Carbon, water, and rocks – what do they all have in common? They move in cycles on our planet and one of my favorite topics to teach is the carbon cycle (standards MS-LS1-6 and MS-LS1-7). And not only because life depends on it! However, I worry that we don’t give it the credit it deserves in how it’s taught. The connectedness of photosynthesis, respiration, and decomposition deserves more than a few arrows going in a circle. Continue reading to learn more about teaching the carbon cycle in your middle school science classroom.
What are the basics of the carbon cycle?
At its core, the carbon cycle has three processes: photosynthesis, respiration, and decomposition. Photosynthesis turns sunlight, carbon dioxide, and water into sugar and oxygen. Respiration extracts that energy back out using oxygen. Decomposition recycles once-living material into the soil. Together they keep energy and matter flowing through ecosystems, powered only by sunlight.
As I write this, it is a beautiful sunny day shining down on the newly-growing grass and flowering plants of the spring. What could be a better time to think about these amazing processes?
At its core, the carbon cycle includes three processes: photosynthesis, respiration, and decomposition. These three processes keep energy and matter flowing through our ecosystems.
Photosynthesis, a process performed by plants, absorbs sunlight, carbon dioxide from the atmosphere, and water. With a bit of help from photosynthetic chloroplasts in the cell, carbon dioxide and water is converted into sugar. And a helpful little by-product, oxygen gas, is released as well.
Next up – respiration. Living things take that very same sugar and extract the energy from it. For those living things (like us) that don’t want to waste a thing, we use oxygen gas as well. Useful little organelles called mitochondria react with the chemicals from the broken-down food (like sugar) with oxygen gas. Just like that – we have changed what was once the Sun’s energy into a type we can use (stored in a molecule called ATP).
Finally, decomposition takes the remaining organic material from living things and recycles them. Nutrients from once-living things are broken down into the soil for use by plants again. This makes a complete cycle in which all that is needed to keep it going is sunlight. Pretty amazing stuff, huh?
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Why does the carbon cycle need a hands-on approach?
It's an amazing feat of nature, and it's tempting to prove the complete cycle with chemical reactions alone. But that isn't enough for students to visualize it. They need to see it in action and take a hands-on approach, so the movement of carbon becomes something they can picture rather than memorize.
I love teaching this subject because it is an amazing feat of nature. I geek out showing students the chemical reactions to prove that it is a complete cycle. But I now know that is not sufficient to help them visualize this process. Students need a hands-on approach and see it in action.
How do you teach the carbon cycle with a role-playing game?
Students become a carbon atom, starting inside a living thing like a plant. They roll a die and move based on the processes that happen: eaten by a consumer, taken up by a decomposer, or released as carbon dioxide. They record each step until their sheet fills, showing the cycle has no beginning or end.
My favorite way to teach the carbon cycle is using a role-playing game. Students take on the role of a carbon atom. They begin as part of a living thing (a plant, for example). Then, they roll a die and move somewhere depending on the processes that occur. They may be eaten and become part of a consumer. They may become part of a decomposer. They could be removed as carbon dioxide gas.
I start students at random locations to spread them out. Then, they begin to roll the die. They record where they begin, what happens to them, and where they are going. They repeat this process at the next location.
They continue to move around the carbon cycle until their sheet is completely filled. This helps teach that there is no beginning or end to the carbon cycle. It also lets them imagine how the atoms are physically moving from one place to another.
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How can students write about the carbon cycle?
Have students narrate a carbon atom's journey: beginning in a worm, eaten by a bird, exhaled as carbon dioxide, turned into sugar by a plant. For a creative twist, ask them to describe the process without naming the organisms, and require them to include respiration, photosynthesis, and decomposition, color-coded for easy checking.
Similar to the previous game, students can take on the role of a carbon atom and write about their journey. They might begin in a worm, be eaten by a bird, exhaled as carbon dioxide, turned into sugar by a plant, and so on.
If your students are creative writers, have them describe the process without naming the living things involved. For example, they could say, “My animal seems to be crawling around in the ground. It crawls out of the soil. But, my animal has been picked up by a bird and eaten!”
You could also require students to include an example of respiration, photosynthesis, and decomposition in their writing. Make it easy to check by having them color-code where each process occurs without using the name!
How do terrariums model the carbon cycle?
A terrarium is a closed system where all three processes occur, making it a perfect anchor phenomenon. Build one with a sealable container, soil, plants, and a little water, plus rocks and sand for drainage. With the right balance, it cycles carbon on its own, and it doubles as a water cycle model too.
I think terrariums are the coolest idea. You can easily use it as an anchor phenomenon for your carbon cycle unit. It’s like an aquarium (aqua meaning water) but for with land (terra meaning land). In its simplest form, a terrarium is a closed system in which all three processes (photosynthesis, respiration, and decomposition) occur.
