Metabolism

In biology, metabolism refers to all of an organism's chemical processes. This can be dichotomized into the synthesis of organic molecules (anabolism) and their breakdown (catabolism). Most commonly, this refers to the digestion of food, and to the disposal of wastes.

Each living cell has a metabolism (cell metabolism); furthermore, multicellular organisms like plants, animals and humans have a "total" metabolism that can differ from that of the individual cells. The metabolic pathways form 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.

Table of contents

1 Human metabolism
2 Unusual metabolisms
3 Etymology
4 See also:

Human metabolism

Human cells obtain most of their energy from chemical reactions involving oxygen. A starting point in measuring human metabolism is with basal metabolic rate.

Unusual metabolisms

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

Etymology

The word metabolism is from the Greek word for "change".