procaryote

Prokaryote refers to a cellular organism that lacks a nucleus and other membrane-bound organelles. The term comes from Greek pro-, meaning before, and karyon, meaning nucleus. In contemporary biology, prokaryotes are the organisms in the two domains Bacteria and Archaea, though the grouping is based on cellular organization rather than a single evolutionary lineage.

Cell structure and genetics: Prokaryotic cells typically measure about 0.2–2 μm and have a cytoplasmic membrane and usually a rigid cell wall. Their genetic material is a single circular chromosome located in a nucleoid region, and many also possess small DNA molecules called plasmids. Ribosomes are 70S. They lack membrane-bound organelles such as mitochondria, chloroplasts, or a true nucleus. Some species form biofilms or possess additional membranes, but these are not comparable to eukaryotic organelles. Reproduction is usually asexual by binary fission, though genetic exchange can occur through transformation, transduction, and conjugation.

Metabolism and ecology: Prokaryotes show a remarkable diversity of metabolisms, including photosynthesis, chemosynthesis, fermentation, and respiration. They occupy nearly every habitat on Earth, from oceans and soils to extreme environments such as hot springs and acidic waters. They are essential drivers of nutrient cycles, enable various industrial processes, and include both beneficial symbionts and significant pathogens.

Taxonomic notes: The term prokaryote is a practical grouping rather than a strict clade, as Bacteria and Archaea are distinct lineages. Eukaryotes are characterized by compartmentalization and organelles, a feature that arose after the divergence of these prokaryotic groups.