When we talk about prokaryotes, we usually refer to a cellular structure without a nucleus in which the genetic material is dispersed in the cytoplasm. Organisms formed by this type of cell are included in the prokaryotic empire, a top-level taxonomic classification that is divided into the Archea S Bacteria domains.
All prokaryotic organisms are unicellular but many can form large colonies and aggregate communities. One of the few exceptions is the myxobacteria (order Myxococcales), a group of bacteria that have the largest known bacterial genome, composed of about 12.5 million nucleotides, and that have phases in their life cycle that some authors consider multicellular. There are also authors who describe some species of magnetotactic bacteria as necessarily multicellular.
On the other hand, eukaryotic organisms are made up of cells that have a nucleus in which genetic material is stored. These organisms are included in the eukaryotic empire and are currently believed to come from prokaryotic organisms through an evolutionary process of endosymbiosis.
within eukaryotes we find four major kingdoms: animalia (animals), planta (floors), fungi (fungi) and protista (protozoa). All are multicellular organisms except protozoa and yeast. (a type of mushroom).
Protozoa are a highly paraphyletic taxonomic group of eukaryotic organisms. are mostly unicellular, although they also contain some multicellular organisms, for example the so-called brown algae. Among the best known unicellular protozoa we can mention the paramecia, the plasmodium or the amoebas.
Yeasts are defined as unicellular microscopic fungi. Strictly speaking, “true” yeasts are only found in the Ascomycota division, which are unicellular throughout their life cycle. But the term yeast has been extended, especially in microbiology, to all fungi in which the unicellular phase predominates in the life cycle, for example the Basidiomycota division.
Therefore, it can be said that there are unicellular eukaryotic organisms and that they are abundant in nature.