LIFE SCIENCE

Detailed explanation-1: -The correct answer is the Alkaline pH of the stomach of insects. Bt toxins are initially inactive protoxins but after ingestion by the insect, these inactive toxins become active due to the alkaline pH of the gut which solubilizes the crystals. Hence, a high pH value is required to make Bt toxins active.

Detailed explanation-2: -Spores made by Bt damage the gut of insect larvae after the larvae eat them. The insect gut must have a pH of 9.0 to 10.5 (high pH) in order to activate the toxin.

Detailed explanation-3: -The Bt toxin is present as a protoxin (inactive form) in Bt cotton. It is activated due to the basic pH of the gut of the cotton bollworm insect. An alkaline pH would mean that the pH would be more than 7. Hence at pH=10, the protoxin would be converted to the active form.