Final answer:
The stage called glycolysis converts 1 glucose molecule into 2 pyruvate molecules, with a net production of 2 ATP molecules.
Step-by-step explanation:
The stage that converts 1 glucose molecule into 2 pyruvate molecules is known as glycolysis. In this process, a single glucose molecule (C6) undergoes a series of enzymatic reactions to form two 3-carbon pyruvate molecules. ATP and NADH are also generated in the process. Glycolysis occurs in two main phases: the energy-consuming phase (investment phase), where 2 ATP are used, and the energy-releasing phase (payoff phase), where 4 ATP and 2 NADH are produced per glucose molecule. Therefore, a net gain of 2 ATP molecules occurs during glycolysis.