The cell requires oxygen, and eukaryotic cells are expensive to run. they require a lot of energy and nutrients, and oxygen is one such component. the oxygen is necessary for aerobic respiration, which allows the cell to do a lot, including evolve, proliferate, adopt new niches, habitats, biochemical habitats, sustain life in extreme conditions, and perhaps eventually co-operate with other cells and create multicellular life. Multicellular life is virtually impossible without aerobic respiration.
