In biology, an organism is any contiguous living system (such as animal, fungus, micro-organism, or plant). In at least some form, all types of organisms are capable of responding to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole.

An organism may be either unicellular (a single cell) or, as in the case of humans, comprise many trillions of cells grouped into specialized tissues and organs. The term multicellular (many cells) describes any organism made up of more than one cell.

All organisms living on Earth are divided into the eukaryotes and prokaryotes based on the presence or absence of true nuclei in their cells. The prokaryotes represent two separate domains, the Bacteria and Archaea. Eukaryotic organisms are characterized by the presence of a membrane-bound cell nucleus, and contain additional membrane-bound compartmentalization called organelles (such as mitochondria in animals and plastids in plants, both generally considered to be derived from endosymbiotic bacteria). Fungi, animals and plants are examples of kingdoms of organisms that are eukaryotes.

In 2002 Thomas Cavalier-Smith proposed a clade, Neomura, which groups together the Archaea and Eukarya. Neomura is thought to have evolved from Bacteria, more specifically from Actinobacteria. See Branching order of bacterial phyla.

Read more about Organism:  Etymology, Semantics, Organizational Terminology, Chemistry, Structure, Life Span, Evolution, See Also

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Adaptive Behavior (ecology) - Nonheritable Adaptive Behavior
... This role is commonly known as an ecological niche, and is simply how an organism lives in an environment in relation to others ... Over successive generations, the organism must adapt to their surrounding conditions in order to develop their niche ... An organism’s niche will evolve as changes in the external environment occur ...
Schinderhannes Bartelsi - Significance
... The organism allows the classification of early arthropods to be resolved, to some degree ... The organism is classified basally to the true arthropods, but is closer to that group than Anomalocaris ... The organism's discovery was most significant because of the huge range extension of the anomalocaridids it caused the group was only previously known from lagerstatte of the lower-to-middle ...
... Antibiosis is a biological interaction between two or more organisms that is detrimental to at least one of them or an antagonistic association between an organism ... The general relationship between an antibiotic and an infectious organism is one of antibiosis ... This word refers to an association of two organisms in which one is harmed or killed by the other ...
Largest Organisms - Fungi
... This organism is estimated to be 2400 years old ... If this colony is considered a single organism, then it is the largest known organism in the world by area, and rivals the aspen grove "Pando" as the known organism with the highest ... It is not known, however, whether it is a single organism with all parts of the mycelium connected ...

Famous quotes containing the word organism:

    Think of the earth as a living organism that is being attacked by billions of bacteria whose numbers double every forty years. Either the host dies, or the virus dies, or both die.
    Gore Vidal (b. 1925)

    Apathy is one of the characteristic responses of any living organism when it is subjected to stimuli too intense or too complicated to cope with. The cure for apathy is comprehension.
    John Dos Passos (1896–1970)

    Language is a part of our organism and no less complicated than it.
    Ludwig Wittgenstein (1889–1951)