Carbon Dioxide - Sources and Sinks

Windows to the Universe/UCAR SciEd

In this lab activity, students use a chemical indicator (bromothymol blue) to detect the presence of carbon dioxide in animal and plant respiration and in the burning of fossil fuels and its absence in the products of plant photosynthesis. After completing the five parts of this activity, students compare the colors of the chemical indicator in each part and interpret the results in terms of the qualitative importance of carbon sinks and sources.

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Notes from our reviewers

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The educator should be well informed about the carbon cycle, sources and sinks. See, for example, this site from Vision Learning: [http://www.visionlearning.com/library/module_viewer.php?mid=95&l=] Activity is very focused on the mechanics of the experiments and doesn't require the student to understand the bigger picture and the reason for doing this experiment. Educator should include a teaching unit on the carbon cycle to tie this experiment into the bigger picture. Teacher prep time is extensive. The activities require equipment and supplies commonly found in a chemistry lab, except for the indicator Bromothymol blue and a sprig of Elodea (available in pet stores as an aquarium plant). There are six test tubes involved: A: control - 1/3 full of BTB; B: test for Part 1 - 1/3 full of BTB; C: test for Part 2 - 1/3 full of BTB; D: test for Parts 3 and 4 - 1/3 full of BTB, wrapped in foil, sprig of Elodea; E: test for Part 5 - 1/3 full of BTB; unmarked: vinegar and baking soda.
Lab demonstration of the main carbon dioxide sinks and sources using simple materials. Large conceptual gap between the actual experiments and their interpretation. While the science here is basic and well established, without a full understanding of the workings of bromothymol blue (BTB), the vinegar-baking soda reaction, plant photosynthesis and animal/plant respiration, the links to CO2 sinks and sources may be lost on students.
A hands-on activity with well-documented steps; leads groups of four students to consider the concepts of respiration and photosynthesis and their relationship to some of the carbon sources and sinks that exist on our planet. It does, however, make some pretty dramatic leaps from these results to their interpretation. Minimal assessment strategies provided.