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? | NCERT solution | Class 11 Biology | Unit-16 Digestion and Absorption



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?

 

Answer:-
(a) Villi are finger like structures that absorb the nutrients from digested food in the intestine. The main function of villi is to absorption of nutrients so they are present in small intestine as this is the place where absorption of food takes place. Villi is not present in stomach because the food is still yet to be broken down therefore, similar finger like structures called “rugae” is present which secrete pepsin and the gastric juices for the digestion to take place in the stomach.

(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:

• Serosa: It is the outermost layer and is made up of a thin mesothelium with some connective tissues.

• Muscularis: It is a thin layer of smooth muscles which are usually arranged into an inner circular and outer longitudinal layer.

• Sub-mucosa: It is a layer of loose connective tissues, containing nerves, blood, and lymph vessels which supports mucosa.
• Mucosa: It is the innermost lining of the lumen of the alimentary canal which is mainly involved in absorption and secretion.
(d) Bile helps in emulsification of fats and also activates lipases. Therefore, bile helps in digestion of fats.