Secondary Compounds
Plants produce and amazing variety of organic compounds over and above their everyday components and metabolites, which are called primary compounds. The primary compounds, carbohydrates, lipids, nucleotides and peptides are shared by all living organisms and are central to life processes. The secondary compounds are derived from everyday components, but are not central to metabolism, hence their name. Often it can be difficult to identify their function; do they help protect against disease or herbivores or environmental stress, or are they just metabolic junk?
Plants produce other kinds of compounds in addition to the phenolics and terpenoids described below. Particularly important (and diverse) are the alkaloids which are nitrogen containing cyclic compounds. This class includes many plant poisons and drugs: caffeine, nicotine, atropine, quinine, cocaine etc.