Q.3:- Answer briefly:
(a) Why are villi present in the intestine and not in the stomach?
(b) How does pepsinogen change into its active form?
(c) What are the basic layers of the wall of alimentary canal?
(d) How does bile help in the digestion of fats?
(b) Pepsinogen changes into its active form by the action of hydrochloric acid.
(c) The walls of the alimentary canal are made up of four layers. These are:
• Muscularis: It is a thin layer of smooth muscles which are usually arranged into an inner circular and outer longitudinal layer.