Secondary metabolism (also called special metabolism) is a term for pathways and small molecule products of metabolism that are not absolutely required for the survival of the organism. Examples of the products include antibiotics and pigments. To distinguish non-secondary ("ordinary") metabolism, the term basic metabolism is sometimes used. Secondary metabolites are produced by microbes, plants and animals, but not by all of them.
The induction of secondary metabolism is linked to particular environmental conditions or developmental stages. For example, when grown in a nutrient-rich medium, most bacteria employ almost solely basic metabolism in order to grow and reproduce. However, when nutrients are depleted, they start producing an array of secondary metabolites in order to promote survival.
Plants produce secondary metabolites as a response to adverse environmental conditions or in particular developmental stages. For example, exposure to UV radiation induces the biosynthesis of UV-absorbing compounds.
