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
B2 (classification) B2 (classification) B2 is a medical based Paralympic classification for blind sport. Competitors in this classification have vision that falls between the B1 and B3 classes. The International Blind Sports Federation (IBSA) defines this classification as "visual acuity ranging from LogMAR 1.50 to 2.60 (inclusive) and/or visual field constricted to a diameter of less than 10 degrees." It is used by a number of blind sports including para-alpine skiing, para-Nordic skiing, blind cricket, blind golf, five-a-side football, goalball and judo. Some sports, including adaptive rowing, athletics and swimming, have equivalents to this class. The B2 classification was first created by