Metabolism is a series of enzyme catalysed biochemical reaction in the living cells. It includes 3 phases namely anabolism, catabolism and amphibolism. Anabolism is a biosynthetic or constructive phase of metabolism in which nutrient molecules are synthesized from simpler forms e.g. photosynthesis, protein synthesis and Glycogenesis. Catabolism is a destructive phase of metabolism in which larger nutrient molecules are broken down into simpler forms e.g. Glycolysis, Glycogenolysis. When anabolism and catabolism operate together, this process is called amphibolism e.g. Krebs cycle.