Question

Bacillus thuringiensis (Bt) produces proteins that kill certain insects and save crops: A. Bt toxin exist in inactive form (prototoxin) in bacteria B. Acidic pH of the insect gut activate toxin C. Bt toxin (protein) is present in beetles D. Due to the alkaline pH in the insect's gut it is converted into active toxin to kill the insects Choose the correct answer from the options given below:

• A. A and B only \
• B. B and C only \
• C. A, B and C only \
• D. A and D only

Hint:

Bt toxin activation requires an Alkaline pH. The highly alkaline midgut of the insect dissolves and activates the toxic crystal, creating a highly targeted bio-defense.

Answer 1

The Correct Option is D

Step 1: Concept The soil bacterium Bacillus thuringiensis synthesizes specific crystalline surface proteins (Cry endotoxins) that act as highly targeted bio-insecticides against specific crop pests.

Step 2: Meaning The toxin is highly selective because its activation requires a specific biochemical environment unique to the digestive tracts of susceptible target insects.

Step 3: Analysis * Statement A is correct: The bacterium produces the Cry protein as an inactive crystalline crystal called a prototoxin, which prevents the toxin from damaging the host bacterium itself. * Statement B is incorrect: The midgut environment of susceptible insects is highly alkaline, not acidic. * Statement C is incorrect: The gene and protein come originally from the bacterium Bacillus thuringiensis, not from beetles. * Statement D is correct: When a susceptible insect eats the crystal, the alkaline pH of its midgut dissolves the protein crystal. Proteases then clip the prototoxin, transforming it into an active toxin that punches holes in the insect's gut lining, killing the pest.

Step 4: Conclusion Statements A and D accurately describe the biology and activation mechanism of the Bt toxin. This matches option D. Final Answer: (D)