Arabic Bulgarian Chinese Croatian Czech Danish Dutch English Estonian Finnish French German Greek Hebrew Hindi Hungarian Icelandic Indonesian Italian Japanese Korean Latvian Lithuanian Malagasy Norwegian Persian Polish Portuguese Romanian Russian Serbian Slovak Slovenian Spanish Swedish Thai Turkish Vietnamese
Arabic Bulgarian Chinese Croatian Czech Danish Dutch English Estonian Finnish French German Greek Hebrew Hindi Hungarian Icelandic Indonesian Italian Japanese Korean Latvian Lithuanian Malagasy Norwegian Persian Polish Portuguese Romanian Russian Serbian Slovak Slovenian Spanish Swedish Thai Turkish Vietnamese

definition - Multicellular organism

definition of Wikipedia

   Advertizing ▼


Multicellular organism

  In this image, a wild-type Caenorhabditis elegans is stained to highlight the nuclei of its cells.

Multicellular organisms are organisms that consist of more than one cell, in contrast to single-cell organisms. To form a multicellular organism, these cells need to identify and attach to the other cells.[1]

Only a dozen or so species of life that can be seen with the naked eye are unicellular. The rest of the nearly two million visible species are multicellular. In particular all but one or two species of the million and a half animals are multicelular, as well as many plants and fungi.


  Evolutionary history

Multicellularity has evolved independently dozens of times in the history of Earth, for example once for plants, once for animals, once for Brown algae, but perhaps several times for fungi, slime molds, and red algae.[2] Multicellularity exists in both prokaryotes and eukaryotes, and first appeared several billion years ago in cyanobacteria. In order to reproduce, true multicellular organisms must solve the problem of regenerating a whole organism from germ cells (i.e. sperm and egg cells), an issue that is studied in developmental biology. Therefore, the development of sexual reproduction in unicellular organisms during the Mesoproterozoic is thought to have precipitated the development and rise of multicellular life.[citation needed]

Multicellular organisms, especially long-living animals, also face the challenge of cancer, which occurs when cells fail to regulate their growth within the normal program of development. Changes in tissue morphology can be observed during this process.

  Hypotheses for origin

There are various mechanisms by which multicellularity could have evolved.

One hypothesis is that a group of function-specific cells aggregated into a slug-like mass called a grex, which moved as a multicellular unit. This is essentially what slime molds do. Another hypothesis is that a primitive cell underwent nucleus division, thereby becoming a syncytium. A membrane would then form around each nucleus (and the cellular space and organelles occupied in the space), thereby resulting in a group of connected cells in one organism (this mechanism is observable in Drosophila). A third hypothesis is that, as a unicellular organism divided, the daughter cells failed to separate, resulting in a conglomeration of identical cells in one organism, which could later develop specialized tissues. This is what plant and animal embryos do as well as colonial choanoflagellates.[3][4]

Because the first multicellular organisms were simple, soft organisms lacking bone, shell or other hard body parts, they are not well preserved in the fossil record.[5] One exception may be the demosponge, which may have left a chemical signature in ancient rocks. The earliest fossils of multicellular organisms include the contested Grypania spiralis and the fossils of the black shales of the Palaeoproterozoic Francevillian Group Fossil B Formation in Gabon.[6]

Until recently phylogenetic reconstruction has been through anatomical (particularly embryological) similarities. This is inexact, as living multicellular organisms such as animals and plants are more than 500 million years removed from their single-cell ancestors. Such a passage of time allows both divergent and convergent evolution time to mimic similarities and accumulate differences between groups of modern and extinct ancestral species. Modern phylogenetics uses sophisticated techniques such as alloenzymes, satellite DNA and other molecular markers to describe traits that are shared between distantly related lineages.

The evolution of multicellularity could have occurred in three ways, and of which the latter, the colonial theory, is most credited by the scientific community:

  The Symbiotic Theory

This theory suggests that the first multicellular organisms occurred from symbiosis (cooperation) of different species of single-cell organisms, each with different roles. Over time these organisms would become so dependent on each other they would not be able to survive independently, eventually leading to the incorporation into one multicellular organism of their genome.[7] Each respective organism would become a separate lineage of differentiated cells within the newly created species.

