Transpiration - Summary
Transpiration is the evaporation of water from the of water from the surface of leaf cells in actively growing plants. This water is replaced by additional absorption soil leading to a continuous column of water in the plant’s xylem. The process of transpiration provides the plant with evaporative cooling, nutrients, carbon dioxide entry and water to provide plant structure. Rates of transpiration depend on the water potential gradient from the soil to the atmosphere and the resistances to its movement through the plant. Water enters the root and travels through the cortex and endodermal layers of cells to reach the xylem where water ascends to the leaf where, if not used in the plant, evaporates. If water loss is greater than water uptake, air bubbles can form in the xylem. Plants reduce water loss by closing their stomata, developing thick cuticles, or by possessing leaf hairs to increase the boundary layer. Stomata are quick to respond to environmental cues to protect the plant from losing too much water, but still allowing in enough carbon dioxide to drive photosynthesis.