eukarüootid

Eukarüootid, known in English as eukaryotes, form a major domain of life characterized by cells with a true nucleus enclosed by a nuclear envelope and by membrane-bound organelles. They contrast with prokaryotes, whose cells lack a nucleus and most internal membranes. Eukaryotes include animals, plants, fungi, and a large and diverse group of protists. They range from single-celled organisms such as yeasts and many algal species to complex multicellular forms such as mammals, trees, and mushrooms.

Cell architecture in eukaryotes features a nucleus containing linear chromosomes, a complex endomembrane system, and a cytoskeleton that supports shape, transport, and movement. Energy metabolism centers are mitochondria, and chloroplasts occur in photosynthetic lineages. Most eukaryotic cells have 80S ribosomes in the cytosol, while mitochondria and chloroplasts retain their own 70S ribosomes. In addition to organelles, eukaryotes often possess specialized compartments for protein processing, lipid synthesis, and waste handling.

Reproduction in eukaryotes is diverse but commonly involves sexual processes such as meiosis and fertilization, alongside various asexual modes. Life cycles range from simple to highly complex, with many lineages exhibiting iterations of growth, development, and sometimes alternation of generations.

Evolutionarily, eukaryotes are believed to have originated about 1.6 to 2.1 billion years ago through endosymbiotic events in which an archaeal host incorporated bacterial symbionts, giving rise to mitochondria and, in photosynthetic lineages, chloroplasts. This framework, the endosymbiotic theory, is supported by genetic and structural evidence.

Eukaryotes inhabit nearly every ecological niche, from oceans to soils to the human body, and display remarkable diversity in metabolism, form, and lifestyle. They play central roles as producers, consumers, decomposers, and symbionts.