| multicellular organism ： ウィキペディア英語版|
Multicellular organisms are organisms that consist of more than one cell, in contrast to unicellular organisms.
All species of animals, land plants and filamentous fungi are multicellular, as are many algae while a few organisms are partially uni- and partially multicellular, like slime moulds and social amoebae such as the genus ''Dictyostelium''.
Multicellular organisms arise in various different ways, for example by cell division or by aggregation of many single cells. Colonial, or organisms are the result of many identical individuals joining together to form a colony, but pluricellular colonies have evolved independently in ''Volvox'' and some flagellated green algae that form coenobia.
In ''Volvox'' the cells comprising the colony arise by cell division and are of two different types, specialized for different functions. The approximately 2000 flagellate somatic cells forming the outer spherical shell of the colony are identical, and are similar in structure to their free-living unicellular relative ''Chlamydomonas'', but are incapable of cell division. Reproduction in ''Volvox'' is carried out specialized cells called "gonidia" that are larger than the somatic cells, lack flagella and cannot swim, but can divide to form new colonies.〔
The evolution of multicellularity from unicellular ancestors has been replicated in the laboratory, in evolution experiments using predation as the selective pressure.〔
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