The Question is from neet-botany plant-physiology plant-water-relations, and it was created by the author K SURESH KUMAR

Question

The cohesion-tension theory explains the ascent of sap in tall trees. Which of the following factors LEAST contributes to the maintenance of the continuous water column?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Cohesion-tension theory of water transport in plants
 **Related Topics**: Transpiration, xylem structure, water potential
 **Prerequisites**: Understanding of water properties (cohesion, adhesion), plant anatomy (xylem), and the process of transpiration.
## SOLUTION PATHWAY
**Given Information**:
  The question asks which factor LEAST contributes to maintaining a continuous water column in the xylem of tall trees, according to the cohesion-tension theory.
  The options describe different mechanisms involved in water transport.
**Method & Steps**:
 1. Understand the cohesion-tension theory: This theory explains how water moves up tall trees against gravity. It relies on the cohesive forces between water molecules (they stick together), the adhesive forces between water molecules and the xylem walls (they stick to the xylem), and the transpiration pull (water evaporating from leaves creates a negative pressure that pulls water upwards).
 2. Analyze each option:
  a. Active transport of water into xylem vessels: While water does enter the xylem, it's primarily driven by osmosis and the pressure gradient, not active transport which requires energy. The cohesion-tension theory relies on passive transport.
  b. Cohesion between water molecules: This is a crucial factor. Cohesion creates a continuous water column preventing breakage.
  c. Adhesion of water molecules to xylem walls: This is also crucial. Adhesion helps the water column stick to the xylem walls, preventing it from falling due to gravity.
  d. Transpiration pull generated by evaporation from leaves: This is the main driving force of the water column movement upwards.
 3. Identify the least contributing factor:  Active transport of water into xylem vessels plays a minimal role in the continuous water column maintenance compared to the others. The other three are essential components of the cohesion-tension theory.
  Result: Active transport is the least important factor.
  Verification: The cohesion-tension theory primarily relies on passive processes (cohesion, adhesion, transpiration pull). Active transport is not a primary mechanism.
 ## OPTION ANALYSIS
A ✓: Active transport of water into xylem vessels: This is not a major factor in maintaining the continuous water column.  The movement is largely driven by passive processes.
B :x: Cohesion between water molecules:  Essential for maintaining the continuous column.
C :x: Adhesion of water molecules to xylem walls:  Essential for preventing the water column from breaking.
D :x: Transpiration pull generated by evaporation from leaves:  The primary driving force of water ascent.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing active and passive transport: Understanding the difference is crucial for grasping the cohesion-tension theory.
  2.Overestimating the role of root pressure: While root pressure contributes to some water movement, it's not the primary mechanism for tall trees.
 **Quick Tips**:
  1.Remember the three key components of the cohesion-tension theory: cohesion, adhesion, and transpiration pull.
  2.Visualize the water column as a continuous chain held together by cohesive forces and anchored to the xylem walls by adhesive forces, with transpiration pull as the driving force.

K SURESH KUMAR · Answer

The correct Option is "Active transport of water into xylem vessels"

K SURESH KUMAR · Answer

Cohesion between water molecules

K SURESH KUMAR · Answer

Adhesion of water molecules to xylem walls

K SURESH KUMAR · Answer

Transpiration pull generated by evaporation from leaves

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