What is the process called where cells convert sugar into lactic acid or ethanol in the absence of oxygen?

The process where cells convert sugar into lactic acid or ethanol in the absence of oxygen is known as fermentation. This biological process occurs when oxygen is scarce or unavailable, allowing organisms to generate energy through the anaerobic breakdown of carbohydrates. During fermentation, different microorganisms, such as yeast and certain bacteria, metabolize sugars and produce byproducts such as ethanol and carbon dioxide or lactic acid, depending on the type of fermentation occurring.

This process is essential in various applications, including the production of alcoholic beverages and bread, as well as in some muscle cells during intense exercise when oxygen levels drop and lactic acid is produced. In contrast, respiration is primarily an aerobic process where glucose is broken down with oxygen to produce carbon dioxide, water, and energy. Glycolysis is the initial step of both aerobic respiration and fermentation, involving the breakdown of glucose into pyruvate, but it does not account for the subsequent anaerobic processes. Photosynthesis, on the other hand, is the process by which plants convert light energy into chemical energy stored in glucose, which is unrelated to the fermentation process.