Fermentation Lab Report

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Lab Exercise 7
The Effect of Temperature on the Rate of Carbon Dioxide Production in Saccharomyces

I. Student Objectives
1. The student will use this lab exercise as the basis for writing a scientific method report. 2. The student will understand how the rates of chemical reactions are affected by temperature. 3. The student will understand the overall fermentation reaction by yeast, starting with glucose as an energy source. 4. The student will understand how to measure fermentation rate.

II. Introduction

The student is to use this lab exercise as the foundation for writing a scientific method report. The instructions for writing the report are found in the addendum section of the lab manual. The purpose of the experiment is to test the effect of five different temperatures on the rate of carbon dioxide production in yeast. The experiment is an example of alcoholic fermentation that is characteristic of yeast. The original energy source of glucose is in the form of molasses in the lab. The carbon dioxide that is measured is in the form of gas bubbles, seen in fermentation tubes. The overall chemical equation is the Gay-Lussac Equation, which states that: Glucose + water produces ethanol + carbon dioxide + ATP. This fermentation reaction is anaerobic, taking place without the presence of oxygen. It is an ancient method of alcoholic fermentation, using yeast, and produces a small amount of energy in the form of ATP. A hypothesis is typically referred to as “an educated guess”. The student is expected to generate a hypothesis for this lab experiment, test it, and then report if the hypothesis has been accepted or rejected, and why. Yeast is an example of a sac fungus, and is eukaryotic and unicellular. The rates of chemical reactions will increase with increasing temperatures, up to a certain point. When living organisms are used in chemical reactions, such as yeast, an added variable becomes important to consider. That variable is the presence of enzymes in the yeast. Enzymes are proteins that function in optimal environmental conditions. The conditions include heat, pH and salinity. Different enzymes function best in different environments. Sometimes, the temperature of an environment becomes too hot, and the action of the enzymes becomes unsustainable. As enzymes are dependent on their protein shape remaining unaltered, if anything should break chemical bonds to change the protein’s conformation, that protein becomes denatured. A denatured protein is one with an altered shape, and that means it cannot function as it was originally designed. The fermentation rate in this experiment is measured in ml/min. It is the rate of carbon dioxide production that is measured over time spent in a water bath. Carbon dioxide is a gas, and the lab has no direct method of gas measure. Thus, an indirect method must be used. Water will substitute for the gas measure’s mark at the conclusion of the experiment, and the amount of water in milliliters will serve as an indirect method of fermentation rate. As this experiment is to be used for a scientific method report, the student must answer and cite the appropriate references for the following questions, as the Introduction of the report is written: 1. When one refers to the temperature of a system, what does this mean? 2. How are chemical reactions, especially their rates, influenced by temperature? 3. Give various examples of the effect of temperature on biological systems. 4. What is yeast?

5. What is the overall fermentation reaction by yeast, starting with glucose as an energy source? 6. What is an enzyme?
7. How are enzymes and the reaction rates they control influenced by temperature? 8. How can fermentation rate by measured?
9. What is the hypothesis of the effect of temperature on the rate of carbon dioxide production?

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