What does the Endosymbiosis Theory explain regarding the origin of certain organelles?

The Endosymbiosis Theory posits that certain organelles, particularly mitochondria and chloroplasts, originated from free-living prokaryotic cells that were engulfed by an ancestral eukaryotic cell. This theory is supported by several lines of evidence, including the similarities between these organelles and prokaryotes in terms of size, shape, and genetic material.

Mitochondria and chloroplasts possess their own circular DNA, similar to bacterial DNA, as well as ribosomes that resemble bacterial ribosomes more than those found in eukaryotic cells. Furthermore, these organelles replicate independently of the cell cycle through a process akin to binary fission, which is characteristic of prokaryotic organisms. Over time, a symbiotic relationship developed where these engulfed prokaryotes provided essential functions—like ATP production in the case of mitochondria or photosynthesis in chloroplasts—in exchange for protection and a stable environment within the host cell.

This theory significantly alters our understanding of cellular evolution by suggesting that complex eukaryotic cells arose through a collaboration between different forms of life rather than strictly through the gradual modification of existing eukaryotic structures. The other options do not accurately reflect the