I use sticky-tack to hang my oversized laminated equations of photosynthesis and respiration on the white board (they extend the entire length of the board). Some interest is generated. I pull out the large, colored, laminated atoms of carbon, hydrogen, and oxygen and intrigue officially settles in. I have the students stand up and I quickly arrange a few tables into a circle and another set of tables into a second circle. The students can hardly wait to see what comes next and they crowd excitedly around me eager to receive some atoms. I divide the atoms, allowing students to form carbon dioxide or water molecules with the atoms given them. I ask them to look at the equations on the board and determine what needs to happen with the atoms. We all are “pulled into the roots of the plant” and enter the first enclosed circle of tables. The big “LIGHT ENERGY” sign is held up and we all link arms and rearrange (albeit a bit awkwardly) our atoms to create a sugar molecule. We release some diatomic oxygen molecules from the plant. Then, as a big unit, still linking arms and holding our unified sugar molecule, we are “eaten” by some kind of herbivore, the students pick cow. We enter the second circle, together as one unit of sugar, and are inside the cow. The oxygen molecules are also brought in. We are broken up and the atoms are rearranged with the oxygen to form carbon dioxide and water molecules again. The big heat energy sign is employed. We repeat the cycle several times giving different students “charge” of directing the group through either respiration or photosynthesis. We follow the carbons and discuss how the same carbon atoms are reused over and over again. They ponder the implications. They get it.
I like this activity for several reasons:
1) It emphasizes the rearrangement of atoms during chemical reactions
2) It demonstrates the actual cycle of the carbon cycle
3) It illustrates the chemical processes of respiration and photosynthesis
4) It engages the students directly with the content
5) It encourages collaboration as students need to juggle the atoms and form the molecules
6) It can be used as a formative assessment by having students take turns directing the group through the either photosynthesis or respiration. As soon as a student has to verbalize the process it is clear whether they understand or not.
I have taken the activity from the US Global Change Research Program (http://www.globalchange.gov/resources/educators/toolkit/materials) site that outlines three carbon cycle activities (at the bottom of the page) to conduct with students in order to guide them towards understanding the concept of the carbon cycle in terms of photosynthesis and respiration. I highly recommend laminating the molecules and signs and equations as students WILL handle them with vigor.
Furthermore, I originally made the activity for my 6th graders in the context of a Global Warming unit. However, I find myself pulling either the molecules or the equations out for other classes, even my IB Biology classes! They come in surprisingly handy. Just this past week I pulled out the laminated pieces and used the entire activity on my 8th graders after realizing they still weren’t understanding the carbon cycle as I presented it to them in the context of a chemistry IMYC unit (I posted about that on Friday).