What does endosymbiotic mean?
Endosymbiotic is an adjective used in biology to describe relationships or structures involving endosymbiosis, in which one organism lives inside the cells or body of another for their mutual benefit. It is most famously applied to the endosymbiotic theory, the well-supported explanation that mitochondria and chloroplasts — the energy-producing and photosynthetic organelles of eukaryotic cells — descended from free-living bacteria that were engulfed by ancestral host cells over a billion years ago and never left. The word also appears in discussions of corals and their photosynthetic algae, nitrogen-fixing bacteria in plant roots, and other intimate internal partnerships. Strictly scientific in register, it rarely appears outside academic or educational contexts. Its enduring fascination lies in what it reveals about life itself: complex cells are not single lineages but living collaborations, stitched together from ancient mergers of once-independent organisms.
adjectiveRelating to or characterized by endosymbiosis, the condition in which one organism lives inside the cells or body of another in a mutually beneficial relationship. In biology, it most often describes organelles such as mitochondria and chloroplasts that are believed to have originated as free-living bacteria engulfed by ancestral eukaryotic cells.
- Of or relating to endosymbiosis; describing an organism, organelle, or relationship in which a partner lives inside another organism to mutual benefit.
"The endosymbiotic origin of mitochondria explains why these organelles carry their own DNA."
"Chloroplasts are widely accepted as the descendants of endosymbiotic cyanobacteria."
"The coral's survival depends on its endosymbiotic algae, which supply most of its energy through photosynthesis."
Every cell in your body is a descendant of an ancient merger: mitochondria were once free-living bacteria that moved in permanently billions of years ago.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of endosymbiotic
Endosymbiotic combines three Greek-derived elements: endo- meaning 'within', syn- meaning 'together', and biosis from bios, 'life'. It derives directly from endosymbiosis, a term coined in the late 19th century by German botanist Albert Bernhard Frank alongside related terms like symbiosis. The adjective became especially prominent after biologist Lynn Margulis championed the endosymbiotic theory of organelle origins in the 1960s. Cognate words sharing the root bios include biology, biotic, antibiotic, and symbiosis.
Related word forms
How endosymbiotic is actually used
A technical term used almost exclusively in scientific and academic writing, particularly in cell biology, microbiology, and evolutionary theory. It is nearly always used attributively (endosymbiotic theory, endosymbiotic relationship).
Easily confused with endosymbiotic
Symbiotic describes any close long-term association between organisms, while endosymbiotic specifically means one partner lives inside the other.