Q.65 Identify two CORRECT statements from the following which are related to the ion transportation
in the root system of plant
P. The proton pumps and H+-pyrophosphatase appear to work in anti-parallel with the vacuolar
ATPase to create a proton gradient across the tonoplast
Q. Calcium is one of the important ion whose concentration is strongly regulated by the
concentration of apoplastic spaces in the millimolar level
R. Solute move through both apoplast and symplast, and xylem parenchyma cells participate in
xylem loading
S. The limitation of Nerst equation for relating the membrane potential to the distribution of ion at
equilibrium is that it cannot distinguish between active and passive transport
(A) P,S (B) Q,R (C) R,S (D) Q,S
R and S are the correct statements about ion transportation in plant roots. R accurately describes dual apoplast/symplast pathways with xylem parenchyma involvement in loading, while S correctly identifies the Nernst equation’s limitation in distinguishing transport types. The right answer is option (C).
Correct Answer
(C) R,S
Statement Analysis
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P: Incorrect. Proton pumps (PM H+-ATPase) and vacuolar H+-pyrophosphatase (V-PPase) work with vacuolar H+-ATPase (V-ATPase) in parallel, not anti-parallel, to establish complementary proton gradients across the tonoplast for secondary ion transport.
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Q: Incorrect. Ca2+ is tightly regulated in apoplast at micromolar (not millimolar) levels (~1-10 μM) to prevent toxicity; cytosolic [Ca2+] stays at nM levels via CAX exchangers.
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R: Correct. Solutes traverse apoplast (cell wall continuum) and symplast (plasmodesmata); xylem parenchyma cells actively load ions into xylem via ABC transporters/HKTs.
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S: Correct. Nernst equation calculates equilibrium potential (E_ion = RT/zF ln([ion]_out/[ion]_in)) assuming passive equilibrium but cannot differentiate active pumping from passive diffusion.
Option Breakdown
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(A) P,S: Wrong—P inaccurate on pump coordination.
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(B) Q,R: Wrong—Q misstates Ca2+ apoplastic levels.
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(C) R,S: Correct—both R (pathways/loading) and S (Nernst limit) valid.
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(D) Q,S: Wrong—Q incorrect.
Introduction to Ion Transportation Root System
Ion transportation root system plant mechanisms like apoplast/symplast pathways and Nernst limitations dominate GATE Life Sciences Q.65. Statements R (xylem loading) and S (active vs passive) correctly capture root mineral uptake against gradients.
Key Root Ion Transport Features
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Apoplast/Symplast (R): Ions move cell walls (apoplast, fast) or cytoplasm (symplast, selective); Casparian strip forces symplastic shift.
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Xylem Loading: Parenchyma pumps K+/NO3- into xylem sap via H+-coupled symporters.
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Nernst Limit (S): E_K+ = -90 mV assumes equilibrium; can’t detect ATP-driven H+-ATPase pumps.
Q. Statement Verification
| Statement | Claim | Correct? | Reason |
|---|---|---|---|
| P | Anti-parallel pumps | ❌ | Parallel action |
| Q | mM apoplastic Ca2+ | ❌ | μM regulation |
| R | Apoplast/symplast + xylem loading | ✅ | Standard model |
| S | Nernst can’t distinguish | ✅ | Equilibrium only |
Answer: (C) R,S.
Common GATE Misconceptions
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P: V-ATPase/PPase both acidify vacuole vacuole, not oppose.
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Q: High apoplastic Ca2+ → pectin cross-linking, but cytosolic nanomolar.
Exam Strategies
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Mnemonic: “Roots Ride Rails (R), Nernst No Reveal (S).”
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High-yield: H+-ATPase powers 90% root transport energy.
Master ion transportation root system plant pathways for perfect plant physiology scores.
