PI Lab #2 Yeast Fermentation By: Marty Paetz, Eban Hammoud & Ryan Moore

Introduction The experiment we conducted, it consisted of variations in temperature to measure the metabolic activity of yeast when added to 0.05mol of glucose. Temperatures included; 5°C, 20°C, 30°C, 40°C and 50°C We used a distilled water sample at 40°C and a 0.05mol solution of glucose at 40°C as our negative and positive controls respectively. We picked these as our controls as we already have previous knowledge on them from the original experiment. My group believed that with each increase in temperature the amount of time it takes for CO2 to be released will be faster in a 20minutes span which may result in more CO2 released. With the lower temperatures we ferment in, we can expect to see a slower fermentation rate (release of CO2) and less amounts of carbon dioxide given off than the higher temperatures. We are able to predict this because previous knowledge from the original lab and a variety of references.

Results Figure 1. In the experiment we analyzed the effects of different temperatures of water on yeast metabolic activity. Using tape all of the test tubes were labeled according to the different temperatures that the tubes would be placed in, including: 5, 20, 30, 40 and 50°C. One of the test tubes consisted of distilled water rather than glucose in order to act as a negative control but was added to 40°C as we know its effects from the original lab. Next each tube was filled with 4.5mL of the 0.05mol solution and were placed into each water baths for 10min. After 10min, we removed the test tubes one at a time and began mixing them with 1.5mL of yeast(saccharomyces cerevisiae) in which we swirled to ensure distribution of the yeast. We made sure the Parafilm was on tight to avoid spillage when swirling and inverting. Using a pasteur pipette we filled the durham tubes up with our new solutions and placed it back inside the original tube upside down. After the following steps were completed, we put the tubes back into each water bath for 20 minutes and at the end we measured the amount of CO2 produced by the yeast that was trapped in the durham tubes. We made sure to record the time we put the tubes in the water and took them out. Our group also did the procedures fast enough that the heat didnt completey escape the test tubes and solutions.

Results Cont. Both the negative and positive control acted the way we expected. The distilled water sample placed in water at 40°C had little to no release of carbon dioxide. The other control with a 0.05mol solution of glucose also placed in a 40°C bath had a higher release of CO2. The sample placed in the 5°C water bath had little to no CO2 release in comparison to the positive control. The sample placed in the 20°C water bath had low amounts of C02 release but was still less compared to the positive control. The sample placed in the 30°C water bath had a mild jump from the 20°C sample but was still low compared to the positive control. The sample placed in the 50°C water bath had a large leap from the 30°C sample and was slightly higher compared to the positive control. The amount C02 released in each sample was expected and similar to our hypothesis. The experiment demonstrated a trend of gradually increasing amounts of C02 dispersed for each rise in temperature. Our error bars were small throughout the graph except on the 40°C control, this was a result of one slight error and could have been from a variety of different things.

Discussion From reviewing our results we have concluded that our results closely relate our hypothesis and follow a steady trend. The information we collected coincides with our hypothesis, that states if we increase water bath temperatures we will see an increase in C02 release for each rise in temp. A possible explanation of the unexpected error bar for the 40°C experimental group could be determined and minimized with a more samples.

Discussion Possible sources of error include : Test tubes not washed well enough Contaminants or impurities in the glucose solution and/or the yeast Test tubes being taken out of the baths too earl

Discussion If the experiment were to be redone, I would include more samples for each group to reduce errors bars. I would add a variety of more water baths to get a better representation of our hypothesis. Last I would test another solution of glucose in order to compare concentration results.