LESSON 6: IF YOU BURY A DEAD ANIMAL IN THE GROUND, WHAT HAPPENS TO IT OVER TIME? (WHAT IS THE CARBON CYCLE?) SUMMARY The carbon cycle is like the water cycle. Students learn about the carbon cycle by playing a game in which they become an atom of carbon moving through the environment. Students model the carbon cycle by moving through stations that represent different phases of the carbon cycle. (This lesson is modified from http://www.montana.edu/wwwwet/journey.html) ESTIMATED TIME 30­50 minutes LEARNING OBJECTIVES Learners will learn... 1. Forms of carbon that make up the carbon cycle. 2. The carbon cycle is not just a one way circuit but a series of pathways. 3. Unlike the water cycle, with its large evaporation (liquid­to­gas conversion) and condensation (gas­to­liquid or gas­to­solid conversion) components that can occur abiotically (without biological life), the carbon cycle’s solid­to­gas and gas­to­solid conversions mostly occur biotically (with biological life). 4. Like the water cycle, the carbon cycle can be traced by following carbon atoms as they are converted from one form to another. Learners will be able to... 1. Describe five different types of carbon. 2. Describe how a solid form of carbon (glucose or sugar) can be converted to a gaseous form of carbon (carbon dioxide). 3. Describe how a gaseous form of carbon can be converted to a solid form of carbon. 4. Rank different forms of carbon by their densities (gases are lighter than liquids, which are lighter than solids). NEXT GENERATION SCIENCE STANDARDS Matter and Energy in Organisms and Ecosystems 5­PS3­1. Use models to describe that energy in animals’ food (used for body repair, growth, motion, and to maintain body warmth) was once energy from the sun. [Clarification Statement: Examples of models could include diagrams, and flow charts.] 5­LS1­1. Support an argument that plants get the materials they need for growth chiefly from ​
air​
and water. [Clarification Statement: Emphasis is on the idea that plant matter comes mostly from air and water, not from the soil.] 5­LS2­1. Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment. Disciplinary Core Ideas PS3.D: Energy in Chemical Processes and Everyday Life ­
The energy released [from] food was once energy from the sun that was captured by plants in the chemical process that forms plant matter (from air and water). (5­PS3­1) LS1.C: Organization for Matter and Energy Flow in Organisms ­
Food provides animals with the materials they need for body repair and growth and the energy they need to maintain body warmth and for motion. (secondary to 5­PS3­1) ­
Plants acquire their material for growth chiefly from air and water. (5­LS1­1) LS2.A: Interdependent Relationships in Ecosystems ­
The food of almost any kind of animal can be traced back to plants. Organisms are related in food webs in which some animals eat plants for food and other animals eat the animals that eat plants. Some organisms, such as fungi and bacteria, break down dead organisms (both plants or plants parts and animals) and therefore operate as “decomposers.” Decomposition eventually restores (recycles) some materials back to the soil. (5­LS2­1) LS2.B: Cycles of Matter and Energy Transfer in Ecosystems ­
Matter cycles between the air and soil and among plants, animals, and microbes as these organisms live and die. Organisms obtain ​
gases​
, and water, from the environment, and release waste matter (​
gas​
, liquid, or solid) back into the environment. (5­LS2­1) BACKGROUND INFORMATION FOR TEACHERS Read the following information as a refresher for yourself­­not your students­­and try to infuse it into the lesson. 1​
First recall that ​
mass must be conserved​
during transformations of different types of carbon. This helps us understand the relative importance of gas, liquid, and solid forms of carbon, because the weight of carbon into your body must equal the weight of carbon out of your body—if you are not gaining or losing weight!! Of course, it is tricky to measure changes in carbon for “boxes” such a watershed, or a forest, or a home. But this is exactly what biogeochemists try to figure out: how much carbon is being lost or gained by a wheat­field, city park, or forest meadow. 2​
Second, continuing the carbon balance of your body analogy: if you measure how much solid carbon you eat (a slice of toast with butter is mostly carbon as sugars or fatty acids [carbohydrates]), then measure how much solid or liquid carbon you produce (“feces” or “urine”), you will discover that for every 10 ounces (a weight equal to about 300 grams) of solid carbon you consume, only about 3 or 4 ounces (~100 grams) of can be measured as “feces” or “urine” <​
