Proteins

To identify the incorrect statements among the given options, let's analyze each one:

1. Statement (A): Bacillus thuringiensis (Bt) is a naturally occurring bacterium and not a transgenic organism. The term "transgenic" refers to genetically modified organisms that have been altered through genetic engineering, typically involving the insertion of genes from another species. Therefore, this statement is incorrect if meant to imply that Bt itself is transgenic.
2. Statement (B): Bt toxin does not directly enter the testes or the ovaries of the insect pest to sterilize it. Instead, the Bt toxin is ingested by the insect, after which it binds to specific receptors in the insect gut, leading to cell lysis and ultimately death. Thus, this statement is incorrect.
3. Statement (C): Proteins encoded by cryIAc and cryIIAb are indeed used in transgenic crops to control cotton bollworms. This statement is correct.
4. Statement (D): In Bacillus thuringiensis, the Bt protein exists as an inactive protoxin. It only becomes active when ingested by the insect and exposed to the alkaline pH of the insect gut where it is cleaved into the active toxin form. Therefore, this statement is incorrect.
5. Statement (E): The alkaline pH of the insect gut plays a crucial role in solubilizing the protoxin protein crystals, activating the toxin, and making it lethal to the insect. This statement is correct.

Based on the analysis above, the incorrect statements are (B) and (D). Therefore, the correct answer is: (B) and (D) only