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Environmental Science
The Carbon Cycle for Middle School
How carbon moves through Earth's systems
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Carbon is an element found in air, water, rocks, soil, living things, and fossil fuels. The carbon cycle is the movement of carbon through Earth’s atmosphere, plants, animals, oceans, and land. This cycle matters because carbon helps build living things and affects Earth’s climate. Understanding it helps students see how forests, oceans, animals, and human activities are connected.
Key Facts
- Photosynthesis: carbon dioxide + water + sunlight -> glucose + oxygen
- Respiration: glucose + oxygen -> carbon dioxide + water + energy
- Combustion releases stored carbon as carbon dioxide when fuels burn.
- Decomposition returns carbon from dead organisms and waste to soil and air.
- Oceans absorb and release carbon dioxide at the surface.
- Carbon can be stored in trees, soils, ocean water, rocks, and fossil fuels.
Vocabulary
- Carbon cycle
- The carbon cycle is the movement of carbon among the atmosphere, living things, oceans, soil, rocks, and fossil fuels.
- Photosynthesis
- Photosynthesis is the process plants use to take in carbon dioxide and make sugar using sunlight.
- Respiration
- Respiration is the process living things use to release energy from food and give off carbon dioxide.
- Decomposition
- Decomposition is the breakdown of dead organisms and waste by decomposers, which returns carbon to the soil and air.
- Fossil fuels
- Fossil fuels are coal, oil, and natural gas formed from ancient living things that store carbon for millions of years.
Common Mistakes to Avoid
- Thinking carbon is only pollution. Carbon is a natural element needed by living things, but extra carbon dioxide from human activities can change climate.
- Forgetting that plants also release carbon dioxide. Plants take in carbon dioxide during photosynthesis, but they also release some carbon dioxide during respiration.
- Assuming carbon disappears when organisms die. Carbon is recycled by decomposers into soil, air, and sometimes long-term storage.
- Confusing carbon storage with carbon movement. A forest, ocean, or fossil fuel deposit can store carbon, while arrows in the cycle show carbon moving from one place to another.
Practice Questions
- 1 A tree takes in 12 grams of carbon from carbon dioxide during photosynthesis in one day and releases 5 grams through respiration. How many grams of carbon are stored in the tree that day?
- 2 A class model shows that the ocean absorbs 40 units of carbon dioxide and releases 35 units back to the atmosphere in the same time period. What is the net change in carbon dioxide stored by the ocean?
- 3 Explain how cutting down a forest and burning the wood can affect the amount of carbon dioxide in the atmosphere.