procariote

Prokaryotes are unicellular organisms that lack a nucleus and other membrane-bound organelles. They comprise one of the two major cellular lineages, alongside eukaryotes, and include the domains Bacteria and Archaea. Prokaryotes are found in nearly every habitat, from soil and freshwater to oceans, deserts, and extreme environments such as hot springs and acidic niches. They are among the oldest life forms, with a fossil record dating back about 3.5 billion years.

A typical prokaryotic cell is smaller than many eukaryotic cells. Its genetic material is usually a single circular chromosome located in a region called the nucleoid. Many prokaryotes carry small, independently replicating DNA molecules called plasmids. The cell envelope generally includes a cytoplasmic membrane and a cell wall; in bacteria the wall often contains peptidoglycan, whereas archaeal walls may contain pseudopeptidoglycan or other polymers. Ribosomes are present for protein synthesis, and some cells have external structures such as flagella for movement or pili for attachment.

Prokaryotes reproduce primarily by binary fission and display a wide range of metabolic strategies. They can be photoautotrophs, chemoautotrophs, photoheterotrophs, or chemoheterotrophs, utilizing diverse energy and carbon sources. Horizontal gene transfer through transformation, transduction, or conjugation contributes to rapid genetic variation.

Ecologically, prokaryotes drive nutrient cycles, decomposition, and various symbiotic relationships. They have significant roles in medicine and industry, serving as pathogens in some cases while enabling biotechnological applications in others. The distinction from eukaryotes rests on cellular organization rather than size, reflecting early divergence in life’s history.