Transpiration

• Transpiration


  The process where excess water evaporates from the aerial parts of plants, mostly through the stomata below the lamina of the leaf
• Plants continuously absorb water from the soil, but not all the water absorbed is used by the plant
• Transpiration pull


  The suction force created by the evaporation of water from leaves, which pulls water up the xylem vessels
• Transpiration stream


  The upward movement of water and mineral salts through the plant
• Factors affecting the rate of transpiration

  • Humidity
  • Temperature
  • Wind
  • Light
• Humidity


  The more humid the air is, the slower is the rate of transpiration
• If the outside air is dry

  Water vapour will diffuse more rapidly out of the leaf, increasing the rate of transpiration
• If the air is damp or humid

  Evaporation is limited, reducing the rate of transpiration
• Temperature


  A rise in temperature increases the rate of evaporation, and thus the rate of transpiration
• Wind


  The stronger the wind, the higher the rate of transpiration, as the moist air around the leaf is blown away
• If the wind is very strong

  The stomata may close because the guard cells lose too much water
• During a cool, wet wind

  The rate of transpiration decreases
• Light


  Light affects the size of the stomatal opening, thus affecting the rate of transpiration. During the night or in the shade, the stomata close and reduce the rate of transpiration. On a sunny day, the stomata open wide and increase the rate
• The movement of water vapor outward also removes heat from the plants, thereby cooling the leaves and preventing them from being scorched by the hot sun