Question

Describe how water within xylem vessels moves toward the top of a tree.

Answer 1

Transport of water to the top of trees occurs in cells collectively known as xylem.The tracheids and vessels join together to form vertically oriented tubes reaching from the roots to leaves.

Two forces combine to move water upward in these tubes.Root pressure and Transpiration.

Root pressure occurs when water flows into the roots through osmosis due to the differences in the concentration of solutes between the soil and roots.This higher pressure in the roots exerts a slight upward force on the fluid column.

Transpiration occurs when water evaporates from leaf surfaces,causing a lower pressure in the leaves.This also exerts a slight upward force on the fluid column.

The xylem conduits are smaller in diameter and act as capillaries.The adhesion of the liquid to the inner capillary walls counteracts gravity and keeps the water from falling.The slight upward forces of root pressure and transpiration pull are enough to move the water to the top of the tree.