclude that 37oC is the optimal temperature for yeast fermentation. There is not enough energy at 25oC to evolve as much CO2 as there is at 37oC. Sucrose and glucose are metabolized best by the yeast cells, with sucrose being metabolized at a somewhat faster rate. The presence of NaF causes less CO2 to evolve, but less ideal temperatures have a greater effect than the presence of the inhibitor. However, fructose kept at a temperature of 37oC is metabolized better than sucrose in the presence of an inhibitor or at less ideal temperatures. Arabinose causes no CO2 to evolve at all, indicating that yeast is unable to metabolize it. We can see from these results that the amount of CO2 evolved as well as the rate at which it evolved is affected by variables such as temperature, type of sugar, and the presence of a glycolysis inhibitor such as NaF.