Vitamin amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B (thiamine), vitamin B (riboflavin), vitamin B (niacin), vitamin B (pantothenic acid), vitamin B (pyridoxine), vitamin B (biotin), vitamin B (folic acid or folate), vitamin B (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones). Vitamins have diverse biochemical functions. Some forms of vitamin A function as regulators of cell and tissue
HMS B2 October 1912. She was commanded by Lieutenant P.B. O’Brien, and was one of several submarines sent to Dover to take part in Channel exercises during the extended lead up to the First World War. "B2" was surfaced and was struck just forward of the conning tower. The accident resulted in the deaths of 15 crew members. The only survivor was the boat's bridge officer, Lt. Pulleyne. The boat was not recovered in order to allow the bodies to remain undisturbed. In recent years the wreck was discovered by amateur divers. HMS B2 HMS "B2" was one of 11 B-class submarines