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What Is Plant Tropism?

on February 7, 2014

God created plants on Day Three of the Creation Week (Genesis 1:11–13), approximately 6,000 years ago. He designed plants with amazing abilities to survive and thrive. One of these special abilities is called tropism. Tropism is a plant’s instinct to grow toward or away from outside influences—such as light, gravity, and touch.1 Plants can survive, sometimes in less than ideal conditions, because their growth is directed by tropism.

Maybe you have noticed plants in a shady or dark environment that are bending toward the light. Seeds that are germinating underground use their sensitivity to gravity to send roots downward and stems upward. Some vining plants, such as morning glory, use a sensitivity to touch to entwine themselves around support objects as they grow. All of these are examples of tropism.

You can observe the wonders of plant tropism by performing the fun experiment listed below.2 You will need an adult to help you. The ability of plants to perform tropism is evidence of an all-wise Designer who created life with the ability to adapt to their environment and grow. The Bible is true—God created plants!

See For Yourself . . .

Lima Bean Experiment

The “Down” Side of Plants

There are several easy-to-do-at-home experiments that allow you to observe plant tropism. This one displays geotropism (response to gravity).

Materials:

4–5 small dried lima beans
1 clear plastic CD case
paper towel or blotting paper

STEP 1 Cut the paper towel or blotting paper so it fits inside the CD case.
STEP 2 Evenly place 4–5 dried lima beans on top of the paper towel. Turn each bean in a different direction.
STEP 3 Moisten the paper towel. Close the CD case so that the beans are held snugly—but not crushed against the sides of the case. Tape the case shut.
STEP 4 Set the CD case in an upright position. Keep the paper towel moist but not soaked until the beans begin to sprout.
STEP 5 As the seeds begin to sprout, note the direction in which the roots and stems are growing. Does the direction the seed is turned affect the direction of growth?
STEP 6 A couple of days after the seeds have begun to grow, rotate the CD case 90° on its side. After a few more days, note whether the direction of growth has changed.

Footnotes

  1. Rich Wendling, "Creepy Crawly Plants," Answers, April–June 2011, 35–36, www.answersingenesis.org/biology/plants/creepy-crawly-plants/.
  2. Ibid.