Eukaryote

The eukaryotes seemingly emerged within the Asgard archaea, and are closely related to the Heimdallarchaeia.^[5] This implies that there are only two domains of life, Bacteria and Archaea, with eukaryotes incorporated among the Archaea. Eukaryotes first emerged during the Paleoproterozoic, likely as flagellated cells. The leading evolutionary theory is they were created by symbiogenesis between an anaerobic Asgard archaean and an aerobic proteobacterium, which formed the mitochondria. A second episode of symbiogenesis with a cyanobacterium created the plants, with chloroplasts.


Eukaryotic cells contain membrane-bound organelles such as the nucleus, the endoplasmic reticulum, and the Golgi apparatus. Eukaryotes may be either unicellular or multicellular. In comparison, prokaryotes are typically unicellular. Unicellular eukaryotes are sometimes called protists. Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion (fertilization).

Eukaryotes are organisms that range from microscopic single cells, such as picozoans under 3 micrometres across,^[6] to animals like the blue whale, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long,^[7] or plants like the coast redwood, up to 120 metres (390 ft) tall.^[8] Many eukaryotes are unicellular; the informal grouping called protists includes many of these, with some multicellular forms like the giant kelp up to 200 feet (61 m) long.^[9] The multicellular eukaryotes include the animals, plants, and fungi, but again, these groups too contain many unicellular species.^[10] Eukaryotic cells are typically much larger than those of prokaryotes—the bacteria and the archaea—having a volume of around 10,000 times greater.^[11][12] Eukaryotes represent a small minority of the number of organisms, but, as many of them are much larger, their collective global biomass (468 gigatons) is far larger than that of prokaryotes (77 gigatons), with plants alone accounting for over 81% of the total biomass of Earth.^[13]


The eukaryotes are a diverse lineage, consisting mainly of microscopic organisms.^[14] Multicellularity in some form has evolved independently at least 25 times within the eukaryotes.^[15][16] Complex multicellular organisms, not counting the aggregation of amoebae to form slime molds, have evolved within only six eukaryotic lineages: animals, symbiomycotan fungi, brown algae, red algae, green algae, and land plants.^[17] Eukaryotes are grouped by genomic similarities, so that groups often lack visible shared characteristics.^[14]