Suck It Up: Capillary Action of Water in Plants

Abstract

Have you ever heard someone say, "that plant is thirsty" or "give that plant a drink of water"? We know that plants, and even bouquets of cut flowers, need water to survive, but have you ever thought about how the water moves within the plant? In this science project, you'll use colored water and carnations to figure out where the water goes.

Objective

In this science project, you'll use food dyes to follow the path of water through a carnation.

Credits

Sandra Slutz, PhD, Science Buddies

Last edit date: 2012-12-07

Introduction

All plants, even those living in deserts, need water to survive. Plants use water to keep their roots, stems, leaves, and flowers healthy and to prevent them from drying out and wilting. The water is also used to carry dissolved nutrients throughout the plant.

Most of the time, plants get their water from the ground. This means that the plant has to transport the water from its roots up throughout the rest of the plant. How does it do this? Water moves through the plant by means of capillary action. Capillary action occurs when the forces binding a liquid together (cohesion and surface tension) and the forces attracting that bound liquid to another surface (adhesion) are greater than the force of gravity.

A simple way of observing this is to take a teaspoon of water and gently pour it in a pool on a countertop. You'll notice that the water stays together in the pool, rather than flattening out across the countertop. This happens because of cohesion and surface tension. Cohesion is the attractive force that pulls similar substances together. In this case, the individual water droplets are being pulled together. The force of the pull is strongest at the edge of the pool. The water droplets at the edge have fewer neighboring water droplets, so they cling more tightly to those around them; this is known as surface tension. Now gently dip the corner of a paper towel in the pool of water. The water is attracted to the paper and "climbs" up the paper towel-this is capillary action.

Figure 1a. The pool of red colored water on this countertop is held together by surface tension and cohesion between the water droplets.	Figure 1b. Capillary action causes the water to "climb" up this paper towel.

In this science project, you'll put a cut carnation into a glass of colored water. What do you think you'll see if the plant uses capillary action to move the water from the stem up to the flower?

Terms and Concepts

Have an adult help you look up the following words. Then think and talk about the questions below. Once you've done that, you'll be ready to start the project!

• Wilt
• Capillary action
• Adhesion
• Gravity
• Cohesion
• Surface tension
• Carnation

Questions:

• Can you identify the different parts of a plant? Point out the roots, stems, leaves, and flowers of plants around you. Or draw a picture of a plant and label all these parts on the drawing.
• What happens to a plant when you forget to water it? What does the plant look like when it is "thirsty"?
• What is capillary action?

Bibliography

• Here is a great website from the Missouri Botanical Garden to help you learn more about plants.
  Schwartz, E., DeBuhr, L., and Addelson, B. (2006). Biology of Plants: Plant Parts. Missouri Botanical Garden. Retrieved February 14, 2008 from http://www.mbgnet.net/bioplants/parts.html
• You can find a good explanation about capillary action here:
  Seavey, M. (1998). Water Properties. Iowa Project WET by the Iowa Academy of Science. Retrieved February 14, 2008 from http://www.uni.edu/~iowawet/H2OProperties.html

Materials and Equipment

For this science project, you will need to gather the following items:

• Water (1/2 C.)
• Measuring cup
• Glass or plastic cup
• Blue or red food dye
• Spoon
• Several white carnations (minimum of 3)
• Knife (ask an adult for help with the knife)
• Camera (optional)

Experimental Procedure

1. Measure out 1/2 cup of water.
2. Pour the water into a glass.
3. Add 20 drops of food dye to the water in the glass. Stir with a spoon until the dye has fully dissolved in the water.
4. With the help of an adult, use a knife to cut the stems of several (at least three) white carnations at a 45° angle. Be sure not to use scissors, as they will crush the stems, reducing their ability to absorb the water.
5. Place the carnations in the colored water.

   Figure 2: These carnations are sitting in a glass of water that has been dyed red.

6. Observe your project 2, 4, 24, 48, and 72 hours after you first put the carnations in the colored water. Write down what you see in a data table like the one below. Don't forget to record what the flowers look like at the beginning of the project! You can also draw pictures or take photos of the flowers at each time interval.

   Hours spent in colored water	Observations
   0
   2
   4
   24
   48
   72

Variations

Here are some additional questions you can investigate with this science project.

• Do you see the same results with other flowers and plants? How about trying another white flower, like a daisy? Or try a plant that is mostly stem, like a stalk of celery.
• What are the results if you use other colors of food dyes? Is the effect easier or harder to see?
• What happens if you increase or decrease the concentration of food dye in the water? Try using one-half, twice, four times, and ten times as much food dye.
• How would you make a multi-colored carnation? Hint: Two methods to try are:
  • Leaving the flower for a day in one color of water and then putting it in another color of water for a second day
  • Splitting the stem in two and putting each half of the stem in a different color of water

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Related Links

• Science Fair Project Guide
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