Exercise 4

• Potometer

  • apparatus that measures the transpiration rate of a plant.
  • Measures the rate of water uptake of a plant which is assumed to be almost equal to the water lost through transpiration
• Factors Affecting Transpiration

  • Boundary Layer
  • Humidity
  • Temperature
  • Wind Speed
• Boundary Layer

  • still, undisturbed air on the surface of the leaf
  • adds to the length of the diffusion path
  • the thicker the boundary layer, the more it decreases the rate of diffusion
• Boundary layer is determined by the leaf size, leaf shape, presence of leaf hairs, and wind speed.
• Larger and more pubescent leaves have larger and thicker boundary layers.
• Humidity

  • the amount of water vapor in the air
  • The higher the relative humidity decreases the rate of transpiration.
• Temperature

  • as temperature increases, the rate of transpiration also increases because water will evaporate faster.
  • however, very high temperature will close the stomata in order to prevent further water loss, and transpiration rate decreases
• Wind Speed

  • primarily affects the rate of transpiration by altering the boundary layer surrounding the leaves.
  • as wind speed increases, this reduces the boundary layer and therefore the rate of transpiration increases.
  • however, further increasing the wind speed will tend to cool the leaf and induce the stomata to close and decreases the transpiration rate