POLKA-DOT CELERY

Objective:

Learn about "capillary action," or how water moves through celery and trees.

Vocabulary:

Capillary action - the upward movement of liquids due to the molecular attraction to the surface.

Materials:

Two cups, ½ filled with water
Green or orange food coloring, 1 teaspoon
Stalk of celery with some leaves on it
Stalk of celery without leaves on it
Knife.

Instructions:

    1.  Mix 1 teaspoon of food coloring into each cup of water.

       2.  Cut both celery stalks at a diagonal about 1 inch from the bottom.

       3.  Put each stalk in one of the cups of colored water.

       4.  Leave the celery in the water for 4 to 5 hours, until you see the color

            gradually going up the stalks.

       5.  Take the celery stalks out of the water and cut diagonally across the stalk.

            (Have an adult help.)  Do you see any color in the stalks?  Which one has the

            most color?  You should see a row of circles colored with the dyed water.

            These are the cut ends of the fine long tubes that travel the length of the

            stalk.  The colored water traveled up the tubes. Trees have similar tubes

            running up their trunks.

How does it work?

Heat from the sun evaporates the water molecules that are in the top of the leaves.  Because water will climb a short way up the wall of certain substances (for example, drinking glasses) the next molecules in line move up to replace the molecules that evaporated.  Water molecules always hold (or bond) tightly together, and when they are squashed into very narrow tubes like those in celery, they grip with enough strength to pull-up the molecules behind them.  The water molecules at the top evaporate, the other molecules move up to take their place, and the water moves up the celery stalk into the leaves.  This is called capillary action.  This only works if the tubes are full of liquid to begin with.  Since the other celery stalk does not have leaves or a surface for the water to evaporate from, the water cannot move up the stalk.  Capillary action is how trees and other plants get water to their leaves.

Questions to ask:

1. Which plants use capillary action?

2. Would the roots of vegetables and trees use capillary action?

Science Projects