The Effect of Sugar Types on the Rate of Yeast Fermentation Abstract In pairs, the biology class conducted a one-experiment study regarding the effect of different sugars, as food sources for yeast, on the speed of fermentation. The experiment called for six test tubes, each with different solutions: yeast-sucrose, yeast-fructose, yeast-glucose, yeast-lactose, yeast-maltose, and yeast-water. The class hypothesized that glucose will significantly increase the speed of fermentation of yeast, compared to the other sugar solutions. Throughout the experiment, the students calculated the amount of CO2 bubbles per minute in order to compare the speed of fermentation between the control group (water solution) and the experimental groups (sugar solutions). The data gathered during the experiment exhibited that yeast with glucose and fructose food sources will have a faster speed of fermentation compared to the yeast with sucrose, lactose, maltose, and water food sources. Introduction Fermentation is the pathway following glycolysis, a metabolic process in cellular respiration in which cells create ATP. Unlike the Krebs cycle, glycolysis and fermentation are anaerobic processes, meaning that they do not require the presence of oxygen to occur. Types of fermentation include alcoholic fermentation and lactic acid fermentation. Similarly, both alcoholic and lactic acid fermentation require pyruvic acid and NADH as reactants (Levine and Miller, 2010). However, alcoholic fermentation produces ethanol, NAD+, and carbon dioxide, whereas lactic acid fermentation produces NAD+ and lactic acid. Fermentation is vital for many organisms, such as yeasts, certain molds, and bacteria, because it allows them to obtain energy required to carry on life processes. Alcoholic fermentation is especially important for human beings, as it is used to produce alcoholic beverages, bread, and many other everyday items (AlbaLois, 2010). On the other hand, lactic acid is a waste product of certain bacteria, which is utilized to create cheese, yogurt, sour cream, and many other important industrial items. Additionally, humans resort to lactic acid fermentation when oxygen is limited. Bacterial fermentation is also used in the medical industry to create certain antibiotics. Yeast, a singlecelled organism that utilizes sugar as a food source, produces energy substances through the breakdown of sugar molecules. Specifically, the type of sugar as source of food, impacts the speed of fermentation in yeast. In this lab, we will calculate the rate of fermentation in yeast with different solutions of sugar, such as sucrose, fructose, glucose, lactose, and maltose, with water as a control group. It is important to humans that yeast uses the best sugar source during fermentation, as it creates industrial items such as bread, alcohol, and yogurt. If the type of sugar source affects the rate speed of fermentation, when you add glucose to a yeast solution, it will cause fermentation to occur at a quicker rate. Materials ● 6 large test tubes ● 6 disposable plastic pipettes ● 2 washers, nuts (weight) to fit on pipette stem ● labels ● stop watch ○ yeast solutions ○ yeast-sucrose ○ yeast-fructose ○ yeast-glucose ○ yeast-lactose ○ yeast-maltose ○ yeast-water (control group) Procedure 1. Label the six test tubes, using the labeling tape, with the name of the six yeast solutions: sucrose, fructose, glucose, lactose, maltose, and water. 2. Fill the bulb section of a pipette with the yeast-sugar solutions. To fill the pipettes, pull up as much liquid as possible into the stem by squeezing the bulb completely and then slowly releasing it. Turn the pipette upside-down and tap the pipette to move the liquid into the bulb. Keep the pipette upside down. Make sure there is no solution in the stem of the pipette. Repeat the procedure for all 6 solutions. 3. Attach to the pipette stem just above the bulb. 4. Fill each of the test tubes 2/3 with warm water (about 37 degrees Celsius) 5. Place each pipette (still upside down) into test tube #1. The pipette should be completely covered by water and have about 2 to 3 cm of water above the tip. 6. You should observe tiny bubbles being released from the tip of the pipette. Count the number of bubbles released over a period of 10 minutes and record your results. What gas is being released? Carbon dioxide. 7. Repeat steps 2 to 4 for each of the remaining solutions. Record your observations for each. 8. Collect data from the class and calculate the average number of bubbles produced by each solution. Results a. The dependent variable of the experiment is the rate in which yeast is fermented, measured in bubbles produced in the test tubes (number of bubbles/minute). b. The independent, or manipulated variable in the experiment is the type of sugar used in the test tube: sucrose, fructose, glucose, lactose, and maltose. c. The confounding variables, or constants, in the experiment include: i. Same-sized test-tubes ii. Identical pipettes iii. Equal-weight nuts iv. Same amounts of sugar/yeast v. Equal time-period observations vi. Same maintained temperature vii. Identical yeast brands d. There were 6 