Biotechnological Applications In Agriculture

Bt cotton is a genetically modified crop carrying cry genes obtained from the soil bacterium Bacillus thuringiensis, as described in NCERT Class 12, Chapter 11 (Biotechnology and its Applications). These genes encode crystalline (Cry) proteins that act as insecticidal toxins against specific groups of insects such as lepidopterans, coleopterans and dipterans. By incorporating the relevant cry gene into cotton, the plant itself produces the toxin and becomes resistant to bollworm without external chemical spraying. Agrobacterium tumefaciens is used merely as a vector to deliver genes into plant cells, not as the source of the toxin gene, so it is incorrect. Escherichia coli is a laboratory host bacterium for cloning and protein production, not the natural origin of cry genes. Thermus aquaticus is the source of the heat-stable Taq polymerase used in PCR, which is unrelated to insect resistance. A consistency check confirms the logic: the toxin must come from an organism that naturally produces an insecticidal protein, and only B. thuringiensis fits this requirement among the options.