Carbon Dioxide Production through Fermentation
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All organisms require constant supply of energy in order to keep bodily functions and to fight against entropy. Basically, sun is the primary source of energy. The energy from the sun is being converted to chemical energy, thereby producing organic compound (like glucose). Atoms of these molecules are being held together by chemical bonds which need to be broken. High energy phosphate bonds capture the released energy and combine it with adenosine diphosphate (ADP) to form adenosine triphosphate (ATP); energy currency of the body.
Cellular respiration and fermentation are two processes that release this energy from the photosynthetic materials to form ATP. Cellular respiration requires oxygen (aerobic process) while fermentation does not (anaerobic process). Thus, aerobic process is far efficient than anaerobic. Loss and gain of electrons (Oxidation-Reduction) occur during these processes. However, the reactions that take place in these processes require less activation energy as they are controlled by enzymes and are expected to occur at favorable temperature to form ATP. Per glucose molecule, cellular respiration generates 36-38 ATP molecules and fermentation on the other hand generates a net of 2 ATP molecules  . The two forms of fermentation are lactic acid and alcohol fermentation. Both cellular respiration and fermentation start with the same first step: glycolysis, after which cellular respiration involves other steps such as Krebs cycle and electron transfer chain.
C6H12 O6 +6O2 6CO2 + 6H2O
C6H12O6 2CO2 + 2C2H5OH
Lactic Acid Fermentation
Unlike the cellular respiration whose end products are carbon dioxide and water, the product of fermentation are carbon dioxide and ethanol due to the fact that glucose is not completely broken down.
This lab investigated alcoholic fermentation by yeast; Saccharomyces cerevisiae.
With yeast suspension mixed with glucose, sucrose, or lactose, CO2 will be released.
In tube 1, CO2 will not evolve because yeast is not present in the solution.
In tube 2, CO2 will not evolve because glucose is not present in the solution.
In tube 3, small amount of CO2 will evolve because of the quantity (little) of yeast present in the solution.
In tube 4, CO2 will evolve because yeast is present in the solution.
In tube 5, CO2 will evolve because yeast is present in the solution containing sucrose.
In tube 6, CO2 will evolve because yeast is present in the solution containing lactose.
Materials and Methods
Five (5) different solutions (distilled water (DW), sucrose, lactose, glucose and yeast: Saccharomyces cerevisiae), four (4) respirometers (test tubes, 1 mL graduated cylinder, pipettes, tubing and binding clips) and pipette pump were used.
4 mL of DW, 3 mL of glucose was added to tube 1.
6 mL of DW, 1 mL of yeast was added to tube 2.
3 mL of DW, 1 mL of yeast and 3 mL of glucose was added to tube 1.
1 mL of DW, 3 mL of yeast and 3 mL of glucose was added to tube 1.
3 mL of DW, 3 mL of yeast and 3 mL of sucrose was added to tube 1.
3 mL of DW, 3 mL of yeast and 3 mL of lactose was added to tube 1.
The pipette pump was used to draw the fermentation solution beyond 0 mL after which the tubing was folded and clamped with the binder clip. Then the binder was carefully open to allow the solution drained to exactly 0 mL on the pipette. The initial reading was taken and recorded. After two minutes of the initial reading, the actual reading was recorded. The readings lasted for twenty minutes with interval of two minutes for each. At the end of the observation, the solutions were disposed and the test tubes were properly rinsed.
This experiment took place on 10th March, 2011 in room 230, Arts and Sciences building, and it lasted for 3 hours (8am to 11am).
Base on the outcome of the experiment, it was very obvious that carbon dioxide evolved from fermentation. First of all, considering tube 1, CO2 did not evolve because there was no yeast; only distilled water and glucose. Also CO2 did not evolve in tube 2 because there was no glucose; only distilled water and yeast. The graph of test tubes 1 and 2 straight line graph (Graph). The CO2 produced in test tube 4 was more than the CO2 in test tube 3, this was due to the fact that the yeast contained in test tube 4 was actually more that of test tube 3. The upward movement of the slope of test tube 3 (0.07 mL - 0.09 mL) and test tube 4 (0.12 mL - 0.2 mL) shows that CO2 was released.
On the graph, there is clear indication that CO2 evolved in the solution that contained sucrose. Meanwhile, the solution that contained lactose was suppose to yield CO2 but the reverse was the case as the slope of the graph remained constant on the graph. This could have happened due to mixture error.
Consequently, the hypothesis of carbon dioxide being produced from fermentation was proved right and the predictions were accurate, except for the prediction of solution that contained lactose.
Answers to Experimental Questions
The independent variable is time (minutes) and it is on the x-axis.
The dependent variables are distilled water, sucrose, lactose, glucose and yeast and it is on the y-axis.
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