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 / Fossil Fuels / Organic animal matter
Photosynthesis / Deposition / Organic Plant matter
Cellular Respiration / Extracting Fossil Fuels / Decomposition
CO2 dissolving in oceans / Burning fossil fuels

  1. What are all of the processes that take CO2 out of the air?
  1. What are the processes that humans are directly involved in the most?
  1. Where is most of the carbon on the planet? (hint: it says in the article)
  1. Where do you think are some places that carbon moves around the fastest?
  1. 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 atmosphere. Because it takes hundreds of millions of years for fossil fuels to form, once we burn them, they’re gone for good (unless you consider hundreds of millions of years to be any time soon).