Ecosystems and Biodiversity Lesson 3 : Ecosystems

1. Introduce the concept of cycles.

What do all living things need? [Animals need air, water, food, nutrients (minerals mainly from food), and space. Plants need air, water, nutrients (minerals usually found in soil), space, and light.] How do living things obtain these needs? [Through interactions with their environment.] Provide each group of students one of the MDNR posters (or display on wall). Ask the students to identify the non-living things found in ecosystems, while you list them on the chalkboard. Students should be able to identify water, air, soil, nutrients, and rocks (nutrients and rocks may not be obvious). Explain that the materials (air, water, and minerals) that have existed on Earth for millions of years are the same as those that exist today. Even dinosaurs that lived long ago once depended upon the same materials that we depend upon today. All of these materials cycle through ecosystems and are used over and over again. How can scientists study and learn about these cycles? [While difficult to observe, scientists learn more about these processes by making careful observations and studying their effects. Scientists look for evidence to support their ideas.]

2. Introduce or review the water cycle.

Provide each group of students with a small amount of water in a cup and a cold mirror. What happens after you dip a finger in water? [The finger feels cool as the water evaporates.] As the sun warms water on the surface of the Earth, it evaporates also. What happens when you exhale on a cold mirror (or the classroom window)? [Water molecules that are a gas condense on windows due to cold temperatures, just as clouds are formed in the sky.]

Show the Water Cycle transparency and lead a discussion around the following questions:

• What causes water molecules to evaporate? [Energy provided by the sun.]

• What causes precipitation? [As the water molecules condense around dust particles and become heavy, they fall to Earth as rain, snow, sleet, etc.]

• What happens to the water once it is on the ground? [It enters the ground flowing into aquifers or runs into lakes and rivers as surface water. Eventually, all water ends up in the oceans (water in deep aquifers and polar ice caps may be stored for thousands of years.)]

• How do you think being located near to the Great Lakes affects the amount of precipitation our state receives? [Generally, areas along the shoreline of the Great Lakes receive higher amounts of precipitation, often referred to as “lake effect.”] In addition, the predominant westerly winds are the reason Michigan has more cloudy days than the states to the west.

3. Investigate the role of plants in the water cycle (indoors or outdoors).

What happens to all of the water that plants take in through their roots every day? Where does it all go? Explain the role of plants in the water cycle (refer to the Additional Background Information about transpiration).

Have students observe stomata on the underside of freshly plucked leaves or on living plants. On sunny days they are surprisingly easy to see with a low power microscope, Discovery scope, or a good hand lens (at least 10X). Look mainly on the underside of the leaves. Refer to Extension 2, Stomata Prints, at the end of this lesson for instructions on how to make “stomata prints.”

Conduct the following investigation to observe evidence of transpiration. It is preferable to conduct this activity outdoors. (If that is not possible, indoor plants will also work. Plants wrapped and used indoors should be placed in a sunny window.) Find a branch of a tree or bush where the end supports several healthy-looking leaves. Inflate the plastic bag by blowing into it. Then fit the bag around the leaves and branch, securing it with the string or twist-tie. The bag must be tightly closed to trap all water vapor and firmly tied to the branch so the plastic bag does not blow away. Next, each group of students should repeat the same procedure, using a variety of locations and plants. This activity should be conducted in an area of the schoolyard that will not be disturbed by other students. 

Return the next day to observe what happened. Students should carefully remove the bag from the branch and measure the amount of water in the bag. More advanced students can count the number of leaves (or estimate the surface area) enclosed in their bag and then calculate the average amount of water transpired by each leaf (or square centimeter) for that day. You might assume that an average large tree has 20,000 leaves (although there really is no “one average,” as trees differ greatly in size and between species). Using that information, students can estimate how much water an entire tree may transpire in a day, month, or year. Challenge students to calculate how much water may be transpired on a daily basis by Michigan’s approximately 11.5 billion trees.

Option: Use the same techniques to investigate other factors that may affect the rates of transpiration, for example, temperature, relative humidity, wind (or air movement), amount of moisture in soil, or type of plant.

4. Tying it all together.

Review the flow of water in the environment, using the Water Cycle transparency. Discuss the importance of having sufficient amounts of clean, usable water for supporting life on Earth. While the Earth will never run out of water, the future availability of clean water is not guaranteed. Michigan residents are surrounded by the Great Lakes. They contain 20% of the world’s available surface freshwater and 90% of the fresh surface water in the United States. Have students share some ideas for activities that might threaten the future availability of clean water. What can students and Michigan residents do today to help guarantee that clean water will be available for future generations?

Examples