Final answer:
Oxygen's primary role in cellular respiration is to act as the final electron acceptor in the electron transport chain, forming water and enabling the production of ATP.
Step-by-step explanation:
The primary role of oxygen in cellular respiration is to act as an acceptor for electrons and hydrogen, forming water. Oxygen is essential because it drives the electron flow through the electron transport chain, which allows for the synthesis of ATP, while simultaneously regenerating NAD+, a molecule required for the continuation of glycolysis and the citric acid cycle.
In the absence of oxygen, organisms may use alternative means to produce ATP, although these methods are typically less efficient. The electron transport chain in the mitochondria is where oxygen plays a critical role, by receiving the electrons from NADH and FADH2, the byproducts of earlier stages of respiration. This process, along with the creation of water, helps to generate a significant amount of ATP, which cells use as an energy source for various functions.