How Might Elevated CO2 Affect Plants Classroom Activity: 9-12 Time: 2 class periods, plus 3-4 weeks with daily 5 minute observations Overview: In this activity, students conduct an experiment to investigate the effect of elevated levels of CO 2 on plant growth. The activity helps students learn about the relationship between CO 2, plants and climate change. Integration with Project BudBurst Students participating in Project BudBurst learn that phenology is the study of the timing of biological events. They learn that because these biological events are influenced by environmental factors such as temperature, phenology can be an important science in understanding the potential impact a changing climate can have on plants and ecosystems. In parallel with students efforts to monitor plant phenology in their local area, this activity lets students explore other climate change-related variables that may impact plants in particular the effect of elevated CO 2, one of the greenhouse gases, on plant growth. Teachers may introduce this lesson at any time during their class participation in Project BudBurst. They may use it as an introduction to Project BudBurst and phenology, to help establish a connection between climate change and plants. Alternatively, they may introduce the lesson during the observation period, while students are waiting for key phenophase events to occur with their study plants. Teachers may emphasize that scientists often use a combination of field observations and controlled experiments to investigate a question. http://www./educators/pdf/pbb_co2plants.pdf Page 1 of 5
Learning Outcomes: Students will be able to: Formulate hypotheses regarding a scientific question Identify independent and dependent variables in their experiment Conduct an experiment investigating the effect of elevated CO 2 on plant growth Collect and summarize data and present results Explain the effect of elevated CO 2 on plant growth using evidence from their investigation. Materials: Two 2-liter clear soda bottles for each team of two students One plastic saucer for each bottle Knife, scissors, tape Potting soil (enough to fill the bottom of the bottles) Seeds of several different species of plants (tomato, wheat, bean, cucumber, clover, etc) Water soluble plant food Straws Hand pump (often sold as balloon pumps or aspirators) Education Standards: Available at: http:///educators/elevatedco2_sg.php Preparation Prepare the soda bottles for use in this activity. These modified soda bottles will serve as growth chambers for the experiment. Use the following procedure for each bottle. Remove the bottle label. Cut the end of the bottle off approximately 2 inches from the bottom and discard the bottom piece. Use a 14-16 oz. plastic container that is at least 4.5 inches in diameter at the top (sour cream, cottage cheese, and salsa containers work well) to serve as the base for the bottle. Poke a few holes in the bottom of these base containers for drainage. After filling the base containers with soil and planting, place the soda bottle with the bottom cut off over the base container. http://www./educators/pdf/pbb_co2plants.pdf Page 2 of 5
Activity 1) Ask students the question How might elevated CO 2 levels affect plants? Discuss with students where these elevated levels may come from. Have students propose hypotheses in response to the question and record these on the board. Guide students to be specific with regards to effects on plants (eg. more growth, less growth, etc). Encourage students to think of various growth measures. Explain to students that they will be working in groups to test these hypotheses. Review the basic setup for the experiment. 2) Have students prepare the soda bottle growth chambers. Have students fill the plastic container bases with soil and set in the saucers. Water the soil so that it is very moist. 3) Have each team of students select a plant type to work with from the seeds available. They should plant two seeds in each pot, and plant at least two pots (one to add CO 2 to and one with normal CO 2 to serve as a control). Leave the bottle tops off until the seedlings emerge. Make sure that each plant species available is selected by two or more teams (replication) to allow conclusions to be checked between teams. 4) After 2-4 days the seedlings should emerge. Once this happens, have the students thin the seedlings to one per pot and place the bottle tops on each pot. Label one bottle +CO 2 and the other Normal CO 2. Set the bottles in a bright spot. Once you place the bottle top on the container, the bottles will trap the moisture inside so be careful not to overwater the plants. 5) Treatments: CO 2 Treatment: Beginning now, and for each school day for the next 3 weeks, enrich the CO 2 in the +CO 2 bottle by blowing 10 breaths into the bottle through a drinking straw. Leave the caps off both bottles, but to reduce the extra CO 2 leakage out of the top of the bottle, cover approximately half of the opening with a piece of tape. Although some air will exchange through the opening, the extra CO 2 will mostly remain in the bottle. Control treatment: In order to ensure that both treatment groups are exposed to the same conditions (except for the extra CO 2), add air to the control group at the same time as you add CO 2 to the +CO 2 group. To add air without adding additional CO 2, use the hand pump to gently pump the room air into the bottle. Pump approximately 25 times per bottle. Remind students not to hold the intake of the hand pump near their faces so they don t pump their exhaled breath into the control bottles. http://www./educators/pdf/pbb_co2plants.pdf Page 3 of 5
