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Question #45130
The Question
A population of cotton bollworms develops complete resistance to Bt cotton after several generations of continuous exposure. Physiological analysis of the resistant caterpillars reveals that the Cry1Ac protoxin is still successfully solubilized and cleaved into its active form within their gut, yet no cell lysis occurs. Based on the principles of evolution and biotechnology, which of the following best explains this phenomenon?
Options
- A.
Directional selection favored a mutation that shifts the midgut pH from alkaline to acidic, preventing the solubilization of the protoxin crystals.
- B.
Directional selection favored a mutation altering the specific receptor proteins on the surface of midgut epithelial cells, preventing toxin binding and pore formation.
- C.
The insect population acquired a mutation that prevents the RNA interference (RNAi) mechanism from silencing their essential cellular genes.
- D.
Disruptive selection led to the production of specialized gut macrophages that phagocytose the active Cry protein before it induces 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
Natural Selection Directionality|Bt Toxin|Cry1Ac
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'alkaline pH activates the toxin' and assume resistance must involve a pH shift.
The trap is failing to read the premise carefully ('protoxin is successfully cleaved') and not understanding the sequential steps of Bt toxicity (Ingestion -> Solubilization -> Activation -> Binding -> Lysis).
If activation occurs but lysis does not, the evolutionary block must be at the receptor binding step, driven by directional selection.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology and Its Applications - Class 12 |
| Concept | Bt Toxin Activation Trigger |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |