Read the following passage carefully and answer the given questions.
Insulin consists of two short polypeptide chains- chain A and chain B, that are linked together by disulphide bridges. Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans, coleopterans and dipterans. Bt toxin protein is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. Transgenic animals that produce useful biological products can be created by the introduction of the portion of DNA (or genes) which codes for a particular product such as human protein (α-1-antitrypsin) used to treat emphysema. Plants, bacteria, fungi and animals whose genes have been altered by manipulation are called Genetically Modified Organisms (GMO). GM plants have been useful in many ways. Genetic modification has: (i) made crops more tolerant to abiotic stresses. (ii) reduced reliance on chemical pesticides (pest-resistant crops). (iii) helped to reduce post harvest losses. (iv) increased efficiency of mineral usage by plants (this prevents early exhaustion of fertility of soil). (v) enhanced nutritional value of food.
The beetles that infest Bt cotton plant are killed:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Due to conversion of protoxins into toxin in alkaline pH of the gut of the insects that causes lysis of midgut epithelial cells.
Option (1) Due to conversion of protoxins into toxin in acidic pH of the gut of the insects that causes lysis of midgut epithelial cells. — Incorrect. The insect gut is alkaline, not acidic. The alkaline pH is what dissolves the crystals.
Option (2) Due to conversion of protoxins into toxin in alkaline pH of the gut of the insects that causes lysis of midgut epithelial cells. — Correct. All three steps are right: protoxin to toxin, alkaline gut, lysis of midgut cells.
Option (3) Due to conversion of toxins into protoxin in alkaline pH of the gut of insects that causes lysis of midgut epithelial cells. — Incorrect. The change runs the other way. The inactive protoxin is turned into the active toxin.
Option (4) Due to conversion of protoxins into toxin in alkaline pH of the gut of the insects that does not cause lysis of midgut epithelial cells. — Incorrect. If the toxin did not burst the midgut cells, the insect would not die. The lysis is what kills it.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Biotechnological Applications in Agriculture – …
