What is the primary phase of metabolism that utilizes oxygen and mitochondria?

The primary phase of metabolism that utilizes oxygen and mitochondria is aerobic metabolism. This process occurs in the presence of oxygen and is characterized by the complete oxidation of substrates, primarily carbohydrates and fats, to produce energy in the form of ATP (adenosine triphosphate). During aerobic metabolism, the electron transport chain, located in the mitochondrial membrane, facilitates the production of ATP by using oxygen as the final electron acceptor. This leads to the efficient generation of a large amount of ATP, which is essential for sustaining prolonged physical activity and supporting various bodily functions.

In contrast, anaerobic metabolism occurs in the absence of oxygen and primarily relies on processes such as glycolysis, leading to the production of energy without the complete oxidation of glucose. While glycolytic metabolism is part of both aerobic and anaerobic pathways, in the context of long-term energy expenditure and efficiency, aerobic metabolism is the key pathway that utilizes oxygen and higher amounts of mitochondria to meet energy demands. Fermentative metabolism also operates without oxygen, producing energy less efficiently than aerobic metabolism and resulting in byproducts like lactic acid. Thus, aerobic metabolism stands out as the correct choice for the phase involving oxygen and mitochondria.