How Does Water Travel Up the Root of a Plant?

Research Question:

• How does water travel through a plant?
• How does osmotic pressure in the root cause water to be transported up into the plant?
• What is osmotic pressure? How does it differ from capillary pressure?
• At what point in the plant does root action cease and capillary action begin?
• Students should distinguish between root pressure and capillary pressure.

Materials:

• Two healthy tomato plants in pots
• Modeling clay such as Plasticine or Fimo
• 100 ml graduated cylinder
• Brick or other sturdy block to support tubing
• Exacto knife
• 2’ plastic tubing with an inner diameter a tiny bit bigger than the diameter of the tomato plant stem
• Collection container (this can be an measuring cup, plasticware, or even the graduated cylinder

:

1. Clip the tomato plant about 4” above the ground. The cut should be made underneath any plant branches.
2. Fit one end of the tubing over the stem of the plant coming out of the ground. There is no need to cover the entire plant stem with tubing. More important is to create a seal between the plant and the tubing with the modeling clay.
3. Drape the other end of the tubing over the brick or other support. Make sure that water from the tubing can drip into a collection container. Trim the tubing if it is too long to hang neatly into the collection container. View the video on the references below for more information on this set up.
4. Fill the tube with water. Tap or shake the tubing to remove any air bubbles.
5. Water one plant with 3/4 cups of water once a day. Water the other plant with two cups of water once a day.
6. Check your plants several times a day. Using the graduated cylinder, measure the water that drips into the collection container. Measure the total amount of water that comes from each plant. Continue measuring and recording for three to four days.

Terms/Concepts: Osmotic pressure, root pressure, capillary pressure, xylem, turgidity, root cortex

References:

• Transport of Water and Minerals in Plants
• Tutor Vista: Root Pressure (video)