Measuring Transpiration

• You can estimate the rate of transpiration by measuring the uptake of water by a plant
• You can assume that water uptake by the plant is directly related to water loss by the leaves
• Setting up the potometer:

  1. cut a shoot underwater at a slant to increase the surface area available for water uptake and prevent air from entering the xylem
  2. assemble the potometer in water and insert the shoot underwater so no air can enter
  3. check that the apparatus is watertight and airtight
  4. dry the leaves, allow time for the shoot to acclimatise and then shut the tap
  5. remove the capillary tube from the beaker of water until one air bubble has formed, then put the end of the tube back in the water
• 1. set up the apparatus and record the starting position of the air bubble
  2. start a stopwatch and record the distance moved by the bubble per unit time (e.g. per hour)
  3. keep the conditions constant throughout the experiment e.g. temperature and humidity