Cellular Biology
Precursor
/prēˈ•kər•sər/
A precursor, in human biology, is an inactive substance converted to an active one (a coenzyme, hormone, or antioxidant). For example, when you take your vitamin A supplement, you're actually consuming beta carotene—your body knows exactly what to do next, and turns that into the vitamin that helps you protect your eyes. The efficiency of this process depends on many things, including the bioavailability of the precursor.