Transport in plants and transpiration practical work

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The 'bubble' potometer can both measure the rate of water uptake and compare rates of transpiration in different environmental conditions.

Measuring the rate of water uptake

The potometer measures the amount of water uptake into the plant shoot. It is not the same as measuring the volume of water transpired out of the leaves. 

The potometer can be a tempermental piece of apparatus to use and often fails to give reliable results unless it is airtight.

Typical procedure:

  • leafy shoot cut under water to avoid air bubbles entering xylem
  • the potometer is filled with water in a basin, making sure there are no air bubbles
  • shoot is inserted into the potometer, again under water
  • potometer is removed from the water and all joints sealed with Vaseline
  • air bubble is introduced into end of capillary tube by exposing the open end of capillary tube to air for short period. As water is drawn up the tube, it creates an air bubble before capillary is placed back in water again.
  • the syringe can…


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