The properties of water explain its movement up through a tree. As water molecules evaporate from leaves, other water molecules move by osmosis to replace them. Because of the hydrogen bonds between these polar molecules, a continuous strand of water molecules is pulled through the leaf. The molecules in the leaf are continuous with the column of water in the stem. The attraction of these molecules to polar molecules in the plant’s vessels helps support the column as it is pulled up by evaporation from the leaves.
The column extends into the roots. As water is pulled toward the stem and leaves, additional water moves into the roots from the soil. Thus, water is pulled up from the roots to the leaves in a continuous chain of hydrogen-bonded water molecules.