Transpiration (the rate, stomata, etc)

• Light intensity

  • The brighter the light the higher the transpiration rate
  • Stomata begin to close as it gets darker (photosynthesis can't happen in the dark, so they don't need to be open to let in carbon dioxide) When the stomata are closed very little water can escpae
• Temperature

  • The warmer it is, the faster transpiration rate.
  • When it's warm water particles have more energy to evaporate and diffuse out of the stomata.
• Air flow

  • the better the air flow, the higher the transpiration rate
  • if air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn't move away. This means there's a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn't happen as quickly.
• Humidity

  • The drier the air around a leaf, the faster transpiration happens
  • If the air is humid there's lots of water already, so a low concentration gradient.
  • Diffusion happens fastest with a high concentration gradient so the drier the faster.
• A potometer can be used to estimate the transpiration rate

  1. You can estimate the transpiration rate by measuring the plant's uptake of water
  2. This because you can assume that water uptake by the plant is directly related to water loss by the leaves
  3. Set up the apparatus as in the diagram, and then record the starting position of the air bubble.
  4. Start a stopwatch and record the distance moved per unit time, e.g. per hour
  5. Keep the conditions constant throughout the experiment, e.g. temperature and humidity

  
• Label the diagram#

  A) reservoir

  B) volume scale

  C) air bubble

  D) capillary tube

  E) beaker of water

  F) cut shoot