Prokaryotic

Prokaryotes are organisms that lack a membrane-bound nucleus and other membrane-bound organelles. The two main groups are Bacteria and Archaea, which together comprise the vast majority of life's prokaryotic diversity. In prokaryotes, genetic material is usually a single circular chromosome located in the nucleoid region. Many species also carry small circular DNA molecules called plasmids that can be exchanged between cells.

Prokaryotes have a cell envelope typically consisting of a plasma membrane and a rigid cell wall. Some also possess an outer membrane, capsule, or S-layer. Most asexual reproduction occurs by binary fission, producing two genetically similar daughter cells. Genetic variation arises through mutations and horizontal gene transfer mechanisms such as transformation, transduction, and conjugation.

Metabolic capabilities are extremely diverse. Prokaryotes occupy nearly every ecological niche and perform processes that are essential to Earth's ecosystems, including photosynthesis (e.g., cyanobacteria), aerobic and anaerobic respiration, fermentation, and chemolithoautotrophy. They play key roles in nutrient cycling, decomposition, and symbiotic relationships; nitrogen fixation by certain bacteria is a notable example. Some prokaryotes are pathogenic, but many more are beneficial or neutral to other organisms.

In evolution, prokaryotes are among the earliest forms of life. Although they share core features with eukaryotes, they diverged early, leading to distinct cellular organization and genetic systems. Prokaryotes remain a foundational subject of microbiology and biotechnology. The term prokaryotic describes this cellular organization, and prokaryotes include the domains Bacteria and Archaea.