Valonia ventricosa, a species of alga with a diameter that ranges typically from 1 to 4 centimetres (0.4 to 1.6 in) is among the largest unicellular species
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea. Many eukaryotes are multicellular, but some are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.8–4.8 billion years ago.[1][2]
Although some prokaryotes live in colonies, they are not specialised cells with differing functions. These organisms live together, and each cell must carry out all life processes to survive. In contrast, even the simplest multicellular organisms have cells that depend on each other to survive.
Most multicellular organisms have a unicellular life-cycle stage. Gametes, for example, are reproductive unicells for multicellular organisms.[3] Additionally, multicellularity appears to have evolved independently many times in the history of life.
Some organisms are partially unicellular, like Dictyostelium discoideum. Additionally, unicellular organisms can be multinucleate, like Caulerpa, Plasmodium, and Myxogastria.
^An Introduction to Cells, ThinkQuest, retrieved 2013-05-30
^Pohorille, Andrew; Deamer, David (2009-06-23). "Self-assembly and function of primitive cell membranes". Research in Microbiology. 160 (7): 449–456. doi:10.1016/j.resmic.2009.06.004. PMID 19580865.
^Coates, Juliet C.; Umm-E-Aiman; Charrier, Bénédicte (2015-01-01). "Understanding "green" multicellularity: do seaweeds hold the key?". Frontiers in Plant Science. 5: 737. doi:10.3389/fpls.2014.00737. PMC 4299406. PMID 25653653.
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A unicellularorganism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists...
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cholera, diphtheria, and anthrax. Because microorganisms include most unicellularorganisms from all three domains of life they can be extremely diverse. Two...
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(amebae) /əˈmiːbi/), often called an amoeboid, is a type of cell or unicellularorganism with the ability to alter its shape, primarily by extending and retracting...
Eukarya or Eukaryota, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, and many unicellularorganisms are eukaryotes. They...
prokaryote (/proʊˈkærioʊt, -ət/, also spelled procaryote) is a single-cell organism whose cell lacks a nucleus and other membrane-bound organelles. The word...
some of which can reach a diameter over 30 cm (12 in). These organisms are unicellular, but they are multinucleate. Some euglenophytes, such as certain...
archaea and bacteria (unicellularorganisms) that produce biomass from the oxidation of inorganic chemical compounds, these organisms are called chemoautotrophs...
derive a population of cells from a single cell. In the case of unicellularorganisms such as bacteria and yeast, this process is remarkably simple and...
contraction of a unicellularorganism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often...
largest known unicellularorganisms. Valonia ventricosa has a coenocytic structure with multiple nuclei and chloroplasts. This organism possesses a large...
whether fundamentally novel living organizations can exist. Simulate a unicellularorganism over its entire life cycle. Explain how rules and symbols are generated...
cell(s) and the external environment is required. Small, particularly unicellularorganisms, such as bacteria and protozoa, have a high surface-area to volume...
contraction of a unicellularorganism away from external chemicals, the complex reactions involving all the senses of multicellular organisms, or the motion...
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amniotic organisms. Teleost fish and mice are organisms most often used to study the connection between serotonin and vertebrate behavior. Both organisms show...
subsequent evolution of multicellular organisms. The Earth formed around 4.6 billion years ago, with unicellular life emerging somewhat later after the...
to exclude multicellular organisms from the traditional definition of a protist, restricting protists to unicellularorganisms. This more constrained definition...
that discoveries made in the model organism will provide insight into the workings of other organisms. Model organisms are widely used to research human...
umbrella of branches that may fuse into a cap. Unlike other giant unicellularorganisms, which are multinucleate, members of this genus possess a single...
through the urethra, which is part of the excretory system. In unicellularorganisms, waste products are discharged directly through the surface of the...
his own invention Monad (biology), a historical term for a simple unicellularorganism Monad (category theory), a construction in category theory Monad...
The unicellularorganism's cytoplasm has distinct separations of an ectoplasm (outer) and endoplasm (inner). As a mitochondriate, aerobic organism it has...
these in a normal human platelet. They are found in animals and in unicellularorganisms including Apicomplexa protozoans. They are also found in Entamoeba...
were constructed. Von Siebold redefined Protozoa to include only such unicellular forms, to the exclusion of all metazoa (animals). At the same time, he...
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