Question

$Bacillusthuringiensis$ forms proteins which contain insecticidal proteins. This protein

• A. Does not kill the carrier bacterium which is itself resistant to the toxin
• B. Is coded by several genes including the gene $cry$
• C. Is activated by acid pH of the foregut of the insect pest
• D. Binds with epithelial cells of midgut of the insect pest, ultimately killing it

Answer 1

The correct option is D Binds with epithelial cells of midgut of the insect pest, ultimately killing it

Bt toxin and its mechanism of action
Bt toxin is an insecticidal crystal protein which kills target insect pests. It is naturally produced by the bacterium, $Bacillusthuringiensis$, during sporulation. The endotoxin that accumulates in bacteria is in an inactive form (protoxin).

When an insect feeds on the plant parts of the genetically modified crop carrying the cry gene, it ingests the inactive toxin molecules as well.
The protoxin gets activated at an alkaline pH in the gut of the insects due to the solubilisation of the crystal proteins. This active toxin generates pores in the epithelium of the midgut of the insects which results in the swelling of cells followed by their lysis. This consequently results in the death of the insect.

Final answer
(A) Binds with epithelial cells of midgut of the insect pest, ultimately killing it