What is produced during fermentation in the absence of oxygen?

During fermentation in the absence of oxygen, the primary products are lactic acid or ethanol, depending on the type of fermentation process. In lactic acid fermentation, which occurs in certain bacteria and muscle cells, glucose is converted into lactic acid along with a small amount of ATP. This process is particularly important in anaerobic conditions, such as during intense exercise in muscles when oxygen is scarce.

In alcoholic fermentation, which occurs in yeast and some other microorganisms, glucose is converted into ethanol and carbon dioxide. This pathway is utilized in the production of alcoholic beverages and bread. Thus, the production of either lactic acid or ethanol represents the key outcomes of anaerobic fermentation, making this the correct response.

The other options listed do not accurately reflect the end products of fermentation processes. Acetic acid is typically produced from the oxidation of ethanol in aerobic conditions. Carbon dioxide and water are byproducts of aerobic respiration rather than fermentation. Glucose is a substrate that gets broken down to produce energy during fermentation, but it is not a product of the process.