The sum total of all the chemical reactions taking place within the body of a living organism is called metabolism. Metabolism can also be defined as the sum total of all the catabolic and anabolic reactions taking place within an organism. 

Catabolic reactions involve breaking down of large complex biomolecules into simpler molecules (e.g. respiration). While anabolic reactions involve building up of large complex biomolecule from smaller and simpler molecules (e.g. photosynthesis).