Metabolism



Metabolism is the uptake and digestion of some kind of food, and the
disposal of waste products. Each living cell has a metabolism (cell
metabolism), as well as multicellular organisms like plants, animals and
humans have a "total" metabolism that can differ from that of the individual
cells. It is a two-part process - one part is called catabolism - when the
body uses food for energy. The other is called anabolism - when the body
uses food to build or mend cells.

The halt of metabolism in a living organism is usually defined as its death.
Some organisms can reduce their metabolism to almost zero for certain
periods of time. Spores of fungi can survive thousands of years in that
state. But every lifeform is bound to have metabolism at some point of its
life cycle, with the possible exception of viruses, which use their hosts'
metabolism.

The correct definition of metabolism is almost as difficult as the
definition of life. For example, according to the definition above, fire has
a metabolism, too (it "eats", for example, wood, converts it to heat, and
disposes ashes).

Unusual Metabolisms

   * Some microbes metabolise the wrought iron on shipwrecks, forming
     structures known as rusticles with the waste compounds they produce.

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