What is fermentation?

Fermentation is defined as a metabolic process that enables cells to convert sugars into acids, gases, or alcohol in the absence of oxygen. In this context, the breakdown of pyruvic acid without oxygen is a hallmark of fermentation, particularly in anaerobic conditions. When oxygen is not available, cells switch to fermentation to extract energy from glucose or other substrates, allowing them to continue generating ATP, albeit in smaller amounts compared to aerobic respiration.

This process occurs in various organisms, including yeast and certain bacteria. For example, in yeast, fermentation leads to the production of ethanol and carbon dioxide, which is critical in both production of alcoholic beverages and in baking. In muscles, lactic acid fermentation occurs when oxygen levels are low, leading to the build-up of lactic acid.

The other choices refer to different metabolic processes. The use of oxygen to produce energy is characteristic of aerobic respiration, and the synthesis of glucose from carbon dioxide describes photosynthesis. Meanwhile, the aerobic metabolism of fats involves oxygen and is a distinct process from fermentation.