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A newborn baby is an example of life

Life is easy to recognise, but hard to define.[1] The study of life is called biology and people who study life are biologists. A lifespan is the average length of life in a species.

All known life on Earth is powered by solar energy. Without energy from the sun no life could exist. Life is based on the chemistry of carbon compounds. In particular, all life uses long-chain molecules such as proteins and nucleic acid. With water, which is essential, the long molecules are wrapped inside membranes to form cells. This may or may not be true of all possible forms of life in the Universe: it is true of all life on Earth today.

Summary[change | change source]


Through natural selection, they adapt to their environment in successive generations. More complex living organisms can communicate through various means.[1][2] Many life forms can be found on Earth. The properties common to these organisms—plants, animals, fungi, protists, archaea, and bacteria—are a carbon and water-based cellular form with complex organization and heritable genetic information.


Definitions of life[change | change source]

One explanation of life is called the cell theory. The cell theory has three basic points: All living things are made up of cells. The cell is the smallest living thing that can do all the things needed for life. All cells must come from pre-existing cells.

Something is often said to be alive if it:


  • mules cannot reproduce, and neither can worker ants
  • viruses and spores are not actively alive (metabolising) until the conditions are right.



A modern approach[change | change source]

A modern definition was given by Humberto Maturana and Francisco Varela in 1980,[3] to which they gave the name autopoiesis:

  1. The production of their own components
  2. The correct assembly of these components
  3. Continuous repair and maintenance of their own existence.

Roth commented that "In short, organisms are self-reproducing and self-maintaining, or 'autopoietic', systems".[4] This approach makes use of molecular biology ideas and systems science ideas.

Gallery of images of life[change | change source]

Related pages[change | change source]

References[change | change source]

  1. 1.0 1.1 Koshland, Daniel E. Jr 2002. "The seven pillars of life". Science 295 (5563): 2215–2216. doi:10.1126/science.1068489. PMID 11910092. Retrieved 2009-05-25.
  2. "organism". Chambers 21st Century Dictionary (online). (1999). 
  3. Maturana H. & Varela F. 1980. Autopoiesis and cognition: the realization of the living. Boston: Reidel.
  4. Roth G. 2013. The long evolution of brains and minds. Heidelberg: Springer. p41, 48