Name: __________________________________________ Date: _____________ Class: ______________
Re Cycle
Below is a picture of the carbon cycle. Label the processes in the word bank on the picture. You can ignore, or try to use
the arrows already drawn in the picture. Identify parts of the picture with the words in the word bank and add your own
arrows that show movement of carbon molecules, where necessary.
 Carbon Dioxide
 Photosynthesis
 Cellular Respiration
 CO2 dissolving in oceans
 Fossil Fuels
 Deposition
 Extracting Fossil Fuels
 Burning fossil fuels
 Organic animal matter
 Organic Plant matter
 Decomposition
1. What are all of the processes that take CO2 out of the air?
2. What are the processes that humans are directly involved in the most?
3. Where is most of the carbon on the planet? (hint: it says in the article)
4. Where do you think are some places that carbon moves around the fastest?
5. Where do you think are some places that carbon moves around the slowest, and is stuck for long periods of time?
Name: __________________________________________ Date: _____________ Class: ______________
Re Cycle: The Carbon Cycle
Think about a 100-year-old oak tree. This tree started off as a tiny acorn, which provided the
initial food for the sapling tree, and over many years the tree grew into a gigantic tree weighing thousands
of pounds. Where did the tree get the material to build itself? A small amount came from the water in the
roots. The vast majority of the matter that went to that tree came from the air! The tree sucked carbon
dioxide (CO2) right out of the air and used it to build up the carbohydrates –mainly cellulose- that make up
its body. What will happen to the carbon in the tree’s wood and leaves when it dies? It might be broken
down by decomposers. It might be burned in a fire. Or, it might end up being buried under the earth and
transformed into fossil fuels.
The carbon cycle is as important to life as the cycling of water. All of the living things on Earth are carbon-based organisms. They
are made out of molecules called organic molecules. Recall the four macromolecules: protein, lipids, carbohydrates, and DNA; they are
organic molecules. At the core of these are carbon atoms. In the food chain, consumers get the carbon that they need to survive by eating
other living things: either plants or animals. Producers, however, get their carbon out of the carbon dioxide in the air. This carbon dioxide in
the air may have taken a long journey to get to that producer, however.
Everyone knows that there is carbon dioxide in the air. We breathe it out. Every animal breathes it out. And indeed, there is a
large concentration of carbon dioxide in the air. However, by far the majority of the carbon on Earth is stored in a surprising place: the
ocean. Carbon dioxide is found in the air, but it dissolves into the mighty oceans, as well. When you open a fresh can of soda pop, carbon
dioxide bubbles, creating the refreshing fizz of the beverage. This is accomplished by adding extra carbon dioxide to the soda pop, so that it
rapidly bubbles out. The oceans are similar. They don’t have as high of a concentration of carbon dioxide as a Pepsi; after all, the oceans
don’t bubble and fizz, but they are vast, and thus lots of CO2 is dissolved in there. When CO2 dissolves into the oceans, it becomes a
molecule called carbonic acid (H2CO3), which makes the oceans slightly acidic. This carbonic acid is the source of carbon dioxide that
aquatic plants for photosynthesis. So, carbon dioxide is found in the air, as well as in the oceans and can dissolve from the air into the ocean,
and can also dissolve from the ocean back into the air. In this way, the carbon dioxide in the atmosphere is at equilibrium with the carbon
dioxide in the sea.
Grass grows everywhere. Just like the great big oak tree, it gets the carbon that it needs to build up its body from the atmosphere. It
does this through a chemical reaction called photosynthesis. Through this chemical reaction, the grass creates food molecules that it uses to
build up its body. Photosynthesis captures the matter out of the air that plants build their bodies out of, and it also captures energy from the
sun that goes into these food molecules. Photosynthesis also produces oxygen gas as a byproduct. That’s good for us because we need
oxygen to breathe! The forests of the world are not only important because they are sources of wood, and habitats for wildlife, but without
all of the trees in the worlds, we would all run out of oxygen and suffocate.
First consumers are the organisms that consume plants. By doing this, they get the carbon in the food molecules, as well as the
energy contained in the food molecules. Animals consume other animals, too. A first consumer might get consumed by a second consumer.
That second consumer might get consumed by a third consumer. All animals (and all living things) take their food molecules and break them
down again. They do this to release the energy contained within them. When this happens,
the carbon in the food molecules is broken down back into carbon dioxide. Then, the
organism breathes it out. This process is called cellular respiration. So, animals and plants
depend on each other. Animals need plants to do photosynthesis so that they have food
molecules for energy, as well as oxygen to breathe. Plants need animals because animals
break down food molecules back into carbon dioxide through cellular reparation, which is
the source of carbon that the plants depend on.
What happens to the matter in an organism when it dies? It will decompose. This
happens when organisms called decomposers, such as bacteria, fungi, and mold, break down
the organism’s body. The food molecules that make up the dead organism’s body will be
taken up by these decomposers and broken down just like an herbivore eats a plant.
Through cellular respiration, the decomposer will convert the food molecules into CO2.
However, sometimes the dead organisms aren’t broken down completely by
decomposers, and this dead organic matter gets buried under the earth. Then, the carbon
that makes up the molecules in the dead organisms’ bodies can take on very different forms.
Over millions of years, if large amounts of dead organic matter is buried under the Earth, the
heat and pressure of the Earth convert it into new chemicals called fossil fuels. The fossil
fuels are coal, oil, and natural gas. They’re called fossil fuels because they are made out of
old, dead living things. It typically takes 100,000,000 years for the fossil fuels to be
converted from organic, living matter, into the fuels of coal, oil, and natural gas. The long
process where fossil fuels form due to the intense heat and pressure under the Earth is called
deposition. Humans dig into the earth and extract these fossil fuels and use these special
chemical for countless purposes. All plastics are made from oil. Natural gas is used to heat
homes and cook food. Oil can be converted into gasoline, which is burned in vehicles for
transportation. All of the fossil fuels are burned in power plants to make electricity. When
these fossil fuels are burned, they turn back into carbon dioxide that ends back up in the
Above: The 4 kinds of macromolecules are
atmosphere. Because it takes hundreds of millions of years for fossil fuels to form, once we
protein, DNA, carbohydrates, and lipids. At
burn them, they’re gone for good (unless you consider hundreds of millions of years to be
the core of all of these molecules is carbon.
any time soon).