IT IS THEORISED THAT BOTH THE MITOCHONDRIA AND CHLOROPLASTS OF EUKARYOTIC CELLS WERE FORMED THROUGH ENDOSYMBIOSIS, EVIDENCE BEING THAT THEY ARE AROUND THE SAME SIZE AS BACTERIA, HAVE NUCLEOIDS/2 MEMBRANE LAYERS/70S RIBOSOMES, AND CAN ONLY BE PRODUCED THROUGH DIVISION OF PREEXISTING MITOCHONDRIA AND CHLOROPLASTS