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Multicellular organism

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	Topics Multicellular organism Topic Home Multicellular organisms are organismOrganism In biology and ecology, an organism is a living complex adaptive system of organs that influence each other in such a way t... s consisting of more than one cellCell (biology) Summary The cell is the structural and functional unit of all living organisms, and is sometimes called the "building block of life.... , and having differentiated cells that perform specialized functions. Most life that can be seen with the naked eye is multicellular, as are all members of the kingdomKingdom (biology) In biology, a kingdom or regnum is the top-level, or nearly the top-level, taxon of organisms in scientific classifica... s PlantEmbryophyte Overview The embryophytes are the most familiar group of plants.... ae and AnimalAnimal Animals are a major group of organisms, classified as the kingdom Animalia or Metazoa.... ia (except for specialized organisms such as MyxozoaMyxozoa The Myxozoa are a group of microscopic, single-celled, parasitic animals.... ns in the case of the latter). Organizational levels Multicellular organisms such as spongesSea sponge The sponges or poriferans are animals of the phylum Porifera.... consist of multiple specialized cellular types cooperating together for a common goal. These cell types include ChoanocyteChoanocyte Choanocytes are cells that line the interior body walls of sponges that contain a central flagellum surrounded by a collar o... s, digestive cells; Sclerocytes, support-structure-secreting cells; PorocytesPorocytes Porocytes are tubular cells which make up the pores of a sponge.... , tubular pore cells; and PinacocytesPinacocytes Pinacocytes are epidermal cells which make up the pinacoderm in sponges. ... , epidermal cells. Though the different cell types create an organized, macroscopic multicellular structure—the visible sponge—they are not organized into true interconnected tissueBiological tissue Biological tissue is a collection of interconnected cells that perform a similar function within an organism.... s. This is illustrated by the fact that a sponge broken up using cheese cloth and a very specific ion cocktail (the classical blender experiment does NOT work) will reaggregate from the surviving cells. If individually separated, however, the particular cell types cannot survive alone. Simpler colonialColony (biology) In biology, a colony refers to several individual organisms of the same species living closely together, usually for mutual ... organisms, such as VolvoxVolvox *Volvox* is one of the best-known genera of green algae and is the most developed in a series of genera that form spheric... , differ in that their individual cells are free-living and can survive on their own if separated from the colony. Tissues More complex organisms such as jellyfishJellyfish Jellyfish are marine invertebrates belonging to the Scyphozoan class, and in turn the phylum Cnidaria.... , coralCoral Overview Corals are marine animals of the , which include sea anemones .... , and sea anemones possess a tissue level of organization, in which differentiated, interconnected cells perform specialized functions as a group. For instance, jellyfish tissues include an epidermisSquamous epithelium The squamous epithelium is epithelium consisting of one or more cell layers, the most superficial of which is composed of fl... and nerve netFacts About Nerve net A nerve net is a type of simple nervous system that is found in members of the phylum cnidaria.... that perform protective and sensory functions, along with an inner gastrodermisFacts About Gastrodermis The gastrodermis is the inner layer of cells that lines a gastrovascular cavity.... that performs digestive functions. The overall spatial organization of differentiated cells is a topic of study in anatomyAnatomy Anatomy , is the branch of biology that deals with the structure and organization of living things.... . Organs and organ systems Even more complex organisms, while also possessing differentiated cells and tissues, possess an organOrgan (anatomy) Overview In biology, an organ is a group of tissues that perform a specific function or group of functions.... level of development, wherein multiple tissues group to form organs with a specific function or functions. Organs can be as primitive as the brain of a flatwormFlatworm The flatworms are a phylum of relatively simple soft-bodied invertebrate animals.... (merely a grouping of ganglion cells), as large as the stem of a sequoiaSequoia Sequoia is a genus in the cypress family Cupressaceae, containing the single living species Sequoia