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Question #47685
The Question
Which of the following statements regarding the activation and mechanism of action of the Bacillus thuringiensis (Bt) delta-endotoxin is INCORRECT?
Options
- A.
The inactive protoxin crystals are solubilized by the alkaline pH of the insect midgut, followed by proteolytic cleavage into an active form.
- B.
The activated Cry toxin binds to specific cadherin-like receptors on the brush border of the midgut epithelial cells.
- C.
The toxin induces insect death by entering the midgut epithelial cells via receptor-mediated endocytosis and inhibiting cellular respiration.
- D.
Mammals remain unaffected by ingested Bt protoxins due to the highly acidic pH of their stomach and the absence of specific target receptors.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Pro-insulin|C-peptide|Disulfide bridges|Biotechnology
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: The exact mechanism of cellular destruction by Bt toxin.
Common Misconception: Students often assume that proteinaceous toxins must be internalized (via endocytosis) to exert lethal effects by inhibiting intracellular processes (like respiration or translation).
However, NCERT explicitly states that Bt toxin acts at the membrane level by creating pores, making it a pore-forming toxin (PFT) that causes osmotic lysis.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Microbes in Human Welfare - Class 12 |
| Concept | Bioactive Molecule Origin |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |