Bacillus thuringiensis forms protein crystals which contain insecticidal protein. This protein:
- is activated by acid pH of the foregut of the insect pest.
- binds with epithelial cells of midgut of the insect pest ultimately killing it
- is coded by several genes including the gene cry
- does not kill the carrier bacterium which is itself resistant to this toxin
Answer
(2) binds with epithelial cells of midgut of the insect pest ultimately killing it
Solution
As per NCERT, the Bt toxin protein exists as an inactive protoxin; once an insect ingests it, the inactive toxin is converted into the active form due to the alkaline pH of the gut, which solubilises the crystals.
⇒ The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis, and eventually the death of the insect.
(1) is wrong as the pH is alkaline, not acidic. (4) is wrong as the bacterium is not killed because the toxin exists inside it as an inactive protoxin, not because the bacterium is resistant.
Answer: (2)