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.
Plants produce other kinds of compounds in addition to the phenolics and terpenoids described below.
Molecules with multiples of 5 carbons and particularly with single carbon side chains are likely to belong to this group, although it may be difficult to see the isoprene units because of cyclization. Many spices and fragrances contain terpenoids. More complex terpenoids include the sterols. These are present in cell membranes and affect their fluidity. A number of animal hormones are sterol derivatives and recently a plant sterol, brassinolide has been discovered to affect plant development.