Final answer:
Water is produced in the electron transport chain during cellular respiration, where oxygen combines with electrons and hydrogen ions to form water.
Step-by-step explanation:
Water is created during cellular respiration when O2 receives electrons and takes H+ from the electron transport chain. During cellular respiration, glucose is broken down in the presence of oxygen, producing not only carbon dioxide and ATP but also water. As the electrons move through the electron transport chain in the mitochondria, they eventually combine with oxygen (the final electron acceptor) and hydrogen ions to form water. This process is critical for the production of ATP and is a key part of how our cells convert the chemical energy stored in glucose into a form that the cell can use.