Which of the following is considered a secondary metabolite?

Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. They often play important roles in plants, including defense against herbivores, attraction of pollinators, and protection against pathogens. Tannins, which are polyphenolic compounds found in many plants, are a prime example of secondary metabolites. They can have astringent properties, help in deterring herbivores, and exhibit antimicrobial activity, which contributes to the plant's survival and fitness.

In contrast, sugars and carbohydrates primarily serve as primary metabolites and are directly involved in energy production and structural functions within the plant. Similarly, amino acids, while vital for protein synthesis and thus essential for growth and metabolism, are also classified as primary metabolites. The distinction between primary and secondary metabolites is crucial in understanding the various roles of compounds within plants, emphasizing the ecological and physiological significance of secondary metabolites like tannins.