RaeAnne SmithHL Biology Y2Soule: Period 710 October 2011 Affect of Sugars on Yeast RespirationIntroductionCellular respiration can be defined as the release of energy, or the breakdown of carbohydratesinto carbon dioxide and water1. Cell respiration takes place in the mitochondria of animals and inthe cytoplasm of plants. The formula for aerobic cellular respiration is:Aerobic respiration occurs when oxygen is present, while anaerobic respiration occurs whenthere is no oxygen present. In anaerobic respiration, ethanol and carbon dioxide are produced.In this investigation, the rate of carbon dioxide production (cellular respiration) of yeast usingdifferent sugars and one artificial sugar will be measured. The natural sugars used in thisinvestigation will be sucrose (table sugar) and lactose (in milk). The artificial sugar that will beused is aspartame (equal). The rate of respiration between the natural sugars will be compared tothat of the artificial sugar. The molarity of the sugar will remain constant at 0.4M for all thesugars used and the amount and type of yeast used will be the same. It is expected that the yeastwill have a higher rate of respiration for the natural sugars than the artificial sugar. As aspartameis about 200 times sweeter than natural sugar, only small amounts are put into packets of equal,and other substances such as dextrose or maltodextrin are used as "fillers" to make it appear asthough there is more aspartame in the packet than there is2. It is predicted that because there isonly a very small amount of sugar in the equal packets, that the yeast will have less tometabolize, and therefore the rate of respiration will be lower.DesignResearch Question: How do natural sugars versus artificial sugars affect the rate of cellularrespiration in yeast?Dependent Variable: The sweetener used - sugar (sucrose and lactose) vs. artificial sugar(aspartame).Independent Variable: The rate of cellular respiration of the yeast.Controlled Variables: Amount of yeast used, type of yeast used, molarity of sugar used,temperature of water.Materials: About 20 packets of Aspartame 20g of Lactose 20g of Sucrose
One large beaker (400mL beaker) One small beaker (150mL beaker) Two 10mL graduated cylinders One 100mL graduated cylinder 2 pipettes Test tubes Test tube stand Lap top Vernier software Gas pressure sensor Mass scale Hot plate Thermometer Weighing papers 30g of yeastProcedure:1. Use the 100mL graduated cylinder to fill large (400mL) beaker with 150mL of water2. Place beaker with water onto hot plate3. Turn the heat up to 4 or 54. Wait about 5 minutes for water to heat to about 40-45 C (optimal temperature for yeast toactivate) while using the thermometer to take the temperature5. Pour 30g of yeast into weighing paper (use the mass scale to measure 30g).6. Once the water is heated, pour measured 30g of yeast into the beaker with the heated water7. Stir the yeast until no clumps remain8. Wait several minutes for yeast to activate (there will be a layer of foam on top of the yeastwhen it is activated)9. Fill the small (150mL) beaker with 100mL of water using the 100mL graduated cylinder10. Measure out 13.68g of sucrose (to make 0.4M) using the weighing paper and mass scale11. Pour the sugar into the small beaker with 100mL of water12. Stir until the sucrose has dissolved (for lactose and aspartame, the water must be heated inorder for the sugars to properly dissolve)13. Set up test tube into test tube stand14. Set up loggerpro software, including the gas pressure sensor15. Use a pipette to measure out 10mL into the 10mL graduated cylinder of 0.4M sucrose waterand pour it into the test tube16. Use the other pipette to measure 10mL of yeast solution into the other 10mL graduatedcylinder.17. Pour 10mL of 0.4M sucrose into test tube
18. Add the 10mL of yeast solution to the test tube19. Shake the test tube slightly so the yeast and water are evenly distributed20. Attach the gas pressure sensor to the test tube21. Measure the rate of respiration with logger pro for 300 seconds (5 minutes)22. Repeat the steps for 5 trials23. Repeat procedure for lactose and aspartame. Rubber Stopper Gas Pressure Computer Sensor Test Tube Yeast/Sucrose solution Figure 1: Set up of the experiment. Not shown is the test tube standData Collection and ProcessingTable 1: Type of sugar vs. rate of respiration dataType ofSugar Rate of Respiration (kPa) [±0.0001] Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 AverageSucrose 0.0209 0.0637 0.0475 0.0448 0.0788 0.0511Lactose -0.0002 -0.0006 -0.0003 -0.0003 -0.0002 -0.0003Aspartame -0.0004 -0.0006 -0.0021 -0.0008 - 0.0006 -0.0009Table 1: This table shows the rate of respiration of the yeast for the different sugars for eachtrial, as well as the average rate for each sugar. One trial was taken for the control group (yeastwith pure water, no sugar) and the rate of respiration was 0.0031kPa.Table 2: Type of sweetener vs. average rate of respirationType of Sweetener (natural sugar vs. Average Rate of Yeast Respirationartificial) (kPa)Natural (Sucrose and Lactose) 0.0254Artificial (Aspartame) -0.0009Table 2: This table shows the average rate of respiration of the sucrose and lactose versus therespiration rate of the aspartame.
