Eukaryote

Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope. Eukaryotes belong to the domain Eukaryota or Eukarya; their name comes from the Greek εὖ (eu, "well" or "good") and κάρυον (karyon, "nut" or "kernel"). The domain Eukaryota makes up one of the domains of life in the three-domain system; the two other domains are Bacteria and Archaea (together known as prokaryotes). Eukaryotes represent a tiny minority of the number of living organisms; however, due to their generally much larger size, their collective worldwide biomass is estimated to be about equal to that of prokaryotes. Eukaryotes evolved approximately 1.6–2.1 billion years ago, during the Proterozoic eon.

Eukaryotic cells typically contain membrane-bound organelles such as mitochondria and Golgi apparatus, and chloroplasts can be found in plants and algae; these organelles are unique to eukaryotes, although primitive organelles can be found in prokaryotes. As well as being unicellular, eukaryotes may also be multicellular and include many cell types forming different kinds of tissue; in comparison, prokaryotes are typically unicellular. Animals, plants, and fungi are the most familiar eukaryotes; other eukaryotes are sometimes called protists.

Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four haploid daughter cells. These act as sex cells (gametes). Each gamete has just one set of chromosomes, each a unique mix of the corresponding pair of parental chromosomes resulting from genetic recombination during meiosis.