Is Movement Unique to Kingdom Animalia?
We are learning about muscles in the human body and how they work, but before we started, we explored the fact that plants also have a means of movement. If you ask your student if plants move, they might say that they don't. But if they think about it a little more, they may realize that plants do indeed move. If you pose the next question as to how do plants move, they may be stumped. Plants obviously do not have muscles, so how do they move? P
Instead of muscles, plants produce special growth hormones, called auxins which accelerate plant growth or movement, called tropism. Plants have all sorts of tropisms according to environmental stimuli, such as the fact that they can gravitate or move toward water or temperature that they prefer, but the most common tropisms are phototropism and gravitropism.
Phototropism means light-movement. The cells on the shady side of the stems and leaves grow faster than those in the sun. This same asymmetrical growth is what makes the sunflowers lean toward the sun. In grasses and similar plants, a growth hormone becomes more concentrated on the shady side, speeding up the growth there. In plants like sunflowers and radishes, on the other hand, a natural chemical slows growth on the sunny side. Either way, the shady side grows faster and the plant leans toward light.
|from Plants for Kids|
A great experiment to show phototropism is the Shoe-box Plant Maze in which a plant, using its phototropism to find the light it needs to grow. I did this with Katie when she was young. Plants For Kids has a wonderful photo tutorial of how to make this maze.
Gravitropism is a turning or growth movement by a plant in response to gravity...roots grow in the direction of gravitational pull and stems grow in the opposite direction. This behavior can be easily demonstrated with any potted plant. When laid onto its side, the growing parts of the stem begin to display gravitropism, as it grows upward.
Gravitropism can also be seen in root growth. See how this bean's roots cross over the bean in order to grow downward.
All of these movements from plants, however, differs from the movements of Kingdom Animalia, which uses muscles for movement. Next week, I will show you what fun things we are learning about muscles.