What does the Endosymbiotic Theory propose about mitochondria?

The Endosymbiotic Theory posits that mitochondria originated from free-living prokaryotes, specifically aerobic bacteria, that were engulfed by a larger ancestral eukaryotic cell. This process is believed to have provided a mutualistic relationship: the engulfed bacteria could perform aerobic respiration, producing ATP, which benefitted the host cell, while the bacteria gained a stable environment and access to nutrients.

As a result of this internalization, the engulfed prokaryotes eventually became an integral part of the eukaryotic cell and transformed into mitochondria. Over time, these once-independent organisms lost some of their original functions and genetic material, relying instead on the host cell for certain biological processes and resources. This theory is supported by the similarities between mitochondria and certain prokaryotes, such as having their own circular DNA, double membranes, and similarities in ribosomal structure.

The other options do not accurately capture this historical relationship. Specifically, considering that mitochondria are not viruses and that they reproduce through binary fission like bacteria rather than being generated from larger prokaryotic cells, helps differentiate the correct answer from the others.