In biology, a host is an organism that harbors a virus or parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna. Examples of such interactions include a cell being host to a virus, a legume plant hosting helpful nitrogen-fixing bacteria, and animals as hosts to parasitic worms, e.g. nematodes.

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