Question

‘Bt’ toxin is a/an
A. Intracellular
B. Intracellular crystalline protein
C. Extracellular crystalline protein
D. Lipid

Answer 1

Hint: It is an insecticidal protein that is secreted by Bacillus thuringiensis. They are protein crystals that are secreted during a particular phase of their growth. They are secreted as protoxins (inactive) but the alkaline pH of the insect gut converts it to an active form by the alkaline pH of the insect gut.

Complete answer: A gram-negative bacterium known as Bacillus thuringiensis produces Bt toxin. A gene from Bt toxin has been cloned from the bacteria and is expressed into plants to provide resistance to pests without the need for insecticides. It secretes toxin extracellularly, which is a crystalline protein that blocks insect gut proteins upon ingestion. It is commonly used as biological insecticides that affect only the target insect pests and does not affect other insects. It can be applied to the crops in two ways; it can be sprayed to the crops or the crop plants can be genetically modified to express this protein that can act on insect pests. It has been used as an insecticide since 1920 and is commonly used in organic farming. Bacillus thuringiensis acts as a source of genes that can be used to genetically modify several food crops because it produces a toxin that helps to deter insects.
Hence, the correct answer is option C.

Note: Different Bt toxin genes are isolated from Bacillus thuringiensis and are incorporated into several crops such as cotton. The choice of genes depends upon the type of crop and the targeted pest.