Final answer:
The main purpose of aerobic cellular respiration is to capture energy in food molecules as ATP, which is option B in the student's question.
Step-by-step explanation:
A major metabolic purpose of aerobic cellular respiration is to capture the chemical energy in food molecules in the form of ATP. This process involves a series of chemical reactions that convert carbohydrates and oxygen into carbon dioxide and water, and in the process, synthesize ATP from ADP and phosphate. The presence of oxygen allows for the complete breakdown of glucose, which not only results in carbon dioxide and water but also enables the production of up to 38 ATP molecules, a significantly higher yield compared to anaerobic respiration, which only produces two ATP molecules. Thus, the correct answer to the student's question is option B.