The original questions were: do carbohydrate sources have an effect on the rate of fermentation? And, which carbohydrate source has the greatest effect on fermentation? Our hypothesis stated that carbohydrate sources will speed up the process of fermentation and polysaccharides will it up the fastest, disaccharides will be relatively fast, and monosaccharide will be the slowest.
Carbon dioxide change is indicative of fermentation therefore, we set up an experiment that included six carbohydrate sources: glucose, lactose, maltose, starch, and cellulose. The answer to the first question to our hypothesis is yes carbohydrate sources do have an effect on fermentation rate; however, the answer to the second question was the reverse of our original hypothesis. Monosaccharides have the greatest or fastest effect, followed by disaccharides, and polysaccharides have the least or slowest effect on the rate of fermentation.
According to our data, Table 2. and Figure 2., the mean decrease in water level with the test tube containing glucose was 8 mm. Maltose and lactose showed a mean decrease of 4mm, and starch and cellulose showed a mean decrease of 2 mm. Why does this occur though?
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Yeast has the ability to ferment glucose to ethanol and carbon dioxide. Yeasts are found to belong to a group of organisms known as fungi. They are known to reproduce quite rapidly by fission, or otherwise known as budding (Kowalczyk 2000). Their cell wall swells at a region, and becomes a bud. The bud breaks off from the rest of the cell and becomes an independent cell. Yeast does not contain chlorophyll, so therefore cannot produce its own food. They feed on sugar from a variety of sources (Delfin 2002). Yeast is used by the wine and beer industry to ferment carbohydrates in their food to alcohol. Yeast is able to take in solutes across their cell membrane by diffusion, facilitated diffusion, and active transport. Glucose is water soluble because of its hydroxyl groups that stick out around it so therefore, simple sugars, such as glucose and fructose, are taken up by facilitated diffusion (Yip 2000). Only under anaerobic conditions, such as alcoholic fermentation, is yeast able to produce ethanol and carbon dioxide. In alcoholic fermentation in yeast, electrons are transferred from NADH to pyruvate which is then converted to alcohol while releasing CO2. This process is also the cause of bread rising, and also produces the alcohol in beer and wine.
This explanation makes it clear why disaccharides and polysaccharides tend to be slower which conflict with our results. Disaccharides are two monosaccharides linked together. Polysaccharides are long chains of monosaccharide subunits linked together. Plants use starch to store food. Cellulose which makes up cell wall structures are designed not to be metabolized and is a primary component of dietary fiber and for most animals is indigestible.
In conclusion, the results of the experiment are consistent with the first part of our hypothesis: carbohydrate sources speed up the rate of fermentation. However, they are not consistent with the second part: polysaccharides will speed up the process the fastest, followed by disaccharides, and finally monosaccharide. The reverse to this is true. Our findings indicate that the monosaccharide glucose had the most profound effect on fermentation rate; carbon dioxide change under laboratory conditions. The things that we controlled were temperature of the water bath, 50-60 degrees C, the number of test tubes, and the amount of contents in the test tubes. However, there were weaknesses in the experiment. I do not think the addition of corn syrup was necessary because it did not serve as an indicator for anything throughout the experiment. In addition, I think that we used too little yeast in the experiment. If we used more yeast, fermentation could have occurred faster. Additionally, we probably could have seen when the rate of fermentation exhausted in each of the tubes with the carbohydrate sources.
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