LESSON 3	Activity 6

Grades:

4th - 12th; Extension: 7th - 12th

Objective:

Students will learn what role trees and forests play in the water cycle. Students will gain a greater understanding of the dynamics of a forest ecosystem by seeing that trees are dependent upon, and play a part in, Earth's processes, including the water cycle. They will also learn that the water cycle is the system by which Earth's fixed amount of water is collected, purified, and distributed from the environment to living things and back to the environment.

Method:

Students will act out the paths that water takes in the water cycle. They will describe the importance of the water cycle to living things and the importance of plants in the water cycle.

Materials:

Cut out paper strips for Catskill Water Cycle game:Cloud, Mountain, Ocean, Stream, Groundwater, and Plant (printed on a different color paper for each destination); copies of Water Cycle Score Sheet (one for each student); envelopes for paper strips; watch or stopwatch; plastic bags; twist ties or string; small graduated cylinders; the Multiple Intelligences sheet.

Overview:

In addition to clouds, oceans, rivers, and valleys, living organisms are part of the water cycle. All living things need water to live because it is essential to their bodily functions. Plants and animals take in water and return it to the atmosphere as vapor (breathing, transpiring) or to the soil as liquid (excreting).

Forests greatly affect watersheds. Trees, small plants, and forest litter absorb rainwater, reducing erosion and runoff. Leaves capture up to 60 percent of precipitation. When rain falls on bare ground, the full force of raindrops can wash soil into streams, making them muddy. But when rain falls on the forest, it drips down through leaves and branches to the forest floor. The forest canopy, as well as layers of plant litter under trees, protect the soil from the full force of rain. Tree roots hold the soil in place so that it doesn't wash away.

Plants use water to transport nutrients and minerals necessary for growth. Plants also use water in photosynthesis. Since most photosynthesis takes place in leaves, and the leaves of a plant can be many feet above ground level, how does water from the soil get to these leaves? Transpiration (evaporation of water from pores, or stomata, on trunk, stem, and leaf surfaces) aids plants to transport water upward through their tissues. Root pressure, the cohesive and adhesive qualities of water (capillary action), and evaporation all contribute to water's circulation through a plant.

Evaporation is most likely the main process whereby water moves up the plant. When the water molecules reach the stomata of the leaves, they are exposed to air and the sun's energy. The exposed molecules receive heat energy from the sun and begin to move faster. This motion makes it easier for the molecules to break away and become water vapor. However, a tension still exists among the water molecules. As one molecule is drawn away, it pulls on the other nearby water molecules, pulling those molecules to the surface.

Plants can absorb large quantities of water; however, they lose most of this water through transpiration. Transpiration coupled with evaporation of surface water is called evapotranspiration. It plays a crucial role in the water cycle. Evapotranspiration returns water to its gaseous state, in which it is carried by winds through the atmosphere until it condenses and returns to Earth as precipitation.

Forests help improve water quality by filtering out impurities that could be potentially harmful in streams or groundwater. As water is absorbed by tree roots and then transpired through leaves, impurities (many of which are good for a tree) remain in the tree.

Although the gradual wearing down and erosion of soil is a natural process, without proper management human activities such as clearing vegetation for development, logging, dam building, farming, and draining wetlands will increase the rate of erosion in watersheds and can reduce water quality. By the same token, reforestation, use of best management practices in forestry and farming, certain types of landscaping, and restoring wetlands can reverse those trends.

Procedure:

Note: Photocopy each part of the Catskill Water Cycle game on a different color paper. Cut the strips apart. Mark each of six envelopes with a large label for each of the following: Cloud, Mountain, Stream, Groundwater, Ocean, and Plant. Put the strips in the corresponding envelope. Use the envelopes to set up six stations around the room.

Intro:

1. Ask: "What is a cycle?" (A sequence of recurring events.) Invite students to name some cycles that are part of their lives (morning, afternoon, night; fall, winter, spring, summer). If you haven't covered the water cycle, ask students whether they have heard of it before. Divide the class into pairs. Ask pairs to write down words that describe what they know about the water cycle or what they think the term water cycle might mean. Then ask them to write their own description of the water cycle. Ask for volunteers to share their descriptions with the class.

