onecelled

Onecelled, or unicellular, describes organisms that consist of a single cell. They can be prokaryotic, lacking a defined nucleus, or eukaryotic, with a nucleus and organelles. Unicellular life is widespread and ecologically essential, with examples including bacteria, archaea, many protists, yeasts, and some algae. Some single-celled organisms live independently; others form loose colonies but remain functionally single cells.

Structure and metabolism: Prokaryotic unicells have a simple cell organization, typically a cell wall, plasma membrane, cytoplasm, ribosomes, and sometimes external appendages such as flagella. Eukaryotic unicells possess a true nucleus and membrane-bound organelles (for example mitochondria; chloroplasts in photosynthetic lineages). Metabolic strategies are diverse: phototrophy, chemotrophy, chemoautotrophy, and heterotrophy, including parasitism.

Reproduction and genetics: Most reproduce asexually through binary fission or budding; some produce spores or undergo multiple fission. Prokaryotes exchange genetic material by horizontal gene transfer (transformation, transduction, conjugation), while some protists engage in sexual processes.

Ecology and importance: Unicellular organisms drive nutrient cycling, decomposition, and primary production; they form microbiomes in soil, water, and hosts. Pathogenic bacteria and protists can cause disease, while beneficial species support fermentation, digestion, and biotechnology. Size varies from submicron bacteria to large protozoa that are visible under light microscopy.

In summary, onecelled organisms represent a vast and diverse portion of life, occupying nearly every habitat and playing foundational roles in ecosystems and human industry.