• Key Stage 3 - Plant Biology
• Key Stage 4 - Photosynthesis & Plant Biology

Set Up:

• Remove the bungs and submerge the entire apparatus (glass tube and both bungs with delivery tubes, plus a 100ml beaker), into a large container of water.

• Assemble the potometer under water (add the bungs to the tube, agitating the equipment under water to ensure all air bubbles are removed).

• Select a woody plant stem with leaves. Hold the plant stem under the water level and cut the end of the stem.

• Push the plant stem into the right angled tubing of the potometer, making sure it has a tight fit - vaseline can help here.

• Still under the water, place the bottom capillary tube of the apparatus into the full beaker of water.

• Lift the entire apparatus out of the water container, keeping the capillary tube inside the filled beaker.

• Secure the plant and potometer on a retort stand.

• Blot the leaves with paper towel so that excess water is removed.

• Bring the equipment towards the end of the bench so that the 100ml beaker of water can be removed from the end of the capillary tube, blot the end of the capillary tube with paper towel, which will leave a visible air bubble, and replace the beaker.

• The air bubble should move up the lower capillary tube as the plant loses water via transpiration.  The time taken for the bubble to move over a set distance is measured.

• A desk fan or hair dryer on the leaves will speed up the process.