Over the past century, several scientists around the world have made the following observations: new mitochondria and plastids can only be generated by old mitochondria and plastids through a process similar to binary fission. both mitochondria and plastids contain dna that is similar in shape and size to that of bacteria. mitochondria and plastids are surrounded by two or more membranes whose composition is similar to a prokaryotic cell membrane. mitochondria and plastids are about the size as bacteria. these observations led scientists to conclude that