A plant cell produces two types of metabolites: primary metabolites involved directly in growth and metabolism (carbohydrates, lipids and proteins), and secondary metabolites considered as end products of primary metabolism and not involved in metabolic activity(alkaloids, phenolics, sterols ,steroids, essential oils, lignins and tannins etc).They acts as defense chemicals.Their absence does not cause bad effects in the plants.
Secondary metabolites are substances which are produced by plants as defense chemicals.Their absence does not cause bad effects to the plants.They include alkaloids, phenolics, steroids, essential oils,lignins,resins and tannins etc.
Secondary metabolites are compounds bio synthetically derived from primary metabolites.Secondary metabolites or secondary compounds are compounds that are not required for normal growth and development, and are not made through metabolic pathways common to all plants.In plant kingdom they are limited to occurrence and may be restricted to a particular taxonomic group genus, species or family). Secondary metabolites are accumulated by plant cells in smaller qualities than primary metabolites. These secondary metabolites are synthesized in specialized cells at particular developmental stages making extraction and purification difficult.