Spiraling the Carbon Cycle Using BioInteractive

In order to develop complex scientific explanations, students need to have many opportunities to grapple with a concept, look at it from various points of view, and analyze data representing different relationships. I plan the sequence and flow of my AP Environmental Science course strategically to ensure I am making these connections using a concept called “curriculum spiraling.”

Curriculum spiraling is the idea that students revisit a concept at numerous points over time, increasing the complexity with each revisit. In this way, students relate their new learning to prior learning, which allows them to frame their learning in the context of previously acquired information.

Curriculum spiraling is a way to both engage students and increase conceptual understanding. Originally proposed by Jerome Bruner (1960) and adopted by the Next Generation Science Standards (National Research Council 2013), curriculum spiraling is an instructional strategy based on an understanding of cognitive development in students. While often applied to curricular development that spans a student’s entire school career, it has broad and far-reaching benefits when designing curriculum for an individual course. When using curriculum spiraling in my course, I like to think of the concept I am trying to teach as a big puzzle that we as teachers help students assemble to understand science. I can add to the story in multiple units, always connecting new knowledge back to previously learned material, always deepening students’ understanding.

One of the best ways I have seen how curriculum spiraling works in practice is through the lens of the carbon cycle. Throughout my course, students continually return to the big idea that Earth is one big interconnected system; the movement of carbon atoms and molecules between different sources and sinks exemplifies this big idea. By constructing connections between processes and across temporal and spatial scales, I create a foundational understanding at the beginning of the year when teaching biogeochemical cycles. I begin by looking at carbon from a geologic perspective; many of my students’ only prior experience with carbon is with the reactions involved in photosynthesis and respiration. They probably haven’t connected these processes to the biogeochemical cycling of carbon that involves many different processes taking place across many different scales on a planetary level. We need to go back in time and start with this basic question: Where did the carbon dioxide in the atmosphere come from?

BioInteractive offers high-quality resources to address this question and teach various aspects of the carbon cycle. I use “The Geologic Carbon Cycle ” animation and the “Earth Systems Activity” to show an anchoring phenomenon to introduce biogeochemical cycles in the ecology unit of AP Environmental Science. My goal is to give students some foundational knowledge about carbon on a geologic time scale and generate questions we can spiral back to throughout the remainder of the year. The narrated animation illustrates how internal earth processes, such as volcanic activity, give rise to the venting of CO₂ to the atmosphere. Why doesn’t CO₂ continue to build up in the atmosphere? Why isn’t our planet like Venus? There must be some processes that balance these processes that add CO₂ through volcanism. In the Earth Systems Activity, they construct a geologic model of the carbon cycle and discover the processes that move carbon on a planetary scale. Students can begin to grapple with the idea of fluxes, sources, and sinks, and I can easily segue into the processes of photosynthesis and cellular respiration. I show the first two parts of the Photosynthesis animation to my class, and we complete the corresponding sections of the student worksheet together as a class.

Students explore the complementary chemical reactions that move carbon quickly from an abiotic reservoir to a biotic reservoir and back again. They take the same molecule of CO₂ released from a volcano and move it from the atmosphere to a living thing. The equation for photosynthesis demonstrates the conservation of matter; the same atoms of carbon are converted, stored, and sequestered. The movement of carbon is so nicely modeled that my students are easily able to expand their conceptual understanding of biogeochemical cycling: the big idea.

Students transfer the ideas of our geologic model to the photosynthesis model; students make the cognitive leap from looking at CO₂ being regulated on a scale of millions of years to a scale of hours! The idea that the same atom of carbon is being moved from one planetary reservoir to another is transferable to the movement of carbon at the molecular level in the individual cells of a plant leaf. They are able to connect the geologic carbon cycle model to the model of photosynthesis, and in doing so are making a deeper connection and expanding their understanding of the processes that move carbon.

