Let’s Get to the Root of Things: Comparing Root Systems and Root Depth
Science and Math for Grades 4–6
INTRODUCTION/ENGAGE
Ask the students to stand up and raise their arms high above their heads. Let’s imagine that your body is a prairie plant.
Where would the soil line be that divides your roots from the above ground portion of the plant?
Would it be at your knees or hips?
It would actually be about your waist. Everything below your waist would be roots in the soil because approximately 65 percent of a prairie plant is actually found underground as an extensive root system. The students can sit back down.
Prairie plants consist of two groups of plants, grasses and forbs. Grasses have long, narrow leaves that originate from the ground or thick stems that are jointed, hollow or tubular, and have non-showy flowers. Forbs typically have colorful flowers, visible stems, and broad leaves.
INTRODUCTION/ENGAGE
Ask the students to stand up and raise their arms high above their heads. Let’s imagine that your body is a prairie plant.
Where would the soil line be that divides your roots from the above ground portion of the plant?
Would it be at your knees or hips?
It would actually be about your waist. Everything below your waist would be roots in the soil because approximately 65 percent of a prairie plant is actually found underground as an extensive root system. The students can sit back down.
Prairie plants consist of two groups of plants, grasses and forbs. Grasses have long, narrow leaves that originate from the ground or thick stems that are jointed, hollow or tubular, and have non-showy flowers. Forbs typically have colorful flowers, visible stems, and broad leaves.
DO/EXPLORE
The students can use their computer skills to find the diagram of prairie plants shown above by going to http://en.wikipedia.org/wiki/Root. Have the students calculate the total size of several prairie plants by adding the depth of the roots to the height of each plant. Then calculate the percentage of the root system area. Calculate this for both grasses and forbs.
REFLECT/EXPLAIN
Were there differences in the root systems of grasses and forbs?
Yes, however, both types of prairie plants are relatively deeply rooted.
Write the following table on the board:
EVALUATE
What are some similarities and differences between the total size and root depth of prairie plants and cultivated plants?
What types of grasses did you find on the prairie plant chart and what were their total sizes and their root depths?
What cultivated plant grows in fields all over the Midwest and is also a type of grass?
Corn
Compare the total size and root depth of the prairie grass and the cultivated grass crop.
Do you think that the roots of most cultivated plants extend as deep into the soil as the roots of prairie plants?
No.
Would these cultivated plants survive a drought as well as a prairie plant?
No.
Why?
Deep root systems enable plants to find more moisture.
Why is it important for prairie plants to have deep root systems?
So they can survive long periods of dry weather and reach deep into the soil for additional moisture
APPLY/EXPAND
You may want to dig out a small clump of grass to use in the following discussion.
Compare the root depth of Kentucky bluegrass – the grass that we grow in many of our lawns – to that of big bluestem.
EVALUATE
What happens to bluegrass when it gets really hot and dry outside?
You can see it turn brown and almost crunches when you step on it. That is because it goes dormant or dies back.
What do you think happens to big bluestem under the same conditions?
It stays green.
Why?
The deep root system of this prairie grass helps the plant find more moisture.
What do many people do to keep their grass green all summer long?
Because most bluegrass roots grow in the top several inches of soil, they depend on moisture at the surface.
That is why people water their yards to keep the grass green in a drought.
