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Activity 1.2
Taking a Ride on the Plant Stem Elevator
The forces of cohesion and adhesion culminate in the ability of water to travel up a straw without a pump. It’s called evapotranspiration and it explains how water travels up the stem of a plant. This next activity demonstrates the ability of water to travel up an actual plant stem by capillary action.

What You Need:

  • Several stalks of fresh celery
  • Food coloring
  • Small drinking glasses
  • A knife (check with an adult first)

What To Do:

  1. Place some food dye (blue or red works best) in a small glass. Add a small amount of water, but make sure the food dye remains concentrated.
  2. Take one stalk of celery and make a clean cut at the bottom. Examine the cut end closely. Do you see the series of small spots along the curve of the celery stalk? These are called vascular bundles and they consist of long tubes that run the length of the stalk.
  3. Remove the celery stalk and rinse in clear water to remove any food coloring on the outside of the stalk.
  4. Using your knife, make a cross-sectional slice through the stalk and examine the vascular bundles. Start from the top of the stalk and make your way down to the bottom until you see that the vascular bundles contain the food coloring. The length of the stalk shows how far the colored water has traveled up the celery stalk.
  5. Using the fingers, see if you can peel away the skin of the stalk to expose the vascular bundles (it’s not as difficult as it sounds as the food coloring makes them easier to see).

What's Going On:

The vascular bundle provides a way by which water and nutrients are moved throughout the plant. They are most easily seen as the veins in a leaf. Comprised of thick walled cells, they are the toughest cells in a plant. In fact, the vascular bundles sometimes get stuck between you teeth when you eat celery.

The vascular bundles are actually comprised of two different types of cells. The phloem cells transport sugars (produced by photosynthesis) and the xylem transports water and dissolved minerals. It’s the xylem tubes that are being dyed in this experiment. Water travels up the narrow xylem tubes due to water molecules clinging to its inside walls (adhesion) and water clinging to itself (cohesion). Collectively, this is called capillary action.

Take It A Bit Further:

Idea One:
Following the preceding procedures, test to see what factors affect the rate of capillary action up the celery stalk. For example, determine the role of temperature by placing celery stalks in warm and cold colored water. You may want to see if soapy water travels up the xylem at a different speed than fresh water. You may want to combine both treatments (i.e., fresh and soapy water with cold and warm water) at the same time. The distance the color travels can be used to calculate the speed the water traveled up the stalk. A bar graph can be prepared to report your data.

Idea Two:
See if you can remove a single vascular bundle from a stalk (with a little practice it’s actually not that difficult). You can insert the end of this single bundle into some concentrated food dye and watch as the color rapidly travels along the xylem.

Go Back to Activity 1.1 Advance to Activity 1.3