A diagram shows an insect larva eating a leaf with Bt protein crystals. In the gut, the inactive protein becomes active; the active toxin binds the surface of the midgut epithelial cells and creates pores, and the cells swell and burst. Which statement explains this?
A
The acidic pH of the insect gut activates the toxin
B
The alkaline pH of the insect gut solubilises the crystals, and the bacterium is safe because it stores the toxin as an inactive protoxin
C
The toxin is active in the bacterium as well, but the bacterium survives by repairing its membrane
D
The toxin acts on the human gut in the same way
Show the answer
The answer is B.
Bt toxin exists as an inactive protoxin in Bacillus thuringiensis. In the insect gut the alkaline pH solubilises the crystals and activates it; the toxin binds midgut epithelial cells, creates pores and causes swelling, lysis and death of the insect.
A.
Activation needs the alkaline pH of the insect gut.
C.
The toxin exists in the bacterium as an inactive protoxin, so it does not harm it.
D.
Activation depends on conditions in the insect gut; the figure concerns insect larvae.
NCERT: Class 12 Biology, Chapter 10, 10.1
Sample 2NEET level
Assertion (A): Bt cotton is resistant to attack by bollworms. Reason (R): RNA interference has been used to make tobacco plants resistant to the nematode Meloidogyne incognita.
A
Both A and R are true and R is the correct explanation of A
B
Both A and R are true but R is not the correct explanation of A
C
A is true but R is false
D
A is false but R is true
Show the answer
The answer is B.
Bt cotton carries cry genes such as cryIAc and cryIIAb from Bacillus thuringiensis, whose proteins control cotton bollworms, so A is true. RNA interference was used against Meloidogyne incognita in tobacco, which is also true, but it is a different technique and does not explain the resistance of Bt cotton.
A.
R does not explain A: Bt cotton's resistance comes from the cry genes of Bacillus thuringiensis, not RNA interference.
C.
R is true: RNAi was used to protect tobacco from Meloidogyne incognita.
D.
A is true: Bt cotton expresses Cry proteins that kill bollworms.
NCERT: Class 12 Biology, Chapter 10 (Biotechnology and its Applications), Biotechnological applications in agriculture
Practise Bt crops and transgenic animals
Practice at the level you choose, with the answer after every question; timed tests with the answers when you submit. Every question is verified against NCERT first.