By Robert Schrader | Updated Aug 30 2022
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In cellular biology, respiration is the metabolic breakdown of sugars to generate energy. Cells can carry out two main pathways: aerobic respiration, which requires oxygen, and anaerobic respiration—commonly called fermentation—which proceeds in the absence of oxygen.
Adenosine triphosphate (ATP) is the direct energy currency produced by both pathways. Aerobic respiration yields approximately 38 ATP molecules per glucose molecule, whereas anaerobic respiration produces only 2 ATP per glucose. The modest ATP output of fermentation primarily allows cells to reinitiate glycolysis after oxygen becomes available.
During intense physical activity, skeletal muscle cells may shift to anaerobic metabolism, leading to the accumulation of lactic acid. This buildup causes the characteristic burning sensation felt in fatigued muscles. Restorative oxygen delivery triggers aerobic respiration, which clears lactic acid and alleviates discomfort.
Ethyl alcohol (ethanol) is the main alcohol found in beer, wine, and spirits. Fermentation of sugars by yeast in an oxygen‑deprived environment produces ethanol. Unlike mammalian cells, yeast do not generate lactic acid; instead, they convert glucose into ethanol and carbon dioxide.
