lifeform

Lifeform is a term used to refer to any living organism, typically any entity capable of growth, reproduction, and maintaining homeostasis. In biology, life forms share a core set of characteristics: organized structure, metabolism, growth, reproduction, response to stimuli, and adaptation through evolution. Most life forms on Earth are cellular, composed of one or more cells that enclose genetic material within a membrane. The cell is generally regarded as the basic unit of life, and organisms may be unicellular or multicellular.

Life forms are classified into major lineages such as Bacteria, Archaea, and Eukarya; within Eukarya lie the kingdoms of plants, animals, fungi, and various protists. A common criterion distinguishing life forms is their ability to self-sustain energy transformations and to reproduce, with heredity encoded in DNA or, in some viruses, RNA. The status of viruses as life forms is debated because they lack independent metabolism and can only reproduce within a host.

Life forms rely on complex biochemistry, most often carbon-based chemistry in water, using energy from sunlight or chemical reactions to synthesize biomolecules and regulate internal conditions. Reproduction can be sexual or asexual, with genetic material transmitted to offspring and subject to mutation and recombination. Evolution shapes the diversity of life forms, from microscopic bacteria to large multicellular organisms, and underpins ecology and ecosystems.

In astrobiology, researchers also consider broader possibilities for life forms that might arise in non-terrestrial environments, though no such life has been confirmed to date.