Effect of the Nature of Different Substrates on the Rate of Cellular Respiration of Yeast

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Cellular respiration is defined as an enzyme mediated process in which organic compounds such as glucose is broken down into simpler products with the release of energy (Duka, Diaz and Villa, 2009). It is a series of metabolic processes and oxidation-reduction reactions. Oxidation of substrates, such as glucose, is a fundamental part of cellular respiration (Mader, 2009). As a catabolic process, it may or may not require the presence of oxygen. The process that requires oxygen is called aerobic respiration while the process that does not require the presence of oxygen is called anaerobic respiration. (Duka, et.al. 2007) Despite of its low yield of only two ATP (energy used by the cells to perform its duties), anaerobic respiration is essential because it continuously synthesizes ATP albeit oxygen is temporarily in short supply. Although anaerobic respiration synthesizes a low yield of ATP (which is the energy used by the cell enables it to perform its duties), it is essential because it is a way to produce ATP even though oxygen is temporarily in short supply. Though this process brings benefits usually, these are accompanied by drawbacks. One of these downsides is the formation of lactate in the muscles because of “oxygen debt”, causing it to “burn” and eventually fatigue, until pyruvate is reduced from lactate (Madur, 2009). Anaerobic respiration can be further divided into two types; namely, alcohol fermentation and lactic acid fermentation. In alcohol fermentation, pyruvate (product of glucose in glycolysis) is converted to 2 molecules of ethanol (C2H5OH) and 2 molecules of carbon dioxide (CO2) while in lactic acid fermentation, pyruvate is reduced directly into lactic acid (Campbell and Reece, 2008). A good example of organism which produces ethyl alcohol and carbon dioxide through the process of alcohol fermentation is yeast (Madur, 2009). As a unicellular fungus, yeast is also an example of a facultative anaerobe, which depicts an organism with...
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