Question

Following are the steps involved in action of toxin in Bt. Cotton
A. The inactive toxin converted into active form due to alkaline pH of gut of insect.
B. Bacillus thuringiensis produce crystals with toxic insecticidal proteins.
C. The alkaline pH solubilises the crystals.
D. The activated toxin binds to the surface of midgut cells, creates pores and causes death of the insect.
E. The toxin proteins exist as inactive protoxins in bacteria.
Choose the correct sequence of steps from the options given below:

• A. E → C → B → A → D
• B. B → C → A → E → D
• C. A → E → B → D → C
• D. B → E → C → A → D

Answer 1

The Correct Option is D

The question involves the action of toxins in Bt. Cotton, specifically focusing on the steps undertaken by these toxins to affect insect pests. Let’s analyze each step logically:

1. Bacillus thuringiensis produces crystals with toxic insecticidal proteins: This is the initial step where Bacillus thuringiensis bacteria produce the toxins in a crystal form. These proteins are specifically designed to target certain insect pests.
2. The toxin proteins exist as inactive protoxins in bacteria: The proteins produced are initially in an inactive form called protoxins. This is a safety mechanism as it prevents the bacteria from being affected by their own toxin.
3. The alkaline pH solubilizes the crystals: Upon ingestion by the insect, the alkaline conditions in the gut are crucial as they dissolve these protein crystals into soluble forms, a necessary step for activation.
4. The inactive toxin is converted into active form due to the alkaline pH of insect gut: The high pH of the insect gut transforms the protoxins into their active form, ready to exert their toxicity.
5. The activated toxin binds to the surface of midgut cells, creates pores, and causes the death of the insect: The activated toxin binds to specific receptors on the midgut cells of the insect, forming pores in the cell walls, leading to cell lysis and ultimately the insect's death due to disruption of gut functionality.

Correct Sequence: Based on the explanation, the correct sequence of steps is B → E → C → A → D.

This sequence is logical as it describes the entire pathway from toxin production in bacteria to the destruction of the insect pest, aligning with the biological action of Bt toxins.