The amount we have always had. And

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.

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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?Let’s think about who may be eating those plants. Humans, for example, are organisms that must obtain food in order to survive. And so, when we eat plant matter, we obtain glucose from the plant.

When we eat meat we are also able to get glucose due to the fact that the animal ate plant matter.Once digested, glucose from that plant is broken down in our cells in order to obtain energy. This process is called cellular respiration. It is essentially the opposite process of photosynthesis, and the waste product is CO2. Organisms get rid of this waste product by exhaling it back into the atmosphere. Every time you breathe, you are part of the carbon cycle because you are exhaling CO2. Thus, you can see how carbon moves throughout our world and affects each and every organism.

Carbon in Fossil Fuels and Trees

Some carbon in our world is suspended for hundreds or even millions of years. Carbon is trapped inside fossil fuels, such as coal and oil. Fossil fuels are composed of the transformed remains of living organisms, and they contain a great deal of energy. We burn fossil fuels for energy, and this process releases the carbon back into the atmosphere in the form of CO2.Another place that carbon is trapped for a long time is within trees. Since trees live for a very long time, the carbon isn’t cycled until the tree either dies or is burned. CO2 is then released back into the atmosphere, and the cycle continues as this CO2 is again used by plants to create food.

Decomposition and Carbon

The other major way that carbon is cycled through living organisms is through decomposition. For example, imagine that it is fall and leaves are turning brown and dropping to the ground. These leaves contain carbon in the form of glucose, as created through photosynthesis. When the leaves fall to the ground, they will eventually decompose.

Decomposition releases the carbon atoms back into the soil. And through the process of respiration, eventually that carbon will be released back to the atmosphere as CO2.

Lesson Summary

The carbon cycle is the process in which carbon travels from the atmosphere into organisms and the Earth and then back into the atmosphere. Plants take carbon dioxide from the air and use it to make food.

Animals then eat the food and carbon is stored in their bodies or released as CO2 through respiration. Carbon is also returned to the atmosphere by burning wood and fossil fuels.

Learning Outcomes

When you are finished, you should be able to:

  • Discuss the importance of carbon in the world
  • Explain the carbon cycle
  • List the sources of trapped carbon
  • Describe how carbon is recycled through organisms
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