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Cellular Respiration: Yeast Fermentation Cellular respiration is the process by which organisms break down organic molecules to make cellular energy. Background Questions 1. Write the equation for aerobic respiration below: 2. In the presence of oxygen, how many ATP molecules are generated by the breakdown of one glucose molecule? 3. Describe the path oxygen takes as it travels from the air to your cells. 4. If the demand for energy outstrips the oxygen available in your muscle cells, what process begins? 5. How many ATP molecules are generated for every glucose in the process above? 6. What byproduct is formed in the process from question 4? Yeast Fermentation In this experiment, we will be applying various treatments to a single celled fungus, Baker’s yeast. When oxygen is scarce, yeast can perform a process similar to lactic acid fermentation called alcohol fermentation. We will attempt to determine under which conditions yeast fermentation occurs optimally by measuring the rate by which it produces carbon dioxide through alcohol fermentation. 1. Write the equation for alcohol fermentation below: 2. How many ATP molecules are generated during this process for every glucose molecule broken down? 3. Before you begin, formulate a hypothesis for each of the experiments below. Temperature: Sucrose Concentration: Nutrient Preference: Experiment 1 – Temperature 1. Label test tubes A through D with a wax pencil. 2. Add 5 mL of 5% glucose solution to each tube. 3. Swirl the yeast suspension until the yeast is distributed evenly in the liquid. Then completely fill the remainder of each tube with yeast suspension. 4. For each tube, slide an inverted, larger tube over the top. Pressing them tightly together, invert the assembly. There should be no air trapped in the top of the smaller tube. 5. Place the tubes in the following treatments: Tube A in ice bath Tube B at room temperature Tube C in 40ûC water bath Tube D in 80ûC water bath 6. Measure the height of the air column in the small tube every 10 minutes for 40 minutes. Experiment 2 – Sucrose Concentration 1. Label tubes E through H. 2. Add 5 mL of the following sucrose concentrations to each tube and fill the remainder of the tube with yeast suspension as above: Tube E 0 (water only) Tube F 5% sucrose Tube G 10% sucrose Tube H 15% sucrose 3. Place larger tube over the top of each tube and invert as above making sure to remove any air bubbles trapped in the smaller tube. 4. Place all four tubes in the 40 degree water bath. Incubate for 40 minutes, measuring the height of air column in the smaller tube every 10 minutes. Experiment 3 – Nutrient Preference 1. Label tubes I through O. 2. Add 5 ml of each of the following to each tube: Tube I 5% fructose Tube J 5% glucose Tube K 5% sucrose Tube L 5% lactose Tube M 5% lactose and ground Lactaid or Dairy Ease Tube N vegetable oil Tube O protein solution 3. Swirl the yeast suspension until the yeast is distributed evenly in the liquid. Then completely fill the remainder of each tube with yeast suspension. 4. Place larger tube over the tube with the treatment and invert. Remove any air bubbles trapped in the smaller tube. 5. Place all 7 tubes in a 40 degree water bath. Incubate for 40 minutes, measuring the height of the air column in the smaller tube every 10 minutes. Data Collection 1. Record initial observations in the table provided for each test. Then make additional observations at 10-minute intervals, and final observations. These observations should include a description of the fermentation activity and a measure of the amount of gas produced by measuring the column of air trapped in the smaller tube. 2. Subtract the starting bubble column from your total after 40 minutes. This will be the adjusted total. This is the value you will graph. Tube Treatment CO2 column (cm) Relative amt. of fermentation Temperature start 10 20 30 40 Adj total (++++, +++, ++, +) A Ice 6 0 1 1 ---- 2 B RT 9 1 1 0 ---- 2 C 400 4 1 4 5 ---- 10 D 800 3 5 1 1 ---- 7 Sugar concentration E 0 2 1 0 0 ---- 1 F 5% 2 3 3 3 ---- 9 G 10% 4 0 1 4 ---- 5 H 15% 3 2 2 4 ---- 8 Nutrient I Fructose 4 1 1 5 ---- 7 J Glucose 2 1 2 3 ---- 6 K Sucrose 1 3 4 3 ---- 10 L Lactose 1 3 1 0 ---- 4 M Lac + lactaid 3 1 3 5 ---- 9 N Lipid 3 1 0 0 ---- 1 O Protein 2 2 0 0 ---- 2 3. Prepare bar graphs of the air column trapped in the smaller tube against each of the following: Temperature Sucrose Concentration Nutrient Preference Questions 1. Which tube served as the control for the second and third experiments? 2. What is the purpose of a control? 3. Under which conditions were the highest CO2 concentrations produced? Temperature: Sucrose Concentration: Nutrient Preference: 4. Could we use this same procedure to measure lactic acid fermentation? _____ Why or why not? 5. How do you explain the difference in the tube containing lactose and the tube with lactose and Lactaid? 6. In the 800 treatment, why might you observe an initial production of CO2, followed by a decrease? 7. Depict the general carbon cycle below. How does aerobic respiration relate to photosynthesis?

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2. In the presence of oxygen, how many ATP molecules are generated by the breakdown of one glucose molecule?
Ans: 36 ATP (Although total 38 ATP is formed in aerobic oxidation of glucose, but 2ATP is utilized in the beginning of glycolysis)

3. Describe the path oxygen takes as it travels from the air to your cells.
Ans: Oxygen is taken up along with air during breathing, which enters from nose and then respiratory track i.e. pharynx, trachea, bronchi. Thereafter oxygen enters to the lungs where it passively diffused from the alveoli into the blood and get attached to hemoglobin of RBC (red blood cells). It is then transported to the body where it gets released and passively diffuses into a cell to be used in cellular respiration.

4. If the demand for energy outstrips the oxygen available in your muscle cells, what process begins?
Ans: Anaerobic respiration will be going to take place in muscle cells due to deficiency of oxygen for production of energy....
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