CARBON CYCLE: Photosynthesis, Decomposition, Respiration and Combustion

Last Updated: Mar 17, 2019 @ 3:31 pm

Carbon Cycle

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. It cycles from the atmosphere into plants and living things.

Over millions of years, the long-term carbon cycle cooks up hydrocarbons. But in the short-term carbon cycle, it just takes days, months or years for carbon to cycle through the environment.

What is the short-term carbon cycle? Let’s go through all 4 phases from start to finish.

1 Photosynthesis

Photosynthesis Process

The first step of the carbon cycle is how plants take carbon dioxide out of the air through photosynthesis. Even though carbon dioxide makes up less than 1% of the atmosphere, it plays a major role for living things.

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

Carbon fuels all living things. For example, animals consume food for energy using O2 and giving off CO2. Eventually, plants die and decay.

Anaerobic decomposition involves bacteria breaking down organic matter such as glucose into CO2 and methane (CH4). The nutrient cycle recycles inorganic and organic material in soil through the process of decomposition. Then, it goes back again through the same process again.

Over vast periods of time, layers of sediment build 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. Over the long-term, the decomposition of dead matter generate these fossil fuel products.

3 Respiration

Short Term Carbon Cycle

Instead of decomposition, plants can either be consumed by a herbivore. Animals rely on plants for food, energy and oxygen. Our cells require oxygen to break down the food we consume through cellular respiration.

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

In other words, the plants use solar energy to break apart that same carbon dioxide in the air. Through photosynthesis, it uses that same carbon for plant material in turn releasing oxygen 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. Carbon dioxide is one of the greenhouse gases contributing to climate change.

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.

Long-term carbon cycle summary

Carboniferous Coal Process

Carbon is in motion in the long-term carbon cycle. But the distinction between the short-term carbon cycle is that this cycle takes millions of years to come full circle.

Instead of carbon converting into sugars, carbon is re-purposed into fossil fuels like coal. When plants are buried and compacted over millions of years, they become hydrocarbons.

When you drive your gas-powered car, you tap into Earth’s carbon reserves deposited hundreds of million years ago. These fossil fuels are released into the air as carbon dioxide and water vapor.

It may stay in the atmosphere for awhile, but eventually plants consume it during photosynthesis. So that same weight from the tank of gasoline gets converted into wood or plant material by photosynthesis.


  1. Fossil fuels. Its funny how modern day environmentalists push a narrative invented by the OOG’s(original oil gangsters).

  2. Examples of carbon sinks = Oceans and forests are the biggest
    Examples of carbon sources = Gasoline vehicles and forest fires

Leave a Reply

Your email address will not be published.