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Yeast Fermentation Adapted from: http: //www. qacps. k 12. md. us/cms/sci/cell/Lab_Yeast. doc
Background Information: Yeast are tiny single-celled (unicellular) fungi. The organisms in the Kingdom Fungi are not capable of making their own food. Fungi, like any other organism, need food for energy. They rely on sugar found in their environment to provide them with this energy so that they can grow and reproduce. Yeast, like bacteria grow in or on their food source. They produce and release digestive proteins (enzymes) into their environment where the sugar molecules are found. Sugar molecules then break down into smaller molecules that can be absorbed by the yeast and used for food (energy).
There are many species of yeast, and each has a particular food source. • Certain yeast feed on a variety of natural sources of sugar such as fruits, nectar from plants, and molasses from the plant crop called sorghum. • Others break down wood and corn stalks. In doing this, a compound called ethanol is produced. This compound can be used in our cars like gasoline. • Another species breaks down sugar from grain into alcohol. Others break down fruits into wine, which is another type of alcohol. • Bread recipes rely on yeast to break down sugar in our dough.
All of these processes are called fermentation, a type of anaerobic respiration (respiration without oxygen). The formula for the yeast fermentation reaction is: C 6 H 12 O 6 Reactant Products >>>>>>> 2 CH 3 CH 2 OH + 2 CO 2 + energy for 2 ATP molecules Glucose breaks down into ethyl alcohol + carbon dioxide + energy for 2 ATP molecules. For the yeast cell, this chemical reaction is necessary to produce the energy for life. The alcohol and the carbon dioxide are waste products produced by the yeast. It is these waste products that we take advantage of. We use the alcohol and the carbon dioxide makes a cake rise when baking.
The chemical reaction, known as fermentation, can be watched and measured by the amount of carbon dioxide gas that is produced from the break down of glucose. Do you think that the volume of carbon dioxide produced during fermentation would be affected by using different masses of sugar? ? In this exercise you will add the same amounts of yeast and water to different amounts of sugar in water bottles and cap them with a balloon to see how much carbon dioxide gas is produced. The more the fermentation, the more that carbon dioxide will be produced, and the more the balloon will expand.
You should include the following components in your lab report: 1. 2. 3. 4. 5. 6. 7. Name(s), date of experiment, title Purpose statement: Prelab questions Procedure-to be created as a class Data table Graph of class data Answers to analysis questions
Prelab Questions 1. Write out the equations for aerobic cellular respiration and anaerobic fermentation. 2. Create a table to compare the two equations. List at least 2 differences and 2 similarities between the equations. 3. What is an advantage to cellular respiration? 4. What is an advantage to fermentation?
Materials • • • 5 yeast packets Sugar Erlenmeyer flask 5 balloons Warm water String Meter stick Rubber band Stopwatch Spoons
Procedure 1. Blow balloon up to circumference of 65 cm and release air. 2. Add 100 ml of hot tap water to flask. 3. Add grams of sugar to flask (5 g, 10 g, 15 g, 20 g, 25 g, 30 g, 35 g) 4. Add 1 complete packet of yeast 5. Place empty balloon over flask opening, secure with rubberband. 6. Gently shake to mix contents. 7. Measure circumference of balloon every 5 minutes for 25 minutes.
Data Table: Group 1 2 3 4 5 5 min 10 min 15 min 20 min 25 min
Analysis Questions 1. Which group’s balloon reached the largest size? 2. What substance was collected in the balloon? How do you know? 3. What were the independent and dependent variables in this experiment? 4. Which group was the control? Why is it considered the control? What is its purpose? 5. Write a brief summary describing what you saw happen in this experiment and then give your explanation of the results. (why)