As we later transition from ecological systems to Earth systems, my students are again presented with an opportunity to look at atmospheric CO₂ in a new way. They carry over the idea that CO₂ in the atmosphere is regulated by processes that work in balance. It’s helpful to be explicit with your students that you are spiraling content. When we revisit the photosynthesis/respiration and geologic carbon cycle models from earlier in the year, I give my students chart paper and some terms and formulas for carbon compounds and ask them to diagram everything they recall about the carbon cycle. I also tell them the goal is to be able to connect these processes to the role of carbon in regulating climate on a planetary scale.

When I want students to explain a connection from one idea to another, I ask them to explain why someone would care about the connection. For example, why do we care where carbon is and what form it is in? They quickly make the connection between concentration of atmospheric CO₂, a greenhouse gas, and global climate. For them to understand how Earth’s climate system works, we need to go back in time. The Paleoclimate: A History of Change Click & Learn looks at Earth’s past and present climate, highlighting the effects of two important factors: solar radiation and the composition of the atmosphere. Students examine patterns of climate change across scales of millions of years. The Click & Learn has graphs showing the relationship between change in CO₂ and temperature over the past 800,000 years. Students relate this to the carbon cycle processes they have previously learned and can explain the difference between natural variability and current climate trends.

By this point in the year, their understanding of the carbon cycle has expanded and students are thinking like scientists: asking questions about the implications of current climate change and the conclusions of the scientific community. As we wrap up our study of Earth systems, I shift scales again, taking my students to the African savanna, where termites facilitate biogeochemical cycling and contribute to soil productivity. The animation How Termites Enrich Ecosystems and the video Termites Digest Wood Thanks to Microbes demonstrate that the activity of termites and soil microbes is critical in decomposing organic compounds and continuing carbon cycling.

We bring all these concepts together during the unit on global change and examining human impact on the environment. Students see the causes of large-scale rainforest loss in the video Mapping the Darién Gap and are able to articulate a scientific argument for preserving rainforests to combat climate change because they have a deep understanding of the role of photosynthesis in storing carbon, the processes regulating Earth’s climate, and the predictable consequences of adding more CO₂ to the atmosphere. Additionally, when we do the hands-on activity “Ocean Acidification,” they easily grasp the chemical reactions because they have been looking at carbon conversions in many different units encompassing many different applications.

Throughout the year, my students have shifted scales, both temporal and spatial. They know that carbon is stored in vast quantities in the atmosphere, lithosphere, and hydrosphere. They can explain the natural earth processes that balance the movement from one reservoir to another. They have a deep appreciation for the process that converts a molecule of inorganic CO₂ into a simple sugar that will fuel most life on our planet. I remind them how far we have come in the understanding of this big idea. Therefore, when students are introduced to the Keeling Curve in the Data Point “Trends in Atmospheric Carbon Dioxide,” they quickly grasp the implications of their calculations: Human activities are responsible for the rate of CO₂ increase.

This is a very powerful Data Point, and I present it in a three-part activity. I show the Keeling Curve to the entire class and guide them through the interpretation using the Educator Materials. Next, they work in lab groups to break down the data by calculating the slope of the line (degrees increase in temperature per year). They now have more evidence to support robust discussion about the cause of increasing CO₂ concentrations during the class discussion that wraps up the lesson. My students have built a strong scientific explanation for the processes involved in the carbon cycle. Continually revisiting the concept and layering on another connection gives students the tools to make those deeper connections. The activity “What is My Carbon Footprint?” works well as a culminating activity, because students understand the impact of their choices and can make decisions based on sound science.

BioInteractive provides research and data from leading scientists that are developed into classroom resources that make it easy for teachers to spiral content. By planning for the spiraling of a concept from simple to complex, we provide powerful opportunities for students to build on and deepen their knowledge at each point of exposure to the topic.

References

Bruner, Jerome. The Process of Education. Cambridge: Harvard University Press, 1960.

National Research Council. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press, 2013. https://doi.org/10.17226/18290.