link​
to a “cow energetics” peer­reviewed reference>. Where is the missing mass? Most of your solid toast (and actually all of the food and drink that fuels you) has been converted to the gas carbon dioxide. This makes measurements very hard—the gas is invisible, even at cold temperatures. And it confuses a lot of students, young and old, who think that “missing” carbon must have been transformed into energy. While Einstein did figure out that E=m​
c2​
​
, humans convert 0 of the mass of carbon they consume into energy. One way to remember this is that ​
c​
in Einstein’s equation happens to be the speed of light, which is ​
fast​
. When a sunbeam leaves our Sun and shoots across the 93­million­mile darkness of space between the Sun and Earth, it still takes that sunbeam 8­something minutes to shoot that gap! So just 1 gram of mass (Einstein’s “m”), multiplied by 30,000,000 meters per second, squared, yields 1 * 30,000,000 * 30,000,000 = 9 with 16 zeroes, in a unit called ergs. No way, considering a quarter­pounder (burger) has a slab of meat in that weighs about 100 grams, are we converting mass to energy! 3​
With today’s lesson, it is important that students recognize that just like there are ​
transformations of water​
molecules from frozen (snow, ice) to liquid to gaseous forms, so too there are ​
transformations of carbon​
atoms from ​
frozen solid​
forms (“dry ice”—available at most grocery stores and a potentially useful demonstration as part of this game), to ​
liquid ​
forms (baking soda dissolved in water leads to a lot of liquid 2­​
1­​
carbon as carbonate anion [CO​
], bicarbonate anion [HCO​
CO​
], to ​
gaseous ​
forms: 3​
3​], or carbonic acid [H​
2​
3​
all ‘carbonated’ beverages are fizzy from the injection of carbon dioxide gas into solution. Carbon dioxide [CO​
] gas is non­toxic, whereas carbon monoxide [CO] gas is deadly. 2​
As illustrated in this game, solid carbon can come in many forms: some rocks such as limestone contain carbon, fossil fuel such as coal is almost 100% carbon, most soils are darkened by soil organic matter which is about half carbon by weight, and most plastics are about 80% carbon. The most important solid form of carbon is probably carbohydrate, illustrated by glucose, which has the formula C​
H​
O​
, meaning each mole of glucose contains 6*12=72 grams of carbon, 12*1=12 grams of 6​
12​
6​
hydrogen, and 6*16=96 grams of oxygen. Glucose is therefore 40% carbon (72 grams of carbon per mole divided by the total weight of a mole of glucose). MATERIALS AND PREPARATION ● If you will use dry ice, be sure to have winter gloves to handle the frozen pieces because the cold temperatures can cause injury to unprotected skin! ● Create signs for each of the nine stations by writing the following names on pieces of paper: ​
soil, fossil fuel, ocean, sky, plant, plastic, animal, human, rock.​
Place each paper in a different location around the room. Place a cup of different colored beads at each station along with the dice. Make a key for what colors of beads go with each station and write it up on the board. ● 9 boxes, about 6 inches (15 cm) on a side (Boxes are used to make dice for the game. Gift boxes used for coffee mugs are a good size or inquire at your local mailing outlet. There will be one die [or box] per station of the water cycle. [To increase the pace of the game, use more boxes at each station, especially at the clouds and ocean stations.] The labels for the sides of the dice are located in the​
​
Carbon Cycle Table below. These labels represent the options for pathways that carbon can follow. Explanations for the labels are provided. For younger students, use pictures. Another option is to use a spinner. It is necessary to design a spinner for each station.) ● 9 different colors of beads and elastic string ​
or​
