TRANSPIRATION

• Transport system


  Movement or transport within organisms
• Osmosis


  1. Water passes through a semi-permeable membrane

  2. Occurs during drought, water moves from areas of high to low water potential

  3. Requires no energy
• Stomata


  • Tiny microscopic pores in the leaf epidermis
  • Bounded by two guard cells that regulate the entry and exit of CO2, O2, and water vapour
• Stomatal transpiration


  Water loss through the stomata in the leaves due to evaporation
• Cuticular transpiration


  Small amount of water loss through cracks in the waxy cuticle
• Transpiration pull


  Tension (force) caused by water loss from leaves that pulls up water from the soil through the plant
• Transpiration pull


  Helps move water up very tall trees
• Stomatal opening and closing


  1. Controlled by turgor pressure of guard cells

  2. Guard cells take up or lose potassium ions to control water uptake and loss
• Environmental factors


  Affect rate of transpiration (light intensity, humidity, wind, temperature, water supply)
• Transpiration cools off leaves
• Cohesion and adhesion


  • Forces acting on water molecules in xylem
  • Cohesion - water molecules attracted to each other
  • Adhesion - water molecules attracted to cell walls
• Processes pulling water upwards


  1. Transpiration

  2. Osmosis

  3. Root pressure

  4. Capillary action