Answer:
the observations that chloroplasts and mitochondria resemble bacteria
Step-by-step explanation:
The Endosymbiotic Theory is a theory that enables us to understand the origin of eukaryotic cells. The Endosymbiotic Theory posits that the mitochondria and chloroplast, which are organelles found in the eukaryotic cells, were once prokaryotic microbes that were first ingested by amoeba-like organisms and subsequently evolved by developing a symbiotic relationship with them. Some of the most important lines of evidence that supports this theory are: 1-chloroplasts and mitochondria resemble prokaryotic cells, i.e., they have a similar size, replicate by binary fission and there are unicellular eukaryotic protists that have filamentous temperature-sensitive proteins at their division plane (similarly to bacteria), and 2- chloroplasts and mitochondria are organelles with their own DNA and their own ribosomes (which are similar to those of bacteria).