using potometers

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

  the rate of air bubble movement is an estimate of the transpiration rate
• 9. only change one variable e.g. temperature at a time and other things such as light intensity must be kept constant
• estimating transpiration rate