Final answer:
Cells produce ATP most efficiently with oxygen. Oxygen allows for the complete breakdown of glucose during cellular respiration, yielding up to 36 or 38 ATP molecules per glucose molecule.
Step-by-step explanation:
Cells produce ATP most efficiently in the presence of oxygen. During cellular respiration, glucose is broken down and energy is transferred to ATP, the cellular energy currency. The initial steps of this process yield only a small amount of ATP, but with the presence of oxygen, the later steps can produce a much larger amount of ATP—up to 36 or 38 molecules from just one molecule of glucose. This optimal ATP production occurs because oxygen acts as the final electron acceptor in the electron transport chain of cellular respiration, allowing for the complete breakdown of glucose to carbon dioxide and water. In summary, while glucose is the energy source, oxygen is crucial for the most efficient ATP synthesis during cellular respiration.