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.
The Bt toxin acts on ______ of insect pest.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Midgut
The Bt protoxin becomes active in the alkaline gut of the insect. The active toxin then acts on the gut itself.
Option (1) Hind gut — Incorrect. The hind gut mainly absorbs water and forms the faeces. The toxin binds earlier, in the midgut.
Option (2) Nervous system — Incorrect. Bt toxin is not a nerve poison. It damages the lining of the gut.
Option (3) Reproductive system — Incorrect. The toxin kills the insect through its gut; it does not act on reproduction.
Option (4) Midgut — Correct. The activated toxin binds to the epithelial cells of the midgut and makes pores in them. The cells swell and burst, and the insect dies.
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.
NCERT Extract:
Biotechnological Applications in Agriculture – “… Bt Cotton: Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. … Actually, the Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect.”