2. Show students the water cycle diagram in Lesson 1. Make sure that students understand the terms evaporation, groundwater, and condensation. Introduce the term transpiration. Use the following questions to focus students' attention:

   • If every living thing needs so much water, how come water isn't used up?
     

   • Where does the water go when a puddle dries up?
     
   • Why don't oceans and lakes dry up like puddles do?
     
   • Where does rain water come from?
     
   • Do you think water always follows the same path as shown in the diagram?

Activity:

1. Explain that the water cycle is really a simplified model for looking at the "journey" of a water molecule. So students may learn more about the different paths water might take, have them play a game in which each group will be a water molecule.

2. Divide students into five approximately equal groups, and have each group begin at one of the stations. Give each group a score card to record the path they will follow in the game. Later, students will have the chance to compare score cards and will have the opportunity to depict their journey in a variety of ways (using multiple intelligences).

3. One student from each group should remove a strip from the envelope at their station. They should read the strip to the group and write the following on their water cycle score sheet: their station stop, what happens to them, and their destination. Have them return the strip to the envelope. When you call out "cycle", groups should move to the next station as directed on the strip.

4. Groups should repeat step 5 above, continuing their journeys until their score sheet is complete.

5. Students can complete the activity in two ways:
   1. Have students go back to their seats and individually write a brief story from a water molecule's point of view that describes their journey through the water cycle.
   2. Groups can depict their journey using one of the following skills: verbal/linguistic, musical/rhythmic, bodily/kinesthetic, visual/spacial, or logical/mathematical. (See Multiple Intelligences,)

Extension:

Note: This activity works best on sunny days after a rain storm or after an area has been watered. A copy, for each group, of the Transpiration Experiment worksheet is also needed.

1. Divide class into small groups. Give each group an empty plastic bag.

2. Identify trees or shrubs on the school grounds. Assign each group a plant.

3. Have each group carefully place its bag over a limb of its tree or shrub. (Facing the sun works best.) Tie the bag with a twist tie or string. Each group should count and record the number of leaves in its bag.

4. Challenge the students to develop a method to estimate the number of leaves on their tree or shrub. Have each group record the estimated number of leaves on its tree or shrub.

5. Leave the bags on the plants for 24 hours. Have the groups carefully remove the bags at the same time and take them back to the classroom.

6. Have each group carefully open their bag and transfer its contents to a small graduated cylinder. Measure the amount of water in the cylinder. Have students calculate the transpiration rate for their whole plant based on their estimation of the number of leaves on the plant.

7. Pool the class data on the chart. Have students estimate the number of days in the growing season. Calculate the transpiration rate for each plant for the growing season.
   

Assessment:

1. Where does rain water come from? Do you think water always follows the same path as shown in the water cycle diagram? Where does the water go when a puddle dries up?

2. Make sure that all groups completed their score sheet. Does their story about their journey (or other depiction using multiple intelligences) follow their score sheet? Are the steps in their journey consistent with natural processes?

3. If the class completed the extension activity: Are their data somewhat reasonable? Ask if they are surprised by the transpiration rate they calculated. What are some of the many variables that could affect the data collected?
   

NYS Learning Standards:

Arts
Standard 1 - Creating, Performing, and Participating in the Arts: Theatre

English
Standard 1 - Language for Information and Understanding: Speaking and Writing
Standard 2 - Language for Literary Response and Expression: Speaking and Writing

Math, Science, and Technology
Standard 1 - Analysis, Inquiry, and Design: Scientific Inquiry
Standard 3 - Mathematics: Uncertainty
Standard 4 - Science: Physical Setting 2,4; The Living Environment 6

Source: Activities adapted from Project Learning Tree, Water Wonders, and Project WET, Thirsty Plants. Adapted by Donna Rogler, Catskill Forest Association.