Transpiration

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Created by
Keren

Cards (9)

    • CO2 moves from air into leaf + O2 out of leaf via diffusion through stomata that is controlled by guard cells
    • Stomata open - Exchange of CO2 + Loss of water vapour (Transpiration)
  • Transpiration stream
    • Water moving up the plant via osmosis and diffusion in the apoplast pathway from the xylem
    • Reaches to leaf for evaporation in the mesophyll cells
    • Water vapour moves into external air along the diffusion gradient
  • Process of the transpiration stream (Passive):
    1. Water evaporates from mesophyll into air spaces of the leaf and move out into the stomata
    2. WP of cell lowered - Water moves into cell via osmosis by adjacent cells, apoplast and symplast pathways
    3. Repeated from leaf to xylem
    4. Adhesion of water with carbs of walls of xylem + Cohesion of water molecules = Capillary action
    5. Water against gravity
    6. Tension results in pull
  • Evidence of Cohesion-tension theory
    • Change in diameter of trees
    • Xylem vessel broken
  • Factors affecting transpiration - Light
    • Needed for photosynthesis
    • Opening and closing of stomata
    • Increase light intensity = Increased number of open stomata - Increased amount of water vapour diffusing out - Increase evaporation - Increase rate of transpiration
  • Factors affecting transpiration - Humidity
    • Relative humidity - Measure of the amount of water vapor in the air compared to total concentration water in the air can hold
    • High RH = reduced water vapour potential gradient = Lower rate of transpiration
  • Factors affecting transpiration - Temperature
    • Increase - Increase kinetic energy of water - Increase rate of evaporation - Increased rate of transpiration
    • Increase - Increase concentration of water vapour external air can hold before saturated - Increased rate of transpiration
  • Factors affecting transpiration - Air movement
    • Air movement or wind - Decrease water vapour accumulation - Increase diffusion gradient - Increase rate of transpiration
  • Factors affecting transpiration - Soil-water availability
    • Dry soil - Water stress - Decrease rate of transpiration