Explanation

Vitamin-K (naphthoquinone) is an essential cofactor is involved in the synthesis of prothrombin in the liver cells which is essential for blood clotting, prevention of haemorrhage and excessive bleeding in wounds. This vitamin is synthesised by colon bacterium hence, a dietary source is not usually necessary. Besides vitamin-K, some vitamin like vitamin-$B_{12}$, vitamin-$B_{1}$, vitamin-$B_{2}$ are also produced by the symbiotic bacteria (E. coli) in the large intestine of human beings