Climate Change and the Carbon Cycle

Performance Assessment

In this lab experience, students design an experiment to confirm that both carbon dioxide dissolution in water and plant photosynthesis contribute to capturing and converting atmospheric CO2. They will correlate their experimental results with the uptake and transformation of carbon dioxide in the carbon cycle and the impact of excess emissions of this greenhouse gas on global warming. Students prepare at least four test tubes with equal amounts of water and a few drops of BTB indicator solution. Then they exhale into the test tubes using a straw to add carbon dioxide. To two of these test tubes they add a single Elodea sprig. They expose one of these test tubes to light and keep one in darkness. They observe that the mixture exposed to light turns blue over time, and the mixture kept in darkness remains green. They attribute these color changes to a net decrease in CO2 concentration, attributable to plant photosynthesis removing CO2 from the water when the mixture is exposed to light. In the guided, open and advanced versions, students will observe that the mixture exposed to light experiences a pH increase.