eucariotos

Eucariotos, or eukaryotes, are a group of organisms whose cells contain a nucleus enclosed by a nuclear envelope and a system of membrane-bound organelles, such as mitochondria and, in many groups, chloroplasts. This cellular organization distinguishes them from prokaryotes, which lack a defined nucleus and many organelles.

The eukaryotic cell features a complex cytoskeleton and an endomembrane system that includes the endoplasmic reticulum and the Golgi apparatus, which coordinate the synthesis, processing, and trafficking of proteins and lipids. Most eukaryotic cells have linear DNA organized into chromosomes within the nucleus, and many possess mitochondria that generate energy; photosynthetic eukaryotes also have chloroplasts.

Reproduction in eucariotos can be asexual or sexual. Most taxa exhibit mitotic cell division, and many undergo meiosis and fertilization as part of sexual life cycles, contributing to genetic variation and adaptation.

Diversity is high: eucariotos include animals, plants, fungi, and numerous protists, spanning unicellular forms to large multicellular organisms. They inhabit virtually every ecosystem, from oceans and soils to extreme environments. Protists, often used as a catch-all for diverse unicellular eukaryotes, highlight the broad range of lifestyles within this group.

Origin and evolution are linked to endosymbiosis. The mitochondrion is believed to have originated from an ancestral aerobic bacterium, while plastids in plants and algae arose from cyanobacterial endosymbiosis. Together with the development of internal membranes and the nucleus, these events gave rise to the modern eukaryotic cell.

Classification in modern taxonomy places eucariotos in the domain Eukaryota (also called Eukarya). Within this domain are major lineages such as Opisthokonta, Archaeplastida, and SAR, with many groups historically classified as protists.