Eukaryoottisia

Eukaryoottisia, a Finnish term for eukaryotes, refers to organisms whose cells contain a true nucleus bounded by a membrane and a set of membrane-bound organelles. Eukaryotes differ from prokaryotes, whose cells generally lack a defined nucleus and internal compartments.

Cell structure includes a nucleus with linear chromosomes, a complex cytoskeleton, and an endomembrane system that includes the endoplasmic reticulum and Golgi apparatus. Mitochondria are common to most lineages and provide cellular energy; chloroplasts are present in plants, algae, and some protists and enable photosynthesis.

Eukaryotes range from single-celled organisms to large multicellular groups. They encompass animals, plants, fungi, and many protists, occupying diverse habitats such as oceans, soils, and freshwater.

Origin and evolution: The prevailing view is that eukaryotes originated through endosymbiotic events in which a host cell incorporated an ancestral proteobacterium that became the mitochondrion, and, in photosynthetic lineages, a cyanobacterium that became the chloroplast. This endosymbiotic theory, together with later cellular innovations, enabled larger cell size, compartmentalization, and multicellularity.

Genomes are typically organized into linear chromosomes within the nucleus; mitochondria and chloroplasts retain their own DNA. Reproduction occurs mainly through mitosis and, in many lineages, meiosis and fertilization, though asexual reproduction is common in some groups. Eukaryoottisia form the biological basis of most life on Earth, from unicellular protists to complex multicellular organisms such as animals, plants, and fungi.