Activity 1: From Soil to Roots

Preparation:

In Step 5, students are asked to observe the root systems of young seedlings. For this activity, any type of seeds may be used so long as the roots have grown about 1 or 2 cm. Pinto bean seeds are easy to obtain and work well. To germinate the seeds, place several seeds in a row along one side of a paper towel as shown in Figure 3.1a. Carefully roll up the paper towel from bottom to top. Place the rolled paper towel into a glass of water so that the seeds are at the top and out of the water glass (Figure 3.1b). Water will wick up through the paper towel and keep the seeds moist. Prepare enough seedlings so that each team of 4 students will have a seed to observe. Assume that just 1/2 of the seeds you prepare will germinate. Set the glasses of seeds in a location where they will not be disturbed. The seeds will need approximately 5 to 6 days for the roots to grow enough for observation. During the germination period, be careful to replace any water that is lost through evaporation. n

Procedures:

Students learn about plant roots and their role in obtaining water and nutrients from the soil for plants to use.

1. Remind students that there are air spaces in soil. These air spaces can be filled with water containing dissolved nutrients. Ask, “How does the plant obtain nutrients from the water that is in the soil?”
   • Students’ responses will vary. If necessary, guide the discussion to mention the plant’s root system.
2. Display a copy of Master 3.1, What Do You Know about Roots? Use a piece of paper to cover all but the first statement. Read the first statement and ask the students to indicate by a show of hands whether they agree or disagree with the statement.
   • This discussion is designed to help you assess the students’ prior knowledge of the topic. If necessary, review for the class the essential features of diffusion and active transport.
     • Diffusion
       • Molecules move randomly due to their kinetic energy.
       • This movement causes molecules to intermingle.
       • The net movement of molecules is from an area of higher concentration to one of lower concentration.
       • The net movement of molecules stops when the concentration of the molecules is the same everywhere.
       • The movement of the molecules comes from their kinetic energy and does not need additional energy (unlike active transport).
     • Active Transport
       • Active transport is a process used by cells to move molecules from an area of lower concentration to one of higher concentration.
       • It requires energy.
       • If your students already have been introduced to the energy molecule ATP, you may mention it as the source of energy for active transport.
3. Continue revealing the rest of the statements, one at a time, and asking students whether they agree or disagree with the statements.
   • After students vote on each statement, ask for 1 or 2 volunteers to explain why they voted as they did. At this time, do not correct wrong answers. The students will come back to these statements later in the lesson. Answers are found and revealed to students in Step 15.
4. Explain that they will now investigate the mechanism by which roots obtain nutrients from the soil. Divide the students into teams of 4. Pass out to each team a young seedling (taken from the paper towel germination) and a hand lens.
   • This activity refers to the way that most plants obtain their nutrients through the root system. Legumes that carry out nitrogen fixation in their roots are a special case and are not dealt with here.
5. Instruct the students to take a minute to observe the seedling’s root system with the hand lens and write down their observations on a piece of paper.
   • The root hairs are white and very fine. Provide a dark background against which the root hairs are more easily visible.
6. After the students have recorded their observations, ask volunteers to describe what they saw.
   • Students will report seeing one large root emerging from the seed. They also will describe fine white hairs growing out from the root.
7. Remind students of the first statement from Master 3.1, What Do You Know about Roots? “Plant roots have tiny hairs that absorb water.” Ask, “Why do you think that plants have so many root hairs?”
   • Student responses will vary. Guide the discussion to bring out that more root hairs mean more surface area with which to contact water and nutrients in the soil. In Lesson 2, students learned about particle size and surface area. In this case, the small projections on the root are another example of the importance of increasing surface area.
8. Ask students, “How do nutrients in the soil water get into the root hairs?”
   • Students’ responses will vary. At this time, accept all answers.
9. Explain that students will now investigate the process by which water enters the root hairs. Keep the class in their teams. Pass out to each team 1 copy of Master 3.2, Moving Water and Nutrients into Roots.
10. Ask students to read over the procedure on the handout. Explain that the cup represents the root hair, the larger container represents the water in the soil, and the food coloring represents the nutrients dissolved in the water.
11. After students have completed their investigations, reconvene the class and ask volunteers to explain what happened when the holes were poked through the cup.
    • Students will report that the colored water slowly entered the cup.
12. Ask students :
    • “Why did the colored water enter the cup?”
      • Students’ responses will vary. Guide the discussion to bring out the fact that although the concentration of water was the same on both sides of the cup, the concentration of the food coloring was higher outside the cup compared with inside the cup.
    • “What is the process called where a substance moves from an area of higher concentration to an area of lower concentration?”
      • The process of diffusion was summarized in Step 2. Students should recall that diffusion involves a net movement of a substance from an area of higher concentration to one of lower concentration.
    • “Where does the energy co me from to drive this process?”
      • Students should recall from the discussion in Step 2 that the kinetic energy of the molecules in solution drives the process.
13. Display a copy of Master 3.3, Experiments with Roots. Cover the bottom section with a piece of paper. Reveal the first experiment and read it aloud. Ask the students what this data tells them about how nutrients move from the soil into the roots.
    • Since the concentrations of some essential elements move from an area of low concentration to one of higher concentration, this suggests that energy was required for the movement and the process involved was active transport.
14. Reveal the second experiment, read it aloud, and discuss its meaning.
    • Students should recognize that since the chemical halts ATP synthesis there would not be energy available to support active transport. Without active transport, those essential elements that depend on active transport to reach high concentrations will exhibit much lower concentrations in the root hairs as compared with the first experiment. Other essential elements that are transported by diffusion will be expected to have their concentrations unchanged.
15. Conclude the activity by displaying Master 3.1, What Do You Know about Roots? once again. As before, ask students to indicate by a show of hands whether they agree or disagree with each statement. Ask volunteers to explain why they changed their minds about their answers.
    • Students should be able to respond to the statements about roots as follows:
    • Before holding a class discussion, give each student 1 copy of Master 3.1, What Do You Know about Roots? Instruct students to write on their copies of Master 3.1 why each statement is true or false. Students should include specific evidence from the lesson that supports their conclusions. Students can use their answers during the class discussion. You may also wish to collect students’ papers to assess their understanding.

