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.
B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Insecticidal protein
Option (1) Proteolytic enzymes — Incorrect. Proteolytic enzymes digest proteins. The crystals are not enzymes; they are the toxin itself.
Option (2) Chitin — Incorrect. Chitin is the hard material of insect bodies and fungal cell walls, not a protein.
Option (3) Insecticidal protein — Correct. The passage says the crystals contain a toxic insecticidal protein. It stays inactive in the bacterium as a protoxin.
Option (4) Flavoprotein — Incorrect. Flavoproteins are proteins that carry a flavin group and work in oxidation–reduction reactions. They are not the Bt toxin.
Note: 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.