CARBON CYCLE: Photosynthesis, Decomposition, Respiration and Combustion

Carbon Cycle

Last Updated: Sep 23, 2018

What is the Carbon Cycle (Long-Term)?

Carbon is the most important element for building the molecules essential for living things.

You and I are both made of carbon. Our cars use carbon in the form of fossil fuels. And carbon is also a pollutant as carbon dioxide in the atmosphere.

Carbon takes up various forms.

And the carbon cycle is both short-term and long-term. Over millions of years, here are main processes of the long-term carbon cycle.

1 Photosynthesis

Carbon dioxide makes up less than 1% of the atmosphere. The first step of the carbon cycle is how plants take carbon dioxide out of the air through photosynthesis.

With CO2 and H2O in the atmosphere, light energy puts these molecules together into complex carbohydrates like glucose. In other words, producers like plants synthesize their food through photosynthesis using sunlight.

If you have the right conditions, this process can repeat for centuries. They decompose and repeats for millions of years. Overall, photosynthesis involves plants consuming energy by reacting CO2 and water to produce oxygen and glucose.

2 Decomposition

After photosynthesis, eventually plants die and decay. Over a long period of time, there will be layers of sediment building on each other. Because of the pressure and heat from within the Earth’s crust, this generates fossil fuels.

For example, coal, oil and natural gas (methane) are some of the common fossil fuels. The decomposition of dead matter generate these fossil fuel products. Anaerobic decomposition involves bacteria breaking down organic matter such as glucose into CO2 and methane (CH4). The result is deposits of oil, coal and natural gas.

3 Respiration

Instead of decomposition, plants can either be consumed by a herbivore. Some animals depend on plants for food, energy and oxygen.

Once it’s consumed, carbon dioxide is released into the atmosphere because of cells respiration. In turn, this CO2 produced from respiring cells can be used in photosynthesis again.

4 Combustion

After extracting fossil fuels, combustion involves burning them to produce energy. For example, humans use fossil fuels to build factories, drive cars and forge cities. However, a byproduct of combustion is that it releases carbon dioxide back into the atmosphere. And as we deplete our oil reserves adding CO2 into the air daily, this affects the carbon cycle with an imbalance of oxygen and carbon.

But there is a limit for how much fossil fuels we can extract. Over millions of years, phytoplankton resting on the ocean surface photosynthesizes and takes in CO2. Using sunlight, it creates a molecule called glucose (C6H12O6) and sinks to bottom of the ocean. Humans discovered these fossil fuels beneath the ocean and started to drill the ancient plankton which became oil.

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