What evidence strengthens the hypothesis that chloroplasts could have been photosynthetic prokaryotes and mitochondria could have been aerobic prokaryotes?
In fact that the chloroplasts are the organelles responsible for photosynthesis in plants leads to the supposition that before symbiosis they were autotrophic prokaryotes. For the reason that the mitochondria are the center of the aerobic cellular respiration, the powerhouse of the eukaryotic cell, it is supposed that they were once aerobic prokaryotes.
An endosymbiotic hypothesis to explain the emergence of aerobic and autotrophic eukaryotic beings is strengthened further by the following evidence chloroplasts as well as mitochondria have their own the DNA, similar to bacterial DNA; mitochondria and chloroplasts reproduce asexually by binary division, like bacteria do; both organelles have ribosomes and synthesize proteins.