Read the passage and answer the following questions:
Genetic modification (GM) has been utilised to create custom-designed plants that serve as alternative resources for industries, producing starches, fuels, and pharmaceuticals. Biotechnology in agriculture has numerous applications, one of which involves developing pest-resistant plants to reduce the reliance on chemical pesticides. This is achieved by introducing the Bt toxin gene from the bacterium Bacillus thuringiensis (Bt) into plants, creating what is known as a bio-pesticide. Notable examples include Bt cotton, Bt corn, rice, tomato, potato, and soybean. Bt toxin is a naturally occurring insecticidal protein produced by certain strains of Bacillus thuringiensis. During a specific phase of their growth, these bacteria form protein crystals containing toxic substances. These crystals harbour inactive protoxins, which, when activated, become lethal to targeted insects. Different Bt toxin genes, such as cryIAc and cryIIAb, have been isolated and introduced into various crop plants, depending on the crop and the specific pests targeted, as Bt toxins are often insect-group specific. By incorporating these genes, plants gain inherent resistance to insects without the need for synthetic insecticides. This advancement in biotechnology has significant implications for sustainable and eco-friendly agricultural practices.
Arrange the following events in the correct sequence after an insect feeds on the Bt toxin crystals:
A. The activated toxin binds to the surface of the midgut epithelial cells.
B. The alkaline pH of the gut solubilises the crystals and the inactive protoxin becomes an active toxin.
C. Pores are created that cause cell swelling and lysis, and the insect dies.
D. The insect ingests the crystals that contain the inactive protoxin.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → D, B, A, C
The Bt toxin made by Bacillus thuringiensis is stored in protein crystals as an inactive protoxin. It becomes harmful only inside the insect:
D. First, the insect ingests the crystals that contain the inactive protoxin.
B. In the gut, the alkaline pH solubilises the crystals, and the protoxin is converted into the active toxin.
A. The activated toxin then binds to the surface of the midgut epithelial cells.
C. At these cells it creates pores, which cause the cells to swell and burst (lysis), and the insect dies.
NCERT Extract:
Biotechnological Applications in Agriculture – “… B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. … Actually, the Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect.”