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Question #45996
The Question
A C4 plant seed breaks dormancy following a brief shower but is immediately subjected to severe drought and high temperatures. The seedling rapidly accumulates Abscisic Acid (ABA) and eventually dies of carbon starvation. Despite possessing the highly efficient C4 pathway, which of the following best explains why carbon assimilation completely halts in this seedling?
Options
- A.
ABA directly inhibits the enzymatic activity of PEP-carboxylase in the mesophyll, preventing the formation of oxaloacetic acid (OAA).
- B.
Extreme ABA-mediated stomatal closure drops intercellular CO2 so low that even the high-affinity PEP-carboxylase cannot maintain the CO2 pump to the bundle sheath.
- C.
High temperatures induce the oxygenase activity of PEP-carboxylase, leading to severe photorespiration and carbon loss in the mesophyll cells.
- D.
Severe water stress breaks down the agranal chloroplasts in the bundle sheath, preventing the light reactions required to generate ATP for the Calvin cycle.
Check Your Answer
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
PEP-Carboxylase|ABA|Stomatal Regulation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often over-extrapolate the NCERT fact that 'C4 plants are highly efficient under water stress and lack photorespiration'.
This creates a misconception that C4 plants are immune to CO2 starvation during drought.
The pivot requires understanding that while C4 plants have a lower CO2 compensation point, absolute stomatal closure via ABA still cuts off the primary carbon source, inevitably halting the Calvin cycle despite the spatial separation of enzymes.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Growth and Development - Class 11 |
| Concept | Seed Dormancy Breaking |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |