Secondary metabolites are organic compounds produced by plants, fungi, and bacteria that are not directly involved in their growth, development, or reproduction. Unlike primary metabolites, which are essential for basic life functions, secondary metabolites often play a role in defense against herbivores, pathogens, and competition. Examples include alkaloids, terpenoids, and flavonoids, which can have various effects on other organisms. These compounds are also important for humans, as many secondary metabolites have medicinal properties. For instance, morphine from the opium poppy is used for pain relief, while quercetin found in many fruits and vegetables has antioxidant effects. Understanding secondary metabolites can lead to new discoveries in medicine and agriculture.