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Life
Ruwenpflanzen.jpg
Plants in the Rwenzori Mountains, Uganda
Scientific classification edit
Domains and Supergroups
Life on Earth:
Non-cellular life[note 1] [note 2]
Viruses[note 3]
Viroids
Cellular life
Domain Bacteria
Domain Archaea
Domain Eukarya
Archaeplastida
SAR
Excavata
Amoebozoa
Opisthokonta
MarsCuriosityRover-Drilling-Sol170++-2.jpg
This article is one of a series on:
Life in the Universe
Astrobiology
Habitability in the Solar System
Habitability of Venus Life on Earth Habitability of Mars Habitability of Enceladus Habitability of Europa Habitability of Titan
Life outside the Solar System
Circumstellar habitable zone Exoplanetology Planetary habitability SETI
vte
Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased (they have died), or because they never had such functions and are classified as inanimate. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. The criteria can at times be ambiguous and may or may not define viruses, viroids, or potential synthetic life as "living". Biology is the science concerned with the study of life.
The definition of life is controversial. The current definition is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve. However, several other biological definitions have been proposed, and there are some borderline cases of life, such as viruses or viroids. In the past, there have been many attempts to define what is meant by "life" through obsolete concepts such as odic force, hylomorphism, spontaneous generation and vitalism, that have now been disproved by biological discoveries. Abiogenesis describes the natural process of life arising from non-living matter, such as simple organic compounds. Properties common to all organisms include the need for certain core chemical elements to sustain biochemical functions.