Final answer:
During glycolysis, 2 ATP molecules are used and 4 ATP molecules are produced per molecule of glucose, leading to a net gain of 2 ATP.
Step-by-step explanation:
In glycolysis, a metabolic pathway, one molecule of glucose is converted through a series of enzymatic reactions into two molecules of pyruvate. During this process, ATP molecules are both used and produced. Initially, 2 ATP are consumed to phosphorylate glucose and its six-carbon derivative, which is a necessary investment to allow the subsequent steps of glycolysis to occur.
As the pathway progresses, a total of 4 ATP molecules are generated via substrate-level phosphorylation. However, since 2 ATP were used at the start, the net gain of ATP during glycolysis is two. Therefore, the correct answer to the question is option a) 2 used, 4 produced, which reflects the net increase of ATP as a result of the glycolysis of one molecule of glucose.