9 different colors of magic markers depending on the variation of this activity you do ● If you use magic markers to track children’s movement you will need a “map” of the cycle for each child with the stations marked on it and a pencil for each child ● A bell, whistle, buzzer, or some sound maker If you do not have the time or ability to create the dice for this activity or purchase the beads, you can vary the activity and use spinners instead of dice and use markers or post­it notes instead of beads. See VARIATIONS ON THE LESSON below for more details. Place each paper in a different location around the room. Place a cup of different colored beads at each station along with the dice. Make a key for what colors of beads go with each station and write it up on the board. It will be important to try to record the bracelet color patterns to get a sense for the many different pathways that a carbon atom can take depending on which parts of the cycle it visited. For example, notice that if the carbon is in fossil fuel or rock, it is most likely that a student will stay there (be stuck there, accumulating those bead colors) for quite a while. On the other hand, notice how relatively speaking, carbon dioxide spends little time in the atmosphere (for example if Sky is represented by yellow beads,very rarely will someone end up with two yellow beads in a row in their bracelets). CARBON CYCLE TABLE Station Die side labels Explanation 1 Soil 2 sides ​
STAY 1 side ​
Ocean 3 sides ​
Sky Carbon as “sugar” is reprocessed in soils Carbon can be leached or washed into rivers and the ocean Most carbon is respired or converted from “sugar” into carbon dioxide 2 Fossil fuel 4 sides ​
STAY 1 side ​
Ocean 1 side ​
Sky Most fossil fuel carbon (e.g., coal, oil, natural gas) has stayed underground for millions of years Some fossil fuel methane gas or crude oil seeps or spills into the ocean Some fossil fuel is burned for energy, releasing carbon dioxide 3 Ocean 3 sides ​
STAY 2 sides ​
Sky 1 side ​
Plant Carbon dioxide dissolves in water to form carbonic acid Carbon “sugar” can be respired into carbon dioxide Carbon dioxide in the ocean can be photosynthesized by phytoplankton 4 Sky 1 side ​
STAY 2 sides ​
Ocean 3 sides ​
Plant Some carbon dioxide stays in the atmosphere Some carbon dioxide dissolves into the ocean, making it more ACIDIC​
!!!!! Most carbon dioxide is photosynthesized into “sugar” in plants 5 Plant 1 side ​
STAY 3 side ​
Sky 1 side ​
Animal 1 side ​
Human Some plant “sugar” is reprocessed in plants Most plant “sugar” is respired into carbon dioxide Some plant “sugar” is eaten by herbivores like cows Some plant “sugar” like broccoli is eaten by humans 6 Plastic 2 sides ​
STAY 3 sides ​
Ocean 1 side ​
Sky Carbon in plastic items just hangs out Most carbon in plastic items (microplastics!) is washed to the oceans Some carbon in plastics is burnt or broken down into carbon dioxide 7 Animal 1 side ​
STAY 4 sides ​
Sky 1 side ​
Human Some animal carbon as “sugar” is reprocessed in animals Most animal carbon is respired from “sugar” into carbon dioxide Some animal carbon (e.g., bacon) is consumed by humans 8 Human 2 sides ​
STAY 4 sides ​
Sky Some human carbon as “sugar” is reprocessed in us Most human carbon is respired from “sugar” into carbon dioxide 9 Rock 4 sides ​
STAY 2 sides ​
Ocean Carbon in calcium ​
carbon​
ate (limestone) forms mountains! Some rock carbon can be leached or washed into rivers and the ocean VARIATIONS ON THE LESSON 1. Making colored bead bracelets. ​
Have different colored beads at each station and give each student an elastic string. Write the key for what colors match each station on the front board. As students circulate through the stations they collect a colored bead at each station they visit. Try to assign colors that would be associated with the stations, for example green for plants, brown for dirt, etc. If students get stuck at a station for multiple turns, they should take a bead from that station during each turn. At the end of the activity, each student will have a bracelet with a visual representation of where they have been. 2. Marking a map. ​
Provide each student with a sheet of paper that has a map of the stations. Place a different colored marker at each station. Have the students make a mark on their maps for each turn they spend at a station using that station’s special color. Then have them make arrows showing how they travel among stations using a pencil to track their movements. INTRODUCTION: 5 minutes 1. Tell the students that the mystery for the day is “If you bury a dead animal in the ground what happens to it over time?” Ask the students what they think the answer is. Then ask them what they think the answer has to do with carbon cycle. Tell them you will revisit their answers after they play a game about the carbon cycle. TEACH: 30 minutes 1. Explain to the students that they are going to play a game where they will be an atom of carbon. Introduce the 9 stations to students. 