For my second class with my smallish group of nine and ten years olds, we focused on plant roots. For this class, I relied heavily on actual examples and some cool pictures.
After we had gone over and talked about the scientific naming homework I had given them the week before, I gave them a picture outlining the various parts of a root, and we talked about what roots are for (bring nutrients and water into the plant from the ground, provide anchorage...), then I proceeded to show them a large selection of examples.
Two main types of roots are tap roots versus fibrous roots. A dandelion plant is a great example of a tap root, and if you can pry one or a few out of the ground, they are perfect for demonstration purposes. A tap root goes down deep, reaching water and nutrients below the surface and anchoring the plant very well. Most trees and woody plants have tap roots. A plant with fibrous roots, however, doesn't spend a lot of time and energy digging deep, it spreads out and grows quickly. Any sort of common fescue (grass) is a great example of this. Plants like this may grow and spread quickly, but may also be more sensitive to heat, drought and erosion.
I covered the table with paper and gave them each a sample to look at and take apart.
There are some other interesting kinds of roots, and I had a little slide show prepared at this point for examples.
Prop roots: Great examples of this are mangroves, sugar cane or Ficus (or Banyan) trees. These roots come out of the stem and reach toward the ground. Their main purpose is to stabilize the plant in places where the soil is not deep. In the case of mangroves, the prop roots actually capture sediment to create soil and land for more mangroves to grow. Mangroves are very important for our coastlines, as they can protect the shoreline from erosion, especially during large storms.
Aerial Roots are the roots that vines send out to help them climb, and they are also the roots of plants that live up in the trees without soil. These plants, which include many orchids, are called epiphytes. Epiphyes are plants that live on other plants getting moisture and nutrients from the rain and air and also sometimes detritus falling around them. In this grouping of root types are also black mangrove and cypress knees, whose purpose is still debated.
Another type of root is the buttress root. Again, this is primarily for stability and something you might see on trees in a rain forest where there is very little soil.
Finally, we have tuberous roots, and these are very important roots indeed! These are root structures that the plant uses to store energy, and we take advantage of these quite often! Bulbs, radish, beets, potatoes and carrots are great examples of this.
I brought out a nice selection of root vegetables at this point and the kids got to look at and sample many of them. Food always goes over well I found!
While they ate, I let them know how important roots can be, not just for the plant, itself, but also for whole habitats. Loss of root structure can also be a loss of soil. This happened in the plains states during the Dust Bowl. Our tilling up of the prairie grasses meant there was nothing left to hold the soil in place. When the years became drier and the winds rose, all of that soil took to the air.
Erosion is a huge problem for our streams and in the rain forests, where the soils are so thin and fragile. Those roots are really needed!
Finally, one quick fact. The largest root structure in the world belongs to an aspen grove in Utah. These trees are clones attached by rhizomes under ground. This grove covers 106 acres!
My class didn't go into the nitty gritty details of plant root structure and growth, but I felt it was a good introduction for them at this age. My aim is always to interest and inspire, not bore with too many facts. I figure if they are interested, they can always delve deeper later.
A good source of information on root structure if you DO want to delve deeper can be found here.
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