The same way our organs have a specialized role to play in the context of the body, each an obligate (necessary) agent taking on a vital role in the community as a whole, this principle of finding one's purpose o to speak in the context of the community is also true on multiple scales. This includes bodies, but also includes organs, cells, organelles (tiny organs in cells) and molecules within cells as we focus inward. If we look outward on broader scales we see this same principal at work in the relationship between species, organisms and entire ecosystems. Cilia, which are tiny hairlike fibers that project out from certain cell types, play vital filtering and expulsion roles when necessary. Cilia in our lungs, for instance, wave rhythmically to keep the airways clear of mucus and dirt.
In the article below we see cilia play a transportation role between an organism and mutualistic organisms that provide vital functions in the organism as well as this filtering and expulsion role. In case of the bobtail squid, a bioluminescent (light emitting) microorganism called Vibrio Fischeri is guided in by cilia in the squid to be cultivated in the correct quantities to act as a cloaking device to hide the squid from predators when it is out and about at night looking for food.
When we consider the complex web of coordinated relationship dynamics going on in biological systems, we often see a blurred line between one organism and the next. The bonds that tie together sustained relationships are built on their ability to serve a role in adaptation, and this often entails negotiating the trade-offs that occur to find the sweet spot of cooperation that enables a creature to nourish itself and continue through time as well as negotiate the hazards of its environment.
From the article: "...Imagine a club scene—a bouncer at a velvet rope selects which individuals get into the club. This... is what cilia do in an organism. ... Motile cilia create fluid-mechanical microhabitats for the active recruitment of the host microbiome... explain[s] the active role that cilia have in ensuring certain bacteria are kept out of an organism while other symbiotic bacteria are selectively permitted to enter."
Read more at: https://phys.org/news/2017-09-cilia-bouncer-bacteria.html#jCp