Arrange the following steps which are involved in action of Bt toxin proteins on insects in correct sequence.
(A) Conversion of inactive toxin into active one by alkaline pH of the gut of insect
(B) Creation of pores that cause cell swelling and lysis which leads to death of insect
(C) Inactive protoxins is ingested by insect
(D) Activated toxin binds to the surface of midgut epithelial cells of insect
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C), (A), (D), (B)
(C) Inactive protoxins is ingested by insect — comes first. The Bt toxin exists in the bacterium as an inactive protoxin, and this is why the toxin does not kill the bacterium itself. The action begins when an insect eats it.
(A) Conversion of inactive toxin into active one by alkaline pH of the gut of insect — comes second. The alkaline pH of the insect’s gut dissolves the crystals and changes the protoxin into the active toxin.
(D) Activated toxin binds to the surface of midgut epithelial cells of insect — comes third. The toxin can bind only after it has been activated.
(B) Creation of pores that cause cell swelling and lysis which leads to death of insect — comes last. The pores form after the toxin has bound to the cells, and the damaged cells finally kill the insect.
NCERT Extract:
Biotechnological Applications in Agriculture – “… 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.”