Biotechnological Applications In Agriculture

The Cry protein produced by Bacillus thuringiensis exists as an inactive protoxin in crystal form and is converted into its active toxic state by the alkaline pH of the insect's midgut, a mechanism detailed in NCERT Class 12, Chapter 11 (Biotechnology and its Applications). After an insect consumes the crystals, the alkaline environment solubilises them, and the activated toxin binds to the surface of the midgut epithelial cells, creating pores that cause cell swelling, lysis and eventually the death of the insect. An acidic foregut condition would not solubilise and activate the protoxin, so that option is wrong. A neutral hindgut pH does not match the specific alkaline requirement that triggers activation. High temperature in the crop region is not the activating factor described for Cry proteins. This pH-dependent activation also explains the selective safety of Bt crops, since the protoxin passes harmlessly through the acidic digestive tract of mammals without being converted to its active form. A biological consistency check supports the answer: the toxin is harmless in crystal form and to organisms with acidic stomachs such as humans, and becomes lethal only where the gut is alkaline, which is the midgut of susceptible insects.