Lesson Plan - Get It!
What happens if you touch a hot stove? Do plants just sit around or do they know what's going on around them (sort of)?
When you touch a hot stove, you immediately withdraw your hand from the heat because it is painful.
This is a response that all humans have to pain — almost a reflex. Plants respond to their environment in similar ways, through touch, light, and gravitational pull.
Before continuing, if you missed or would like to review the previous lessons in our Plants series, now's your chance. You can find them in the right-hand sidebar under Related Lessons.
Have you ever seen a plant growing towards a window? That is called "phototrophism," when plants respond to light in their environment by moving towards the light source.
Plants grow this way by releasing a special hormone that promotes growth to that area. Not all plant responses involve chemicals, though. Gravitropism is a plant response to the force of gravity acting on the plant. This is one reason that most plants grow perpendicular to Earth's surface. Most plant roots grow down into the soil, while the stem and body of the plant grow above ground. However, gravity can act on plants and reverse the growth, as shown in the image below:
Image by Kleuske [cropped], via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Finally, thigmotropism is the response to touch. This is a little harder to visualize, so take a moment to watch a quick Motile Productions video on Thigmotropism:
Did you notice how the plant moved around until it "felt" an object to attach to? There are also plants that respond to human touch like The Makahiya (Shy) Plant (silent video):
These plant responses enable plants to adapt to the environment and survive. Think about how light sources can change over time.
- How might plants use phototropism to obtain the sunlight needed for photosynthesis?
Thigmotropism provides plants with structures to support growth away from the surface, allowing for improved access to nutrients and sunlight.
Discuss what you have learned with a parent or teacher before moving on to the Got It? section to review plant behaviors.