Final answer:
The breakdown of glucose in the absence of oxygen is termed fermentation, which is a part of anaerobic metabolism. Glycolysis is the initial step in this process and can lead to the production of lactic acid in animal cells under anaerobic conditions.
Step-by-step explanation:
The breakdown of glucose in the absence of oxygen is known as fermentation. This is a type of anaerobic metabolism that occurs when oxygen is not available, distinguishing it from aerobic cellular respiration that requires oxygen. Glycolysis is the initial stage of this process, where glucose is converted into two molecules of pyruvate and a net gain of two ATP molecules. This process takes place in the cytoplasm of cells and is a universal mechanism found in nearly all living organisms. In the absence of oxygen, cells may undergo fermentation to produce energy. Lactic acid fermentation is one type that commonly occurs in animal cells under anaerobic conditions.