Mitochondria and chloroplasts exhibit several characteristics that indicate they may have once been independent prokaryotic cells before being engulfed by eukaryotic cells. These supportive features include:
- Size: Both mitochondria and chloroplasts are relatively small compared to eukaryotic cells, resembling the size of prokaryotic cells. This similarity in size suggests that they may have originated from smaller, simpler organisms.
- Presence of Their Own DNA: Mitochondria and chloroplasts contain their own circular DNA, similar to bacterial DNA. This DNA is distinct from the nuclear DNA found in eukaryotic cells, indicating that these organelles have a separate genetic identity, reminiscent of prokaryotic organisms.
- Self Replication by Binary Fission: Both organelles replicate independently of the eukaryotic cell cycle through a process similar to binary fission, which is how prokaryotic cells reproduce. This capability to reproduce on their own supports the idea that they may have originated as independent cells.
Given these characteristics, the correct answer would be d) all. Each feature contributes to the evidence that mitochondria and chloroplasts were once free-living prokaryotes that played a crucial role in the evolution of eukaryotic cells through the process of endosymbiosis.