Here's why:
* Aerobic Respiration: Cellular respiration, in its most efficient form, is aerobic respiration. This means it requires oxygen as the final electron acceptor in the electron transport chain.
* Electron Transport Chain: The electron transport chain is the stage of cellular respiration that produces the majority of ATP (the cell's energy currency). This process relies on oxygen to accept electrons and create a proton gradient that drives ATP synthesis.
Without oxygen, cellular respiration can still occur, but in a much less efficient way called anaerobic respiration (fermentation). This process produces far less ATP and relies on other molecules (like pyruvate) as the final electron acceptor.
