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carbon fixation
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Diagram of the reductive pentose phosphate cycle in photosynthesis, showing carbon dioxide fixation and reduction steps. Arrows trace the transformation of CO2 and RuBP through intermediates like PGA, DPGA, and Gal3P, with ATP and NADPH inputs and the net production of one Gal3P molecule for sugar or starch synthesis.
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carbon fixation

biochemistry
Also known as: carbon assimilation, carbon dioxide fixation
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Diagram of the reductive pentose phosphate cycle in photosynthesis, showing carbon dioxide fixation and reduction steps. Arrows trace the transformation of CO2 and RuBP through intermediates like PGA, DPGA, and Gal3P, with ATP and NADPH inputs and the net production of one Gal3P molecule for sugar or starch synthesis.
C3 carbon fixation pathway Pathway of carbon dioxide fixation and reduction in photosynthesis, the reductive pentose phosphate cycle. The diagram represents one complete turn of the cycle, with the net production of one molecule of Gal3P. The nine molecules of ATP and six molecules of NADPH come from the light reactions.

Carbon fixation is a crucial biochemical process in photosynthesis where plants convert atmospheric carbon dioxide (CO2) into organic compounds. This process primarily occurs during the "dark reactions" of photosynthesis, which utilize the chemical energy from ATP and NADPH produced during the light-dependent reactions.123

The most common pathway is the Calvin-Benson cycle, where the enzyme RuBisCO attaches CO2 to a five-carbon molecule (RuBP). This forms an unstable six-carbon molecule that splits into three-carbon compounds. These compounds are then converted into sugars like glucose, with some recycled to regenerate RuBP. This C3 pathway results in a three-carbon acid, phosphoglycerate (PGA), as the first stable product.134

Some plants have evolved alternative pathways, C4 and CAM, to improve carbon fixation efficiency, especially in warmer or drier climates, by minimizing a process called photorespiration.12

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
6 Britannica Sources
  1. photosynthesis - Differences in carbon fixation pathways
  2. plant - Specific variations in photosynthesis
  3. Calvin cycle
  4. photosynthesis - Elucidation of the carbon pathway
  5. photosynthesis - Stage 1: Carboxylation
  6. photosynthesis - Photorespiration

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