Word
Endosymbiosis
A relationship in which one organism lives inside another; some such relationships gave rise to cell organelles
Examples
Endosymbiosis helps explain the bacterial ancestry of mitochondria.
An organism living inside a host may participate in endosymbiosis without becoming a permanent organelle.
Origin
The word combines endo, meaning within, with symbiosis, living together. The general relationship is broader than the evolutionary theory of organelle origins. Living inside a host and becoming an inherited part of its cell are related possibilities, not identical events.
How it connects
The word distinguishes living within another organism from living alongside it.
This word appeared in The partnership inside a cell, the Involves connection for September 17, 2026, which asked: Can one organism become part of another?
Check yourself
Which example most directly describes endosymbiosis?
One organism lives within the cells of another. Exactly. The defining relationship is residence within a host, not similarity or proximity.
What the sources establish
Endosymbiosis describes an internal association; organelle evolution involves a more specific inherited integration.
Sources
On the Origin of Mitosing Cells (Lynn Sagan, Journal of Theoretical Biology), 1967 article record and abstract, organelle-origin proposals
Mitochondrial Evolution (Michael W. Gray, Cold Spring Harbor Perspectives in Biology), Introduction and genomic evidence for mitochondrial ancestry