Choose the correct option for the toxic protein produced by B. thuringiensis

Options

A. It acts in acidic medium and binds to epithelial cells of foregut
B. It acts in neutral medium and binds to epithelial cells of hindgut
C. It acts in alkaline medium and binds to epithelial cells of foregut
D. It acts in alkaline medium and binds to epithelial cells of midgut

Explanation

**Step-by-Step Solution:**

1. **Identify the Bacteria**: The question asks about the toxic protein produced by *Bacillus thuringiensis* (often abbreviated as Bt). This bacterium is known for its ability to produce a specific toxin that is harmful to certain insects.

2. **Understand the Toxic Protein**: The toxic protein produced by *Bacillus thuringiensis* is known as *Cry protein*. This protein is produced in the form of crystalline inclusions that are toxic to specific insect larvae.

3. **Mechanism of Action**: When insects ingest the plants that have been treated with *Bacillus thuringiensis*, the alkaline conditions in their mid-gut dissolve the crystalline form of the *Cry protein*. This conversion allows the protein to interact with the epithelial cells of the insect's mid-gut.

4. **Effect on Insects**: The binding of the *Cry protein* to the mid-gut epithelial cells disrupts the gut function, leading to the insect's inability to digest food properly, ultimately resulting in death.

5. **Choose the Correct Option**: Based on the understanding that the toxic protein is the *Cry protein* and the mechanism involves an alkaline medium in the insect's gut, we can conclude that the correct answer to the question is option D, which states the correct conditions and effects of the *Cry protein*.

**Final Answer**: The correct option for the toxic protein produced by *Bacillus thuringiensis* is option D.

---