Metabolism is the uptake and digestion of food, and the disposal of waste products in livingorganisms. Because this process can happen at many levels within an organism, we can identify several kinds of metabolism:
When concerning an organism in its entirety, metabolism (also called total metabolism) is all of the living organism\'s chemical processes. The organism's metabolism can be dichotomized into the synthesis of organic molecules (anabolism) and their breakdown (catabolism).
When concerning a particular substance, metabolism (also called specific metabolism) is the chemical activity involving this substance in a living organism. This is commonly the digestion of food, and the disposal of wastes.
When concerning a particular living cell, metabolism (also called cell metabolism) is all of the chemical processes in that cell.
The word metabolism comes from the Greek word for "change".
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).