What are the arguments for the endosymbiotic theory?

There are several facts that could prove that mitochondria and plastids - eukaryotic organella descend from prokaryotic organisms. One of the arguments is that the metioned organella posses their own DNA to control the processes within them. It is similar in structure to the prokaryotic one - circular. Another argument is that they possess their own ribosomes, standard ones found in the cytoplasm and on the rough endoplasmic reticulum of the cells are size 80s, however those found in the organella are 70s, just like in prokaryotes. 

Another facts are that both the organella and prokaryotes are similar in size. During cell division, the mitochondria and plastids like prokaryotic cells, divide by binarry fission.