Transpiration rate

• Transpiration


  Water is diffused through open stomata and into the air. Evaporated water on the leaves.
• Factors affecting transpiration rate

  • Humidity
  • Light intensity
  • Temperature
  • Air movement
• Increase in humidity

  Transpiration rate decreases
• High relative humidity

  Rate of diffusion is lowered, transpiration rate is reduced
• Increase in light intensity

  Transpiration rate increases
• Bright light

  • Increases rate of photosynthesis
  • Causes stomata to open, allowing more water vapour to diffuse out
• Stomata closing as it gets darker


  Water can't escape
• Increase in temperature


  Transpiration rate increases
• Increase in temperature


  • Increases rate of photosynthesis
  • Increases demand for water, more drawn up from roots
• Increase in air movement (wind)

  Transpiration rate increases
• Still air around leaf

  • High concentration of water particles outside leaf, diffusion doesn't happen as quickly
• Windy conditions


  • Water vapour swept away, low concentration of water outside leaf, diffusion happens quickly
• Transpiration rate is affected by:

  • temperature
  • humidity
  • light intensity
  • wind speed.
• You can measure loss of mass to estimate transpiration.

  
• The plant could actually lose a small amount of mass in other ways , e.g. it loses oxygen during photosynthesis. 
• You can also estimate transpiration rate by measuring water uptake by a plant.