Many plants, fungi, and microbes of certain genera and families synthesize a number of organic compounds (biomolecules) which are not involved in primary metabolism and seem to have no direct function in the growth and development of organisms. Such compounds are called secondary metabolites. A wide variety of other chemicals like nicotine, caffeine, quinine, strychnine, opium, etc., (also extracted at a commercial level from plants) are produced by plants actually as a defense against grazers and browsers.