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Question #47680
The Question
In a controlled ecosystem, the mutualistic mycorrhizal fungi of a dominant plant species are replaced by a non-symbiotic endophyte that consumes plant carbon but fails to facilitate phosphorus and water absorption. Assuming the Gross Primary Productivity (GPP) remains initially unchanged, what will be the cascading effect on the ecosystem's energetics?
Options
- A.
Increased respiratory cost (R) for active ion uptake decreases Net Primary Productivity (NPP), thereby limiting secondary productivity.
- B.
Net Primary Productivity (NPP) increases as the carbon 'tax' paid to the fungi is abolished, enhancing secondary productivity.
- C.
Gross Primary Productivity (GPP) decreases immediately due to phosphorus deficiency, while secondary productivity remains constant due to the 10% law.
- D.
The plant shifts to passive mineral absorption, maintaining constant respiratory losses (R) and stabilizing the energy flow to herbivores.
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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
Arbuscular_Mycorrhiza|Pathogen_Defense|Induced_Systemic_Resistance
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating Plant Physiology (Mineral Nutrition) with Ecology (Ecosystem Energetics).
Students often treat 'R' (Respiration) in the GPP - R = NPP equation as a static value.
The trap is assuming that losing a carbon-consuming fungal partner automatically increases NPP (Option B), while failing to account for the severe metabolic penalty (increased ATP/Respiration) the plant incurs by having to actively pump ions without the fungal hyphal network.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Microbes in Human Welfare - Class 12 |
| Concept | Mycorrhiza Nutrient Dynamics |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |