1. Define: Bioavailability: The rate at and the extent to which a nutrient is absorbed and used. Quantity provided by food Precursors: Substances that precede others; with regard to vitamins, compounds that can be converted into active vitamins, also known as Provitamins Neural Tube Defects: Malformations of the brain, spinal cord, or both during embryonic development that often result in lifelong disability or death Rickets: The vitamin D- deficiency disease in children characterized by inade...