Why does the inner wall of alimentary canal do not digest through the digestive enzymes?

Study the following statements and select the incorrect ones. (i) Pyramids of energy and yearly biomass production can never be inverted, since this would violate the laws of thermodynamics. (ii) Pyramids of standing crop and numbers can be inverted, since the number of organisms at a time does not indicate the amount of energy flowing through the system. (iii) There are certain limitations of ecological pyramids such as they do not take into account the same species belonging to two or more trophic levels. (iv) Saprohytes are not given any place in ecological pyramids even though they play a vital role in the ecosystem.

Digestive juice lacking enzyme but aiding in digestion is: