Lab 8 Cellular Respiration and Fermentation Objectives: 1. Observe the effects of cellular respiration on temperature in a closed system. 2. Investigate carbon dioxide production in both germinating pea seeds and crickets. 3. Perform an investigative study of the rate of cellular respiration in both pea seeds and crickets at various temperatures. 4. Compare the alcoholic fermentation of glucose, sucrose, and starch by yeast. Introduction All organisms must have a continual supply of external energy in order to maintain bodily functions and to combat entropy.
Ultimately this source of energy is the sun.
As you learned in the previous lab, plants can convert the sun’s energy into usable forms of chemical energy (E. g. , glucose). In order for the energy to be made useful the chemical bonds that hold the atoms of these molecules together must be broken. The released energy is captured by high-energy phosphate bonds and combined with adenosine diphosphate (ADP) to form adenosine triphosphate (ATP), which is the energy currency of the body.
There are two processes that release this energy from the photosynthetic materials to form the energy molecule ATP.
Those processes are cellular respiration and fermentation. Cellular respiration is an aerobic (requires oxygen) process, while fermentation is an anaerobic (occurs without oxygen) process. These enzyme-controlled reactions that occur during these processes are both oxidative (loss of electrons) and reductive (gain of electrons). Because the reactions are enzyme controlled they require less activation energy and therefore occur at nonlethal temperatures, continually releasing small amounts of energy that can be used to from ATP.
When compared to fermentation, the formation of ATP via cellular respiration is a relatively efficient process, as there are 36-38 ATP molecules formed per glucose molecule. Fermentation on the other hand only generates a net of 2 ATP molecules. This may bring up the question of why the body would even bother with fermentation and not just stick with the high-energy process of cellular respiration. Recall that ATP is the body’s energy currency and energy is needed for the body to continue all of its metabolic processes.
Now recall that cellular respiration requires oxygen. During times when the body is in oxygen debt (I. e. , there is little oxygen available for metabolic processes) the cell still needs energy and therefore it uses it’s next best option for energy production and proceeds with fermentation. There are two forms of fermentation, lactic acid and alcoholic fermentation. In today’s lab we will investigate alcoholic fermentation by yeast. The equations for cellular respiration, lactic acid fermentation, and alcoholic fermentation are listed below:
Cellular Respiration Glucose + Oxygen Carbon Dioxide + Water C6H12 O6 +6O2 6CO2 + 6H2O Alcoholic Fermentation Glucose Carbon Dioxide + Ethyl Alcohol C6H12O6 2CO2 + 2C2H5OH Lactic Acid Fermentation Glucose Lactic Acid C6H12O6 2C3H6O3 Exercise I Cellular Respiration and Heat Production Body heat in birds and mammals is generated through the metabolic process of cellular respiration.
Your task in this exercise is to investigate the null hypothesis that simple organisms do not produce heat as a by-product of cellular respiration. In order to test this null hypothesis there have been 3 250-mL flasks setup. Each flask has a two-hole rubber stopper with one of the holes closed off with cotton and the other hole housing a thermometer. One of the flasks has 6 live crickets, one has 6 germinating pea seeds, and the other is empty. You need to read the temperature of the thermometers in each of the flasks and decide whether the null hypothesis is supported or refuted.
Questions to answer 1. What were the temperatures in the bottles? Pea Seed Flask ________ Cricket Flask ________ Empty Flask ________ 2. Did the results support or refute the null hypothesis? How did you come to this conclusion? 3. Explain why the one flask was left empty. Exercise II Cellular Respiration and Carbon Dioxide Production In this exercise you will test the null hypothesis that living organisms do not produce carbon dioxide. Recall from the previous lab that the presence of carbon dioxide in water produces carbonic acid.
The reduced pH can be indicated by using the pH indicator bromothymol blue, which turns yellow in acidic conditions. To test the efficacy of bromothymol blue as a pH indicator you should place 3 drops of bromothymol blue in a test tube containing 3 mL of water and exhale into the water/bromothymol blue solution through a drinking straw. 1. What happened to the color of the water/bromothymol blue solution? Now to further test the null hypothesis, you will investigate whether or not crickets and germinating pea seeds produce carbon dioxide as part of their cellular respiration.
Follow the directions below: 1. Place 3 drops of bromothymol blue into each of three test tubes containing 3 mL of water. 2. Place several short segments of glass tubing into each test tube so that the crickets and seeds will be kept out of the solution. 3. Place 6-10 pea seeds in one test tube, 3 crickets in another test tube, and nothing else in the last test tube. 4. Gently (to prevent a sudden increase in pressure from injuring the crickets) insert a rubber stopper into each of the three test tubes. Place the test tubes in the test tube rack for 25 minutes.
