In aerobic respiration glycolysis is linked with Krebs cycle through acetyl Co-A because pyruvic acid (end product of glycolysis) first converted into acetyl Co-A. The acetyl Co-A enters in the Krebs cycle. The formation of acetyl Co-Ais involved with some Co-factors like Mg ions, thiamine pyrophosphate, NAD+ Co-A and lipoic acid. Vitamin A (retinol) is necessary for rhodopsin of rod cells and iodopsin of cone cells of retina. It is also essential for maintenance of epithelial cells and called anti-infection vitamin. Vitamin K is necessary for synthesis of prothrombin, blood clotting and electron transport chain. Vitamin- B6 is a coenzyme for amino acid and fatty acid metabolism.