Final answer:
Oxygen is essential in aerobic respiration, a process where cells break down glucose in the presence of oxygen to produce ATP, CO2, and water. This process provides about 95% of the ATP needed by the cells, especially in muscles.
Step-by-step explanation:
Oxygen is required in aerobic respiration, which is a cellular process that releases energy by breaking down organic compounds. Aerobic respiration is a complex series of reactions that includes Glycolysis, the Transformation of Pyruvate, the Krebs Cycle, and Oxidative phosphorylation. During this process, glucose and oxygen react to form carbon dioxide and water. It's the presence of oxygen as the final electron acceptor that allows for the complete breakdown of glucose, a necessary step for the production of ATP, the energy currency of the cell. This process is crucial as it accounts for about 95 percent of the ATP required for a cell’s activities, particularly in resting or moderately active muscles. Without oxygen, aerobic respiration cannot proceed, and an organism must resort to anaerobic processes such as glycolysis, which yields far less energy.