Final answer:
The organelle evolved via endosymbiosis, most likely from aerobic bacteria for mitochondria or from photosynthetic cyanobacteria for chloroplasts. Mitochondria likely evolved earlier than chloroplasts because all eukaryotes have them, indicating an earlier endosymbiotic event. This is supported by the DNA and replication similarities between mitochondria, chloroplasts, and prokaryotes.
Step-by-step explanation:
The organelle indicated by the arrow is most probably a mitochondrion or a chloroplast, which, according to the Endosymbiotic Theory, evolved from a free-living bacterium. Mitochondria are believed to have evolved from aerobic bacteria that were engulfed by a primitive eukaryotic cell, while chloroplasts likely originated from photosynthetic cyanobacteria that were similarly engulfed. The evidence that mitochondria were incorporated into the ancestral eukaryotic cell before chloroplasts includes the fact that all eukaryotes have mitochondria or mitochondria-like organelles, whereas only a subset has chloroplasts. This suggests that the endosymbiotic event leading to mitochondria occurred earlier in the evolutionary history of eukaryotes.
Supporting Evidence for the Endosymbiotic Theory
- Mitochondria and chloroplasts have their own DNA, similar to that of prokaryotes.
- They also replicate independently of the cell's nucleus, much like bacteria.
- The double membrane structure of these organelles is consistent with the engulfing mechanism of endosymbiosis.