{{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 obligate aerobe is an organism that requires oxygen to grow. Through cellular respiration, these organisms use oxygen to metabolise substances, like sugars or fats, to obtain energy. In this type of respiration, oxygen serves as the terminal ...
, 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
Fish physiology is the scientific study of how the component parts of fish function together in the living fish. It can be contrasted with fish anatomy, which is the study of the form or morphology of fishes. In practice, fish anatomy and physi ...
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 parasi ...
, 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 symbiont
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 parasi ...
s, 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 para ...