Case/Source based questions. Human digestive system is a tube running from mouth to anus. Its main function is to breakdown complex molecules present in the food which cannot be absorbed as such into smaller molecules. These molecules are absorbed across the walls of the tube and the absorbed food reaches each and every cell of the body where it is utilised for obtaining energy. (a) Name the glands present in the buccal cavity and write the components of food on which the secretion of these glands act upon. (b) Two organs have a sphincter muscle at their exit. Name them. (c) What will happen if: (i) mucus is not secreted by the gastric glands. (ii) Villi are absent in the small intestine.