{{wiktionary, obligate
As an adjective, obligate means "by necessity" (antonym '' facultative'') and is used mainly in biology in phrases such as:
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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 e ...
, an organism that cannot survive without oxygen
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Obligate anaerobe
Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environm ...
, 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 (biology), morphology of fishes. In practice, ...
to describe those that respire entirely from the atmosphere
* Obligate biped,
Bipedalism
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...
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
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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 parasit ...
, 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