Final answer:
Oxygen is the ultimate electron acceptor in cellular respiration, essential for producing ATP by accepting electrons which, combined with protons, forms water.
Step-by-step explanation:
In cellular respiration, the process of transferring electrons from electron donors to electron acceptors is crucial for the production of ATP. During the electron transport chain, oxygen acts as the final electron acceptor. It combines with electrons and protons to form water, a process essential for the generation of the proton gradient that drives ATP synthesis.
Without oxygen, the electron transport chain would cease, halting ATP production and leading to cell death if no alternative pathway is used. Other options like carbon dioxide, nitrogen, and hydrogen do not serve as electron acceptors in cellular respiration. Carbon dioxide is a product of cellular respiration, nitrogen's role is more related to amino acid and nucleotide metabolism, and hydrogen is involved as a proton rather than an electron acceptor.