Eukariot

An eukariot, or eukaryote, is an organism whose cells contain a membrane-bound nucleus and a set of organelles. Eukaryotes form the domain Eukarya and include animals, plants, fungi, and numerous protists. They are distinguished from prokaryotes, whose cells lack a nucleus and most membrane-bound organelles.

Eukaryotic cells typically exhibit compartmentalization via internal membranes, a well-developed cytoskeleton, and an endomembrane system. The nucleus houses linear chromosomes organized with histones. Energy production generally relies on mitochondria, and photosynthetic lineages possess chloroplasts. Others carry lysosomes, peroxisomes, and other organelles that support specialized functions.

The nucleus stores the genetic material and coordinates gene expression. Eukaryotes often have multiple, linear chromosomes and a nuclear envelope that separates transcription from translation. Most eukaryotes reproduce sexually, involving meiosis and fertilization, while many also reproduce asexually by mitosis or other processes.

Evolutionarily, eukaryotes are thought to have arisen through endosymbiotic events, with mitochondria derived from an alpha-proteobacterium and, in plants and algae, chloroplasts from cyanobacteria. This endosymbiotic theory is supported by organelle genomes and other cellular features.

Today, eukaryotes display extensive diversity in form and ecology, from single-celled protists to multicellular plants and animals. They are studied across biology disciplines, including cell biology, evolution, ecology, and medicine.