RaeAnne SmithHL Biology Y2Soule: Period 710 October 2011

Affect of Sugars on Yeast Respiration IntroductionCellular respiration can be defined as the release of energy, or the breakdown of carbohydrates into carbon dioxide and water1. Cell respiration takes place in the mitochondria of animals and in the cytoplasm of plants. The formula for aerobic cellular respiration is:

c6H 12O6+6O2→6CO2+6H 2O

Aerobic respiration occurs when oxygen is present, while anaerobic respiration occurs when there 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 using different sugars and one artificial sugar will be measured. The natural sugars used in this investigation will be sucrose (table sugar) and lactose (in milk). The artificial sugar that will be used is aspartame (equal). The rate of respiration between the natural sugars will be compared to that of the artificial sugar. The molarity of the sugar will remain constant at 0.4M for all the sugars used and the amount and type of yeast used will be the same. It is expected that the yeast will have a higher rate of respiration for the natural sugars than the artificial sugar. As aspartame is 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 as though there is more aspartame in the packet than there is2. It is predicted that because there is only a very small amount of sugar in the equal packets, that the yeast will have less to metabolize, and therefore the rate of respiration will be lower.

DesignResearch Question: How do natural sugars versus artificial sugars affect the rate of cellular respiration 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 yeast

Procedure:1. Use the 100mL graduated cylinder to fill large (400mL) beaker with 150mL of water 2. Place beaker with water onto hot plate3. Turn the heat up to 4 or 5 4. Wait about 5 minutes for water to heat to about 40-45°C (optimal temperature for yeast to activate) 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 yeast when it is activated)9. Fill the small (150mL) beaker with 100mL of water using the 100mL graduated cylinder 10. 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 in order 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 water and pour it into the test tube16. Use the other pipette to measure 10mL of yeast solution into the other 10mL graduated cylinder. 17. Pour 10mL of 0.4M sucrose into test tube18. Add the 10mL of yeast solution to the test tube

19. 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.

Data Collection and Processing

Table 1: Type of sugar vs. rate of respiration data

  Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Average Sucrose  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  -0.0009

Table 1: This table shows the rate of respiration of the yeast for the different sugars for each trial, as well as the average rate for each sugar. One trial was taken for the control group (yeast with pure water, no sugar) and the rate of respiration was 0.0031kPa.

Table 2: Type of sweetener vs. average rate of respiration Type of Sweetener (natural sugar vs. artificial)

Average Rate of Yeast Respiration (kPa)

Natural (Sucrose and Lactose) 0.0254 Artificial (Aspartame) -0.0009

Table 2: This table shows the average rate of respiration of the sucrose and lactose versus the respiration rate of the aspartame.

Rubber Stopper

Yeast/Sucrose solution

Test Tube

Gas Pressure Sensor

Computer

Figure 1: Set up of the experiment. Not shown is the test tube stand

Type of Sugar Rate of Respiration (kPa) [±0.0001]

Graph 1: This is a sample graph, taken from trial 2 of sucrose. The slope is taken at about 120 seconds 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 yeast's respiration of the sucrose, bubbles began to form as the rate of respiration (or pressure) began to increase (usually around 150 seconds).

Graph 2: This graph shows the average rate of respiration for each of the sweeteners used. The sucrose 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 the average rate of respiration for the artificial sugar (aspartame).

Table 3: P-value of sucrose, lactose & aspartameP-

ValueSucros

eLactos

eAspartam

eSucrose X 0.0007 XLactose 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= 0.0511

ii. 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 water

ConclusionThe results of the experiment showed that sucrose had the highest rate of respiration, as was predicted. The results also showed that both lactose and aspartame were unable to be metabolized properly by the yeast, causing the slope to be negative. The results of the t-test performed showed a p-value of 0.0007 between both sucrose and lactose and sucrose and aspartame, 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 statistically significant. Although one of the natural sugars (sucrose) did cause the yeast to have a higher respiration rate, the other natural sugar (lactose) did not. This suggests that the rate of respiration of yeast does not depend on whether the sugar is natural or artificial, but whether the yeast has the proper enzymes to metabolize the sugar presented to it. The yeast has certain enzymes designed to metabolize glucose and galactose specifically, but these enzymes are not able to properly process lactose 3. This presents a reason for the yeast producing a negative slope when given lactose. Equal packets also sometimes contain lactose to create bulk, since only small amounts of aspartame are needed. In this case, the yeast would be unable to metabolize the lactose.

EvaluationThe most significant possible source of error could have come from a leak in the gas pressure sensor. This would affect the data by creating a negative slope when there could have been a positive 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 to prevent a leak, or a leak from the tube connecting to the rubber stopper. A solution to this source of error would be to The next most significant source of error could have come from the temperature of the yeast solution. The water that the yeast was placed into to activate, was heated to 42°C. After the yeast was activated in this solution, it was used for the first set of trials. While the first trials were being done, the yeast solution had time to cool down, and by the time it was used for the next set of trials, the yeast solution was a different temperature. The different temperatures could have affected the yeast respiration rate. With the warmer temperatures, the molecules move faster, enabling for more collisions, which could have caused the rate of respiration to be higher

for 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 a thermometer 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 every trial. On top of the yeast solution there was a thick layer of foam. When using the pipette to put the solution into the 10mL graduated cylinder, some foam was also added to it. The foam made it difficult to determine whether the yeast solution had reached 10mL, or if it appeared that way because of the foam on top of the yeast. This could have resulted in there being less than 10mL of yeast for some trials, while others have 10mL of yeast. This could affect the data because there 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 yeast solution, 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 could have been used as well, such as splenda (sucralose). There is also a type of yeast that is genetically engineered by scientists to contain the enzyme lactase, enabling the yeast to metabolize lactose4. The rate of respiration between the genetically engineered yeast and the normal yeast could be compared.

Sources:[1] http://www.anaerobicrespiration.net/[2] http://www.equal.com/equal-classic/faqs#saccharin01 [3] http://www.madsci.org/posts/archives/2005-11/1132509463.Cb.r.html[4] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC195890/