What is the Carbon Cycle?
The carbon cycle is the continuous movement of carbon atoms between the atmosphere, living organisms, oceans, soil, and rocks. Photosynthesis pulls carbon dioxide out of the air, while respiration, decomposition, and combustion return it, keeping the element in constant circulation.
The carbon cycle is the natural process by which carbon moves between the atmosphere (as CO2), living things, oceans, and geological reservoirs through photosynthesis, respiration, decomposition, and combustion.
- 1.Atmospheric CO2 — Carbon dioxide in the air, absorbed by plants and oceans.
- 2.Photosynthesis — Plants and algae convert CO2 into organic carbon (glucose).
- 3.Consumption — Carbon moves through food chains as animals eat plants and each other.
- 4.Respiration & Decomposition — Organisms and decomposers release CO2 back into the air and soil.
- 5.Fossilization — Some buried carbon slowly forms coal, oil, and natural gas over millions of years.
- 6.Combustion — Burning fossil fuels releases stored carbon back into the atmosphere as CO2.
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Step-by-step worked examples
A power plant burns 500 kg of pure carbon. How much CO2 is released into the atmosphere?
m(CO2) = m(C) × 3.67 m(CO2) = 500 × 3.67 = 1,835 kg
A forest fixes 24 kg of carbon into new wood in one season. What mass of CO2 did it remove from the atmosphere?
m(CO2) removed = m(C) × 3.67 = 24 × 3.67 = 88.08 kg CO2
Global fossil fuel burning releases about 9 gigatonnes (Gt) of pure carbon per year. Estimate the annual CO2 released.
m(CO2) = m(C) × 3.67 = 9 × 3.67 ≈ 33.03 Gt CO2 per year
Flashcards
Quick quiz
Q1.Which process removes CO2 from the atmosphere and stores it in plants?
Q2.Which process releases stored carbon back into the atmosphere as CO2 fastest?
Q3.Burning 200 kg of pure carbon produces about how much CO2?
Q4.Where is most of Earth's carbon stored long-term?
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Common mistakes
Carbon only exists in the atmosphere as CO2. — Correct: Carbon also exists in living organisms, oceans (dissolved CO2 and carbonate), soil, and rocks.
Photosynthesis and respiration do the same thing to carbon. — Correct: Photosynthesis removes CO2 from the air and stores it as organic carbon; respiration releases CO2 back into the air.
Fossil fuels are a renewable part of the carbon cycle. — Correct: Fossil fuels form over millions of years, so burning them releases carbon far faster than it is naturally replaced.
The carbon cycle and the greenhouse effect are unrelated. — Correct: Excess CO2 released by human activity accumulates in the atmosphere and enhances the greenhouse effect.
FAQ
What is the carbon cycle?
It's the natural circulation of carbon between the atmosphere, living organisms, oceans, soil, and rocks via photosynthesis, respiration, decomposition, and combustion.
What is the formula for CO2 produced from burning carbon?
m(CO2) = m(C) × 3.67, based on the molar mass ratio of CO2 (44 g/mol) to carbon (12 g/mol).
What are examples of the carbon cycle in action?
A tree absorbing CO2 through photosynthesis, an animal exhaling CO2 through respiration, and a factory burning coal are all part of the carbon cycle.
How is the carbon cycle related to climate change?
Burning fossil fuels adds carbon to the atmosphere faster than natural sinks like forests and oceans can absorb it, increasing greenhouse warming.