(i) Raw green plants contain fibre and cellulose. Our digestive system does not secrete any enzyme capable of digesting cellulose. Cellulose is digested by enzyme cellulose present in ruminating animals like cow. Also, our oesophagus serves only as a pathway to transport food from mouth to stomach. It does not possess any digestive gland. Hence, no secretion of enzymes occurs.
(ii) Although we may require enzyme action any time, they must be produced in an inactive form. Enzymes are capable of digesting a variety of bio molecules (proteins, fats, etc). If produced in active form, they may act upon the body cells and tissues and digest them leading to degeneration of body tissues.
(iii) Although HCl provides a highly acidic medium in our stomach, but it does not harm the walls of the stomach. The mucus-secreting cells (goblet cells) present in the inner lining of stomach secretes mucus and lines the wall of stomach with a mucus layer. Thus, prevents it from the action of HCl.
(iv) The student has a thirst for knowledge. He is curious to know about the human body and what happens to the food that we eat.
