Plants are an important source of molecules and structures of economic, industrial and pharmaceutical interest. Cellulose and its derivatives are used in many fields, from the paper industry to medical and analytical applications. High quality leaf concentrates and isolates are used for human nutrition. Important drugs are of plant origin. This document represents an educational and scientific tool for applied biochemistry. It describes the biochemistry of some important natural substances of plant origin, their chemical composition, extraction, human interest and various applications.