2. Divide the students as evenly as possible among the stations. They will start the activity at the station to which you assign them. 3. Have a quick discussion before the activity in which students identify the different places carbon CAN and CANNOT go from their station in the carbon cycle. (If you are fossil fuel carbon, you cannot go directly into a plant.) Discuss the conditions that cause the carbon to move­­for this exercise, there are three main processes: photosynthesis is how gaseous carbon dioxide is converted into carbohydrates by plants; respiration is the reverse process by which carbohydrates are “burned” back to carbon dioxide; and the gas carbon dioxide can also dissolve in water to make that water more acidic. Explain that carbon movement depends mostly on life­­plants turn CO​
into “sugar” and non­plants turn “sugar” back into CO​
. Sometimes 2​
2​
carbon atoms will not go anywhere. The die for each station can be handed to that group and they can check to see if they covered all the places carbon can go. The​
​
Carbon Cycle Table provided earlier in this document gives an explanation of possible carbon movements from each station. 4. Students should discuss the form in which carbon moves from one location to another. Most of the movement from one station to another will take place when carbon is in its gaseous form. However, any time carbon moves into a plant, it is mostly in the form of a solid carbohydrate (glucose/”sugar”), with these molecules serving as food for plants, for animals, and humans. 5. In this activity, a roll of the die determines where carbon will go. Students line up behind the die at their station. Students roll the die and go to the location indicated by the label facing up. If they roll ​
STAY​
, they move to the back of their station line. 6. When students arrive at the next station, they get in line. When they reach the front of the line, they roll the die and move to the next station (or proceed to the back of the line if they roll ​
STAY​
). 7. Students should keep track of their movements. This can be done by having them keep a journal or notepad to record each move they make, including ​
STAY​
s​
. Students may record their journeys by leaving behind personal stickers at each station. Ideally a photo of their bracelets could serve as a snapshot of all their color­coded pathways. 8. Tell students the game will begin and end when you tell them. 9. Start the activity and run it for several minutes to let the students experience several stations. WRAP­UP: 5­10 minutes 1. Ask the students which stations were visited the most? 2. Did each student (carbon molecule) have the same path? 3.
4.
5.
6.
Ask the students how is the carbon cycle like the water cycle? Do the students remember doing a similar activity about the water cycle? (The water cycle is xxxx Discuss the carbon cycle with students and help them understand that it is not a well defined cycle, but a series of pathways. Carbon rarely completes a full cycle through each of these 9 stations, but instead follows a multitude of pathways, some shorter than others. Remind the students about the mystery of the day: “If you bury a dead animal in the ground what happens to it over time?” Ask them if their original answers to that question have changed and what the mystery has to do with the carbon cycle. (The body decomposes with parts of it turning into gas, into food for other animals, into parts of the soil, etc. Make sure they understand that the mass does NOT disappear!! Carbon is a key ingredient of all living things and all things that used to be alive. It cycles through our environment just like water ­­ not on some straight path that is always the same but through many different paths. Just like they did in the game. Matter (such as carbon) cycles between the air and soil and among plants, animals, and microbes as these organisms live and die. Organisms obtain ​
gases​
, and water, from the environment, and release waste matter (​
gas​
, liquid, or solid) back into the environment.) Ask the students what their bracelets might have looked like if there had NOT been a fossil fuel station. (Lots of carbon gets locked up in fossil fuels for long periods of time. That station was the one kids should have been stuck at the most besides the rock station. So, without the fossil fuel station, kids would have moved around the more and had a wider variety of beads instead of possibly getting trapped at the fossil fuel station.) POSSIBLE EXTENSION ACTIVITIES 1. For more advanced students, compare their carbon cycles to more traditional diagrams of the carbon cycle like this one: