Which type of metabolism is characterized by the absence of oxygen?

The correct answer is anaerobic metabolism, which is defined as a biological process that occurs in the absence of oxygen. This type of metabolism allows cells to generate energy through processes such as glycolysis, where glucose is broken down into pyruvate. In the absence of oxygen, pyruvate is further converted into lactate, producing energy without the use of oxygen.

Anaerobic metabolism is particularly important during short bursts of intense exercise when the oxygen supply is inadequate to meet the energy demands. This pathway is crucial for activities requiring quick energy, such as sprinting or weightlifting.

In contrast, aerobic metabolism involves oxygen and occurs primarily during endurance activities, where energy production is more efficient but slower. Lipolysis refers specifically to the breakdown of fats for energy, and oxidative phosphorylation is a stage of aerobic metabolism that creates ATP through the use of oxygen and is dependent on the electron transport chain. These processes are not characterized by the absence of oxygen and thus do not fit the definition required for the question.