Explain the role of rumen in the digestion process in ruminants.

Rumen is the largest chamber of the stomach in ruminants; it is mainly used for storing food. Ruminants are mostly grass-eating animals. Grass and leaves are rich in cellulose. Cellulose digestion partially takes place in the rumen because of the presence of special cellulose-digesting bacteria and protozoa in it. The food that is partially digested is called cud; it enters the reticulum chamber and is sent back to the mouth for further chewing.