Hydrogen bonds drive cohesion in xylem water transport

Steps:

• Examine the diagram: R represents a bond between water molecules in xylem.
• Recall transport mechanism: Water moves via transpiration pull, requiring cohesion to maintain continuous column.
• Distinguish bond types: Hydrogen bonds form between water molecules (cohesion); ionic bonds are not primary in water transport.
• Match to options: Cohesion in lumen fits hydrogen bonding role for upward flow.

Why B is correct:

• Cohesion via hydrogen bonds between water molecules prevents column breakage, enabling tension from transpiration pull (as per cohesion-tension theory).

Why the others are wrong:

• A: Adhesion involves water to vessel walls, not molecule-to-molecule bonding.
• C: Ionic bonds don't occur between water; adhesion targets vessel walls, not lumen.
• D: Ionic cohesion isn't relevant; water transport relies on hydrogen, not ionic, bonds.

Final answer: B