Carbon fixation

Carbon fixation is a photosynthetic process that occurs in plants, algae, and some species of bacteria. It involves the conversion of carbon dioxide (CO2) into organic compounds, primarily carbohydrates. This process is crucial for life on Earth as it is the primary means by which carbon is removed from the atmosphere and made available to living organisms.

Process

Carbon fixation occurs in the chloroplasts of plant cells and the cytoplasm of photosynthetic bacteria. The process begins when a molecule of carbon dioxide combines with a five-carbon sugar called ribulose bisphosphate (RuBP). This reaction is catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), which is the most abundant protein on Earth.

The product of this reaction is a six-carbon compound that quickly splits into two molecules of a three-carbon compound, 3-phosphoglycerate (3-PGA). These molecules can then be used to produce glucose, other sugars, or other organic molecules.

Types of Carbon Fixation

There are three primary types of carbon fixation: C3, C4, and CAM.

• C3 carbon fixation is the most common and the oldest pathway. It is named after the 3-PGA, the first stable product of this process.

• C4 carbon fixation evolved in certain plants as an adaptation to high light intensities, high temperatures, and dryness. It is named after the four-carbon compound, oxaloacetic acid, which is the first product of this process.

• CAM carbon fixation is a water-conserving, night-time fixation process used by many succulents and cacti. It is named after the family Crassulaceae, in which many of these plants are found.

Importance

Carbon fixation is a critical component of the global carbon cycle. By converting inorganic carbon dioxide into organic compounds, it provides the primary source of energy for the vast majority of life on Earth. It also plays a significant role in mitigating climate change by reducing the amount of carbon dioxide in the atmosphere.

See Also

• Photosynthesis
• Calvin cycle
• Carbon cycle
• Climate change

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