Transpiration

• Phloem

  • Living
  • Transports food minerals up and down the plant
  • Translocation
• Xylem

  • Dead cells
  • Hollow inside
  • Strong and stiff = supports the plant
  • Water and minerals from roots to shoots
  • Contain lignin = strengthen cell walls
• Transpiration is the loss of water from a plant
• Transpiration is caused by evaporation and diffusion
• Factors affecting transpiration

  • Temperature
  • Light intensity
  • Wind
  • Humidity
• As temperature increases, transpiration increases (more evaporation)
• As light intensity increases, transpiration increases at a decreasing rate (more stomata open wider)
• As wind speed increases, transpiration increases
• AS humidity increases, transpiration decreases (diffusion rates are lower)
• Stomata

  Guard cells

  • When flaccid = close (less evaporation)
  • When turgid = open (more evaporation)
• Investigating transpiration

  1. Cut a shoot underwater
  2. Assemble potometer and add a ensure no air can enter the apparatus
  3. Start a stopwatch and measure how far an air bubble travels per unit time (eg. 5 seconds)
  4. This gives an estimate of the transpiration rate