What does the Endosymbiosis Theory suggest about mitochondria and chloroplasts?

The Endosymbiosis Theory posits that mitochondria and chloroplasts originated as independent prokaryotic organisms that were engulfed by a larger ancestral eukaryotic cell. This engulfment is believed to have led to a symbiotic relationship, where the engulfed prokaryotes provided the host cell with essential functions, such as ATP production in the case of mitochondria and photosynthesis in the case of chloroplasts.

Over time, these once free-living bacteria became integral parts of the eukaryotic cell, losing some of their independence and their original functions, while retaining their own DNA and machinery necessary for some of their processes. This theory is supported by several lines of evidence, such as the presence of circular DNA within mitochondria and chloroplasts, which is reminiscent of bacterial genomes, and the similarities in ribosomal structures.

The other choices do not accurately encapsulate the essence of the Endosymbiosis Theory. While it is true that these organelles are vital for eukaryotic cells, they were not created within the eukaryotic cell, nor did they evolve from ancient viruses. The theory emphasizes their origins as engulfed prokaryotes, making the correct understanding of their evolution critical