Activity 2: From Roots to the Plant

Preparation:

Use a sharp knife to cut celery stalks into pieces approximately 5 cm (2 inches) long. Make sure that the cut surfaces are flat and will allow the celery to rest upright when placed into the paper cups. Approximately 2–3 hours before class begins, put one piece of celery into a cup containing the food coloring. Wrap the other piece of celery in plastic wrap until needed.

Procedures:

This activity helps students think about how plants have specialized tissues for moving water and nutrients from the roots to all other parts of the plant.

1. Explain that getting nutrients into the plant roots is an important first step . Ask students, “How does water, and the nutrients it contains, get from the roots to the rest of the plant?”
   • Accept all reasonable answers at this time.
2. Hold up a piece of celery and a cup containing food coloring . Ask students to predict what the celery will look like after it has been in the food coloring solution for a while.
   • Do not correct misconceptions at this time. Students will come back to this in Step 4. If students are unfamiliar with the existence of a vascular system in plants, they may predict that the entire stalk of celery will be blue inside. If they know that plants have a vascular system, they would predict that there are specific places within the stalk that are blue (blue dots seen on the surface of the cut end).
3. Display a copy of Master 3.4, The Plant Vascular System. Briefly review the information on the master so that students understand that plants have specialized mechanisms for moving water and nutrients.
4. Reconvene the class and hold up the piece of celery that has been in the food coloring. Ask volunteers to use what they have learned about the plant vascular system to explain why their earlier predictions were or were not accurate.
   • Students should see that the food coloring was transported up the celery stalk and was visible as a series of colored dots along the top of the stalk. Some students may have seen this demonstration before and remember what the result is, but have not thought about what it means about the existence of a specialized mechanism for transporting water and nutrients.
   • Reinforce that the movement of water took place through the plant’s xylem system, which explains why the food coloring was present in discrete places in the celery.
5. Conclude the activity by reminding students that photosynthesis produces sugars in the leaves. Ask them how the sugars, needed for energy, reach the lower parts of the plant.
   • Students should recall from Master 3.4, The Plant Vascular System that phloem tissue is used to transport sugars downward from the leaves. You can point out that in the case of the celery stalk, the xylem and phloem tissues lie next to each other in structures called vascular bundles.

Activity 3: Soil Formation and Horizons

This activity introduces students to soil formation. The way in which soil is formed results in layers, called soil horizons.

