**4. Research on plants secondary metabolites**

In the plant kingdom, more than 50,000 secondary metabolites have been discovered, and they exert a wide range of effects on the plant as well as other living organisms. Their functions involve induction of flowering, fruit set and abscission, maintenance of perennial growth or signal deciduous behavior. Many plant secondary metabolites act as antimicrobials and perform the role of attractants or, conversely, as repellents. They are used as herbs in the traditional medicine in many ancient communities as plant secondary metabolites have shown to possess various biological effects. Plant secondary metabolites are classified according to their chemical structures into several classes. The classes of secondary plant metabolites include phenolics, alkaloids, saponins, terpenes, lipids, and carbohydrates. They act as antibiotic, antifungal, and antiviral and therefore are able to protect plants from pathogens as well as serious leaf damage from the light because they contain important UV-absorbing compounds [18]. Further, secondary metabolites of plants also have ecological importance whereby they improve soil quality by influencing soil decomposition. Tannins and terpenes affect cycling of C and N by increasing N immobilization in the soil. They also defend plants from pathogens and diseases, attract pollinators, aid in seed dispersal, and help plants recover from injury [19].
