Question

Assertion :Some bacteria produce vitamin B${}_{12}$. Reason: Vitamins are obtained when they are alive.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Both Assertion and Reason are incorrect.

Answer 1

The correct option is C Assertion is correct but Reason is incorrect.

Neither fungi, plants, nor animals are capable of producing vitamin B${}_{12}$. Only bacteria and archaea have the enzymes required for its synthesis, although many foods are a natural source of B${}_{12}$ because of bacterial symbiosis. Animals must obtain vitamin B${}_{12}$ directly or indirectly from bacteria. B${}_{12}$ is produced by bacteria in the large intestine (colon), since B${}_{12}$ is produced below the ileum (where B${}_{12}$ is absorbed), it is not available for absorption. Thus, herbivorous animals must either obtain B${}_{12}$ from bacteria in their rumens or (if fermenting plant material in the hindgut) by re-ingestion of cecotrope faeces. A common semi-synthetic form of the vitamin is cyanocobalamin, which does not occur in nature but is produced from bacterial hydroxycobalamin. Because of its stability and lower production cost, this form is then used in many pharmaceuticals and supplements as well as a food additive. In the body, it is converted to the human physiological forms methylcobalamin and 5'-deoxyadenosylcobalamin.

Therefore, the correct answer is option (C).