Why do cells of all multicellular organisms need oxygen?

Cells of all multicellular organisms need oxygen primarily for cellular respiration, a process that generates ATP, the energy currency of the cell. Oxygen serves as the final electron acceptor in the electron transport chain, allowing for the efficient production of ATP from glucose and other nutrients. Additionally, oxygen helps in the oxidation of metabolic substrates, facilitating the breakdown of these substrates to release energy. Without oxygen, cells would rely on less efficient anaerobic processes, leading to insufficient energy production for survival.