Friday, May 3, 2002
Kids' experiment: Why do roots grow down?
You've probably heard the kindergarten song that ends, "Remember the seed in the little paper cup/first the root grows down and then the plant grows up." But why? Why does the root grow down and the plant grow up? As you have probably guessed or learned, it is because of gravity. All life on our planet has evolved with gravity. Plants have specialized cells that sense the gravitational pull. When the roots sense gravity, the cells signal growth toward gravity. In stems and leaves, the signal sends the growth in the opposite direction of gravity. Notice I did not say "down" or "up." You can do a simple experiment to try to confuse your plant to grow sideways. Which way will it grow?
Up, down or sideways
Gather six glass jars, about the size of a large mayonnaise jar and fill them one-half full of a seed-starting mixture. Water well, pouring off extra liquid. For this experiment we'll use bean seeds. Press down the soil so it is compact. Plant two or three seeds in each jar, placing the seeds on the sides so you can see them through the glass. Push them into the soil with a pencil to a depth of one inch. Now, press down the soil again in the jars so it is really firm. Lay two of the jars on their sides. Two jars will always stay upright throughout the experiment. These are your "control jars," and you use them to observe normal growth.
Write your predictions for each jar on a small piece of paper and hide it under the jar. Wait one week. Check how the plants in the jars on the side are growing. Are they growing sideways? Down, up? Now, lay two of the four upright jars on their side. Watch them for another week. Do the plants continue toward the top of the jar or do they turn? Check your predictions. Were you right?
© 2002 The Carlisle Mosquito