1. Display a copy of Master 3.5, Soil Horizons. Ask students to make observations about the soil they see in the pictures.
2. The main observation that students should make is that there appear to be layers in the soil that differ by color and thickness. Explain that soil includes layers and that the layers are called soil horizons. Give each student a copy of Master 3.6, Where Does Soil Come From? Ask students to work in teams of 2-3 to make and record observations.
   • Give teams 2–3 minutes to write brief observations. In the next step, students will get additional information.
3. Give each student a copy of Master 3.7, Soil Formation. Instruct them to use the information on this master to add information and detail to the descriptions they wrote on Master 3.6.
   • Encourage students to talk with their team members as they work through this. It may be helpful if students use a different color pen or pencil to make their changes or additions. In this way, they can easily see how their initial observations compare with the new information they are adding. Students can also make notes on Master 3.7 to cross-reference the steps on Master 3.6.
   • It may be helpful to point out to students that the cross-section of soil represented on Master 3.6 is the same total thickness throughout. Soil is formed through the breakdown of bedrock and addition of organic materials. It is not formed only by the addition of material on top of bedrock.
4. Conclude the activity by reviewing the information on Masters 3.6 and 3.7. Explain to students that horizons in soils from different areas are likely to be different—some thicker or thinner.
   • This is also an opportunity to go back to what students have learned about soil in Lesson 2. In that lesson, students learned about soil texture and the dependency that plants have on getting water and nutrients from the soil. In this activity, students have learned about the soil horizons in which roots grow.

Activity 4: The Dust Bowl

In this activity, students investigate the relationships between farming practices and protecting the topsoil.

1. Remind students that in the previous activity they learned about the formation of soil and soil horizons. Explain that although it takes many years to form fertile soil, it can be destroyed in a relatively short time.
2. Ask, “What factors do you think contribute to the disruption of the soil horizons?”
   • Student responses will vary. Some will mention natural factors such as weather (hot and dry) while others may mention human influenced factors such as farming practices.
3. Explain that students are going to investigate a severe example of soil destruction that occurred in the Great Plains region of the United States back in the 1930s.
4. Ask students to refer back to their copies of Master 3.6, Where Does Soil Come From? and Master 3.7, Soil Formation, and ask , “Which soil horizon is the most important to plant health?”
   • Students should recall that the topsoil (layer A) contains minerals and organic materials that are important to plant health.
5. Pass out to each student 1 copy of Master 3.8, Disrupting the Soil Horizons: the Dust Bowl. Instruct students to read the handout and on a separate piece of paper describe how the dust bowl was related to:
   • weather conditions
   • economic conditions
   • farming practices
     • If appropriate, you can assign this for homework.
6. After students have completed their assignment, reconvene the class . Ask volunteers to report how the weather, economy, and farming practices contributed to the creation of the Dust Bowl.
   • Students should report the following:
7. Explain that the most important government response to the Dust Bowl was to encourage farmers to change their farming practices . To conclude the activity, teams will look more closely at farming practices and their effects on the soil.
8. Arrange students in teams of 2–3. Pass out to each team 1 copy of Master 3.9, Farming Practices. Instruct the teams to read the short descriptions of farming practices and to follow the directions on the handout.
   • Give teams about 10–15 minutes to discuss the farming practices and write down their conclusions.
9. Ask for volunteers to report their conclusions about each farming practice.
   • Teams should report the following:
     • Crop rotation addresses the problem of nutrient depletion. By rotating crops with different nutritional requirements, one crop can restore to the soil an essential element that was removed by the previous crop.
     • Strip farming addresses the problem of soil erosion. The roots help hold the soil together. Positioning the cultivated strip perpendicular to the prevailing winds minimizes erosion from the bare strips.
     • Contour farming addresses the problem of water runoff. The furrows made by the plow (perpendicular to the slope) serve as dams that slow water runoff during rainstorms.
10. Explain that return of rain to the Great Plains, the end of the Great Depression, and the implementation of better farming practices helped the country recover from the Dust Bowl. Ask, “Do you think the US could ever experience another Dust Bowl? Why or why not?”
    • Student responses will vary. Some students may believe that the lessons learned from the 1930s will enable today’s farmers to avoid the mistakes of the past. Other students may be concerned that global warming may lead to another Dust Bowl.
11. Project Master 3.10, Dust Study. Ask a volunteer to read the study aloud to the class. Ask, "does this data cause you to revise your thinking about a return of the Dust Bowl?”
    • Some students may be surprised by these findings and think that another Dust Bowl is more likely than before.
12. Explain that scientists believe that this increase in dust emissions may be due to several factors including increased windstorm frequency, drought cycles, and changes in land use patterns. This movement of dust can have significant effects on both the area where the dust is removed and the area where it is deposited.