"My third graders didn't have a lot to say about grasses when we first started discussing them," reports Durham, NC, teacher Judy Rucker. "They frankly thought grasses were rather boring, and were uninspired when I asked what they knew or wanted to know about them," she adds.
When Judy challenged the students to explore to discover what they could learn about grasses around the schoolyard, the kids perked up. For starters, they noticed the range of places grass grew: sidewalk cracks, lawns, and gardens. "When the kids tried to pull some grass up, they were amazed at how difficult it was, which prompted questions about their root systems," notes Judy. Students dug up a shovelful of grass to bring into the classroom, then worked in groups recording observations and questions: Can grasses grow in water as well as soil? Why are roots so strong? Will grass grow back when it's cut? How does this compare with a plant like lima beans? How tall will grass grow? Next, armed with store-bought ryegrass and fescue, each group set up a GrowLab investigation.
While their inquiries proceeded, the class located the world's grasslands on a map, and each group chose one area to study. They were charged with researching the people and animals dependent on the biome, then developing a creative presentation. "Through our discussions, I realized that while students understood how important grasses were to many animals, they firmly believed that humans did not eat grasses," explains Judy. In response, she guided students to resources that revealed that grains such as oats, wheat, rye, and barley came from grass plant seeds. She then challenged them to read labels of food they'd eaten that week, and detail everything that contained a form of grain. "They soon began to realize how utterly dependent we are on grasses," she adds.
The exercise also uncovered some interesting cultural connections to different grains. Students noticed, for instance, that the Asian kids had much more rice in their diets, while corn predominated in the diets of Hispanic children. "Now we're inspired to try growing our own rice under a range of conditions," says Judy. "And we're eager to further explore how different cultures use grass family plants."
Let's face it, grasses are tough. They're well adapted to survive in a wide range of conditions, from polar areas to the tropics, from deserts to marshes.
Could your tomato plants endure mowing, baseball games, grazing zebra, and even burning, with such resilience? What makes these plants so well adapted to such seemingly brutal treatments? Unlike most plants, which grow primarily from their tips, grasses grow from near their bases in the lower joints or "nodes" beneath the blade (leaf). So when the top of the blade of a grass plant is chewed or mowed, the grass plant continues to grow from below. The narrow grass leaves prevent overheating and drying out, enabling grasses to survive well in habitats with strong sun where larger-leaved plants might suffer.
Grasses also have extensive root systems with many fine rootlets that hold tenaciously onto soil particles and enable the plants to find available water, even under dry conditions. (It's been estimated that the roots of one grass plant, laid end to end, could extend 387 miles!) Many types of grass have underground stems (rhizomes) that hold soil and send up new shoots. This adaptation can be particularly helpful to survival in areas that burn often, such as prairies.
Consider trying some of the following activities to prompt students to explore what makes a grass a grass.
Before starting a unit, consider having students create word webs to uncover their concepts about grass. Write the word "grass" on a chart (or have students write it on individual papers), then have students volunteer words and phrases that the word grass brings to mind. As each idea is added, have students connect it in a way that illustrates relationships between words. Then have students make a list of questions about grass, drawing from their word associations. (Note: Try doing this activity again once students have explored grasses in depth, then compare how their ideas have changed.)
Sorting Out Grass
Two weeks before starting a unit on grasses, plant a variety of grass seeds (lawn grasses, popcorn, wheat, rye, oats, for example) and a variety of nongrasses (beans, tomatoes, radishes, and others) in separate 3- or 4-inch containers, labeling them a, b, c, and so on. Challenge students to observe the plants carefully, sort the containers into two groups based on the appearance of their leaves, and explain to the class why they grouped them as they did. (Hopefully, some of the students will divide the plants into grass -- based on the long, narrow leaves with parallel veins -- and nongrass plants.)
Have teams carefully observe the plants in all containers with hand lenses, inviting each group to pull up one plant from each container to examine it more closely, then to draw its entire structure. Have groups record their observations and drawings and graph the daily growth of plants in each container. Ask, What did you observe that told you some plants were grasses? How did they differ from the other plants? Were all of the grasses exactly the same? What questions do you have about grasses?
Invite groups of students to explore the textures, smells, and life within a small section of a lawn, playing field, meadow, or other grassy patch. Before beginning, have students make a list of things they expect to find on their journey. Have them use hand lenses to explore the patch above ground, then dig up small samples with hand trowels. Ask them to describe how the soil feels and smells, and how the soil layers differ. Pose questions such as What evidence of living or once-living plant or animal life can you find? How does the temperature of the grass patch differ from that of nearby pavement? (As grass plants transpire, cooling takes place.) How many grass plants do you estimate grow in a square meter? Why might they be able to grow in such crowded conditions? Suggest that students write and illustrate a story describing what it would be like living in their patch of grass, if they were small enough to call it home.
Ask your students, How do you think grass plants manage to keep growing after we mow, picnic, or play soccer on them, or once cows graze on them? Do you think other plants -- beans or tomatoes, for instance -- could withstand the same treatment? Then invite students to explore this question by setting up the following investigation.
Plant grass seed in a container. When the grass is about two inches high, cut it off evenly at about half an inch above the soil (simulating mowing or grazing). Pull out one of the cut-off grass plants and attach it to a chart for later comparison. Ask students to predict what will happen in a week to the plants in the container. If they suggest that they'll grow, ask, From what part of the plant do you think the growth will take place?
A week later, pull out another "mown" plant and compare it with the uprooted plant. Ask, Where do you think the growth took place? What do you observe to lead you to that conclusion? How do you think the way grass grows helps it survive in different circumstances?
Consider doing the experiment again, but adding a bean plant. Ask students to predict how each plant will look in a week. Ask, Do you think that grasses or beans are better adapted for mowing and grazing? What have you observed to support your answer?
Try watering two containers of grasses with different methods. Water one regularly from the top and one from the bottom. Ask students to predict how the roots will look after four weeks in each container. Then have them pull the grass after four weeks and examine it. Ask, Do the results agree with your predictions? What does this tell us about grasses' adaptations to different environmental conditions? (Grass roots are essentially lazy. They'll search for water only if they have to. If water is always available to them in the top layer of soil, they're not forced to search more deeply.)