Transpiration and the Potometer

Looking at how plants take up water is an essential experiment in Biology. A small piece of plant in this case some water cress is inserted into a tube at the top making a water tight seal. The potometer shown here allows an air bubble to be brought into the apparatus, using a syringe, so that the movement of the bubble can be monitored with time. As the plant transpires, water is sucked up the tube and evaporates from the leaves. By knowing the volume of the capillary tube the amount of water lost be minute can be calculated.