Final answer:
Glycolysis is the first stage of cellular respiration that converts glucose into pyruvate. Pyruvate can undergo fermentation without producing any ATP. If oxygen is present, pyruvate can move into the mitochondria for cellular respiration, which produces a large amount of ATP.
Step-by-step explanation:
Glycolysis is the first stage of cellular respiration that occurs in the cytoplasm of the cell. During glycolysis, glucose is converted into two molecules of pyruvate, each containing three carbon atoms. When oxygen is not available, pyruvate can undergo fermentation to produce either ethanol or lactate, depending on the organism. Fermentation does not produce any ATP molecules.
If oxygen is present, pyruvate can move into the mitochondria to undergo the process of cellular respiration. In the mitochondria, pyruvate is further broken down through a series of reactions, including the Krebs cycle and the electron transport chain. These reactions generate a large amount of ATP, with a net gain of 30-32 ATP molecules per glucose molecule.