Life (biology)

Life is the condition of organisms that maintain themselves through processes such as metabolism, growth, and reproduction. No single definition captures every known and proposed form of life.

Cell: The smallest structural and functional unit of most living organisms, bounded by a membrane and containing organized molecular machinery. Cellular organization is a common criterion for distinguishing organisms from nonliving systems.
Adenosine triphosphate: A nucleotide that cells use to transfer energy for many biochemical reactions. ATP couples energy-releasing reactions to the work required for cellular maintenance.
Abiogenesis: The natural emergence of life from nonliving matter through chemical and physical processes. Abiogenesis names the central scientific problem of explaining life's first appearance.
Astrobiology: The study of the origin, evolution, distribution, and detection of life in the universe. Astrobiology must decide what evidence would count as life beyond Earth.
Virus: An infectious agent that replicates only inside the cells of a host organism. Viruses evolve and carry genetic information but depend on host cells for reproduction.
Metabolism: The chemical reactions that acquire and transform matter and energy in an organism. Metabolism sustains the organized activity associated with life.
DNA: A molecule that stores hereditary information in most organisms. DNA provides a durable information store that cells copy and use.
Miller–Urey experiment: A 1953 experiment that produced amino acids by applying electrical sparks to a mixture of gases and water. It demonstrated that some organic building blocks can form under simulated early-Earth conditions.
Mars 2020: A NASA mission that landed the Perseverance rover on Mars in 2021 to study geology and search for signs of ancient microbial life. Its instruments seek preserved evidence of past habitability and possible biosignatures.
Prion: An infectious protein that propagates by inducing misfolding in normal versions of the same protein. Prions transmit structural information without cells, genes, or metabolism.

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