{{wiktionary, obligate
As an adjective, obligate means "by necessity" (antonym ''
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 ...
'') 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
Obligate anaerobes are microorganisms killed by normal Atmosphere of Earth, 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 vi ...
, 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 animal moves by means of its two rear (or lower) Limb (anatomy), limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from ...
designed to walk on two legs
*
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 nutrition and energy requirements are met by consumption of animal tissues (mainly mus ...
, an organism dependent for survival on a diet of animal flesh.
* Obligate chimerism, a kind of organism with two distinct sets of DNA, always
* Obligate hibernation, a state of inactivity in which some organisms survive conditions of insufficiently available resources.
*
Obligate intracellular parasite
Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. They are also called intracellular pathogens.
Types
There are two main types of intracellular parasites: Facultative and Obligate ...
, 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
Photoperiod is the change of day length around the seasons. The rotation of the earth around its axis produces 24 hour changes in light (day) and dark (night) cycles on earth. The length of the light and dark in each phase varies across the season ...
, a plant that requires sufficiently long or short nights before it initiates flowering, germination or similarly functions
*
Obligate symbiont
Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term
symbiosis
Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biological interaction, between two organisms of different species. The two organisms, termed symbionts, can fo ...