Name two major functions of gut microbiota in the colon.

• A. Fermentation producing short-chain fatty acids
• B. Synthesis of vitamin K
• C. Fermentation producing short-chain fatty acids and synthesis of vitamin K and some B vitamins
• D. Barrier function

Answer: (C)

The colon’s resident microbes mainly contribute by turning indigestible fibers into energy-rich compounds and by supplying essential vitamins. Through anaerobic fermentation, they produce short-chain fatty acids such as butyrate, propionate, and acetate. Butyrate is a key fuel for colonocytes, supporting the health and integrity of the lining, while the other SCFAs influence systemic metabolism and inflammation. At the same time, many gut bacteria synthesize vitamins that the host can’t always obtain in sufficient amounts, notably vitamin K and several B vitamins, which support blood clotting and various metabolic processes. So, combining fermentation into short-chain fatty acids with vitamin production captures two major, well-established roles of colon microbiota, making this the best choice. Other functions like barrier function are important and related, but the two outputs above are the primary demonstrable activities highlighted here.