Question

The Bt toxin is not toxic to human beings because
A. The pro Bt toxin activation requires temperature above human body temperature
B. The Bt toxin regulates only insect-specific targets
C. The Bt toxin formation from pre Bt toxin requires pH lower than that present in human stomach
D. Conversion of pro Bt toxin takes place only in highly alkaline conditions

Answer 1

Hint: Bt toxin is produced from Bacillus thuringiensis. It can kill the insects when it turns into its active form. The Insect's gut has alkaline pH which is suitable for its conversion. Human beings do not have a highly alkaline condition in their body.

Complete answer:
Bacillus Thuringiensis is a soil bacterium. Proteins that kill insects like tobacco budworm, armyworm, beetles and dipterans are produced by Bacillus thuringiensis. It can be fatal to certain herbivorous insects. The mode of action of Bt toxin is different from usual bacteria.
When the insect ingests bt toxin, it exists in its inactive form that is prototoxin. It is converted to its active form toxin when it gets alkaline pH. The alimentary canal of insects has alkaline pH which solubilised crystals. Activated toxins bind to the epithelial cells in the midgut of insects. It creates pores and due to this cell swells and lyses. It can eventually cause the death of insects.
As Bt toxin is present in its inactive form, it cannot kill bacteria themselves. It needs an alkaline medium to turn on its active form. Humans do not have high alkaline conditions in their body, so the conversion of pro Bt toxin to Bt toxin (inactive to active) does not take place. That’s why it is not harmful to human beings.
From the above information we have found that the Bt toxin is not harmful to human beings because conversion of pro Bt toxin takes place only in highly alkaline conditions.

Hence, the correct answer is option (D).

Note: Bt toxin is used as an insecticide by producing a crystal-shaped protein that is a (Cry toxin) that specifically kills certain insects. It is also used to resist plants from certain insect attacks. Bt cotton is the recombinant plant which is resistant to insects. It is used for organic farming.