Transpiration Pull in Xylem Transport

Steps:

• Water evaporates from mesophyll cell walls in leaves, creating tension.
• This tension pulls water molecules up through xylem vessels via cohesion.
• Cohesion between water molecules and adhesion to xylem walls maintain the column.
• Root pressure contributes minimally; evaporation drives the main ascent.

Why C is correct:

• Evaporation from mesophyll walls initiates transpiration pull, the primary force in the cohesion-tension theory for xylem transport.

Why the others are wrong:

• A: Active transport requires energy for ions, not bulk water movement in xylem.
• B: Epidermis evaporation is minimal due to cuticle; mesophyll drives most loss.
• D: Photosynthesis uses little water compared to transpiration volume.

Final answer: C