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Question #45951
The Question
During micropropagation, an apical meristem explant fails to proliferate into a callus despite optimal auxin and cytokinin concentrations in the nutrient medium. The parent plant from which the explant was excised exhibited severe necrosis and distortion in its youngest developing leaves, while its older leaves remained healthy. Which specific nutrient constraint in the parent plant, due to its phloem-immobility, directly arrested the totipotent expression of the explant, and what is its primary cellular role?
Options
- A.
Nitrogen; it is locked in older senescing tissues, preventing the synthesis of nucleic acids required for the S-phase of the explant.
- B.
Phosphorus; it is immobilized in the parent's root system, halting ATP synthesis and phosphorylation cascades in the meristem.
- C.
Calcium; it is sequestered in the structural components of older tissues, preventing cell plate formation and mitotic spindle assembly in the explant.
- D.
Magnesium; it cannot be translocated to the shoot apex, leading to a failure in ribosome subunit association during callus growth.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Meristematic Totipotency|Nutrient Immobility|Seed Dormancy Breaking
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating Mineral Nutrition (mobility of elements) with Cell Cycle (role of Calcium in cytokinesis/spindle formation) and Plant Tissue Culture.
The common misconception is assuming primary macronutrients (NPK) are always the limiting factors for growth, ignoring the specific 'immobility' clue (young leaves affected first) and the structural necessity of Calcium for meristematic division.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Growth and Development - Class 11 |
| Concept | Meristematic Totipotency |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |