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Carbon Cycle & Greenhouse Effect Cheat Sheet
A printable reference covering photosynthesis, respiration, combustion, carbon reservoirs, greenhouse gases, and climate feedbacks for grades 7-10.
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The carbon cycle explains how carbon moves through the atmosphere, oceans, living things, soil, and rocks. Students need this cheat sheet because carbon is central to life, energy use, ecosystems, and climate change. It connects biology, chemistry, Earth science, and human activity in one system. Understanding these links helps students explain why rising greenhouse gases affect global temperatures. The most important processes are photosynthesis, cellular respiration, decomposition, combustion, ocean exchange, and long-term carbon storage in rocks and fossil fuels. Greenhouse gases such as CO₂, CH₄, N₂O, and H₂O absorb outgoing infrared radiation and warm the lower atmosphere. Human activities add extra carbon to the atmosphere when fossil fuels are burned and forests are removed. Climate change occurs when Earth’s energy balance shifts because more heat is trapped than before.
Key Facts
- Photosynthesis removes carbon dioxide from the air using the equation 6CO₂ + 6H₂O + light energy -> C₆H₁₂O₆ + 6O₂.
- Cellular respiration returns carbon dioxide to the air using the equation C₆H₁₂O₆ + 6O₂ -> 6CO₂ + 6H₂O + energy.
- Combustion releases stored carbon quickly, such as CH₄ + 2O₂ -> CO₂ + 2H₂O + energy.
- Major carbon reservoirs include the atmosphere, oceans, living organisms, soils, fossil fuels, and carbonate rocks.
- The ocean both absorbs and releases CO₂, and colder ocean water can usually dissolve more CO₂ than warmer ocean water.
- Greenhouse gases absorb infrared radiation, and important examples include CO₂, CH₄, N₂O, H₂O vapor, and ozone.
- Human activities increase atmospheric CO₂ mainly through fossil fuel burning, cement production, and deforestation.
- A positive climate feedback strengthens warming, while a negative climate feedback reduces or slows warming.
Vocabulary
- Carbon cycle
- The movement of carbon among the atmosphere, oceans, living things, soil, rocks, and fossil fuels.
- Carbon reservoir
- A place where carbon is stored for a short or long time, such as forests, oceans, soil, or limestone.
- Greenhouse effect
- The natural warming process in which gases in the atmosphere absorb and re-radiate infrared energy from Earth.
- Greenhouse gas
- A gas that absorbs infrared radiation, including CO₂, CH₄, N₂O, H₂O vapor, and ozone.
- Carbon sink
- A reservoir or process that removes more carbon from the atmosphere than it releases.
- Carbon source
- A reservoir or process that releases more carbon into the atmosphere than it removes.
Common Mistakes to Avoid
- Thinking the greenhouse effect is always bad: this is wrong because the natural greenhouse effect keeps Earth warm enough for life, while the enhanced greenhouse effect causes extra warming.
- Confusing weather with climate: this is wrong because weather describes short-term conditions, while climate describes long-term patterns over many years.
- Forgetting that plants also respire: this is wrong because plants remove CO₂ during photosynthesis but also release CO₂ during cellular respiration.
- Treating all greenhouse gases as equally powerful: this is wrong because gases differ in heat-trapping ability, lifetime in the atmosphere, and total concentration.
- Assuming carbon disappears when fuel burns: this is wrong because atoms are conserved, so carbon in fuel becomes CO₂ and other carbon-containing products.
Practice Questions
- 1 A forest absorbs 120 tons of CO₂ in one year and releases 75 tons through respiration and decay. What is the forest’s net CO₂ change for that year?
- 2 Methane burns according to CH₄ + 2O₂ -> CO₂ + 2H₂O. If 3 molecules of CH₄ burn completely, how many molecules of CO₂ are produced?
- 3 Atmospheric CO₂ rises from 390 ppm to 420 ppm. What is the increase in ppm, and what does ppm mean?
- 4 Explain why cutting down a forest can increase atmospheric CO₂ in two different ways.