What type of metabolism can only occur in the presence of oxygen?

Aerobic metabolism refers to the process of producing cellular energy in the presence of oxygen. This metabolic pathway is essential for organisms that utilize oxygen to efficiently convert glucose and other substrates into adenosine triphosphate (ATP), the energy currency of the cell.

During aerobic metabolism, the process involves glycolysis, the citric acid (Krebs) cycle, and the electron transport chain. Oxygen acts as the final electron acceptor in the electron transport chain, allowing for the complete oxidation of substrates. This results in a significantly higher yield of ATP compared to anaerobic processes, which typically produce energy less efficiently and can lead to the accumulation of lactic acid in some cases.

In contrast, anaerobic metabolism does not require oxygen and is utilized when oxygen levels are low or unavailable, leading to less efficient ATP production. Facultative metabolism refers to organisms that can switch between aerobic and anaerobic metabolism depending on oxygen availability. Obligate metabolism pertains to organisms that strictly require certain environmental conditions, which may or may not include oxygen, but the distinction is not as clearly defined as aerobic versus anaerobic.

In summary, aerobic metabolism is characterized by its reliance on oxygen for efficient energy production, making it the correct answer.