One of the application of biotechnology is to get pest resistance plants. Justify the statement with reference to Bt. cotton.

Bt cotton is created by using a bacterium Bacillus thuringiensis. This bacterium produces a protein that kills certain insects such as Lepidopterans and Dipterans. B. thuringiensis forms protein crystals (Cry) during a particular phase of their growth. These crystals contain a toxic insecticidal protein. Bt toxin does not kill the bacterium because it exists as inactive protoxins in the body of Bacillus. Once an insect ingests the inactive toxin, it gets exposed to the alkaline pH of the gut, which solubilizes the crystals and converts it into an active form. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis and eventually causes the death of the insect. Specific Bt toxin genes such as Cry I AC and Cry II AB are isolated from Bacillus thuringiensis and incorporated into cotton plants to form Bt cotton.