enkeltcelled

Enkeltcelled, or single-celled, organisms consist of a single cell that carries out all life processes. They are among the oldest and most abundant forms of life and inhabit nearly every environment on Earth, from soil and oceans to the bodies of plants and animals. The group spans prokaryotes, such as bacteria and archaea, and many eukaryotic forms, including yeasts, protists, and some algae.

In terms of cell organization, prokaryotic single cells have no nucleus and a simpler internal structure, while eukaryotic single cells possess a nucleus and membrane-bound organelles. Despite differences, both types perform metabolism, growth, response to stimuli, and reproduction within a single cell. Reproduction is typically asexual, most often by binary fission in prokaryotes or mitotic division in eukaryotes; some species also undergo budding or spore formation. They may be autotrophic or heterotrophic and employ a variety of energy sources, including light, organic compounds, or inorganic chemical reactions. Motility is common, achieved by flagella, cilia, or amoeboid movement.

Ecologically, unicellular organisms drive nutrient cycling, primary production, and decomposition. They play essential roles in human industry and research, with Saccharomyces cerevisiae in baking and brewing and Escherichia coli as a model organism. Some unicellular species are pathogens or symbionts, while most are harmless or beneficial. The study of single-celled life forms informs biology, ecology, and biotechnology.