Bt toxin produced by Bacillus thuringiensis is resistant to:

Insects

The correct answer is Option (2) –Insects

Bt toxin, short for Bacillus thuringiensis toxin, is a naturally occurring protein produced by the bacterium Bacillus thuringiensis (Bt). This toxin gene has been isolated and cloned from the bacterium and subsequently expressed in various plants. This genetic modification is employed to confer resistance to insects without the need for chemical insecticides, essentially creating a form of bio-pesticide. Some notable examples of genetically modified crops that contain the Bt toxin gene include Bt cotton, Bt corn, Bt rice, Bt tomato, Bt potato, and Bt soybean, among others.

In the case of Bt Cotton: Certain strains of Bacillus thuringiensis naturally produce proteins that are toxic to specific insects, including lepidopterans (such as tobacco budworm and armyworm), coleopterans (beetles), and dipterans (flies and mosquitoes). B. thuringiensis forms protein crystals during a specific phase of its growth, and these crystals contain the insecticidal proteins. Interestingly, the Bt toxin proteins initially exist in an inactive form known as protoxins.

When an insect consumes plant tissues containing these inactive toxin crystals, the alkaline pH environment within the insect's gut triggers the activation of the protoxins. The activated toxin then binds to the surface of the midgut epithelial cells in the insect's digestive system. This binding results in the formation of pores in the cell membranes, leading to swelling and lysis of the cells. Ultimately, this process causes the death of the insect.

In summary, Bt toxin is a natural insecticidal protein produced by Bacillus thuringiensis. When the Bt toxin gene is introduced into plants, it confers resistance to specific insect pests by producing the toxin within the plant tissues. When insects feed on these modified plants, they ingest the Bt toxin, which becomes active in their digestive systems and leads to their demise. This approach has been widely adopted in agriculture as a means of reducing the need for chemical pesticides and promoting environmentally friendly pest control.