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Question #47578
The Question
An actively dividing onion root tip is treated with a specific chemical alkaloid, resulting in an artificial spike in its Mitotic Index (MI). However, overall tissue growth ceases, and subsequent cytological analysis reveals cells with a polyploid condition. Which of the following accurately describes the mechanism of the applied chemical?
Options
- A.
It inhibits tubulin synthesis during the G2 phase, causing cells to accumulate before entering prophase.
- B.
It binds to tubulin dimers to prevent microtubule polymerization, arresting cells at metaphase.
- C.
It inhibits the Anaphase Promoting Complex (APC), preventing cohesin cleavage and causing aneuploidy.
- D.
It disrupts actin microfilaments, preventing cell plate formation during telophase.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Tubulin|Spindle Apparatus|Anaphase-Promoting Complex
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often mistakenly equate a high Mitotic Index (MI) exclusively with rapid, healthy cell proliferation (e.g., cancer or normal meristematic growth).
This question tests the understanding that an 'arrest' in mitosis also mathematically increases the MI because cells accumulate in the M-phase without completing cytokinesis.
Furthermore, it tests the precise molecular target of colchicine (tubulin polymerization, not synthesis) and its genetic consequence (polyploidy vs. aneuploidy).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Cell Cycle and Cell Division - Class 11 |
| Concept | Mitotic Index Implications |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |