Science and Engineering Practices
Lesson Overview
In this lesson, students will be figuring out the connection between human activity and greenhouse gases. They’ll do this by collecting data about local trees and analyzing and interpreting data about deforestation, which will serve as the example in this lesson of one human activity that can affect levels of greenhouses gases in the atmosphere. Students will then apply what they’ve learned to the construction of a written argument that helps answer the driving question: What happens to carbon dioxide levels in a local community when trees are removed (or added) by humans?
Building Towards:
PE-MS-ESS3-5: Ask questions to clarify evidence of the factors that have caused the rise in global temperatures over the past century.
Science and Engineering Practices
● Analyzing and Interpreting Data- Analyze and interpret data to determine similarities and differences in findings (MS-ESS3-2)
● Engaging in Argument from Evidence- Construct an oral and written argument supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon or a solution to a problem. (MS-ESS3-4)
Disciplinary Core Idea: MS-ESS3.D Global Climate Change
Human activities, such as the release of greenhouse gases from burning fossil fuels, are major factors in the current rise in Earth’s mean surface temperature (global warming).
In order to fully address DCI MS-ESS3.D, this lesson should be followed by lessons that allow students to figure out the connection between changes in greenhouse gas levels and a rise in Earth’s mean surface temperature.
Crosscutting Concepts: Cause and Effect
● Relationships can be classified as causal or correlational, and correlation does not necessarily imply causation.
● Cause and effect relationships may be used to predict phenomena in natural or designed systems.
Lesson Level Learning Goals
● Ask questions to identify and clarify evidence that various human activities can increase the carbon dioxide in the atmosphere.
● Analyze and interpret local and national data to provide evidence that there is a relationship between the increase in carbon dioxide in the atmosphere and human activities that result in the decrease of carbon sinks.
● Construct and present an oral and written argument supported by empirical evidence and scientific reasoning to support the claim that human activity can cause an increase in the carbon dioxide in the atmosphere.
Student should be familiar with the following concepts before starting this lesson:
● TBD (this is a holding spot if we need to add anything.)
Investigation 1
The Lesson Level Learning Goal for Investigation 1 is: Ask questions to identify and clarify evidence that various human activities can increase the carbon dioxide in the atmosphere. Students will build towards this goal by engaging with different phenomena.
First, they will figure out that plants absorb carbon dioxide from their environment by using an indicator tool to observe changes in carbon dioxide levels in a controlled environment.
Next, they will be introduced to a tool that they will then apply to collect quantitative data from a subset of local trees.
Materials
Bromothymol blue indicator solution
Water
Small jars (container) with lids
Straws
Pipette
Water plants (Elodea, etc.)
Goggles for students
Paper towels
Preparation
For each student, mix a few drops of the indicator solution into a small jar or container of water just before class starts. The water should be a faint blue color.
Background information for teacher
Bromothymol blue is a pH indicator solution that scientists use as a tool to observe changes in carbon dioxide levels in solution. As students exhale carbon dioxide into the cup of water, they will observe a change in color from blue to yellow
Instructional Sequence
● Instruct students to find a partner and pass out pre-prepared jars of indicator solution. Have the students to take a moment to observe their cup. Ask them to share what they think is in the cup.
● Pass out the straw and instruct students to use the straw to gently blow into the solution for 30 seconds. Once the allotted time has passed, have the students make observations about their jars and share what they see. (They will have noticed that the solution has changed color from blue to yellow.)
● Based on this new observation, have the students discuss what they think was in the jar at the start? What has been added to it to cause a color change? Use this conversation as a way to assess your students’ prior knowledge about respiration and carbon dioxide. If needed, prompt your students to think about what they exhaled into the jar when blowing bubbles.
● After eliciting student responses about what was in the jar, you can tell students that the jar contained an indicator solution that scientists use as a tool to observe changes in carbon dioxide levels in solution. When they exhaled, they added carbon dioxide to the jar, causing the indicator to change color.
● Ask the students, “What do you think will happen when we put the plant in the jar?” Take some predictions and then have one student from each pair place a plant in their jar and the other partner leave their jar as is. Students should cover both jars and place them along a windowsill or other area with sunlight.
● Students must wait about 20 minutes (or until the next class period) before they can see results. (While you and your students wait, you can use this time at your discretion.)
● After students have waited the 20 minutes, instruct them to make observations about any changes to the solution in the cups and ask them what they think happened. They will have observed that the cup with the plant indicates a decrease in carbon dioxide levels while the carbon dioxide levels in the control cup will not change. Ask them to use their results to write a claim about why the solution in the cup with the plant returned back to the original blue color.
● Ask students to use their observations to answer the question “What role do plants play in an ecosystem?”. Have the students share their ideas and thoughts.
● Students will have figured out that plants can absorb carbon dioxide, so you can now introduce the lesson’s driving question: “What happens to carbon dioxide levels in a local community when trees are removed (or added) by humans?” Tell them that for the rest of the lesson, they’ll be working to answer this question.
