Inactive protoxins is converted into its active toxin by:

The correct answer is Option (2) → Basic pH of the gut

Option (1) Acidic pH of the gut — Incorrect. The pH is reversed. The midgut of the insect larva is alkaline, not acidic, and the toxin crystals dissolve and become active only at an alkaline pH.

Option (2) Basic pH of the gut — Correct. Bacillus thuringiensis keeps its toxin as inactive protoxin crystals, so the toxin does not kill the bacterium itself. When an insect eats the crystals, the alkaline (basic) pH of its gut dissolves them and turns the protoxin into the active toxin. The toxin then makes pores in the midgut cells, and the insect dies.

Option (3) Neutral pH of saliva — Incorrect. Saliva only wets the food in the mouth. The protoxin is activated in the gut, after it has been swallowed.

Option (4) Acidic pH of hemolymph — Incorrect. Hemolymph is the blood of insects. The toxin acts inside the gut on the cells lining it; it is activated there, not in the blood.

Note: A similar question was also asked in CUET (UG) 2022 on 30-08-2022 (Slot 2) and on 16-07-2022 (Slot 1).

NCERT Extract:
Biotechnological Applications in Agriculture – …