What Is the Carbon Cycle? - Diagram, Process & Definition

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  • 0:01 Carbon: A Crucial Element
  • 0:47 Definition of the Carbon Cycle
  • 2:42 Photosynthesis &…
  • 4:27 Fossil Fuels & Trees
  • 5:10 Decomposition & Carbon
  • 5:40 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

The carbon cycle is the process by which carbon moves from the atmosphere into the Earth and its organisms and then back again. Gain a deeper understanding of how the carbon cycle works in this lesson.

Carbon: A Crucial Element

When was the last time you saw a periodic table? You may remember the chart that hung on the wall of your last science class. Within it is all of the key information for every element that exists on Earth. Some of the elements that are on that table are rare and obscure, like yttrium and californium. Some are precious and valuable, such as gold and silver.

But there is one element on the periodic table that is absolutely crucial to every living organism. It is also a key component of our atmospheric air. And it cycles through our Earth, living organisms, and the air constantly. This element is carbon, and, in this lesson, we will take a look at a very important process called the carbon cycle.

Definition of the Carbon Cycle

Carbon is an element found in many different forms and locations within our Earth and atmosphere. As previously mentioned, it is found abundantly in living organisms. We would not even exist without this element. The key molecules that make up our bodies, such as proteins, carbohydrates, and DNA, contain carbon as a major component. Carbon is also found abundantly in our atmosphere in the form of carbon dioxide, or CO2. Additionally, carbon is also trapped within the Earth in the form of fossil fuels.

The carbon cycle is essentially nature's way of reusing carbon atoms in different ways and in varying places. It is the process in which carbon travels from the atmosphere into organisms and the Earth and then back into the atmosphere. But, how does this process work, and what moves the carbon?

It is important to remember that our Earth and its atmosphere as a whole is a closed environment. The matter that exists now is all that we will ever have. Have you ever heard the phrase, 'Matter cannot be created nor destroyed?' Think of water, as an example. Water cycles through the Earth and atmosphere constantly. It evaporates from our oceans and other bodies of water and is held within clouds. Then, the water is released in the form of rain. Water is never created or destroyed, just recycled.

Similarly, we have a fixed amount of carbon on Earth and in the atmosphere. We are in our own bubble, with essentially nothing escaping or entering our world. We are not getting intergalactic deliveries of needed elements like carbon. That means that all of the carbon we have on Earth and in the atmosphere is the same amount we have always had. And so, when new organisms are being formed, carbon is needed to form those key molecules, such as protein and DNA. But, where does it come from? This is where the carbon cycle comes in.

Photosynthesis & Cellular Respiration

As we mentioned before, carbon is found in many different forms and in many different locations. We already know that it's in our atmosphere. But only certain organisms can actually use carbon in this form. Let's start by looking at the process by which carbon in the atmosphere, in the form of CO2, is obtained and harnessed by plants on Earth. This process is called photosynthesis.

Plants are able to make sugar compounds using a few simple ingredients: CO2, water (or H2O), and the sun's energy. This can be represented by the following equation: 6CO2 + 6H2O + sunlight = C6H12O6 + 6O2. Now you can see that through photosynthesis, the carbon atoms have been taken from carbon dioxide and used to create C6H12O6, or glucose. And, where will the carbon go from there?

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