Fermentation Lab

 Fermentation, a process that can occur in the absence of oxygen, partially breaks down carbohydrate by glycolysis to capture a small amount of energy in the form of ATP.  The initial reactions of fermentation and respiration are the same, but fermentation stops after glycolysis whereas respiration continues into the Krebs Cycle.  The carbohydrate leftovers are different depending upon the organism that performs the fermentation; usually one product is more oxidized (electron-poor) than the starting molecule and the other is more reduced (electron-rich).  In the case of yeast fermentation, the products from one glucose (C₆H₁₂O₆) molecule are two molecules of ethanol (C₂H₅OH) and two molecules of CO₂.  Human anaerobic (oxygen-free) muscle produces two molecules of lactic acid (C₃H₆O₃).  Even though the products are different, each fermentation results in a limited, anaerobic breakdown of carbohydrate with energy release.  Since the process does not completely break down the carbohydrate, it does not release much energy that can be captured in the form of ATP.  In yeast fermentation, there are 2 ATP molecules produced for each glucose molecule that is fermented.  This is a low yield compared to that of respiration, but the ability to perform fermentation allows the yeast to survive and grow in environments where no oxygen exists.