This kind of severely co-dependent symbiosis can be seen frequently, such as in the relationship between clown fish and Riterri sea anemones. In these cases, it is extremely doubtful whether either species would survive very long if the other became extinct. However, the problem with this theory is that it is still not known how each organism's DNA could be incorporated into one single genome to constitute them as a single species. Although such symbiosis is theorized to have occurred (e.g., mitochondria and chloroplasts in animal and plant cells – endosymbiosis), it has happened only extremely rarely and, even then, the genomes of the endosymbionts have retained an element of distinction, separately replicating their DNA during mitosis of the host species. For instance, the two or three symbiotic organisms forming the composite lichen, while dependent on each other for survival, have to separately reproduce and then re-form to create one individual organism once more.

  The Cellularization (Syncytial) Theory

This theory states that a single unicellular organism could have developed internal membrane partitions around each of its nuclei[8] Many protists such as the ciliates or slime molds can have several nuclei, lending support to this hypothesis. However, simple presence of multiple nuclei is not enough to support the theory. Multiple nuclei of ciliates are dissimilar and have clear differentiated functions: The macronucleus serves the organism's needs, while the micronucleus is used for sexual-like reproduction with exchange of genetic material. Slime molds syncitia form from individual amoeboid cells, like syncitial tissues of some multicellular organisms, not the other way round. To be deemed valid, this theory needs a demonstrable example and mechanism of generation of a multicellular organism from a pre-existing syncytium.

  The Colonial Theory

The third explanation of multicellularisation is the Colonial Theory proposed by Haeckel in 1874. This theory claims that the symbiosis of many organisms of the same species (unlike the symbiotic theory, which suggests the symbiosis of different species) led to a multicellular organism. At least some, it is presumed land-evolved, multicellularity occurs by cells separating and then rejoining (e.g., cellular slime molds) whereas for the majority of multicellular types (those that evolved within aquatic environments), multicellularity occurs as a consequence of cells failing to separate following division.[9] The mechanism of this latter colony formation can be as simple as incomplete cytokinesis, though multicellularity is also typically considered to involve cellular differentiation.[10]

The advantage of the Colonial Theory hypothesis is that it has been seen to occur independently in 16 different protoctistan phyla. For instance, during food shortages the amoeba Dictyostelium groups together in a colony that moves as one to a new location. Some of these amoeba then slightly differentiate from each other. Other examples of colonial organisation in protista are Volvocaceae, such as Eudorina and Volvox, the latter of which consists of up to 500–50,000 cells (depending on the species), only a fraction of which reproduce.[11] For example, in one species 25–35 cells reproduce, 8 asexually and around 15–25 sexually. However, it can often be hard to separate colonial protists from true multicellular organisms, as the two concepts are not distinct; colonial protists have been dubbed "pluricellular" rather than "multicellular".[12] This problem plagues most hypotheses of how multicellularisation could have occurred.



Multicellularity allows an organism to exceed the size limits normally imposed by diffusion, conferring the competitive advantages of an increase in size. It also permits increasing complexity by allowing the differentiation of numerous cellular lineages within an organism.

