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Question #45223
The Question
In a laboratory experiment, a resistant strain of Helicoverpa armigera (cotton bollworm) is fed Bt cotton leaves. Researchers observe that the inactive cry protoxin crystals are successfully solubilized in the insect's midgut, but the insect survives without any midgut epithelial lysis. Biochemical analysis reveals that the protoxin remains uncleaved. Integrating principles of biotechnology and enzyme kinetics, which of the following best explains this specific mechanism of resistance?
Options
- A.
A mutation altered the midgut pH, causing midgut proteases to lose their optimal pH and fail to lower the activation energy for protoxin cleavage.
- B.
The alkaline pH of the midgut directly denatured the protoxin, preventing it from binding to the specific receptors on the midgut epithelial cells.
- C.
The insect evolved a mechanism to secrete acidic juices in the midgut, which directly increases the activation energy required for crystal solubilization.
- D.
The midgut epithelial cells lack the specific membrane receptors required to enzymatically cleave the solubilized protoxin into its active form.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Bacillus_thuringiensis|Cry_Protein|Enzyme_Denaturation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often oversimplify NCERT's statement 'alkaline pH activates the Bt toxin' by assuming pH alone does the chemical conversion.
The trap relies on distinguishing between 'solubilization' (driven directly by alkaline pH) and 'cleavage' (driven by midgut proteases, which are pH-dependent enzymes).
Option D is a highly attractive distractor because receptor mutation is a common resistance mechanism, but it fails to explain why the protoxin remains uncleaved.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biomolecules - Class 11 |
| Concept | Enzyme Activation Energy Lowering |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |