Final answer:
Glycolysis in the energy-consuming phase requires two ATP molecules to start the reaction for each glucose molecule, resulting in a net gain of two ATP energy molecules.
Step-by-step explanation:
Glycolysis can be divided into two phases: energy consuming (also called chemical priming) and energy yielding. The first phase is the energy-consuming phase, so it requires two ATP molecules to start the reaction for each molecule of glucose. However, the end of the reaction produces four ATPs, resulting in a net gain of two ATP energy molecules.