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Question #46925
The Question
A botanist attempts to initiate callus formation by taking a leaf explant from a 50-year-old standard herbarium specimen and culturing it on a nutrient medium supplemented with an optimal Auxin to Cytokinin ratio. Despite providing ideal physical conditions, the explant fails to undergo dedifferentiation. Which of the following is the primary physiological reason for this failure?
Options
- A.
The explant lacks apical meristems, which are the exclusive sites of cellular totipotency in angiosperms.
- B.
Irreversible desiccation and protein denaturation have destroyed the enzymatic machinery and receptors required for phytohormone signaling.
- C.
The endogenous Auxin and Cytokinin in the dried tissue are permanently locked in a high ratio that strictly promotes rooting instead of callus formation.
- D.
The nutrient medium lacks the specific enzymes required to rehydrate and reactivate the dormant plasmodesmata in the preserved tissue.
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
Museum vs. Herbarium Logic|Meristematic Totipotency|Seed Dormancy Breaking
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the formula 'Auxin + Cytokinin = Callus' and 'Herbarium = Plant preservation' without integrating the physiological state of the tissue.
The trap lies in applying the dynamic physiological rules of plant growth regulators (PGRs) to taxonomically preserved, necrotic (dead) tissue.
Failing to recognize that hormone signaling strictly requires living, metabolically active cells with intact protein receptors leads to selecting distractors based on hormone ratios (Option C) or meristem locations (Option A).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | The Living World - Class 11 |
| Concept | Museum vs. Herbarium Logic |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |