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Carbon Cycling


DQCs: Grandma Johnson & Forest Carbon

BACKGROUND: Carbon cycles are one important representation of carbon movement among organisms. Within the carbon cycle, we view all living organisms, dead organic substances in the soil, and the atmosphere as a closed system. Within this system, processes? like photosynthesis, consumption, aerobic respiration, and decomposition move carbon between temporary stores (pools). Hence, carbon in the atmosphere today (CO2) may be in built into the leaves of a plant tomorrow and may be part of a fungus cell wall the next day. Energy moves among the organisms making up this complex web of the living, non-living, and the atmosphere. A key difference between matter and energy is that the carbon, in this narrowly defined system, stays constant, but energy originates outside of the system and must be constantly renewed through primary productivity.


Faculty assume students understand these quite sophisticated ideas and others below, but research shows that they often do not. This is the hidden curriculum?.


HIDDEN CURRICULUM • Principled Thinking? Addressed

  • Principles?: Conservation of Matter? (the biosphere is closed with respect to matter; energy and matter are related (energy can cycle through ecosystems in conjunction with matter as chemical bond energy; energy and matter are not interchangeable).
  • Processes: Generation? (photosynthesis); Transformation? (building of biomolecules within an organism, consumption of one organism by another); Oxidation? (autotrophic respiration, heterotrophic respiration, decomposition)
  • Scale & Time: Students: the molecular and cellular processes that take place in photosynthesis, movement of C between organisms and other parts of the ecosystem; where photosynthesis/respiration occur in organisms such as plants, bacteria and animals; and how these molecular/cellular/organismal processes collectively contribute to ecosystem processes.
  • Forms & Representations: Ecosystems Matter & Energy Flow (Students can interpret Energy pyramids; Box-and-arrow diagrams, including what they are and the principles they illustrate; recognize that glucose (and other organic) molecules are a form of potential chemical energy; recognize the different forms energy can assume in ecosystems.



The following 4 steps bring you through the process of selecting and using Diagnostic Question Clusters, interpreting student responses so you can focus on the concepts and thinking students appear to find most challenging, using active-teaching methods to help students make progress on these challenges, and finally gauging student improvement.

1. Select the DQC you want to use: the DQCs appropriate to use with these processes and topics are Grandma Johnson & Forest Carbon. Both focus on the outcomes listed in the table above. For each question the specific outcomes are described in more detail on the DQC pages.

2. Administer DQC and make a Diagnosis. First give students the Diagnostic Questions you chose (e.g. in class, as homework - see DQC pages). Then look at their responses and try to figure out what these responses mean (diagnosis). In other words, identify students' unprincipled thinking concerning Carbon Cycling. See diagnostic interpretations for Grandma Johnson and Forest Carbon DQC's.

3. Use student-active approaches to help students improve their understanding of the concepts and principled thinking. Once you figure out what your students need help with, you can use a variety of student-active approaches in class/as homework that should help them make progress. Below is a list of outcomes concerning Carbon Cycling and associated active teaching approaches. These are examples you can use and modify as you wish.

4. Evaluate progress. Did students make gains on the outcomes you are focusing on here? To evaluate this, you can give them the same questions you used above (perhaps in a different way) or similar questions that get at the same outcomes (use Forest Carbon if you used Grandma Johnson before).


Outcome: Students Better Understand

Active Teaching Approach

1.Carbon flow through an ecosystem - decomposition, photosynthesis, assimilation of C by different components of the system in different time scales.

Ecosystems C Flow

2. Photosynthesis - atmosphere as C source

Analyzing von Helmont

3. Movement of carbon through a simplified ecosystem

Follow the Carbon

4.Carbon cycle in marine ecosystem; interplay between photosynthesis and decomposition re CO2 concentration in the atmosphere

The Geritol Solution