Final answer:
In the investment phase of glycolysis, two ATP molecules are used per molecule of glucose to phosphorylate it and prepare it for cleavage into three-carbon molecules.
Step-by-step explanation:
The first phase of glycolysis, known as the energy investment phase, uses two ATP molecules per molecule of glucose. These ATP molecules phosphorylate glucose to form fructose-1,6 biphosphate, which is then split into two three-carbon molecules known as glyceraldehyde 3-phosphate (G3P).
During the second phase of glycolysis, also referred to as the energy payoff phase, no additional ATP is invested, but four ATP molecules are produced per molecule of glucose. This results in a net gain of two ATP molecules for the cell after compensating for the two ATPs used during the investment phase.