Q.60 Formation of gas bubble leading to collapse of tension in liquid phase during water transport in xylem is
called:
1. Capitation
2. Adhesion
3. Cavitation
4. Cohesion
Formation of gas bubble leading to collapse of tension in liquid phase during water transport in xylem is called 3. Cavitation.
Detailed Explanation
Cavitation occurs when extreme negative pressure (tension) in xylem vessels causes dissolved gases to form vapor bubbles that expand rapidly, breaking the continuous water column. This interrupts water transport via cohesion-tension theory.
Mechanism:
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Transpiration pull creates -2 to -20 atm tension
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Gas bubbles nucleate (air-seeding through pit membranes)
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Bubble expands → embolism blocks conduit
-
Adjacent functional xylem conduits compensate
Option Analysis
1. Capitation: Wrong—economic term (income/charge limitation), not plant physiology.
2. Adhesion: Wrong—forces between water molecules and xylem walls; supports tension but doesn’t cause failure.
3. Cavitation: Correct—gas bubble formation and tension collapse in xylem sap under drought/freezing stress.
4. Cohesion: Wrong—water molecule attraction maintaining column; disrupted by cavitation.
Introduction
Formation of gas bubble leading to collapse of tension in liquid phase during water transport in xylem is called cavitation, creating embolisms that block water conduction. This critical failure mode limits plant hydraulic capacity under drought stress.
Cavitation Process
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Tension buildup: Transpiration → -10 atm xylem pressure
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Bubble nucleation: Air-seeding through pit membrane pores
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Rapid expansion: Vapor bubble grows → conduit blockage
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Embolism: Air-filled xylem vessel non-functional
Cavitation Prevention Strategies
| Plant Adaptation | Function |
|---|---|
| Pit membrane tori | Seal conduits against spread |
| Thick vessel walls | Withstand higher tensions |
| Root pressure | Refill embolized vessels |
| Multiple conduits | Redundancy bypasses blockages |
Consequences and Recovery
-
PLC (Percent Loss Conductivity) measures vulnerability
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Vulnerability segmentation: Sacrificial conduits protect stem
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Nighttime refilling: Root pressure dissolves emboli
Exam Key Points
Cavitation ≠ Embolism (bubble formation vs. air blockage). Cohesion/adhesion enable transport; cavitation disrupts it. Classic NEET physiology distinction!
Memory Aid: “Cavi-tension → bubble → Collapse → xylem Crisis”.
