C4 carbon fixation

Examples of C4 carbon fixation in the following topics:

• CAM and C4 Photosynthesis

  • In contrast to C4 metabolism, which physically separates the CO2 fixation to PEP from the Calvin cycle, CAM temporally separates these two processes.
  • Decarboxylation of malate during the day releases CO2 inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate by RuBisCO.
  • Due to the inactivity required by the CAM mechanism, C4 carbon fixation has a greater efficiency in terms of PGA synthesis.
  • Plants that do not use PEP-carboxylase in carbon fixation are called C3 plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle.
  • Over 90% of plants use C3 carbon fixation, compared to 3% that use C4 carbon fixation; however, the evolution of C4 in over 60 plant lineages makes it a striking example of convergent evolution.

• Nitrogen Fixation: Root and Bacteria Interactions

  • The NH3 resulting from fixation can be transported into plant tissue and incorporated into amino acids, which are then made into plant proteins.
  • Soil bacteria, collectively called rhizobia, symbiotically interact with legume roots to form specialized structures called nodules in which nitrogen fixation takes place .
  • Through symbiotic nitrogen fixation, the plant benefits from using an endless source of nitrogen from the atmosphere.
  • As in any symbiosis, both organisms benefit from the interaction: the plant obtains ammonia and bacteria obtain carbon compounds generated through photosynthesis, as well as a protected niche in which to grow.
  • Abiotic nitrogen fixation has been omitted.

• The Calvin Cycle

  • The Calvin cycle is organized into three basic stages: fixation, reduction, and regeneration.
  • The light-independent reactions of the Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration.
  • RuBP has five atoms of carbon, flanked by two phosphates.
  • This process is called carbon fixation because CO2 is "fixed" from an inorganic form into organic molecules.
  • Only one carbon dioxide molecule is incorporated at a time, so the cycle must be completed three times to produce a single three-carbon GA3P molecule, and six times to produce a six-carbon glucose molecule.

• The Role of Prokaryotes in Ecosystems

  • Prokaryotes play vital roles in the movement of carbon dioxide and nitrogen in the carbon and nitrogen cycles.
  • Carbon is one of the most important macronutrients.
  • Although the largest carbon reservoir in terrestrial ecosystems is in rocks and sediments, that carbon is not readily available.
  • A large amount of available carbon is found in land plants, which are producers that use carbon dioxide from the air to synthesize carbon compounds.
  • Gaseous nitrogen is transformed, or "fixed," into more-readily available forms such as ammonia through the process of nitrogen fixation by natural means, especially by microorganisms (prokayotes) in the soil.

• Covalent Bonds and Other Bonds and Interactions

  • Its biosynthesis involves breaking the triple bond of molecular nitrogen, or N2, followed by the formation of several carbon-nitrogen single and double bonds.
  • Covalent bonds are commonly found in carbon-based organic molecules, such as DNA and proteins.
  • The four bonds of methane are also considered to be nonpolar because the electronegativies of carbon and hydrogen are nearly identical.
  • Both water and carbon dioxide have polar covalent bonds, but carbon dioxide is linear, so the partial charges on the molecule cancel each other out.
  • Its biosynthesis involves the fixation of nitrogen to provide feedstocks that eventually produce the carbon-nitrogen bonds it contains.

• Essential Nutrients for Plants

  • About half of the essential elements are considered macronutrients: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
  • The first of these macronutrients, carbon (C), is required to form carbohydrates, proteins, nucleic acids, and many other compounds; it is, therefore, present in all macromolecules.
  • On average, the dry weight (excluding water) of a cell is 50 percent carbon, making it a key part of plant biomolecules.
  • Some plants use it for nitrogen fixation; thus, it may need to be added to some soils before seeding legumes.