One of the applications of biotechnology is the production of insect resistant crop plants." Justify the statement with reference to Bt-cotton.

Explanation

The "cry.gene-.crylAc. and .crylAb. from Bacillus thuringiensis coding for the toxins are transferred to cotton plants. The proteins encoded by these genes control the cotton bollworms.
These Bt cotton plants express the Bt toxin gene by produceings the toxin that provides insect resistance.
Bt toxin is a toxic insecticidal protein formed in the form of protein crystals that kills certain insects.
It exists as inactive protoxin once an insect ingests 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 epithelial cells of the midgut and creates pores which causes cell swelling and lysis and finally the death of the insect.