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A protist (/ ˈ p r oʊ t ɪ s t / PROH-tist) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus.Protists do not form a natural group, or clade, but are a polyphyletic grouping of several independent clades that evolved from the last eukaryotic common ancestor.
Reproduction in Protozoa can be sexual or asexual. [38] Most Protozoa reproduce asexually through binary fission. [39] Many parasitic Protozoa reproduce both asexually and sexually. [38] However, sexual reproduction is rare among free-living protozoa and it usually occurs when food is scarce or the environment changes drastically. [40]
Protistology is a scientific discipline devoted to the study of protists, a highly diverse group of eukaryotic organisms. All eukaryotes apart from animals, plants and fungi are considered protists. [1]
Protists reproduce asexually or sexually. If the protists reproduce asexually, they do so through binary fission, multiple fission, budding, and fragmentation. If the protists reproduce sexually, they do so through a syngamy process where there is a fusion of the gametes. If this occurs in an individual it is recognized as autogamy.
Some modern authors prefer to exclude multicellular organisms from the traditional definition of a protist, restricting protists to unicellular organisms. [ 9 ] [ 10 ] This more constrained definition excludes all brown , the multicellular red and green algae , and, sometimes, slime molds (slime molds excluded when multicellularity is defined ...
Many protists reproduce sexually, as do many multicellular plants, animals, and fungi. In the eukaryotic fossil record, sexual reproduction first appeared about 2.0 billion years ago in the Proterozoic Eon, [64] [65] although a later date, 1.2 billion years ago, has also been presented.
This is a highly diverse group of organisms that are not easy to classify. [62] [63] Several algae species are multicellular protists, and slime molds have unique life cycles that involve switching between unicellular, colonial, and multicellular forms. [64] The number of species of protists is unknown since only a small proportion has been ...
In the process of evolution, single-celled organisms have developed in a variety of directions, and thus their rich morphology results in a large spectrum of swimming modes. [8] [2] Many swimming protists actuate tail-like appendages called flagella or cilia in order to generate the required thrust. [9]