Graph 1: This is a sample graph, taken from trial 2 of sucrose. The slope is taken at about 120seconds because the yeast did not begin to metabolize the sugar until then.Qualitative Observations:The changes during respiration of the yeast were very slight. During the yeasts respiration of thesucrose, bubbles began to form as the rate of respiration (or pressure) began to increase (usuallyaround 150 seconds).Graph 2: This graph shows the average rate of respiration for each of the sweeteners used. Thesucrose had the highest rate of respiration, while the lactose and aspartame had negative slopes,suggesting that the yeast was unable to metabolize the lactose and aspartame.
Graph 3: This graph shows the average rate of respiration of the natural sugars versus theaverage rate of respiration for the artificial sugar (aspartame). Table 3: P-value of sucrose, lactose & aspartame P-Value Sucrose Lactose Aspartame Sucrose X 0.0007 X Lactose X X 0.1031 Aspartame 0.0007 X X Table 3: This table shows the results of a t-test performed on the average respiration rates for each sugar. The p-value is shown, and the red ones are considered to be statistically significant (less than 0.05).Sample Calculationsi. Average for Sucrose: = (trial 1 + trial 2 + trial 3 + trial 4 + trial 5) / 5 = (0.0209 + 0.0637 + 0.0475 + 0.0448 + 0.0788) / 5 = 0.2557 / 2 = 0.0511ii. 0.4 Molarity for Sucrose: = C12H22O11 = (12.011 x 12) + (1.0079 x 22) + (15.999 x 11)
= 144.132 + 22.1738 + 175.989 = 342.29 = 0.4 x 342.29 = 136.8 = 136.8/1000 = x/100 =1000x = 136.8 (100) = 13.68g of sucrose in 100mL of waterConclusionThe results of the experiment showed that sucrose had the highest rate of respiration, as waspredicted. The results also showed that both lactose and aspartame were unable to bemetabolized properly by the yeast, causing the slope to be negative. The results of the t-testperformed showed a p-value of 0.0007 between both sucrose and lactose and sucrose andaspartame, meaning that the difference between them is extremely statistically significant. The p-value between the lactose and aspartame though, was only 0.1031, which is not statisticallysignificant. Although one of the natural sugars (sucrose) did cause the yeast to have a higherrespiration rate, the other natural sugar (lactose) did not. This suggests that the rate of respirationof yeast does not depend on whether the sugar is natural or artificial, but whether the yeast hasthe proper enzymes to metabolize the sugar presented to it.The yeast has certain enzymes designed to metabolize glucose and galactose specifically, butthese enzymes are not able to properly process lactose 3. This presents a reason for the yeastproducing a negative slope when given lactose. Equal packets also sometimes contain lactose tocreate bulk, since only small amounts of aspartame are needed. In this case, the yeast would beunable to metabolize the lactose.EvaluationThe most significant possible source of error could have come from a leak in the gas pressuresensor. This would affect the data by creating a negative slope when there could have been apositive slope because the air would be leaking out from the test tube, lowering the pressure.This could be the result of the rubber stopper not being pushed in far enough in the test tube toprevent a leak, or a leak from the tube connecting to the rubber stopper. A solution to this sourceof error would be toThe next most significant source of error could have come from the temperature of the yeastsolution. The water that the yeast was placed into to activate, was heated to 42°C. After theyeast was activated in this solution, it was used for the first set of trials. While the first trialswere being done, the yeast solution had time to cool down, and by the time it was used for thenext set of trials, the yeast solution was a different temperature. The different temperatures couldhave affected the yeast respiration rate. With the warmer temperatures, the molecules movefaster, enabling for more collisions, which could have caused the rate of respiration to be higherfor the first set of trials, when the yeast was warmer. A solution to this problem would be to keep
the yeast solution in a warm water bath, in order to keep the temperature constant, and to have athermometer in the solution to check for changes in temperature.The final most significant source of error could have been the amount of yeast used for everytrial. On top of the yeast solution there was a thick layer of foam. When using the pipette to putthe solution into the 10mL graduated cylinder, some foam was also added to it. The foam made itdifficult to determine whether the yeast solution had reached 10mL, or if it appeared that waybecause of the foam on top of the yeast. This could have resulted in there being less than 10mLof yeast for some trials, while others have 10mL of yeast. This could affect the data becausethere would be more yeast to metabolize the sugar, which could increase the rate of respiration.A solution to this would be to use a spoon to remove the excess foam on top of the yeastsolution, leaving only the liquid, useable substance.A possible extension to this investigation could be to compare the effect of monosaccharides,disaccharides and polysaccharides on yeast respiration rate. More types of artificial sugars couldhave been used as well, such as splenda (sucralose).There is also a type of yeast that is genetically engineered by scientists to contain the enzymelactase, enabling the yeast to metabolize lactose4. The rate of respiration between the geneticallyengineered yeast and the normal yeast could be compared.Sources: http://www.anaerobicrespiration.net/ http://www.equal.com/equal-classic/faqs#saccharin01 http://www.madsci.org/posts/archives/2005-11/1132509463.Cb.r.html http://www.ncbi.nlm.nih.gov/pmc/articles/PMC195890/