What is the role of oxygen in cellular respiration

The site above can help. It says that... "Without oxygen, cellular respiration could not occur because oxygen serves as the final electron acceptor in the electron transport system. The electron transport system would therefore not be available. Glycolysis can occur without oxygen. Although glycolysis does not require oxygen, it does require NAD+. Cells without oxygen available need to regenerate NAD+ from NADH so that in the absence of oxygen, at least some ATP can be made by glycolysis

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