These worksheets look at how carbon, a vital element to living things, is recycled naturally.

Carbon is a non-metallic element that has a great deal of significance for living things. It is an element that has an incomparable ability to bind to an unusually high number of different elements. The elements unique structure of have four available electrons to form bonds helps it form multiple stable bonds with other small elements. This helps living things form complex molecules like amino acids, proteins, and DNA. The carbon cycle is the process whereby Mother Nature will constantly recycle this element. It plays a vital role in the homeostasis of all living things on Earth. Since it is cycle, you can pretty much view it from any angle, but I would say it begins with plants. Plants use carbon dioxide that is found in Earth's air to make energy from sunlight. Animals love tasty green things, so they eat the plants and breathe in oxygen. They also breathe out with more carbon dioxide than they breathed in. The plants then use all this extra carbon dioxide to keep it going. As the plants and animals die, decomposers break down their remains and return nutrients to the soil and carbon dioxide to the atmosphere.

These worksheets look at just about every aspect of the Carbon cycle. We look at how this element is recycled and how oxygen seems to affect the progress of the cycle. We also take a look at several compounds and process that seemingly affect the efficiency of this process. We look at how food chains also affect the process. We also look at how forms of human pollution are having long term consequences for the planet.

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The Cycle

The ocean also takes a lot of excess carbon out of the atmosphere because CO2 in the air reacts with sea water.

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QUESTIONS: The Cycle

Processes that put carbon into the air are called sources. Human respiration puts it back into the atmosphere when we exhale CO2. Carbon also returns to the environment through the process of the decay of plants and animals.

What Is Carbon?

It forms a major part of rock formations like limestone and marble. It dissolves in large bodies of water, including the ocean. It is also found in fossil fuels like coal, natural gas, and petroleum.

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QUESTIONS: What Is It?

Almost every human industry uses it in some way. Any industry that uses coal, methane gas, or crude oil (a precursor of gasoline) uses carbon.

The Oxygen Cycle

Oxygen is the most common element in the human body where it exists primarily in the form of water. While carbon accounts for 18% of the human body, oxygen makes up 65% of it.

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Question Set: The Oxygen Cycle

Cellular respiration (which is also part of the C cycle) is not the only natural process that uses oxygen. Decomposition, which releases carbon from dead plants and animals back into the soil and the atmosphere uses up oxygen.

Photosynthesis

Photosynthesis and cellular respiration are opposite reactions. During photosynthesis, photosynthetic organisms use the energy from sunlight to convert CO2 and water into the simple sugar glucose.

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Question Set: Photosynthesis

Because all living things breathe in some way, all living things contain some form of carbon. Activities like eating and excretion are also contribute to this cycle, as the element is being taken into and passed back out of living organisms.

Atmospheric CO2

The layer of gases that surrounds the Earth is called the atmosphere. The Earth's atmosphere is made up of nitrogen, oxygen, water vapor, and very small amounts of other gases like argon and CO2.

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Question Set: Atmospheric CO2

Carbon removed by the ocean becomes calcium carbonate, which some aquatic organisms use in order to make their shells. When these organisms die, the carbon in their shells returns to the environment in the form of sedimentary rock. If too much of it is removed from the air by the ocean, it can become carbolic acid and reenter the atmosphere in the damaging from of acid rain.

Food Chains

Plants are considered to be at the bottom of the food chain because they create usable energy through the process of photosynthesis.

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Questions: Food Chains

When animals eat plants, the energy in the plants, as well as the carbon in the plants, becomes available for the animal's body to use.

Oceans

There are many ongoing processes on Earth that are part of the carbon cycle: photosynthesis, eating, excreting, decomposition, burning, etc.

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Oceans Question Series

About half of the CO2 removed from the atmosphere is dissolved on the surface of the ocean. Because the ocean takes more carbon from the atmosphere than it puts back into it, the ocean is sometimes called a carbon sink.

Changes in the Carbon Cycle

For many millions of years the level of carbon in the atmosphere has remained relatively constant.

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Question Set: Changes in the Cycle

Human activity is not the only change that has occurred in the carbon cycle. The amount of CO2 in the Earth's atmosphere has increased several times during prehistoric times because of volcanic eruption, which sends gases like CO2 into the atmosphere.

The Carbon Cycle and Energy

Plants use ATP to sustain their own lives. Because plants produce ATP, they are known as producers in the food chain. When terrestrial or aquatic animals eat plants, their bodies digest the plants in order to make the chemical energy stored there available for their own bodies to use.

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Energy Questions

When living organisms die, the carbon (and the energy) that is stored in their bodies returns to the environment, where it becomes available to new plants in the form of nutrients.

Deforestation

If there aren't enough trees to keep the amount of CO2 in the atmosphere at the right levels, the planet's climate changes, something which is happening right now.

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Deforestation Questions

Deforestation is having a negative effect on the carbon cycle, a process on which all life on Earth depends.