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Question #47519
The Question
An evolutionary biologist hypothesizes that if heterosporous pteridophytes like Selaginella had evolved Kranz anatomy, the evolutionary transition to a true seed habit would have occurred much faster. What is the primary physiological rationale behind this hypothesis, considering the specific metabolic demands of heterospory?
Options
- A.
Kranz anatomy would decouple fertilization from water dependence by concentrating CO2 around the archegonia, fulfilling the final requirement for the seed habit.
- B.
The suppression of RuBisCO's oxygenase activity would yield surplus photoassimilates, offsetting the high metabolic cost incurred by the sporophyte in retaining and nourishing the megaspore.
- C.
The presence of dimorphic chloroplasts would enable the exosporic female gametophyte to independently synthesize sufficient starch for embryogenesis in arid conditions.
- D.
The initial fixation of CO2 by PEPcase in the mesophyll would directly synthesize the complex sporopollenin required to protect the megaspore wall from desiccation.
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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
Pteridophyte Heterospory Evolution|Seed Dormancy Breaking|Seed Embryology
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating the evolutionary cost of the 'precursor to seed habit' (sporophytic nourishment of the retained female gametophyte) with the physiological benefit of C4 photosynthesis (elimination of photorespiratory loss yielding higher net assimilation).
The trap lies in Option C, which tests the student's ability to remember that heterosporous gametophytes are dependent (endosporic), unlike the independent (exosporic) gametophytes of homosporous pteridophytes.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Kingdom - Class 11 |
| Concept | Pteridophyte Heterospory Evolution |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |