Trees and water
Water movement
Photosynthesis requires water, carbon dioxide and light. In trees, it takes place in the leaves in the crown. This is ideal for light and CO2, but not for water, which is collected by the roots down below. It's no problem for a tree, though, because it is a veritable living pump. Through a highly efficient system of ducts, water is transported from deep underground to the topmost leaves. But how do trees pump all this liquid to their crowns? Oddly enough, by losing water! When the leaves transpire, they create suction that draws water through the xylem all the way from the base of the tree.
From bottom to top... to bottom!
The image of a water pump ignores one important aspect of how liquids circulate in trees, however. Once the sugars have been produced by the leaves, they have to be transported, dissolved in water, to all parts of the tree. A tree has an incredible number of microscopic ducts, all interconnected and working together. Think of a city's road network, with its express lanes, collector lanes and detours... but in three dimensions!
