Question

Which of the following statement is incorrect?

(i) Recombinant DNA technology is used to improve crop plants by increasing their productivity, by making them more nutritious, and by developing disease resistant.

(ii) Bt cotton is resistant to bollworm infestation.

(iii) Bacillus thuringiensis form cry protein during any phase of their growth.

(iv) Bacillus thuringiensis is not harmed by self-cry protein because of its occurrence as protoxin (inactive).

(v) Protoxin cry protein is changed into active cry protein in the stomach of insects due to alkaline pH in the stomach.

A. (i), (ii) and (iv)
B. (i) and (iv)
C. Only (iii)
D. All of the above

Answer 1

Hint: Bacillus Thuringiensis is an aerobic, Gram +ive and spore-forming bacteria. It is usually called Bt. It is found in water, soil, insect faeces, plant surfaces, insects, etc. It is commonly used as a bio-insecticide to manage the infestation of butterfly caterpillars. Caterpillars consume the spores sprinkled onto plants and get destroyed. 
Complete Step-by-step answer:
Recombinant DNA technology is used to enhance crop plants by improving their productivity, making them more nutritious, and developing disease resistance.
Bt cotton is genetically engineered cotton that is insect resistant. The butterflies that feed on Bt cotton die because of the Bt toxin in the modified plant.
Bacillus thuringiensis is not affected by self-cry protein due to its occurrence as protoxin (inactive). Cry protoxin is changed into its active state when there is a pH reduction in the insect’s intestine. They are cytolytic in action, generating pores in the intestine and destroying them.
Bacillus thuringiensis forms Bt toxin protein crystals only during a certain stage of their growth, i.e.during sporulation. It exists as an inactive protoxin, till an insect ingests it, after ingestion, it transforms into an active form because of the alkaline pH of the gut which solubilises the crystal and enables the toxin to bind to the gut epithelium and causes cell death through lysis and swelling.
Therefore the correct answer is Option C.
Note: Bacillus Thuringiensis creates an insecticidal protein during sporulation. The Bt-toxin gene is introduced into plants to develop a wide range of pest-resistant plants by genetic engineering. E.g., Bt corn, Bt cotton, etc.