Multicellular organisms are those organisms consisting of more than one cell, and having differentiated cells that perform specialized functions. Most life that can be seen with the naked eye is multicellular, as are all animals (i.e. members of the kingdom Animalia) and plants (i.e. members of the kingdom Plantae). In biology and ecology, an organism (in Greek organon = instrument) is a living complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole. ... Cells in culture, stained for keratin (red) and DNA (green). ... Embryonic stem cells differentiate into cells in various body organs. ... Phyla Subregnum Parazoa Porifera (sponges) Subregnum Agnotozoa Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (dicyemids) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to flatworms, echinoderms, etc. ... Ernst Haeckels presentation of a three-kingdom system (Plantae, Protista, Animalia) in his 1866 Generelle Morphologie der Organismen. ... Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants Adiantum pedatum (a fern... Divisions Green algae land plants (embryophytes) non-vascular embryophytes Hepatophyta - liverworts Anthocerophyta - hornworts Bryophyta - mosses vascular plants (tracheophytes) seedless vascular plants Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongue ferns seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering...

A group of similarly differentiated cells performing a function in a multicellular organism is known as a tissue. Although some single-celled organisms, such as myxobacteria, have differentiated cells, the differentiation is less dramatic than that typically found in multicellular organisms. Biological tissue is any substance made up of cells that perform a similar function within an organism. ... E. coli magnified 10,000 times. ... Families & Genera Archangiaceae    Archangium Cystobacteraceae    Cystobacter    Melittangium    Stigmatella Myxoccaceae    Myxococcus    Angiococcus Polyangiaceae    Chondromyces    Nannocystis    Polyangium The myxobacteria are a group of bacteria that predominantly live in the soil. ...

A multicellular organism can work on a number of levels. For instance, a sponge works on a cellular level as the different cells are almost like many separate organisms co-operating together for a common goal. This is illustrated by the fact you can put a sponge in a blender and the cells of the sponge will aggregate again to form another sponge. They have no tissues, organs or organ systems which require a higher level of organisation. More advanced organisms such as jellyfish, coral and sea anemones work on a tissue level of organisation, as their cells can aggregate to form different tissues. For instance, a jellyfish has an outer epidermis and an inner gastrodermis, an example of different tissues to serve a different purpose. Classes Calcarea Hexactinellida Demospongiae The sponges or poriferans (from Greek poros pore and ferro to bear) are animals of the phylum Porifera. ... In biology and ecology, an organism (in Greek organon = instrument) is a living complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole. ... Look up Tissue on Wiktionary, the free dictionary The word tissue has several meanings: Aerial tissu is an acrobatic art form, and is one of the circus arts. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues that perform a specific function or group of functions. ... In biology, an organ is a group of tissues which perform some function. ... Orders Stauromedusae Coronatae Semaeostomeae Rhizostomae Jellyfish are marine invertebrates belonging to the Scyphozoan class, and in turn the phylum Cnidaria. ... Subclasses Alcyonaria Zoantharia See text for orders. ... Families Many, see text. ...

More advanced still are organisms with an organ level of development, whereby groups of tissues form organs such as a primitive brain in platyhelminthes (merely a grouping of ganglion cells). Finally, the most advanced organisms (like mammals) have organ systems whereby groups of organs act together for a common purpose with each organ focusing on a particular task. An example would be the digestive system. for instance the small intestine focuses on absorption of food into the blood stream, the stomach on crushing food and killing bacteria with its acidic environment, the pancreas for creating enzymes that catalyse the digestion of food, etc. Classes Monogenea Trematoda Cestoda Turbellaria The flatworms (Platyhelminthes, Greek platy: flat; helminth: worm) are a phylum of relatively simple soft-bodied invertebrate animals. ... In biology, an organ is a group of tissues which perform some function. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues that perform a specific function or group of functions. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... It has been suggested that Unstirred Water Layer be merged into this article or section. ... In anatomy, the stomach (in ancient Greek στόμαχος) is an organ in the gastrointestinal tract used to digest food. ... The pancreas is an organ in the digestive system that serves two major functions: exocrine - it produces pancreatic juice containing digestive enzymes. ... Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ...

Multicellular organisms must solve the problem of regenerating the whole from germ cells (i.e. sperm and egg cells), an issue that is studied in developmental biology. The overall spatial organization of differentiated cells is a topic of study in anatomy. A germ cell is a kind of cell that is part of the germline, and is involved in the reproduction of organisms. ... The signifier sperm can refer to: (mass noun, from Greek sperma = seed) a substance which consists of spermatozoa and which is a component of semen (mass noun) semen itself (informally, count noun with plural sperm or sperms) a single spermatozoon (= sperm cell) sperma ceti (Latin ceti, genitive of cetus = whale... A human ovum An ovum (from Latin, loosely, egg or egg cell) is a female sex cell or gamete. ... Developmental biology is the study of the process by which organisms grow and develop. ... Anatomical drawing of the human muscles from the Encyclopédie. ...

Multicellular organisms can suffer from cancer, when cells fail to regulate their growth within the normal program of development. All cells are microscopic because they cannot be viewed by the human eye. When normal cells are damaged beyond repair, they are eliminated by apoptosis. ...

See also

Cellular differentiation Embryonic stem cells differentiate into cells in various body organs. ...

Evolution of multicellularity The first organisms that existed were undoubtedly unicellular. ...