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Question #45451
The Question
In a newly discovered resistant strain of Helicoverpa armigera (cotton bollworm) feeding on Bt cotton, researchers observe that the Cry protoxin is successfully solubilized by the alkaline pH of the midgut and cleaved into its active form. Furthermore, the active toxin successfully binds to the specific receptors on the midgut epithelial cells. Despite this, no pore formation, cell swelling, or lysis occurs. Which of the following best explains this specific mechanism of resistance?
Options
- A.
The receptor allows binding, but a mutation in its associated downstream secondary messenger cascade prevents the signaling required for toxin penetration and pore formation.
- B.
The alkaline pH of the midgut solubilizes the protoxin but is insufficient to cleave it into the active form without specific acidic proteases.
- C.
The insect has downregulated the expression of specific midgut epithelial receptors, preventing the active toxin from anchoring to the membrane.
- D.
The active protein toxin is neutralized by RNA interference (RNAi) mechanisms within the midgut lumen before it can induce cell swelling.
Check Your Answer
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
Cry_Gene_Specificity|Bt_Toxin_Activation_Trigger|G-protein_Receptors
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the NCERT sequence (Alkaline pH -> Activation -> Binding -> Lysis) as a purely physical, uninterrupted domino effect, failing to recognize that 'binding' and 'pore formation' are distinct events bridged by intracellular signaling.
The question uses a 'Premise-Contradiction' trap: students who don't read carefully will choose Option C (receptor downregulation), which is the most common real-world resistance mechanism, ignoring the stem's explicit statement that binding did occur.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Chemical Coordination and Integration - Class 11 |
| Concept | Secondary Messenger Cascade |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |