{{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 ...
, 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 environme ...
, 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 phys ...
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
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Obligate carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other so ...
, 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.
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Obligate intracellular parasite
Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host.
Types of parasites
There are two main types of intracellular parasites: Facultative and Obligate.
Facultative intracellular pa ...
, 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
Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
, a plant that requires sufficiently long or short nights before it initiates flowering, germination or similarly functions
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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 parasit ...
s, organisms that can only live together in a symbiosis