Assertion (A): Bt toxin is not toxic to the organism producing it.
Reason (R): Bt toxin protein exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form of toxin.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both assertion and reason are true and reason is the correct explanation of assertion
Assertion (A): Bt toxin is not toxic to the organism producing it. — True. A is about the safety of the bacterium. Bacillus thuringiensis makes the toxin and stores it in protein crystals, yet the bacterium itself is not killed.
Reason (R): Bt toxin protein exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form of toxin. — True. R is about when the toxin becomes active. In the bacterium the protein is an inactive protoxin; the alkaline pH of the insect gut converts it into the active toxin.
Why R explains A? Inside the bacterium the toxin stays in its inactive protoxin form, so it cannot harm the cell that makes it. It turns active only in the gut of an insect that eats it. So R gives the reason why the toxin does not kill the bacterium, and R is the correct explanation of A.
NCERT Extract:
Biotechnological Applications in Agriculture – “… 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.”