Potometer

• what does a potometer do?

  Estimate transpiration rates
• what is a potometer?

  A special piece of apparatus used to estimate transpiration rates

  • measures water uptake by a plant- but it is assumed that water uptake by the plant is directly related to water loss by the leaves
• step 1?

  cut a shoot underwater to prevent air entering the xylem

  Cut it at a slant to increase the surface area available for water uptake
• step 2?

  Assemble the potometer in water and insert shoot underwater, so no air can enter
• step 3?

  remove apparatus from water but keep the end of the capillary tube submerged in a beaker of water
• step 4?


  check apparatus is waterlight & airtight
• step 5?

  dry leaves, allow time for shoot to acclimatise , then shut trap
• step 6?

  remove end of capillary tube from beaker of water until 1 air bubble has formed, then put the end of the tube back in the water
• step 7?

  Record starting position of air bubble
• step 8?

  • start a stopwatch
  • and record the distance moved by the bubble ,
  • per unit time
• What is an estimate of the transpiration rate?

  The rate of air bubble movement
• What must be remembered?


  Only change one variable at a time

  All other conditions must be kept constant