Final answer:
Under anaerobic conditions, only two ATP molecules can be produced from one molecule of glucose.
Step-by-step explanation:
Under anaerobic conditions (without oxygen), only two ATP molecules can be produced from one molecule of glucose. This is because the process of glycolysis, which occurs in the cytoplasm, is the only step of cellular respiration that can proceed without oxygen. In glycolysis, one molecule of glucose is broken down into two molecules of pyruvate, producing a net gain of two ATP molecules.