plant organ system

• Transpiration


  Loss of water form the plant

  Evaporation and diffusion

  Loss of water creates a shortage of water in leaf, so more is drawn up through xylem vessels

  Creating a transpiration stream
• Light intensity affecting rate of transpiration

  1. Brighter light, greater transpiration rate

  2. Stomata close as to gets darker, photosynthesis can't happen in the dark, so they don't need to let in CO2. With closed stomata, little water can escape
• Temperature affecting rate of transpiration

  1. Warmer it is, faster transpiration occurs

  2. Particles have more energy to evaporate and diffuse out of stomata
• Air flow affecting rate of transpiration

  1. Better air flow, greater rate of transpiration

  2. Water vapour is more easily swept off of leaf, maintaining a low concentration of water outside so diffusion happens quickly
• Humidity affecting rate of transpiration

  1. Transpiration decreases as humidity increases

  2. If it is humid, there isn't much difference in concentration of water inside and outside of leaf, so there is less of a gradient for water to diffuse down
• Using a Potometer to estimate transpiration rate


  1. Measures uptake of water from a plant

  2. Assume water uptake is directly related to water loss

  3. Set up apparatus and rest record starting position of air bubble

  4. Start stopwatch and record distance moved by bubble per unit time

  5. Keep conditions constant

  
• Guard cells


  The two cells that surround the stomatal pore and regulate the opening and closing of the pore.

  When the leaf has a lot of water, cells will fill and go turgid, opening the stomata to allow gases can be exchanged for photosynthesis

  When the leaf has too little water, guard cells lose water and go flaccid, closing the stomata and stopping too much water from escaping

  Sensitive to light - close at night to reserve water when gas exchange is not needed (as photosynthesis cannot occur at night)
• Where do you find stomata

  Underside of the leaf usually where it is more shaded and cooler so less water is lost