In this lesson, students will study photosynthesis and then transfer their understanding of this topic to a consideration of how trees can help reduce the negative impacts of the greenhouse effect. They will read a Web page describing the greenhouse effect, carbon dioxide's role as a greenhouse gas, and the role of humans in exacerbating this effect.

Students will also browse the Web site of an organization that sponsors tree planting programs and consider how these programs might help reduce or slow down the increase of the greenhouse effect. They will conclude by writing paragraphs telling younger kids about the benefits of trees and plants.

Geography, life science, environmental science

Standard 8: "The characteristics and spatial distribution of ecosystems on Earth's surface"

Two hours

• Computer with Internet access
• Writing materials

Students will

• read information on the Internet concerning the greenhouse effect and tree planting programs, and answer questions about this information; and
• write things they would tell younger kids about the benefits of trees and plants.

Ask students if they have ever heard the advice that it's good to talk to your plants. Do they know the reason for this advice? Discuss their ideas, and explain that they will be learning some things that will help answer this question.

Have students research photosynthesis on the Internet. Ask them to write down any words that are new to them, and answer the questions below. The following Web sites will help them get started:

Arizona State University: What is Photosynthesis?
PBS: Illuminating Photosynthesis
The Photosynthesis Process
Why Leaves Change Color

• What is the sun's role in photosynthesis? [Answer: Plants convert the sun's energy into a sugar called glucose, which is the main source of plant nutrition.]
• How do plants absorb carbon dioxide? [Answer: Through openings in the leaves, called stomata.]
• What is chlorophyll, and what does it do? [Answer: It is a green pigment in the plants' chloroplasts. It traps energy from sunlight and stores it as chemical energy, which splits water molecules into hydrogen and oxygen atoms.]
• How is glucose created? [Answer: The chemical energy is used to created glucose from the hydrogen and carbon dioxide.]
• Why do plants release oxygen? [Answer: Because they don't need the oxygen that is created when the sunlight breaks down water molecules in the chlorophyll.]

Discuss the reasons why plants are beneficial to people, according to this video. Also discuss the reasons why talking to plants might benefit them.

Ask students if they have ever heard about any programs to plant trees in cities or other areas. What do they remember hearing? Do they remember what the purposes of these programs were? What benefits, including—but not limited to—the one mentioned in the video, can students think of for planting new trees in one's community? In other parts of the world?

Have students go to the following two Web sites. At the first, they should browse the site to read about this organization's tree planting programs. At the second, they should read the entire page.

American Forests
What is the Greenhouse Effect?

Have students answer these questions about the information on the Web sites, either individually or in small groups or pairs:

• Why do we need to be concerned about the greenhouse effect?
• How are human activities contributing to the greenhouse effect?
• How might tree-planting programs help keep the greenhouse effect from becoming more of a problem?
• What other benefits might tree-planting programs have?
• One quote from the American Forests Global ReLeaf Web site is that "these trees help clean the air and water, filter polluted runoff, slow global warming and erosion, and provide habitat for wildlife." Rewrite or add to this sentence using the word "photosynthesis" and at least one other vocabulary word from the Web sites they have explored.

Discuss students' answers as a class.

Ask students to imagine this scenario:

It's a hot day, and you're hanging out at a park or other outdoor place in your town. You notice a group of kids who are a little younger than you. They're busy planting trees. You approach them and say hello. They are getting a little tired, so they sit down with you in the shade. They tell you that they are glad to be planting trees because trees are pretty and provide shade on a hot day like this.

You know that they're right, but you also know there's more to it than that. What would you tell them about the other benefits of planting trees that you've learned about?

Have students write what they would tell these kids. They should write at least two paragraphs, which should include:

• at least four vocabulary words;
• an explanation of how more trees could play a role in helping to alleviate the global warming problem; and
• at least one example from the American Forests tree planting campaign to explain why a local tree planting initiative might be a good idea.

Since they are writing for a slightly younger audience (kids in grades 3-5), they should be careful to make their descriptions clear.

As an option, have students include drawings or diagrams to help illustrate what they are saying.

Have students research and report on other reasons why plants and trees are beneficial. These sites will be helpful:

Earth Day 2001 Worldwide Report
Benefits of Trees: The National Arbor Day Foundation
Forests (about forests in the Chesapeake Bay area, but relevant to forests elsewhere)

American Forests
Cities for Climate Protection
EPA Kids Site: Greenhouse Effect
The Photosynthesis Process