When celery is placed in a glass of colored water, the color slowly makes it way up the stalk. The purpose of this experiment for sixth-grade students is to reinforce the concept of photosynthesis, a topic that is introduced in earlier grades and built upon in following years. The experiment is also a good way to teach middle school children about the process by which plants absorb and use nutrients and water to grow.
Preparing the experiment takes a minimal amount of time, but observation occurs for several days. Cut the end off a stalk of celery so it is about 4 inches long. Use the top portion of the celery with the leaves. Place the stalk of celery in a glass of water dyed with red or purple food coloring and leave it somewhere sunny. While the sun isn't needed for the experiment to work, the heat it gives off accelerates the results of the experiment. This is because the plant absorbs the water more quickly when it is hot, which is a benefit if timing for the project is tight. Watch it for a couple of days and see what happens to the food coloring. An alternative is to place four stalks of celery in four separate glasses and take them out at two hours, four hours, six hours and eight hours to compare the movement of the food coloring. This method does not require sunlight. Sixth-grade students can record their observations in a science journal so that discussion among groups can occur when the experiment is finished.
There are several educational benefits to performing a simple celery and sun experiment with sixth graders. They will be able to see how a plant uses its capillaries to transport nutrients and water throughout the entire structure, supporting healthy leaves, stems and fruit. This process is called translocation, an important part of learning about plant life cycles and photosynthesis.
While the food coloring will likely travel up the length of the celery without sunlight, a cloudy day may alter the results of the experiment. If sun is scarce, use a growing light as an alternative. Most directions for this experiment recommend red or purple food coloring because it is dark enough to be seen as it moves through the celery. Yellow and green may not work as well because the color will blend with the color of the celery. Place the glasses on newspapers or paper towels to prevent staining the work surface if a glass is spilled.