Chemical reactions form new products. Photosynthesis is one of Earth’s most important chemical reactions, if not THE most important one! By breaking down this reaction into the reactants and products, students will understand how trees:

• • remove carbon dioxide from the atmosphere through stomata (crucial for atmospheric carbon sequestration and mitigating climate change),
  • take in water through circulatory tissue called xylem, managing stormwater and improving water quality,
  • create oxygen, a life-giving gas essential for life on Earth, and
  • produce sugar in the form of glucose (as all photosynthetic organisms do, forming the base of all food chains)

Trees also provide other ecosystem services, including:

• • • Providing habitat
    • Reducing atmospheric and surface temperatures
    • Providing raw materials for many products 
    • Economic benefits (property value, etc.)

Human Impact –

Humans can have both positive and negative impacts on the environment (deforestation/reforestation). Sustainable forestry (managing forests to meet current needs and desires of society for forest resources without compromising the availability of these for future generations).

Trees are a valuable natural resource that we use in our daily lives, from the materials that make up our homes to the paper products that we use daily. But what other services do trees provide, and how do they do it (chemistry, structure/function)? In this learning experience, students investigate through collecting data and making detailed observations of a particular school yard or neighborhood tree. This learning experience also investigates how humans have impacted the local and national forests, past and present, and concludes with students educating their community on the science, importance, and local history of trees (by putting a QR code on their tree of focus that connects to a student-made web page about their findings).

Begin with a local, engaging tree story. The example given in the slides for this learning experience is the Buist Park Sophora Tree. This tree was chosen for its location in southwest Philadelphia, its strikingly massive size, and its age. Because this tree is located in a densely populated urban area and is also over a century old, it has lived through many changes in our city’s landscape and may provoke many discussion questions. After showing photos and reading a short, engaging passage about the tree, also allow students to navigate a 360° view of the tree using Google Maps. Finally, show students an image of the seed that this huge tree came from and begin to explore the question, “How do trees get the mass they need to grow?”

Oak tree time lapse – To reinforce the above concept and further engage your students, show the Oak Tree Time Lapse video. Students should continue to wonder, “How do trees get the mass they need to grow?”

Common responses – After students have had an opportunity to share their ideas to the question, show The Mass of Trees – Where Does It Come From? video. This video was chosen to help students see that most people, including early scientists and grown ups, do not have the correct answer to this question (giving convincing motivation to educate the public)!

Introduce photosynthesis – Arguably the most important chemical reaction on the planet. Students will need to unpack this crucial process in order to understand how trees [like the Bruist Park sophora] grow so large from such a tiny seed.

Local tree investigations – They will be collecting data on local trees in order to answer their questions and communicate their findings to the public. Depending on the location, you may or may not need completed permission slips for students. Before the trip, be sure to outline expectations, goals, and instructions:

Here student teams will use tools to find the circumference, height, and species of their tree. It is helpful if the teacher is able to identify the tree(s) ahead of time to be able to confirm student findings. Student teams record their data in their notebooks or create a lab sheet for them and use clipboards.

Circumference – measure the distance around the trunk of the tree at a height of 4.5 feet above the ground.

Height – students will find a stick about the length of their arm, create a  right triangle their your arm and the stick, walk away from the tree until the top of the tree aligns with the tip of the stick, then walk toward the tree, counting strides (Stride length can be found by counting the number of steps it takes to walk 10 feet and dividing that number by 10. Most people will have a stride length around 2 feet.). A video showing how to do this is linked in the slide deck.

Species – use a phone app (teacher phone) such as iSeek to identify the tree species.

Using i-Tree to Assess Tree Benefits

Two forms (google spreadsheet or pdf for printing) have been created if you would like students to record their data before entering the data in iTree.  They will copy their data into the iTree form to calculate the benefits of their tree.

Open the  iTree  Then, read the top of the page and click “Get Started.”

The fields will match the data collection form for easy transferring of their data.

Click on the green button to get results.

NOTE: Be sure students save their progress by copying the link at the bottom of the page and saving it OR emailing the results to the teacher.

By clicking on “Equivalents,” students will notice how much CO2, stormwater, and pollution this tree alone has captured. This will be quite surprising to students. Ask students how trees do these things? They will likely reply “PHOTOSYNTHESIS” without actually knowing how this process works.

Photosynthesis – Give students a bit more information about photosynthesis via a short definition, chemical equation, and diagram (see Learning Experience slides). Students will now know that trees do in fact get their mass from the air, but how do trees take in CO2, stormwater, and air pollution?

Initial Model – Have students make an initial model, with as much detail as possible, that shows how trees do the following:

• Remove CO2 and pollution from the air.
• Release O2
• Absorb stormwater

Have partners share and compare models and make a class consensus model together

Structure/Function Investigations

Students will engage in a series of 3 investigations to explore the structures that support photosynthesis. Each investigation follows a routine:

1. Engage students by reviewing the class model.
2. Elicit student understanding of a particular structure/function relationship we have questions about.
3. Explore a structure/function relationship using materials/tools.
4. Explain the structure/function relationship.
5. Evaluate student new understanding by revisiting the model. This is an opportunity for formative assessment via exit ticket or notebook check.

Investigations –

1. Stomata Peel – How do gases get in and out of a plant/tree? Students use nail polish, clear tape, and microscopes to view the tiny “mouths” found on leaves. This video can support this lesson. Add to initial models when finished.
2. Transport Tissue Dissection – How does water get from the roots to the top of a tree? This video can support this lesson. NOTE: This lesson requires celery to be left in colored water for 1 day. You can prepare this in advance or have students set up this experiment at the end of the stomata lesson. Add to initial models when finished.
3. Chloroplasts – How do plants harness solar energy to turn carbon dioxide and water into sugar and oxygen? This video can support this lesson. Add to initial models when finished

Students share their new understanding through informational signs. Signs are made using Google Slides (set to File → Page Setup → Custom → 8.5” x 11”).

1. Decide as a class on the format and content for the signs.
2. Include the tree’s common and scientific name.
3. Use Omni Calculator to find the tree’s age. Give the age, as well as other data collected by students (circumference, height).
4. Use iTree data (previously saved or emailed) to tell the benefits of the tree.
5. Students can also explain how trees do what they do (based on class explorations) on their signs.

An optional extension is to link tree signs to a student-made website that elaborates on the information given on the sign. This is an opportunity to partner with the Digital Literacy teacher if you have one to facilitate this project with the students in the computer lab. Create a blank Google Site for each team and share with student team members. Students can elaborate using information learned in class, including photos of their explorations of plant structures/functions. Students can also dive deeper into specific benefits of urban trees using the following resources:

1. Air Pollution Removal by Urban Forests – The two paragraphs under the heading How do trees remove air pollution? are most valuable and can be clipped from the full article to give students a snapshot of this topic.
2. A Breath of Fresh Air: How Trees Help Mitigate Climate Change – This short article can be used to relate the absorption of CO2 to climate change mitigation.
3. How Do Trees Reduce Stormwater and Flooding? This source from PennState Extension has an informative video with an accompanying transcript that students can use to pull essential information.
4. Benefits of Urban Trees This website has a snapshot of urban tree benefits and also addresses environmental justice.
5. What is Sustainable Forestry?
6. Philly Tree Plan (Executive Summary) 
7. Philly to hire its first city forester, and plant thousands of trees over the next decade – Philadelphia Inquirer article (paywall)