eukaryóta

Eukaryota, also called eukaryotes, is a domain of life comprising organisms whose cells contain a true nucleus enclosed by a nuclear envelope, as well as a complex internal membrane system and organelles such as mitochondria and, in plants and many algae, chloroplasts. This internal organization distinguishes them from prokaryotes, whose cells lack such compartments. Eukaryotic cells typically measure several to thousands of micrometers and use a cytoskeleton made of microfilaments, intermediate filaments, and microtubules to maintain shape, enable movement, and organize activities.

Eukaryota includes a wide range of organisms, from unicellular protists to complex multicellular forms such as plants, animals, and fungi. They possess linear chromosomes housed in the nucleus, with most species reproducing sexually via meiosis and fertilization, though many also reproduce asexually. Genome size and organization vary greatly across lineages.

The origin of eukaryotes is linked to endosymbiotic events in which a host cell engulfed an ancestral bacterium, leading to mitochondria; photosynthetic plastids in plants and algae arose from additional endosymbioses. The earliest eukaryotes appeared in the fossil record around 1.8–1.5 billion years ago, and the group underwent extensive diversification.

Current taxonomy places Eukaryota as a domain containing several major clades or supergroups, such as Opisthokonta (animals, fungi, and relatives), Archaeplastida (plants and algae), SAR (stramenopiles, alveolates, rhizarians), and Excavata. Relationships among these groups are a subject of ongoing research and discussion. Eukaryotes play central roles in ecosystems and biology, as producers, consumers, pathogens, and model organisms.