LEAVES ARE THE LUNGS OF PLANTS

In plants, water moves from the root to the leaves via the stem. The water then leaves the xylem in the leaf and evaporates into the atmosphere. Water movement is driven by the evaporation through small pores on the undersides of leaves called stomata.  The stomata of a leaf permit the leaf to control evaporative cooling and water loss. This process...
• Cools the the plant
• Moves nutrients up from the root 
• Maintains the turgor pressure in cells 

Turgor pressure  is important for the following reasons:
• It maintains the plant in an upright position so that it can take advantage of light.
• It is important for the functioning of the guard cells, which surround the stomata and regulate water loss and carbon dioxide uptake.
• It is the force that pushes roots through the soil.