- Big Ideas
- Essential Questions
- Content Outcomes Addressed
- Standards Addressed
- Pre- and Post-Assessment
- Investigation 1: Grass Growth
- Investigation 2: Grazing: Why Is There Always Enough?
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- Grass grows from the bottom, which helps it survive where other plants cannot.
- Why can animals eat the grass without killing it?
- How does grass grow in places where other plants do not?
Content Outcomes Addressed
- Students will understand what helps and prevents grasses from growing.
- Students will be able to explain how grasses grow.
- Students will be able to explain why grass is not killed when animals graze it or fire burns it.
- Disciplinary Core Ideas: LS1.A, LS1.B, LS1.C, LS2.A, PS3.D
- Science and Engineering Practices: 1, 3, 4, 6, 7, 8
- Crosscutting Concepts: 1, 2, 4, 5, 6
- Writing: W.K.2, W.K.3, W.K.6, W.1.2, W.1.6, W.2.2, W. 2.6, W.3.6, W.3.7,W.4.7
- Speaking and Listening: SL.K. 1, SL.K.5, SL.1.1, SL. 1.5, SL.2.1, SL.2.5, SL.3.1, SL.3.5, SL.4.1. SL.4.5, SL.5.1, SL.5.5, SL.6.1, SL.6.5, SL.7.1, SL.7.5, SL.8.1, SL.8.5
- Mathematical Practice: MP.1, MP.2, MP.3, MP.5, MP.8
National Geography Standards: 4, 7, 8, 14
Grasses adapt to the environment. While most plants grow from the top, grasses grow from the bottom. This means that they will not die off due to grazing because they replace lost parts by “pushing up” the surviving parts that have not been eaten by animals. Burning actually mimics a natural process and places rich nutrients in the soil, allowing grasses to grow back. But grasses that don’t receive light will wither and die over time.
- precipitation: rain, hail, sleet, or snow, all of which are formed by condensation of moisture in the atmosphere and fall to the ground when the air cannot hold anymore
Pre- and Post-Assessment
- To assess prior knowledge, ask students to predict how grass would be affected if it were cut, burned, or put in the dark. Students can draw pictures or explain their ideas in words. Repeat this activity for post-assessment with the added question, Why is grass affected the way it is in each of these situations?
- Grass dies when it is cut or burned.
Investigation 1: Grass Growth
How does the unique way grass grows help it to survive?
- Piece of string or ruler (for measuring)
- 3 similar patches of grass close together
- Bucket (or something else to cover a patch of grass)
- Notebooks, pens/pencils
- Take students to the three patches of grass. In their notebooks have students either describe or sketch what they see. Tell the students that you are going to do different things to each patch, and they’ll need to hypothesize what will happen in their notebooks.
- Measure each patch of grass with a ruler or length of string (Tie a knot at the spot in the string where the grass is the highest for comparison purposes later.)
- Cut (or have a student cut) the first patch close to the ground. Cover the second patch with a bucket. Water the third patch regularly. Have students hypothesize: Which will grow the fastest? The slowest? Which will look the healthiest? The weakest?
- Check the progress of the patches frequently over the next few weeks. Use the ruler or string to see how long it takes for the cut plants to return to their original height. Have students record the changes in each patch using sketches or descriptions.
When precipitation is erratic, drought and fire prevent large forests from growing. But grasses can survive fires because they grow from the bottom instead of the top. Their stems can grow again afterbeing burned off. The soil of most grassland is also too thin and dry for trees to survive, but there is just enough for grasses to thrive.
- Did any of the results surprise you? Why?
- How are grasses different from other plants?
- If you needed to grow grass quickly, what would you do to it?
To facilitate scientific thinking, step back and let your students do most of the thinking and planning. Have the students form small groups, and then present them with the question, “What helps grass growth? What hurts grass growth?”
Show the students the materials they have available to answer this question. As students develop their investigations, walk around and ask them how they are planning their approach. Ask guiding questions to help them develop a meaningful experiment. Ask students what data they will be collecting.
Once you approve their investigations, students can carry them out as you circulate. Check to see that students are recording quantitative data in a table or spreadsheet and qualitative data in words or pictures in notebooks.
Allow students time to analyze their data and draw conclusions. Before any presentations, have student groups meet with each other to share their findings. Allow the class to have a discussion about how to consolidate the findings of each group (most groups will have similar conclusions). You should just observe during this discussion. Then you can make clear any requirements for the class presentation, such as an explanation of the various experimental set-ups, background information on grass from notes, data, and conclusions, etc. Students can divide up parts of the presentation to work on.
The class can present one PowerPoint that sums up all the group findings. Students should take turns reading slides or explaining images.
Investigation 2: Grazing: Why Is There Always Enough?
Have you ever wondered why there is always enough grass for all those big grassland mammals to eat? To find out why, do the following experiment with your students.
- 2 similar patches of grass
- Wire mesh
- Notebooks, pens/pencils
- Choose two patches of grass that are similar.
- Use some wire mesh to make a protective covering over each patch to keep animals out.
- Water the grass every other day until it is about 2 inches (5 cm) tall.
- Using scissors, cut off the tops of the grass in one patch. Do not cut the second patch of grass.
- Continue watering every other day, and observe each patch for changes for one week.
- Have students record their observations.
- After three weeks, help the students evaluate their data and observations and write a conclusion. Guide your students in concluding that grassland mammals are merely giving the grass a “haircut.”
Help students understand that as long as the roots are left undisturbed, the grass will continue to grow, providing a constant source of food for mammals to eat. Be sure to point out that even with this adaptation, grass can be cut too much. Discuss overgrazing with the students.