The evolution of eukaryotic cells most likely involved: endosymbiosis of an oxygen-using bacterium in a larger host cell−the endosymbiont evolved into mitochondria. evolution of an endomembrane system and subsequent evolution of mitochondria from a portion of the golgi. endosymbiosis of an oxygen-using photosynthetic bacterium in a larger host cell−the endosymbiont evolved into mitochondria. endosymbiosis of an oxygen-using scavenger bacterium in a larger host cell−the endosymbiont evolved into lysosomes.