EXPLAIN OPTION NO.3

Q 46
Which of the following statements about Bacillus thuringiensis are correct? ​

(A) One of the toxin produced by the bacteria is thurioside, which is active against different ​groups of insect larvae. ​
(B) The toxin accumulates inside the bacteria during sporulation.​
(C) Upon ingestion by susceptible insects they are converted into active form and kill them by inhibition of ion transport in the midgut.​
(D) The proteins encoded by the gene Cry || Ab controls corn borer.​

(1) B only 
(2) A and B
(3) A, B and C 
(4) A, B, C and D ​
 

Dear Student,

The correct answer is option (3)
The explanation of option (C) is given below:
When Bt toxin is ingested by susceptible insect larvae, the crystal proteins of Bacillus thuringiensis are dissolved and converted into its active form by when comes in the contact of midgut proteases. The midgut of larvae has alkaline pH. The active form of toxin then binds to specific receptors present on the surface of the luminal membrane of midgut and form pores that disturbs the transmembrane ionic gradients and osmotic balance. This leads to the disruption of the epithelium and results in the death of the insect.
The toxin accumulates as crystals inside the bacteria during sporulation. Hence, option (B) is also correct.
Thurioside toxin is produced by bacterium Bacillus thuringiensis which is able to destroy different groups of insects. Hence option (A) is also correct.
The proteins encoded by the gene cry IIAb controls cotton bollworms and cry IAb controls corn borer. Hence, option (D) is incorrect.

Regards

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