trials in total, each for a different modification of the independent variable. In other words, the trials were performed once, each involving a different type of sugar (or water). e. The control involved in the experiment was the trial performed using water instead of sugar, to ferment yeast. All data was compared to this control. f. Table 1: This table represents the results of each trial, done with different combinations of sugar/yeast in a test tube. The results include the sugar type used, paired with the number of CO2 bubbles produced, and the class average. Additionally, it is noted that the larger number of bubbles produced, the faster the rate of fermentation was. In turn, the test tubes with the fructose and glucose food sources had faster rates of fermentation, while the test tube with water had a slower rate of fermentation. g. Figure 1: This graph reiterates the information and results presented in the table. Titled “Bubbles Produced by Sugar/Yeast Fermentation,” the bar graph presents each trial (the test tube number and sugar used) and the amount of bubbles, or speed of fermentation, produced. Table 1: Number of CO2 Bubbles Produced in Each Test Tube Number of CO2 Bubbles Produced in Each Test Tube Test Tube Number 1 2 3 4 5 6 Sugar Type Sucrose Fructose Glucose Lactose Maltose Water Number of Bubbles Produced 15 13 12 9 11 0 Class Average 14 16 16 5 12.8 1 This table represents the amount of CO2 bubbles/minute produced in each test tube. The table also indicates the individual results and class average results. Figure 1: Number of Carbon Dioxide Bubbles Produced by Yeast Fermentation This bar graph illustrates the results, or CO2 bubbles/minute produced in each test tube, with different sugar sources. The larger the number, the faster fermentation occurs. Conclusion After performing this experiment, I was able to determine that the original hypothesis, that glucose will drastically increase the speed of fermentation in yeast, should be accepted. Although it failed to mention fructose equally increasing the rate of fermentation, the hypothesis was correct about glucose being the most effective sugar source. Obviously, both fructose and glucose produced 16 carbon dioxide bubbles, as seen in the class average results; whereas, other sugars produced 14 or less bubbles, confirming that the fructose and glucose source increase fermentation speed. However, my individual data does not support my hypothesis; sucrose increases the rate of fermentation more than the other types of sugar, according to my individual results. Despite this, the class average, consisting of more data combined into one result, is more accurate since it includes a larger sample size. Clearly, the class average data and my individual data illustrate the most effective and ineffective sugar sources regarding yeast fermentation. Through the class average data, I was able to conclude that fructose and glucose produce the largest amount of carbon dioxide bubbles (16), meaning they increased the speed of fermentation drastically. Additionally, I can state that lactose and maltose produced the least amount of bubbles (5 and 12), proving that their rates of fermentation were much slower. However, my classmates and I performed the experiment only once, causing the results to be slightly inaccurate or flawed. When comparing my individual results to the class average results, the data tended to be slightly different. This slight difference proves that performing an experiment just once does not give you the opportunity to compare your results to previous data, which can cause slight errors. In the future, I will perform the experiment at least three times, instead of once, which may reduce experimental error. Based on my introduction and results, I can conclude that fructose and glucose may be used in the industrial business to produce items such as bread, yogurt, and alcohol, more efficiently. Since the two sugars (fructose and glucose) are the best food sources for yeast during fermentation, factories and other businesses will most likely take advantage of their abilities. My results also allow me to understand that certain sugars perform better than others during fermentation. Moreover, I can consider varying conditions such as temperature, amount of sugar, and amount of yeast, in order to extend my investigation. By consistently using the same sugar source, I can determine whether a hot or cold environment, or large or small amount of sugar/yeast will affect fermentation. Undoubtedly, this experiment has allowed me to see how and which sugar sources can drastically affect the speed of fermentation. Works Cited Alba-Lois, Luisa, Ph.D. "Yeast Fermentation and the Making of Beer and Wine." Nature.com. Nature Publishing Group, 2010. Web. 20 Feb. 2015. <http://www.nature.com/scitable/topicpage/yeast-fermentation-and-the-making-of-beer14372813>. Levine, Joseph S. Fermentation. Miller & Levine Biology 2010. By Kenneth R. Miller. N.p.: Pearson Prentice Hall, 2010. 262-65. Print. "Yeast." HowStuffWorks. HowStuffWorks.com, n.d. Web. 19 Feb. 2015. <http://science.howstuffworks.com/life/fungi/yeast-info.htm>.