In animal tissues, one notices the presence of all such
categories of compounds like nitrogen bases, nucleosides or nucleotides, etc. These are called primary metabolites. However, when one analyses plant, fungal, and microbial cells, one would see thousands of compounds other than these called primary metabolites, e.g. alkaloids, flavonoids, rubber, essential oils, antibiotics, colored pigments, scents, gums, spices. These are called secondary metabolites. A list of secondary metabolites is given in the table below.