Transpiration

A plant gives off most of the water it takes in. Root hairs, each one a single long cell with a thin wall, take in water and the minerals dissolved in it. This raw sap crosses the root into the xylem and rises to the leaves. There water evaporates and escapes as vapour through the stomata. This loss, transpiration, pulls more water up the stem behind it, like drinking through a straw, so a tall tree lifts water tens of metres without a pump. A waxy cuticle keeps water in over the rest of the leaf, and many leaves have more stomata underneath than on top.