Water transport from roots to leaves occurs mainly because...

Water transport from roots to leaves occurs mainly because of ____________.
a. pressure flow
b. differences in source and sink solute concentrations
c. the pumping force of xylem vessels
d. transpiration, tension, and cohesion of water
e. a and b

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Key Concepts

Transpiration

Transpiration is the process where water evaporates from the surfaces of leaves and other aerial parts of the plant. This evaporation creates a negative pressure within the leaf air spaces, drawing water upward from the roots through the plant's vascular system. Transpiration is essential for cooling the plant, nutrient distribution, and maintaining water flow within the xylem vessels.

Cohesion-Tension Theory

The cohesion-tension theory explains how water moves upwards against gravity in plants. It relies on the cohesive properties of water molecules—owing to hydrogen bonding—that allow them to stick together and form a continuous water column. When water evaporates from the leaves, it creates tension (negative pressure) that pulls the cohesive column of water upward through the xylem.

Xylem Vessels

Xylem vessels are specialized conductive tissues in plants that transport water and dissolved minerals from the roots to the leaves. Their structure, which includes long, narrow cells with thickened walls, supports the continuous water columns required for effective water transport driven by the transpiration pull and maintained by the cohesion of water molecules.

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