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How do plants remove carbon dioxide from the atmosphere through photosynthesis?

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World map shaded to show annual carbon dioxide emissions by country in 2022, with China, the United States, and India highlighted as top emitters in dark red. A bar chart below lists the top ten emitting countries by million metric tons. — Greenhouse gas Map of annual carbon dioxide emissions by country in 2014.

Plants remove carbon dioxide ( $C O_{2}$ ) from the atmosphere through photosynthesis, a light-energized process that converts inorganic carbon into organic compounds.12

The Process of Carbon Fixation

During photosynthesis, plants absorb $C O_{2}$ from the air through leaf stomata. Once inside, the gas undergoes carbon fixation, where it is reduced to form organic products like sucrose and starch. This occurs in two primary stages:341

Light Reactions: Plants capture solar energy to produce ATP and NADPH.1
Dark Reactions: Using the energy generated in the light reactions, plants fix $C O_{2}$ into stable compounds, such as 3-phosphoglycerate (PGA), via the Calvin-Benson cycle.51

Variations in Carbon Pathways

Different plants have evolved specialized mechanisms to optimize this process:
* C3 Plants: Use the standard Calvin-Benson cycle to fix $C O_{2}$ directly into a three-carbon compound.5
* C4 Plants: Utilize a spatial separation strategy, concentrating $C O_{2}$ in bundle-sheath cells to minimize energy loss from photorespiration.6
* CAM Plants: Employ crassulacean acid metabolism, opening their stomata at night to take up $C O_{2}$ while keeping them closed during the day to conserve water.34