Metabolism (from Greek μεταβολισμός (metabolismos), "outthrow") is the whole set of chemical reactions that happen in living organisms. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories.
- Catabolism breaks down organic matter, for example to harvest energy in cellular respiration.
- Anabolism uses energy to construct components of cells such as proteins and nucleic acids.