6) Once the setup is complete, have the students describe the experimental setup and CO 2 enrichment technique in their notebooks. Also have them record their observations of the plant and bottle conditions in their notebooks throughout the experiment. 7) Water the plants when necessary by adding water to the saucers. Do not pour water into the top opening or remove the bottle top from the base. Water with a watersoluble plant food each time. 8) At the end of 3 weeks, remove the bottles from the bases, measure the heights, number of leaves, and any other growth parameter of interest. Each student team will record these values in their notebooks, make a graph of the results for each growth parameter, and then share their results with the class. Be prepared that some plants will respond more than others. If the responses generally seem small, it may be because other factors limited the plant growth (e.g., there was not enough light, water, or nutrient to support good growth). Discuss this with the students. As with any true experiment, there may be unexpected results. 9) Discuss the results with the students, considering the following questions: What did we find? Did all plants respond the same? Why or why not? For the plants that grew better under high CO 2, do these results mean that these plants will benefit from a warming climate? Are there other factors that may influence the growth of these plants? What about the additional effect of changing weather (heat, drought, etc.)? If plants respond to more CO 2 by taking more in, might they take enough in to reduce the CO 2 concentration in the atmosphere? If so, what will happen to the CO 2 when those plants die? 10) Have students prepare a scientific report summarizing the experiment, including Introduction, Methods, Results, and Discussion. They should also include references. Suggested Activity Extension Students may try many different experiments with this type of bottle-exposure chamber system. They can experiment with other plant species not examined in class, or they can vary other conditions such as less water, less nutrients, and/or different temperatures. Arrange to have students exchange papers anonymously to provide peer review feedback. Give students specific guidance on what to look for in each section. Encourage students to provide constructive feedback, while avoiding critical remarks. http://www./educators/pdf/pbb_co2plants.pdf Page 4 of 5
Students may conduct research on connections between climate change and phenology, starting with the Project BudBurst website, Science section (http:///science/phenology_climatechange.php). For students monitoring plants using the Project BudBurst protocols, they may hypothesize what they think may happen to their study plant as a result of climate change, explaining mechanisms involved. Background Information Plants depend on a steady supply of atmospheric CO 2 for survival. Through the process of photosynthesis, plants take CO 2 out of the air and turn it into sugars, starches, and other organic molecules. Many plants benefit from increasing CO 2, increasing growth rates, size, and yield in response, as long as there is sufficient light, water, and other nutrients to support the growth. Different species respond differently, with some species responding far less than others. The projected increases in atmospheric CO 2 over the next century may double the average global concentration from approximately 386 ppm (parts per million) in 2008 to 700-800 ppm by the end of this century. Recent experiments have suggested that many plants will likely respond to such an increase with increased growth, if all other environmental conditions remain the same. This exercise is designed to demonstrate the principle that increased CO 2 can act to enhance plant growth. Because the plant response should be rapid and obvious, and cannot depend on elaborate CO 2 control or monitoring equipment, human breath is used as the source of CO 2 (this contains approximately 10,000 ppm CO 2). Student Assessment Suggestions: Communication of scientific findings is an important skill for students in science classes to learn. Teachers may have students write a science paper summarizing their team s experiment, including Introduction, Methods, Results, and Discussion, and use these papers to assess students understanding. Teachers may also use students peer review feedback as part of their assessment. Source: Adapted from Global Climates Past, Present, and Future, developed by Sandra Henderson, Steven R. Holman, and Lynn L. Mortensen at the United States Environmental Protection Agency, June 1993. This teacher resource was made possible, in part, by support from the National Geographic Education Foundation. http://www./educators/pdf/pbb_co2plants.pdf Page 5 of 5