How does Bt cotton kill bollworms without being poisonous to humans?
Bt cotton carries a cry gene from Bacillus thuringiensis that makes a protoxin -- an inactive crystal protein.
Bt cotton carries a cry gene from Bacillus thuringiensis that makes a protoxin -- an inactive crystal protein. When a bollworm eats the plant, the alkaline pH of the insect's gut dissolves and activates the protoxin into a toxin that ruptures its gut cells and kills it. The human stomach is acidic and lacks the specific receptors, so the protein is simply digested harmlessly. Needing an alkaline gut and specific receptors makes the toxin pest-specific.
Key point
The Bt protoxin is activated only in the insect's alkaline gut, so it kills the pest but is harmlessly digested by humans.
Common mistake
assuming a plant that kills insects must also be toxic to people.
Memory tip
Bt is an inactive crystal until the insect's alkaline gut switches it on.
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