Final answer:
Vitamin B-12 is naturally and abundantly found only in animal-derived foods and is produced by certain bacteria. It is essential for various metabolic processes in the body, and a deficiency can lead to significant health issues.
Step-by-step explanation:
Vitamin B-12 is an essential nutrient involved in numerous critical physiological processes. It is only found naturally and in abundance in foods of animal origin, such as liver, egg, meat, and fish. Neither plants nor animals can synthesize Vitamin B-12; it is produced solely by certain microorganisms. Herbivores obtain this vitamin by ingesting food contaminated with these bacteria, while humans and other omnivores predominantly obtain it through consumption of animal products. Vegan and vegetarian diets often lack sufficient B-12, necessitating supplements or fortified foods to meet the daily requirement of 5 µg/day. Deficiency in Vitamin B-12 can lead to conditions such as megaloblastic anemia, demyelination of nerve cells, neurological issues, and infertility.
Additionally, only tiny amounts of Vitamin B-12 are needed by humans, with the average blood concentration in a healthy adult being about 3.5 x 10-8 M. The structure of Vitamin B-12 is complex, containing cobalt and a corrin ring, making it similar to a heme. It plays several roles in the body, including the methylation of homocysteine to methionine, and the conversion of glutamic acid to ß-methyl aspartic acid, which are critical for metabolism and cell function.