Fermentation Is an Anaerobic Process

Our initial hypothesis was an alternative hypothesis because we concluded that the rate of fermentation would would increase until 3% of total yeast composition, plateau from around 3%-6% of yeast composition and decrease after 6% of yeast composition which signifies that we predicted that there would be a change in the data points we collected. Therefore the ANOVA testing that we conducted was accurate because the results of the tests supported our alternative hypothesis.

I terms of the slope found in “Graph: 1”, as the m in y=mx begins to decrease that means the change in carbon dioxide pressure/the change in time (rate of fermentation) is decreasing also.

So, for 0g of sugar we have a slope of 0.0023 and at 3% of total yeast composition where we hypothesized that, that sugar amount would increase the rate of fermentation we saw an increase in the slope as well (0.0130). From 3% – 4% where we expected a plateau, we saw that begin in the graph also with only the slight change of the slopes from 0.

0130 (0.12g) to 0.0125 (0.16g). We also hypothesized that any amounts of sugar above 6% of total composition would cause the yeast cells to crenate and in turn, cause the rate of fermentation to decrease. We saw a drastic decline from the slope of 6% (0.0155) total yeast composition to the slope of 8% (0.0030) total yeast to help support this claim as well.

Fermentation is an anaerobic process in which energy from the glucose produced from glycolysis can be produced without oxygen. There are two types of fermentation but we specifically experimented on alcoholic fermentation.

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When oxygen is scarce, glucose is still metabolized to pyruvic acid via glycolysis.

In the first step, a carboxyl group is removed from pyruvate and released as carbon dioxide (which is why we could measure the amount of carbon dioxide production/ the rate of fermentation in our experiment) producing a two-carbon molecule called acetaldehyde.

In the second step, NADH is oxidized to form NAD+ by passing its electrons to acetaldehyde forming ethanol (alcohol). The net gain of ATP is two molecules (Danovaro, 2010). The increase, plateau and decrease we see in the rate of fermentation when we maneuver the amount of sugar mixed in with the yeast is an example of the crabtree effect. Although fermentation occurs in anaerobic surrounding, the crabtree effect allows yeast to produces ethanol (alcohol) in aerobic conditions with high glucose (sugar) concentrations (Hagman, 2014).

In the scientific journal known as, “A Study on the Fundamental Mechanism and the Evolutionary Driving Forces behind Aerobic Fermentation in Yeast.” the authors explained that, “It is clear that short-term Crabtree positive yeasts started consuming O2 and producing CO2 at high rates immediately after a glucose pulse,” (Hagman, 2015) This directly correlates with our project because the crabtree effect allows the process of fermentation to continue even while being in aerobic conditions