Identify the incorrect statements.
(A) Bacillus thuringiensis is a transgenic organism.
(B) Bt toxin enter the testes or the ovaries of the insect pest, sterilize it and thus prevent it's multiplication.
(C) Proteins encoded by cryIAc and cryIIAb control cotton bollworms.
(D) Bt protein exists as active toxin in the Bacillus.
(E) Alkaline pH of the insect gut solubilizes the toxin protein crystals.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (D) only
(A) Bacillus thuringiensis is a transgenic organism. — False. Bacillus thuringiensis is a natural soil bacterium that makes the toxin on its own. The transgenic organisms are the crops, such as Bt cotton, into which its cry genes were put.
(B) Bt toxin enter the testes or the ovaries of the insect pest, sterilize it and thus prevent it’s multiplication. — False. The toxin does not act on the reproductive organs. It acts in the midgut and kills the insect.
(C) Proteins encoded by cryIAc and cryIIAb control cotton bollworms. — True. These are the genes put into Bt cotton. cryIAb controls corn borer; the choice of gene depends on the crop and its pest.
(D) Bt protein exists as active toxin in the Bacillus. — False. It is kept as an inactive protoxin, which is why it does not kill the bacterium itself.
(E) Alkaline pH of the insect gut solubilizes the toxin protein crystals. — True. This is the step that turns the protoxin into the active toxin.
NCERT Extract:
Biotechnological Applications in Agriculture – “… Bt Cotton: Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. … Actually, the Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect. Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton (Figure 10.1). The choice of genes depends upon the crop and the targeted pest, as most Bt toxins are insect-group specific. The toxin is coded by a gene named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms, that of cryIAb controls corn borer.”