Carbon Cycle

Carbon Cycle

Middle School

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Learning Objectives

• Define the carbon cycle and identify where carbon is found on Earth.

• Describe processes that release and absorb carbon, like respiration and photosynthesis.

• Distinguish between carbon sources, sinks, and releasing agents.

• Understand the connection between the carbon cycle and the greenhouse effect.

Key Vocabulary

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Carbon Cycle

The continuous movement of carbon atoms through Earth's living and nonliving systems, including atmosphere and oceans.

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Combustion

The process of burning fossil fuels, which releases carbon dioxide (CO₂) gas into the atmosphere.

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Photosynthesis

The process where plants use sunlight, water, and CO₂ to create their food and release oxygen.

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Decomposition

The breakdown of dead organic matter by bacteria and fungi, which returns carbon to the soil and air.

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Carbon Sink

A natural reservoir, such as a forest or ocean, that absorbs and stores more carbon than it releases.

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Carbon Source

A process or activity that releases more carbon into the atmosphere than it absorbs, like burning fossil fuels.

​What is the Carbon Cycle?

• ​The carbon cycle is the continuous movement of carbon through Earth's systems.

• All living things, including plants and animals, are based on the carbon atom.

• Carbon is also stored in the atmosphere, oceans, soil, and fossil fuels.

Multiple Choice

The carbon cycle describes the movement of carbon through which parts of the world?

• Only the living world

• Only the nonliving world

• The living and nonliving world

• Only the Earth's atmosphere

How Carbon Enters the Atmosphere

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Respiration

• All living things perform cellular respiration for energy.

• This process releases carbon dioxide as a waste product.

• Animals and plants both add CO₂ to the air.

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Combustion

• Burning organic matter releases carbon dioxide into the air.

• This includes materials like wood and fossil fuels.

• Fossil fuels include coal, oil, and natural gas.

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Decomposition

• When organisms die, decomposers break them down.

• This important process releases carbon dioxide into the air.

• It also returns other nutrients back to the soil.

Multiple Choice

Which of these processes is a 'carbon source,' meaning it releases carbon into the atmosphere?

• Photosynthesis

• Combustion

• Fossil fuel formation

• Diffusion into the ocean

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How Carbon Is Removed from the Atmosphere

Photosynthesis

• Processes that absorb and store carbon, like photosynthesis, are known as carbon sinks.

• Plants, algae, and phytoplankton take in carbon dioxide (CO₂) from the atmosphere to make their food.

• This process converts the gas into sugars, a form of organic carbon, storing it in the organism.

Ocean Diffusion

• Large bodies of water, especially the oceans, are another major carbon sink for the planet.

• They absorb carbon dioxide directly from the air at the water's surface through a process called diffusion.

• Absorbing too much CO₂ can lead to ocean acidification, which harms marine life.

Multiple Choice

According to the slide, how do oceans remove carbon dioxide from the atmosphere?

• Through underwater photosynthesis

• By the formation of fossil fuels

• Through diffusion from the air

• By marine animals respiring

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Carbon and the Greenhouse Effect

• Carbon dioxide (CO₂) is a type of gas known as a greenhouse gas.

• These gases act like a blanket, trapping some of the sun’s heat.

• Human activities, like burning fossil fuels, add extra greenhouse gases to the atmosphere.

• This excess gas traps more heat, leading to a global warming pattern.

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Multiple Choice

What is the primary reason the buildup of CO₂ in the atmosphere is a concern?

• It can cause a cooling pattern in the climate.

• It is a greenhouse gas that can cause a warming pattern.

• It reduces the amount of oxygen available for breathing.

• It is toxic to plants.

Sinks, Sources, and Releasing Agents

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Carbon Sinks

• Carbon sinks are places where carbon is stored for long periods.

• Long-lived trees and all living organisms can act as carbon sinks.

• Limestone rock, plastics, and buried organic matter are also carbon sinks.

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Carbon Sources

• Carbon sources describe the ways carbon is released into the atmosphere.

• The burning of fossil fuels is a major source of carbon.

• Decomposition, respiration, and erosion of limestone are all carbon sources.

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Releasing Agents

• Releasing agents are events that trigger sources to release stored carbon.

• Natural events like volcanic activity and forest fires are releasing agents.

• Combustion and many different human activities act as releasing agents.

Multiple Choice

Based on the descriptions, which of the following is considered a 'releasing agent'?

• A long-lived tree

• Decomposition

• A forest fire

• Limestone rock

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Common Misconceptions

Misconception	Correction
The carbon cycle is always a very fast process.	Parts of the cycle, like forming fossil fuels, can take millions of years.
Only animals respire and release CO2.	Plants also respire and release CO2, but absorb more than they release.
All carbon is in the form of carbon dioxide gas.	Carbon also exists as a solid (coal, limestone) and a liquid.

Multiple Choice

If a large population of phytoplankton in the ocean were to die off, what would be the likely impact on the carbon cycle?

• It would decrease the amount of carbon in the atmosphere because there is less decomposition.

• It would increase the amount of carbon in the atmosphere because there is less photosynthesis.

• It would have no effect on the carbon cycle.

• It would increase the amount of carbon stored as fossil fuels immediately.

Multiple Choice

Which of the following is an example of a carbon sink?

• Clouds

• Limestone

• Earthquakes

• Basalt

Multiple Choice

A community wants to reduce its carbon footprint. Based on your knowledge of the carbon cycle, which of the following two actions would be most effective?

• Increase the weathering of limestone and decrease decomposition.

• Launch a major tree-planting initiative and reduce the burning of fossil fuels.

• Promote animal respiration and prevent forest fires.

• Encourage volcanic activity and reduce the creation of plastics.

Multiple Choice

Scientists discover a new bacterium that is extremely efficient at decomposition. If this bacterium became widespread, what would be a predictable consequence for the carbon cycle?

• The rate of carbon release from dead organic matter would increase.

• The amount of carbon absorbed by the oceans would decrease.

• The rate of fossil fuel formation would speed up dramatically.

• The rate of photosynthesis in plants would slow down.

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Summary

• The carbon cycle is the constant movement of carbon through Earth's systems.

• Respiration, combustion, and decomposition are key processes that release carbon.

• Photosynthesis, diffusion into oceans, and fossil fuels absorb and store carbon.

• Excess atmospheric CO₂, a greenhouse gas, contributes to climate warming.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4