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A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea.
Originally, the group included not only single-celled microorganisms but also some "lower" multicellular animals, such as rotifers, corals, sponges, jellyfish, bryozoans and polychaete worms. [12] The term Protozoa is formed from the Greek words πρῶτος (prôtos), meaning "first", and ζῷα (zôia), plural of ζῷον (zôion), meaning ...
Microbiology (from Ancient Greek μῑκρος (mīkros) 'small' βίος (bíos) 'life' and -λογία 'study of') is the scientific study of microorganisms, those being of unicellular (single-celled), multicellular (consisting of complex cells), or acellular (lacking cells).
A microorganism, or microbe, [a] is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from sixth century BC India.
O. R. Collins showed that the slime mold Didymium iridis had two strains (+ and −) of cells, equivalent to gametes, that these could form immortal cell lines in culture, and that the system was controlled by alleles of a single gene. This made the species a model organism for exploring incompatibility, asexual reproduction, and mating types. [59]
Valonia ventricosa is among the largest known single-celled organisms. Its thallus consists of a thin-walled, tough, multinucleate cell with a diameter that ranges typically from 1 to 4 centimetres (0.4 to 1.6 in), although it may achieve a diameter of up to 5.1 centimetres (2.0 in) in rarer cases.
The vegetative phase in the life cycle of a zooxanthellae is the predominant form of the organism. [14] In this form, the single-celled organism has a thin cell wall. As opposed to the zoospore, the zooxanthella contains numerous chloroplasts. Once the cell continues growing, however, chloroplasts decrease in abundance. [14]
Monera (/məˈnɪərə/) (Greek: μονήρης (monḗrēs), "single", "solitary") is historically a biological kingdom that is made up of prokaryotes. As such, it is composed of single-celled organisms that lack a nucleus. The taxon Monera was first proposed as a phylum by Ernst Haeckel in 1866.