The genesis of the cell structures present in eukaryotic cells is explained by the endosymbiotic theory. The idea is that larger bacteria may have housed energy-producing microorganisms, which then developed into mitochondria.
A symbiotic relationship between oxygenated prokaryotic organisms and host anaerobic eukaryotes antecedents is thought to be the origin of mitochondria, chloroplasts, and other cell structures in eukaryotic cells.