Facultative vs. Obligate

By Jaxson

  • 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 for plants

    Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production. It can survive in either environment

    Facultative biped, an animal that is capable of walking or running on two legs as well as walking or running on four limbs or more, as appropriate

    Facultative carnivore, a carnivore that does not depend solely on animal flesh for food but also can subsist on non-animal food. Compare this with the term omnivore

    Facultative heterochromatin, tightly packed but non-repetitive DNA in the form of Heterochromatin, but which can lose its condensed structure and become transcriptionally active

    Facultative lagoon, a type of stabilization pond used in biological treatment of industrial and domestic wastewater

    Facultative parasite, a parasite that can complete its life cycle without depending on a host

    Facultative photoperiodic plant, a plant that will eventually flower regardless of night length but is more likely to flower under appropriate light conditions.

    Facultative saprophyte, lives on dying, rather than dead, plant material

  • Obligate

    As an adjective, obligate means “by necessity” (antonym facultative) 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, 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

  • Facultative (adjective)

    Of or relating to faculty, especially to mental faculty

  • Facultative (adjective)

    Not obligate; optional, discretionary or elective

  • Facultative (adjective)

    That grants permission or power to do something

  • Facultative (adjective)

    Able to perform a particular life function, or to live generally, in more than one way

  • Facultative (adjective)

    At which a given function is positive.

  • Obligate (verb)

    To bind, compel, constrain, or oblige by a social, legal, or moral tie.

  • Obligate (verb)

    To cause to be grateful or indebted; to oblige.

  • Obligate (verb)

    To commit (money, for example) in order to fulfill an obligation.

  • Obligate (adjective)

    Able to exist or survive only in a particular environment or by assuming a particular role.

    “an obligate parasite”

    “an obligate anaerobe”

    “ux|en|an obligate seeder (a plant able to reproduce only from seed.)”

  • Obligate (adjective)

    Absolutely indispensable; essential.

  • Facultative (adjective)

    occurring optionally in response to circumstances rather than by nature

    “facultative adjustment in relation to competitive abilities”

  • Facultative (adjective)

    capable of but not restricted to a particular function or mode of life

    “a facultative parasite”

Oxford Dictionary

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