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Carbon Dioxide - Sources and Sinks

Windows to the Universe

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.

Activity takes about three 40-min lesson periods and some preparation. Additional materials required.

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Climate Literacy
About Teaching Climate Literacy

Biogeochemical cycles of greenhouse gases / Carbon cycle
About Teaching Principle 2
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Natural processes of CO2 removal from atmosphere is slow; Long residence time of some GHG
About Teaching Principle 4
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Human activities have increased GHG levels and altered global climate patterns
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Other materials addressing 6c

Energy Literacy

Environmental quality is impacted by energy choices.
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7.3 Environmental quality.
Movement of matter between reservoirs is driven by Earth's internal and external sources of energy.
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2.5 Energy moves between reservoirs.
Greenhouse gases affect energy flow through the Earth system.
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2.6 Greenhouse gases affect energy flow.

Excellence in Environmental Education Guidelines

2. Knowledge of Environmental Processes and Systems:2.1 The Earth as a Physical System:B) Changes in matter
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B) Changes in matter.
2. Knowledge of Environmental Processes and Systems:2.1 The Earth as a Physical System:C) Energy
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C) Energy.
2. Knowledge of Environmental Processes and Systems:2.2 The Living Environment:D) Flow of matter and energy
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D) Flow of matter and energy.
2. Knowledge of Environmental Processes and Systems:2.4 Environment and Society:A) Human/environment interactions
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A) Human/environment interactions.

Notes From Our Reviewers The CLEAN collection is hand-picked and rigorously reviewed for scientific accuracy and classroom effectiveness. Read what our review team had to say about this resource below or learn more about how CLEAN reviews teaching materials
Teaching Tips | Science | Pedagogy | Technical Details

Teaching Tips

  • 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.

About the Science

  • 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.

About the Pedagogy

  • 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.

Technical Details/Ease of Use

  • The instructions, including the four figures, are clear.

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