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Question #46262
The Question
In Dianthus, which exhibits free-central placentation, a chemical mutagen disrupts microsporogenesis, causing a complete failure of meiosis. The resulting microspore mother cells directly undergo mitosis to form pollen grains. If these pollen grains successfully pollinate a normal wild-type Dianthus flower, which of the following correctly identifies the ploidy of the resulting embryo and Primary Endosperm Nucleus (PEN), and the ultimate fate of the ovule?
Options
- A.
3n Embryo, 4n PEN; Seed abortion due to disrupted maternal-paternal genomic balance in the endosperm.
- B.
3n Embryo, 4n PEN; Normal seed development as the free-central placenta provides direct, unhindered nutrition.
- C.
4n Embryo, 5n PEN; Seed abortion due to the inability of the free-central placenta to support a polyploid mass.
- D.
2n Embryo, 3n PEN; Normal seed formation because the diploid pollen undergoes reductional division in the pollen tube.
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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
Gynoecium Placentation|Microsporogenesis|Ploidy Shift
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often mechanically memorize 'Embryo = 2n, Endosperm = 3n' without understanding the stoichiometry of Double Fertilization.
This question forces them to recalculate ploidy based on a gametic mutation (2n male gametes).
Furthermore, it tests the 'NCERT-Plus' application that endosperm viability strictly depends on genomic balance, and without a viable endosperm, the embryo aborts regardless of the anatomical advantages of the ovary's placentation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Morphology of Flowering Plants - Class 11 |
| Concept | Gynoecium Placentation |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |