During aerobic respiration. #H_2O# is formed. Where does the oxygen atom for the formation of the water come from?

Question

Isabella Anderson · Accepted Answer

The oxygen was found in one of the reactants of the process, but we cannot state for certain which compound.

All that can be said is that this oxygen atom was originally one of the atoms in the reactants of the process (the #C_2H_(12)O_6# or the #O_2#). It is not possible to be certain as to which of these molecules was the source of that particular oxygen atom. So, it was either part of the food that was consumed to produce the glucose, or the oxygen that was transported from the lungs via the blood to the cell. But which one? Impossible to say. One #H_2O# molecule will contain an oxygen atom from the #O_2# and the next could contain one from the sugar.

Vivian Aronson · Answer

undefined Molecular oxygen (O2) that organisms breathe in provides the oxygen atom needed for the formation of water during aerobic respiration.

Ruby Armstrong · Answer

undefined The oxygen atom used in the formation of water during aerobic respiration primarily comes from molecular oxygen ($O_2$) that is breathed in by organisms during the process of respiration. This molecular oxygen serves as the final electron acceptor in the electron transport chain of aerobic respiration, where it combines with hydrogen ions (protons) to form water ($H_2O$). Specifically, oxygen accepts electrons and protons to form water molecules in the mitochondrial electron transport chain during oxidative phosphorylation.