Final answer:
In cellular respiration, the oxygen atoms that form water are derived from molecular oxygen (O2) and are the final electron acceptors in the electron transport chain, combining with protons to produce water.
Step-by-step explanation:
The oxygen atoms used to form water in the complete reactions of cellular respiration are derived from molecular oxygen (O2). The process of cellular respiration involves the oxidation of carbohydrates, such as glucose, where these carbohydrates are broken down to produce carbon dioxide (CO2), water (H2O), and energy in the form of ATP (adenosine triphosphate).
Oxygen plays a critical role in cellular respiration as the final electron acceptor in the electron transport chain. When electrons reach the end of this chain, they are used to reduce an oxygen molecule to oxygen ions. These ions then combine with hydrogen ions (protons) to form water. This reaction highlights the importance of oxygen in enabling the process of oxidative phosphorylation, which produces the majority of ATP during cellular respiration.