Question

Given below are certain characteristics of thurioside protein. Which of the statement given is correct?
i. It is activated by the alkaline pH of the gut of the insect pest ultimately killing it.
ii. It binds with the epithelial cells of the midgut of the insect pest ultimately killing it.
iii. It does not kill the carrier bacterium which is itself resistant to this toxin.
A. (i) and (ii)
B. (i) and (iii)
C. (ii) and (iii)
D. (i), (ii), and (iii)

Answer 1

Hint: Thurioside is a toxin generated by the bacterium Bacillus thuringiensis . Therefore, it is of bactericidal origin. It is used as a bio-insecticide, as it is very effective against disease-causing insects such as mosquitoes, moths, flies, etc. If consumed by mistake, it acts like stomach poison.
Complete Step-by-step answer:
Thurioside is obtained from the bacteria Bacillus thuringiensis and is used as a bioinsecticide. The toxin helps by killing the insects or pests by inhibiting the transport of ions, and the formation of pores in the gut which finally leads to the bursting of cells.
This gene for toxin is also introduced in transgenic plants which offer resistance to the crops from pests. 
Bacillus thuringiensis forms the protein crystals, which contain a toxic insecticidal protein.
Initially, Bt toxins are inactive protoxins but after ingestion by the insects, their inactive toxin becomes active because of the alkaline pH of the gut, which solubilizes the crystals.
The activated toxin binds to the surface of the midgut, and epithelial cells swell and lysis, further resulting in the death of the insect.
Therefore the correct answer is Option A.

Note: Bt Crops are transgenic crops that generate the same toxin as the bacterium Bacillus thuringiensis in the plant cell, thus, which protects the crops from pests. The bacterium secretes specific proteins referred to as the “cry proteins” that are toxic to insects. A few of the Bt crops contain cotton, corn, brinjal, etc. Bt is a bacterium that is not toxic to humans or other mammals but is toxic to some insects when ingested.