Affect of Sugars on Yeast Respiration

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RaeAnne Smith
HL Biology Y2
Soule: Period 7
10 October 2011
Affect of Sugars on Yeast Respiration
Introduction
Cellular 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: c6H12O6+ 6O2→6CO2+6H2O

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.

Design
Research 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 plate
3. 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 temperature 5. 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 water 7. Stir the yeast until no clumps remain

8. 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 scale 11. Pour the sugar into the small beaker with 100mL of water 12. 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 stand

14. Set up loggerpro software, including the gas pressure sensor 15. Use a pipette to measure out 10mL into the 10mL graduated cylinder of 0.4M sucrose water and pour it into the test tube 16. Use the other pipette to measure 10mL of yeast solution into the other 10mL graduated cylinder. 17. Pour...
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