Endosymbiotique

Endosymbiotique refers to a specific type of symbiotic relationship where one organism lives inside another. This is distinct from ectosymbiosis, where the symbiont lives on the surface of the host. In an endosymbiotic relationship, the smaller organism, known as the endosymbiont, resides within the tissues or cells of the larger organism, the host.

This type of interaction can be mutualistic, commensalistic, or parasitic, depending on the benefit or harm to each organism. In many cases of endosymbiosis, both the host and the endosymbiont benefit. For example, some insects rely on endosymbiotic bacteria to digest food that they cannot break down on their own. The bacteria receive nutrients and a protected environment, while the insect gains essential nutrients.

A classic and highly significant example of endosymbiosis is the theory explaining the origin of mitochondria and chloroplasts in eukaryotic cells. According to endosymbiotic theory, these organelles were once free-living prokaryotic organisms that were engulfed by an ancestral host cell. Instead of being digested, they formed a stable relationship, eventually losing their independence and becoming integral parts of the eukaryotic cell. Mitochondria are believed to have originated from aerobic bacteria, and chloroplasts from photosynthetic cyanobacteria. This event was crucial for the evolution of complex life on Earth.