Materials
Photos of local trees
Copies of Carbon Sink Calculation Tool
Calculators
Tree Identification Resources (The teacher will need to collect the appropriate resources for their location. These can be online resources or physical tree identification guides.)
Copies of Observation Tool
Large flexible measuring tape
Other observation tools: Paper and pencils for bark rubbing, thermometers, etc.
Preparation
Prior to lesson, take pictures of trees around the school.
Background information for teachers
Hardwood vs. Softwood: The difference between hardwoods and softwoods is not based solely on how “hard” or dense a wood is. Instead, the classification is based on the structure of the wood. Hardwoods come from angiosperm trees (usually deciduous) and softwoods come from gymnosperm trees (usually conifers). This information is usually included in tree identification resources.
Carbon Sink Calculation: Scientists have determined certain statistical relationships between easy to measure traits of trees and some traits that might be more difficult to measure. The coefficients in the Carbon Sink Calculation Tool are the product of these relationships, and they allow us to identify a tree’s biomass without having to actually measure all of the tree’s biological material. These relationships differ based on the structure of the wood, so it is useful to use the hardwood vs. softwood classification system. You’ll notice that although students are measuring the trees’ diameter in centimeters, the final biomass is measured in kilograms. This change in unit is based on the predetermined statistical relationships.
In order for the class to figure out the role that tree species and size have on a tree’s ability to store carbon, you’ll need students to look at least 2 or 3 different tree species (or sizes). If your school is in a monoculture (an area where the trees are all the same species), you can give students additional sample measurements to use with the Carbon Sink Calculation Tool.
Instructional Sequence
● Show students pictures of different local trees to begin a discussion about how trees might differ from one another. Ask students “How are trees different?” and invite them to share what differences they observe in the photo and what differences have they observed in their own experiences. Students might cite differences in factors such as height, circumference, leaf shape, bark texture, color.
● Now ask students what might be some differences that they can’t immediately observe. After eliciting student responses, present students with the Carbon Sink Calculation Tool. Tell students that scientists use this tool to get a closer look beyond the surface observations that we’re able to make. You can refer back to the indicator solution from earlier in the lesson as another example of a tool that helps us make observations that aren’t possible otherwise. Take a moment to explain to students that the equations in this tool are not arbitrary. Rather, the scientific community has built up evidence about relationships between different factors that have allowed them to create these complex models of how factors like species and diameter interact. This types of empirically-based model is essential in helping us learn about things we can’t see or measure directly.
● Ask students to look closely at the equations, and ask them what parts of the necessary data can they collect. Can we directly measure diameter? If not, what can we measure? Is there other information that we would want to know?
● Once students have generated a small list, tell them that they’ll be going outside to observe trees around the school. Tell students that they will be recording their data in their science notebooks? (Potential factors to record: environmental conditions, leaf collection, bark rubbing, etc. You can use the Observation Tool to help guide student observations or create your own observation protocol. In order to use the Carbon Sink Calculation Tool, students will need to record the trees’ circumference, so be sure that circumference is part of the observation students will be recording. You can demonstrate protocols in the classroom or in the field depending on your classroom management style.)
● Have students go outside and gather qualitative and quantitative information about trees around the school. (Again, depending upon your management style, you can group students and have each group collect data about one specific variable, have each student collect a variety of measures, etc.)
● After students have returned to the classroom, give them more time to complete the calculations from the Carbon Sink Calculation Tool.
● Now have students work together to create a table to display the class data. At a minimum, the table should include tree species, diameter, and carbon storage. Prompt students with the question “What role do different species and size trees play in the local environment?” Through this display students will figure out that trees differ in a variety of ways including not only observable factors but also in their ability to store carbon.
● Ask students, “Based on the calculations and results we’ve charted, what can we say? What does this data mean?” Encourage students to make statements based on their data. For example, a student might figure out “Based on our data, we can say that as the diameter of a tree increase, the tree’s ability to store carbon increases.” If students need more prompting, ask “ Based on your data, what is the relationship between the diameter of the tree and the tree’s ability to store carbon?”
Investigation 2
The Lesson Level Learning Goal for Investigation 2 is: Analyze and interpret local and national data to provide evidence that there is a relationship between the increase in carbon dioxide in the atmosphere and human activities that result in the decrease of carbon sinks. Students will build towards this goal by comparing and contrasting data related to deforestation.
From Investigation 1, students will have figured out that since trees absorb carbon dioxide, they can affect carbon dioxide in the environment. In this investigation, students will figure out that human activity can affect the number of trees in an environment. This will allow students to establish that human removal of trees can affect carbon dioxide in the environment.
Materials
Costa Rica Land Cover Figures
Copies of selected readings
Instructional Sequence
● Show students the Costa Rica Land Cover Figures (1940, 1961, 1977, 1997, 2005) from the “Forest losses and gains: where do we stand?” article. (These figures show a loss of tree coverage over time, with a slight recovery of forested area in the early 2000s.) Have students make specific statements (not inferences) about what they see.
○ http://www.unep.org/vitalforest/Report/VFG-02-Forest-losses-and-gains.pdf