  See also


  1. ^ Becker et al, Wayne M. (2009). The world of the cell. Pearson Benjamin Cummings. p. 480. ISBN 978-0-321-55418-5. 
  2. ^ Bonner, John Tyler (1998). "The Origins of Multicellularity" (PDF, 0.2 MB). Integrative Biology: Issues, News, and Reviews 1 (1): 27–36. DOI:10.1002/(SICI)1520-6602(1998)1:1<27::AID-INBI4>3.0.CO;2–6. ISSN 1093-4391. http://courses.cit.cornell.edu/biog1101/outlines/Bonner%20-Origin%20of%20Multicellularity.pdf. 
  3. ^ Multicellular development in a choanoflagellate; Stephen R. Fairclough, Mark J. Dayel and Nicole King
  4. ^ In a Single-Cell Predator, Clues to the Animal Kingdom’s Birth
  5. ^ A H Knoll, 2003. Life on a Young Planet. Princeton University Press. ISBN 0-691-00978-3 (hardcover), ISBN 0-691-12029-3 (paperback). An excellent book on the early history of life, very accessible to the non-specialist; includes extensive discussions of early signatures, fossilization, and organization of life.
  6. ^ El Albani, Abderrazak; A, Bengtson S, Canfield DE, Bekker A, Macchiarelli R, Mazurier A, Hammarlund EU, Boulvais P, Dupuy JJ, Fontaine C, Fürsich FT, Gauthier-Lafaye F, Janvier P, Javaux E, Ossa FO, Pierson-Wickmann AC, Riboulleau A, Sardini P, Vachard D, Whitehouse M, Meunier A. (1 July 2010). "Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago". Nature 466 (7302): 100–104. DOI:10.1038/nature09166. ISSN 0028-0836. PMID 20596019. 
  7. ^ Margulis, Lynn (1998). Symbiotic Planet: A New Look at Evolution. New York: Basic Books. p. 160. ISBN 978-0-465-07272-9. http://www.questia.com/PM.qst?a=o&d=96971657. 
  8. ^ Hickman CP, Hickman FM (8 July 1974). Integrated Principles of Zoology (5th ed.). Mosby. p. 112. ISBN 978-0-8016-2184-0. 
  9. ^ Wolpert, L.; Szathmáry, E. (2002). "Multicellularity: Evolution and the egg". Nature 420 (6917): 745. DOI:10.1038/420745a. PMID 12490925.  edit
  10. ^ Kirk, D. L. (2005). "A twelve-step program for evolving multicellularity and a division of labor". BioEssays 27 (3): 299–310. DOI:10.1002/bies.20197. PMID 15714559.  edit
  11. ^ AlgaeBase. Volvox Linnaeus, 1758: 820.
  12. ^ Strickberger's evolution: the integration of genes, organisms and populations By Brian Keith Hall, Benedikt Hallgrímsson, Monroe W. Strickberger

  External links



All translations of Multicellular organism

sensagent's content

  • definitions
  • synonyms
  • antonyms
  • encyclopedia

Dictionary and translator for handheld

⇨ New : sensagent is now available on your handheld

   Advertising ▼

sensagent's office

Shortkey or widget. Free.

Windows Shortkey: sensagent. Free.

Vista Widget : sensagent. Free.

Webmaster Solution


A windows (pop-into) of information (full-content of Sensagent) triggered by double-clicking any word on your webpage. Give contextual explanation and translation from your sites !

Try here  or   get the code


With a SensagentBox, visitors to your site can access reliable information on over 5 million pages provided by Sensagent.com. Choose the design that fits your site.

Business solution

Improve your site content

Add new content to your site from Sensagent by XML.

Crawl products or adds

Get XML access to reach the best products.

Index images and define metadata

Get XML access to fix the meaning of your metadata.

Please, email us to describe your idea.


The English word games are:
○   Anagrams
○   Wildcard, crossword
○   Lettris
○   Boggle.


Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.


Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !

English dictionary
Main references

Most English definitions are provided by WordNet .
English thesaurus is mainly derived from The Integral Dictionary (TID).
English Encyclopedia is licensed by Wikipedia (GNU).


The wordgames anagrams, crossword, Lettris and Boggle are provided by Memodata.
The web service Alexandria is granted from Memodata for the Ebay search.
The SensagentBox are offered by sensAgent.


Change the target language to find translations.
Tips: browse the semantic fields (see From ideas to words) in two languages to learn more.

last searches on the dictionary :

3178 online visitors

computed in 0.031s

   Advertising ▼

I would like to report:
section :
a spelling or a grammatical mistake
an offensive content(racist, pornographic, injurious, etc.)
a copyright violation
an error
a missing statement
please precise:



Company informations

My account



   Advertising ▼