CASE STUDY
Some strains of Bacillus thuringiensis produce protein that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). Bacillus thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. The Bt toxin proteins exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form due to alkaline pH of the gut which solubilise the crystals.
Bt toxin exists as inactive protoxins, it is converted into an active form of toxin due to :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Alkaline pH of the insect’s gut
Option (1) Enzymes in insect’s gut — Incorrect. The passage gives the pH of the gut, not its enzymes, as the cause.
Option (2) Acidic pH of the insect’s gut — Incorrect. The condition is reversed: the gut of these insects is alkaline, not acidic.
Option (3) Binding with collagen in insect’s gut — Incorrect. Collagen is an animal connective-tissue protein; it plays no part in activating the toxin.
Option (4) Alkaline pH of the insect’s gut — Correct. The alkaline pH dissolves the crystals and turns the inactive protoxin into the active toxin. This is why the toxin does not harm the bacterium itself.
Note 1: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
Note 2: A similar question was also asked in CUET (UG) 2025 on 28-05-2025 (Slot 1) and on 26-05-2025 (Slot 2), and in CUET (UG) 2022 on 16-07-2022 (Slot 1).