Is the evaporation of water from plants from high water potential in soil to low water potential in air along a water potential gradient.
Sites of Water Loss
Leaves - most via stomata some via cuticle
Factors Affecting Transpiration Rate:
Increase in temperature = increase in the rate of transpiration because: water molecules have more kinetic energy and so the rate of diffusion increases.
Increase in humidity = decrease in the rate of transpiration because : water surrounding the leaf becomes saturated with water vapour and this decreases the water potential gradient.
3. AIR MOVEMENT
Increase in air movement = increase in transpiration rate because: air currents move saturated air away from the surface of the leaf and so maintains the water potential gradient.
4. LIGHT INTENSITY
Light intensity affects stomatal opening and if stomata are open more - more water is lost.