The endosymbiotic theory hypothesizes that mitochondria and chloroplasts were formed when <u>prokaryotic </u>cells were engulfed by larger cells that were precursors to <u>eukaryotic </u>cells.
prokaryotic ; eukaryotic
They are the “last trophic level” in some hierarchies because they feed on everything (National Geographic). However, according to the strict trophic level definition they would be primary consumers