When an insect feeds on the Bt plant, the insect dies due to the conversion of inactive protein to active protein in:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Alkaline pH of the gut.
Option (1) Alkaline pH of the gut. — Correct. The active toxin then binds to the cells lining the midgut and makes pores in them. The cells swell and burst, and the insect dies.
Option (2) Acidic pH of the gut. — Incorrect. The place is right but the pH is wrong. The protoxin crystals dissolve and become active only at an alkaline pH, and the insect gut that does this is alkaline.
Option (3) Acidic pH of saliva. — Incorrect. Both parts are wrong. The toxin is not activated in the saliva, and the pH it needs is alkaline, not acidic.
Option (4) Alkaline pH of saliva. — Incorrect. The pH is right but the place is wrong. The crystals pass on to the gut, and it is there that they are activated.
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.”