The process called that converts glucose into energy in the absence of oxygen is known as fermentation. Fermentation allows cells to generate energy anaerobically, producing molecules like ethanol or lactic acid as byproducts, depending on the organism. This process is particularly important in yeast for alcohol production and in muscle cells during strenuous activity when oxygen levels are low. While fermentation is less efficient than aerobic respiration, it enables energy production in hypoxic conditions.