Observe and record any color change in the bromothymol blue in the chart below. | |Beginning Color |Ending Color | |Cricket Tube | | | |Pea Seed Tube | | | |”Empty” Tube | | | Questions to Answer 1. What is the purpose of the “Empty” tube in the experiment? Explain your answer. 2. Did the results of your experiment support or refute the null hypothesis? 3. What would you conclude from the experiment?
Exercise III Yeast Fermentation of Different Sugar Sources Yeast are unicellular fungi that can survive and even thrive on the low energy yield of fermentation when conditions are anaerobic (oxygen is absent). Recall that the fermentation of glucose yields ethyl alcohol, carbon dioxide, and a net of 2 ATP molecules. This process is used commercially in the alcoholic beverage industry and in the production of bakery products. In producing bakery products the carbon dioxide caused the bread to rise as small air (carbon dioxide) pockets are formed and the alcohol is evaporated during the cooking process.
In this exercise you will determine if different carbohydrates are fermented by yeast at the same rate. Glucose is a monosaccharide and is the primary carbohydrate energy source for the cells of many organisms. Sucrose (table sugar) is a disaccharide that is composed of the monosaccharides glucose and fructose. Starch is a polysaccharide composed of many glucose subunits and acts as the primary energy storage of plants. Test the null hypothesis: There will be no difference in the ability of yeast to ferment glucose, sucrose, and starch.
You will be using a Durham tube to investigate the rate of fermentation by yeast of various carbohydrate sources. See the figure below. Durham Tube A Durham tube is composed of two test tubes. The smaller tube is placed, inverted, inside the larger tube. You will need to put the solution (10 ml of carbohydrate source your testing and 1 ml of Yeast solution) to be tested in the smaller test tube, place the larger test tube on top of the smaller tube, and then invert the two tubes trying not to loose any of the yeast/carbohydrate suspension.
You will need to measure the air bubble at the top immediately after inverting the tubes. Allow fermentation to proceed for 20 minutes, measuring the air bubble in 5 minute increments. Use the formula V=h (( r2) to find the volume of the air collected. The height of the bubble is the difference between your initial reading and your final reading after 20 minutes. You will need to perform this task for each of the different carbohydrate sources, as well as water. Table for recording results in Exercise IV | |Time | | | | |Tube |0 |5 |10 |15 |20 |V CO2/20 min |V CO2/hr | |1 | | | | | | | | |2 | | | | | | | | |3 | | | | | | | | |4 | | | | | | | | Questions to answer 1.
Which carbohydrate was fermented by the yeast at the highest rate? Slowest rate? 2. Did the results support or refute the null hypothesis? Explain. 3. What is the independent variable? 4. What is the dependent variable? 5. Do you suspect the rate of fermentation would have occurred at a different rate if the temperature was different? If yes what would you hypothesize about the rate of fermentation at a cooler temperature? At a warmer temperature? 6. What would you conclude from the results of this experiment? Exercise IV Why does my wine only have 12% alcohol? You may have wondered why some alcoholic beverages have more (or less) alcohol in them than others.
For example, most beer has about 5-6% alcohol by volume, while wine typically has 10-12%, and some hard liquors have quite a bit more. Liquors are distilled and therefore have another step after the fermentation process that allows them to have higher alcohol content. What about beer and wine? Beer and wine are subject to fermentation by the yeast Sacchromyces cerevisiae (sacchar-sugar; myces-fungi; ceres-Greek goddess of agriculture), which produces as ethanol as a waste product. However, alcohol is toxic to microorganisms, including yeast. The question is at what level does alcohol kill yeast? You will be testing the effects of 4, 8, 12, and 16 % alcohol concentration on yeast suspension (yeast mixed with 10% sucrose).
Durham tubes will be used to capture CO2 as a means of testing the yeast’s ability to ferment the sucrose in the varying alcohol concentrations. The glucose and alcohol solution have been “pre-mixed” for you by either your lab instructor or teaching assistant. You will need to add 10 ml of the glucose/alcohol solution and 1 ml of the yeast solution. Experimental Design: How are you going to test the effects of alcohol on yeast fermentation? Think details. Data Collection: In the space below design a table to collect your data. *Be sure you leave the lab as clean or cleaner than you found it. Put everything back where it goes. ———————– Yeast Suspension
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Cellular Respiration. (2016, Sep 28). Retrieved from https://graduateway.com/cellular-respiration/