River of Doubt

Sample Discovery Activity: Warning: Tree Under Construction

Lesson Introduction

Trees are built to last. As with all living things, different species have adapted to their different living conditions over time. For example, in dry areas trees tend to have deeper roots so that they can find moisture in the arid soil, while in wet areas their roots can stay near the surface and still obtain enough water for the tree's survival. Likewise, in windy areas a tree's roots need to be well anchored it to remain upright, while in calmer environments trees can do quite well with shallow root systems. Trees are breathtaking examples of the wonder, and the success, in nature's engineering.

In the rainforest, the trees are very tall. Some of the trees can even grow as tall as a 20-story building! The 1992 expedition's team members remarked about the beauty of the rainforest trees in the River of Doubt video. These trees often have wide root bases, called buttresses, which spread out like fans. In this lesson, the students will build a model of a rainforest tree to experiment with different-sized bases. They will discover the relationship between the height of a structure and the size of its base, and they can then compare the structure of a tree to the structure of the human body, and even to the structure of local buildings.

Objectives
The students will:
1. build a model of a rainforest tree.
2. experiment with different-sized bases to represent tree roots.
3. draw an appropriate conclusion on why rainforest trees need broad root systems.

Time Allotment
one 40-minute session

Materials
for each group:
toothpicks, wooden skewers or spaghetti
peas, marshmallows,
or spice drops
1 ruler
paper
pencils or pens
camera for assessment pictures

Advanced Preparation
Arrange the students into cooperative groups.

Procedure
Tap Prior Knowledge
1. Ask students why trees have roots. See if they have some ideas about what roots do for trees. Accept all answers.

Share with Neighbor
2. Invite students to work together in groups to plan how they think the tallest possible tree can be built. What shape would it have? Give them a few minutes to plan and sketch out their plans on a piece of paper. Once plans have been sketched, ask students about the role that roots played in their designs.

Hands-on Activity
3. Distribute the toothpicks, wooden skewers or spaghetti, and the peas, marshmallows or spice drops to the groups. Have each group of students build a model tree using these supplies. The tree itself should be built one piece on top of the other to represent the tall trees of the rainforest. Allow the students to design and build their trees in any way they choose. Let them make and test their hypotheses regarding what method works best, although working with triangular shapes and connecting the individual triangles allows for a structure resembling the buttresses on the rainforest trees.

4. Be sure that students keep track of the results of each trial so that they can discuss the methods they tried, and know which worked best. Encourage them to perform repeated trials of each condition and to keep data in a graph form if appropriate. Use rulers to measure the exact height and width of the base on each trial. All information should be recorded on the group's paper.

Proposing Explanations and Solutions: Introduce the Scientific Concept
5. After 10-15 minutes of testing, begin a discussion of the results. Explain the importance of a base to hold up a structure. The taller the tree, the more important a wide root system is to hold it upright. To support the height and weight of their trunks, tall rainforest trees have adapted by growing wide bases. Flowing out from the bases are shallow surface root systems called buttresses. They look like fans. They surround the trees and give them extra needed support. The roots can grow as high as 30 feet and they spread even longer on the ground.

6. Ask the students what they found out about the size of the tree's base during the building activity. Did a wider base hold up a taller tree? Encourage further testing if necessary. Have them write their conclusions down on their papers, next to the data. Through trial and error, the students should have discovered that the support of the tree needed to be expanded and secured to give a solid foundation so it would not tip over as they added height to the tree.

7. Review the idea of making a model in science. Models are used often because they allow scientists to look at how things work on a smaller scale. It isn't possible to bring an actual tree into the classroom lab, so a model is helpful.

Connect to Other Everyday Examples
8. Tell students to think of their bodies as tall upright structures. How do they stay that way, without toppling over? Have them try to stand with their feet close together. Does it make a difference? Like the buttress roots of the tall rainforest trees, the human body has feet which fan out to spread its weight so it can be distributed evenly and provide better balance.

Home Activity/Parent Involvement
With help from parents and other members of their families, have students list many
different kinds of plants and trees found locally. How have they adapted to the
environment they are in?

For example, prairie plants have long roots systems, often stretching farther into the ground than the plant grows above ground, even as far as 25 feet into the soil! This
enables these plants to find water in the dry climate, and survive through prairie fires.
Have students make sketches of what they find in their journals.

Lesson Assessment
Collect and check the written summaries from each group for evidence that the students
understand the relationship between a tree's height and the size of its base. They should state that rainforest trees need broad root systems because they are so tall. Look at the data that is recorded and the appropriateness of the students' conclusions.

Also, each group will have a model tree representing a rainforest tree with a broad base. Take photos of these models for students' portfolios.

Books to Read
Buildings, Bridges, & Tunnels, by Jackie Gaff, New York: Random House, 1991
Discovering Trees, by Keith Brandt, New Jersey: Troll Associates, 1982
Explore the World of Man-made Wonders, by Simon Adams, Racine, WI: Western Publishing Company, 1991

Taking Action/Additional Activities
Trees are an important resource for all of us. We depend on wood and wood products for a variety of uses, and many people are involved in forestry and the use of forest resources. Have students list some of the wood products they can locate around their homes and bring in the lists to share with the class. Or, have them trace the route of a tree from the moment it is felled to the endpoint of production and the consumer that uses it. List all of the people involved in the process. Select one person and investigate his/her career, training required, financial rewards, etc.

Compare the height of the rainforest trees to the tall buildings around the school. Take students outside to look at the Sears Tower if you can see it and imagine if a rainforest tree could get to be as tall. Try to find a 20-story building to make a comparison. Then, take a trip downtown to look closely at the structure of the Hancock building on Michigan Avenue. If it is not possible to visit the building in person, ask students to bring in photos and drawings of it. Point out how it is built with its widest point at the bottom. What other structures around Chicago are built in this way?

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