What mechanism moves water from roots to shoots in most plants?

• A. Transpiration pull created by water loss from leaves.
• B. Capillary action within xylem tissue.
• C. Root pressure generated by mineral uptake.
• D. Phloem transport pulling water upward.

Answer: (A)

Water is moved from roots to shoots mainly by transpiration pull in the xylem, driven by cohesion-tension. When leaves transpire, water evaporates from the surface of cells and creates negative pressure in the leaf xylem. This tension pulls the entire water column upward from the roots. Water molecules stick together (cohesion) and adhere to the xylem walls (adhesion), so the continuous column remains intact all the way to the top. This upward pull is powered by evaporation at the leaves, not by energy from roots.

Capillary action alone is too weak to lift water high in a tall plant. Root pressure can cause some upward movement and guttation, but it’s usually insufficient to move water to great heights. Phloem transport involves moving sugars (and water accompanying them) through the phloem, not driving the ascent of water through the xylem.