sempervirens... (up to 90 meters (300 feet) in height), or as complex and multifunctional as a vertebrateVertebrate Summary Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns.... liverLiver The liver is an organ in vertebrates, including humans.... . The most complex organisms (such as mammals, trees, and flowers) have organ systems wherein groups of organs act together to perform complex related functions, with each organ focusing on a subset of the task. An example would be a vertebrate digestive system, in which the mouthMouth The mouth, also known as the buccal cavity or the oral cavity, is the opening through which an animal takes in f... and esophagusEsophagus The esophagus, or gullet is the muscular tube in vertebrates through which ingested food passes from the mouth area to... ingest food, the stomachStomach In anatomy, the stomach is an organ in the gastrointestinal tract used to digest food.... crushes and liquifies it, the pancreasPancreas The pancreas is an organ in the digestive system that serves two major functions:... and gall bladder synthesize and release digestive enzymes, and the intestineIntestine In anatomy, the intestine is the portion of the alimentary canal extending from the stomach to the anus and, in humans and o... s absorb nutrients into the bloodBlood Blood is a highly specialised circulating tissue consisting of several types of cell suspended in a fluid medium known as pl... . Evolutionary history The oldest known taxonomically resolved multicellular organism is a red algae, Bangiomorpha pubescens, found fossilized in 1.2 billion year old rock from the EctasianEctasian The Ectasian is the second geologic period in the Mesoproterozoic era and lasted from 1400 Ma ago to 1200 Ma.... period of the MesoproterozoicMesoproterozoic The Mesoproterozoic Era is a geologic era that occurred between 1600 Ma and 1000 Ma.... era. In order to reproduce, true multicellular organisms must solve the problem of regenerating a whole organism from germ cellGerm cell A germ cell is a kind of cell that is part of the germline, and is involved in the reproduction of organisms.... s (i.e. spermSperm The term sperm is derived from the Greek word sperma and refers to the male reproductive cells.... and eggOvum An ovum is a haploid female reproductive cell or gamete.... cells), an issue that is studied in developmental biologyDevelopmental biology Developmental biology is the study of the process by which organisms grow and develop.... . Therefore, the development of sexual reproductionSexual reproduction Sexual reproduction is a type of reproduction that results in increasing genetic diversity of the offspring.... in unicellular organisms during the Ectasian period is thought to have precipitated the development and rise of multicellular life. Multicellular organisms also face the challenge of cancerCancer Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these cells to... , which occurs when cells fail to regulate their growth within the normal program of development. Hypotheses for origin There are various mechanisms which are disputed as being the first responsible for the emergence of multicellularity, but it is difficult to say which is correct. This is because all the suggested mechanisms are viable, but establishing which was responsible for the first multicellular life requires mostly speculation. One hypothesis is that a group of function-specific cells aggregated into a slug-like mass called a grexGrex (biology) A grex is a multicellular aggregate of amoeba of the groups Acrasiomycota or Dictyosteliida that can be formed when the amo... , which moved as a multicellular unit. Another hypothesis is that a primitive cell underwent nucleus division, thereby becoming a syncytiumSyncytium In biology, a syncytium is a large region of cytoplasm that contains many nuclei.... . A membrane would then form around each neucleus (and the cellular space and organelles occupied in the space), thereby resulting in a group of connected and specialised cells in one organism (this mechanism is observable in DrosophilaDrosophila *Drosophila* is a genus of small flies whose members are often called small fruit flies, or more appropriately vinegar fli... ). A third theory is that, as a unicellular organism divided, the daughter cells failed to separate, thereby resulting in a conglomeration of identical cells in one organism which could each then specialize. See also Cellular differentiationCellular differentiation MultipotentGerm layer ... EukaryoteEukaryote Overview \|-\| style = "background: pink; padding: 4px;" \| Animalia - Animals... Evolution of multicellularityEvolution of multicellularity The first organisms that existed were undoubtedly unicellular....