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The Carbon Cycle

The Carbon Cycle

The Carbon Cycle

Carbon is found on Earth in different forms - there is carbon in organisms and there is carbon in the atmosphere. The carbon cycle ensures a steady flow of carbon from one form to the next.

All life on Earth is based on organic chemistry - this means the chemistry of carbon. Organisms need carbon to build the complex molecules that make up their cells and other structures.

Carbon is stored in the atmosphere in a form that can be used by green plants. What is the name of this chemical?


The carbon cycle shows how carbon is passed between organisms and how carbon makes it back to the atmosphere.

When carbon is in the atmosphere, we call it inorganic, because it isn't bound in an organism.


Carbon in the form of carbon dioxide, CO2CO_2 makes up 0.03 -0.04% of the atmosphere. It is exchanged with organisms via two main process. What process removes CO2CO_2 from the atmosphere?

Photosynthesis fixes carbon from the carbon dioxide into glucose. The glucose can then be combined with other elements to make additional complex organic compounds, like proteins and lipids in the plant's body.

Which of these equations represents photosynthesis?


The carbon is then passed on along the food chains from plants to animals via consumption.

When an organism dies, the carbon is passed on to decomposing organisms such as bacteria and fungi.


What process returns carbon dioxide to the atmosphere from organisms?

Which of these types of organisms are responsible for returning carbon dioxide to the atmosphere from respiration? Pick all the options you think are correct.

You can select multiple answers

What process can also return carbon dioxide to the atmosphere that does not include respiration from an organism?

Millions of years ago, the process of fossilisation removed carbon from the active cycle and locked it away in rocks as fossils. In the last 200 years or so, we have been digging some of these up as fossil fuels and burning them. This has released CO2CO_2, that has not been part of the cycle for millions of years, into the air.

What is the combustion of fossil fuels doing to the levels of CO2CO_2 in the atmosphere?

Without human activities that use combustion, the level of CO2CO_2 in the atmosphere would remain relatively constant at about 0.03%. So without any human interference...