Transpiration

• How does temperature affect the rate of transpiration?

  -when temperature increases, transpiration rate increases

  -it increases the kinetic energy of water molecules, which accelerates the rate of evaporation and diffusion out into the atmosphere

  -this reduces the water potential around the leaf
• How does humidity affect the rate of transpiration?

  -when humidity increases, transpiration rate decreases

  -the air inside leaves is saturated with water vapour, so humidity is 100%

  -the atmosphere humidity is never greater than 100%

  -this creates a water potential gradient between the leaf and atmosphere, so water diffuses out of the leaf down the water potential gradient

  -when water vapour diffuses away, it leaves concentric rings of decreasing humidity the further away from the leaf you go
• How does wind/air speed affect the rate of transpiration?

  -when wind speed increases, transpiration rate increases

  -movement of surrounding air blows away the layer of humid air at the leaf surface

  -this increases the water potential gradient between the inside and outside of the leaf

  -so water vapour diffuses out through the stomata more quickly
• How does light intensity affect the rate of transpiration?

  -when light intensity increases, transpiration rate increases

  -the stomata open widest in the middle of the day and close at night