Earth is a huge example of a terrarium. Life processes occur inside this sealed system and cycle carbon atoms around. The only addition necessary is sunlight to keep it going.
To build a terrarium, you will need a sealable container, soil, plants, and a little bit of water. However, it is ideal to add some rocks and sand to help with drainage. If you have the balance correct, the plants will grow using carbon dioxide given off by the soil decomposition and sunlight. The plant will also produce carbon dioxide as it uses respiration.
This is also a great model for the water cycle. You will see water droplets collect (or condense) on the top of the container. They will then fall (precipitate) on soil. Water absorbed by the plant through its roots will be removed through transpiration from the leaves as water vapor.
How do escape rooms help review the carbon cycle?
Escape rooms are a great review tool because students need the background content to solve them but enjoy hunting for the secret password. A digital version skips the printing, cutting, and laminating, so all you need are devices. Students click clues, collect password pieces, then unscramble the final word, which makes grading easy.
Escape rooms are a great tool for reviewing. Students will need the background content to succeed but they enjoy the challenge of finding the secret password. I really like digital versions to avoid the hassle of printing, cutting out clues, and laminating them so they can be reused. Instead, all you need are devices for students to access the document.
A digital escape room is a document (like a Google Slide set or PowerPoint) with links to clues. I like to make ones that use a picture in which students look for clues and click on them to access them. Then, each question gives them a piece of the final password. After collecting all the clues, they will unscramble the word to get the final password. It makes it easy for you to grade! Try out my carbon cycle digital escape room with your class today!
I also have a huge list of digital escape rooms that cover nearly every middle school science standard. Try them out and engage your students during test review!
How do anchor charts help teach photosynthesis and respiration?
Have students collaborate to build the chart in pieces: one group labels photosynthesis, another writes the balanced equation (6CO2 + 6H2O → C6H12O6 + 6O2), another draws plants, and another illustrates a cell's chloroplast. Repeat for respiration, add arrows between the processes, and add pieces to the chart as students learn.
While I do prefer a hands-on approach to the carbon cycle, it is never bad for students to see complex processes like the carbon cycle in a picture form. You could even have students collaborate together to show different aspects of it.
For example, have one group make a label for Photosynthesis. Have another group write the balanced chemical formula (6CO2 + 6H2O à C6H12O6 + 6O2). You could have a third group make pictures of plants. A fourth group could illustrate a picture of a cell to highlight the chloroplast as the location in which photosynthesis occurs.
Then, repeat the same process for respiration. Add some arrows showing the movement from one process to the other. Use it in your unit by adding the pictures to the anchor chart as students learn about the processes.
What demonstrations show photosynthesis and respiration?
For respiration, dissolve sugar in warm water, add active dry yeast in an Erlenmeyer flask, cap it with a balloon, and watch the balloon inflate over about 30 minutes. For photosynthesis, submerge a weighted leaf in water in sunlight and watch bubbles form. Add a leaf in a dark cabinet as a control and count bubbles to quantify.
Showing photosynthesis and respiration in class sounds like a difficult task. But, you can easily show it with some common materials.
For respiration, get a large Erlenmeyer flask, balloon, sugar, warm water, and active dry yeast. Show the materials to students and ask them the purpose of each as you add them to the flask. Dissolve the sugar in warm water. Then, add the yeast and mix them together. Place the balloon over the top of the flask and let it sit for about 30 minutes. You will start to see the balloon inflate slowly.
It’s also a great way to show students how bread is made. Show them the flask after about 30 minutes. They may notice how there are lots of bubbles in the water that look like a slice of bread!
Photosynthesis is even easier. Simply get a flask, a leaf, and something with weight to attach to the leaf (such as a rock you place on top). Submerge the leaf in water and put it in sunlight. After some time (if there is bright sunlight, maybe just 30 – 60 minutes), bubbles will start to form on the leaf.
Add a control to this experiment. Compare this leaf with one put underwater but in a cabinet with no sunlight. Have students quantify the amount of photosynthesis happening by counting the bubbles on the leaves.
How does the carbon cycle connect to climate change?
The carbon cycle is a natural lead-in to the greenhouse effect and climate change. In a balanced terrarium, photosynthesis uses the same amount of carbon dioxide that respiration generates. Adding extra greenhouse gases to a closed system increases the greenhouse effect, which is exactly what is happening on a planetary scale.
The carbon cycle is also a great lead-in to the greenhouse effect and climate change. In our terrarium example, the same amount of carbon dioxide is being used by photosynthesis as is generated by respiration. Adding additional greenhouse gases to a closed system increases the greenhouse effect.
Teaching the carbon cycle can seem daunting at first glance. Like many things in middle school science, we can break the concepts down into smaller pieces and look at each step. With a full understanding of these amazing processes, our students may appreciate all the awesome science happening right outside their window.