{{wiktionary, obligate
As an adjective, obligate means "by necessity" (antonym ''
facultative
{{wiktionary, facultative
Facultative means "optional" or "discretionary" (antonym '' obligate''), used mainly in biology in phrases such as:
* Facultative (FAC), facultative wetland (FACW), or facultative upland (FACU): wetland indicator statuses ...
'') and is used mainly in biology in phrases such as:
* Obligate aerobe, an organism that cannot survive without oxygen
* Obligate anaerobe, an organism that cannot survive in the presence of oxygen
* Obligate air-breather, a term used in fish physiology to describe those that respire entirely from the atmosphere
* Obligate biped, Bipedalism designed to walk on two legs
* Obligate carnivore, an organism dependent for survival on a diet of animal flesh.
* Obligate hibernation, a state of inactivity in which some organisms survive conditions of insufficiently available resources.
* Obligate intracellular parasite, a parasitic microorganism that cannot reproduce without entering a suitable host cell
*
Obligate parasite
An obligate parasite or holoparasite is a parasitic organism that cannot complete its life-cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce. This is opposed to a facultative parasite, ...
, a parasite that cannot reproduce without exploiting a suitable host
* Obligate photoperiodic plant, a plant that requires sufficiently long or short nights before it initiates flowering, germination or similarly functions
* Obligate symbionts, organisms that can only live together in a
symbiosis
Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...