Carbon fixation - wikipedia Carbon fixation For other uses, see Carbon cycle and Carbon sequestration. Cyanobacteria such as these carry out photosynthesis. Their emergence foreshadowed the evolution of many photosynthetic plants, which oxygenated Earth 's atmosphere. Carbon fixation or сarbon assimilation is the conversion process of inorganic carbon ( carbon dioxide ) to organic compounds by living organisms. The most prominent example is photosynthesis, although chemosynthesis is another form of carbon fixation that can take place in the absence of sunlight. Organisms that grow by fixing carbon are called autotrophs. Autotrophs include photoautotrophs, which synthesize organic compounds using the energy of sunlight, and lithoautotrophs, which synthesize organic compounds using the energy of inorganic oxidation. Heterotrophs are organisms that grow using the carbon fixed by autotrophs. The organic compounds are used by heterotrophs to produce energy and to build body structures. `` Fixed carbon '', `` reduced carbon '', and `` organic carbon '' are equivalent terms for various organic compounds. Contents 1 Net vs gross CO fixation 2 Overview of pathways 3 Oxygenic photosynthesis 3.1 Evolutionary considerations 3.2 Carbon concentrating mechanisms 3.2. 1 CAM plants 3.2. 2 C plants 3.2. 3 C plants 4 Other autotrophic pathways 4.1 Reductive citric acid cycle 4.2 Reductive acetyl CoA pathway 4.3 3 - Hydroxypropionate and two related cycles 5 Chemosynthesis 6 Non-autotrophic pathways 7 Carbon isotope discrimination 8 References 9 Further reading 9.1 Descent of plants and algae Net vs gross CO fixation Graphic showing net annual amounts of CO fixation by land and sea - based organisms. It is estimated that approximately 258 billion tons of carbon dioxide are converted by photosynthesis annually. The majority of the fixation occurs in marine environments, especially areas of high nutrients. The gross amount of carbon dioxide fixed is much larger since approximately 40 % is consumed by respiration following photosynthesis. Given the scale of this process, it is understandable that RuBisCO is the most abundant protein on Earth. Overview of pathways Six autotrophic carbon fixation pathways are known as of 2011. The Calvin cycle fixes carbon in the chloroplasts of plants and algae, and in the cyanobacteria. It also fixes carbon in the anoxygenic photosynthetic proteobacteria called purple bacteria, and in some non-phototrophic proteobacteria. Oxygenic photosynthesis In photosynthesis, energy from sunlight drives the carbon fixation pathway. Oxygenic photosynthesis is used by the primary producers -- plants, algae, and cyanobacteria. They contain the pigment chlorophyll, and use the Calvin cycle to fix carbon autotrophically. The process works like this : 2H O → 4e + 4H + O CO + 4e + 4H → CH O + H O In the first step, water is dissociated into electrons, protons, and free oxygen. This allows the use of water, one of the most abundant substances on Earth, as an electron donor -- as a source of reducing power. The release of free oxygen is a side - effect of enormous consequence. The first step uses the energy of sunlight to oxidize water to O, and, ultimately, to produce ATP ADP + P ⇌ ATP + H O and the reductant, NADPH NADP + 2e + 2H ⇌ NADPH + H In the second step, called the Calvin cycle, the actual fixation of carbon dioxide is carried out. This process consumes ATP and NADPH. The Calvin cycle in plants accounts for the preponderance of carbon fixation on land. In algae and cyanobacteria, it accounts for the preponderance of carbon fixation in the oceans. The Calvin cycle converts carbon dioxide into sugar, as triose phosphate ( TP ), which is glyceraldehyde 3 - phosphate ( GAP ) together with dihydroxyacetone phosphate ( DHAP ) : 3 CO + 12 e + 12 H + P → TP + 4 H O An alternative perspective accounts for NADPH ( source of e ) and ATP : 3 CO + 6 NADPH + 6 H + 9 ATP + 5 H O → TP + 6 NADP + 9 ADP + 8 P The formula for inorganic phosphate ( P ) is HOPO + 2H. Formulas for triose and TP are C H O - CH OH and C H O - CH OPO + 2H Evolutionary considerations Somewhere between 3.5 and 2.3 billion years ago, the ancestors of cyanobacteria evolved oxygenic photosynthesis, enabling the use of the abundant yet relatively oxidized molecule H O as an electron donor to the electron transport chain of light - catalyzed proton - pumping responsible for efficient ATP synthesis. When this evolutionary breakthrough occurred, autotrophy ( growth using inorganic carbon as the sole carbon source ) is believed to have already been developed. However, the proliferation of cyanobacteria, due to their novel ability to exploit water as a source of electrons, radically altered the global environment by oxygenating the atmosphere and by achieving large fluxes of CO consumption. Carbon concentrating mechanisms Many photosynthetic organisms have not acquired inorganic carbon concentrating mechanisms ( CCM ), which increase the concentration of carbon dioxide available to the initial carboxylase of the Calvin cycle, the enzyme RuBisCO. The benefits of CCM include increased tolerance to low external concentrations of inorganic carbon, and reduced losses to photorespiration. CCM can make plants more tolerant of heat and water stress. Carbon concentrating mechanisms use the enzyme carbonic anhydrase ( CA ), which catalyze both the dehydration of bicarbonate to carbon dioxide and the hydration of carbon dioxide to bicarbonate HCO + H ⇌ CO + H O Lipid membranes are much less permeable to bicarbonate than to carbon dioxide. To capture inorganic carbon more effectively, some plants have adapted the anaplerotic reactions HCO + H + PEP → OAA + P catalyzed by PEP carboxylase ( PEPC ), to carboxylate phosphoenolpyruvate ( PEP ) to oxaloacetate ( OAA ) which is a C dicarboxylic acid. CAM plants CAM plants that use Crassulacean acid metabolism as an adaptation for arid conditions. CO enters through the stomata during the night and is converted into the 4 - carbon compound, malic acid, which releases CO for use in the Calvin cycle during the day, when the stomata are closed. The dung jade plant ( Crassula ovata ) and cacti are typical of CAM plants. Sixteen thousand species of plants use CAM. These plants have a carbon isotope signature of − 20 to − 10 ‰. C plants C plants preface the Calvin cycle with reactions that incorporate CO into one of the 4 - carbon compounds, malic acid or aspartic acid. C plants have a distinctive internal leaf anatomy. Tropical grasses, such as sugar cane and maize are C plants, but there are many broadleaf plants that are C. Overall, 7600 species of terrestrial plants use C carbon fixation, representing around 3 % of all species. These plants have a carbon isotope signature of − 16 to − 10 ‰. C plants The large majority of plants are C plants. They are so - called to distinguish them from the CAM and C plants, and because the carboxylation products of the Calvin cycle are 3 - carbon compounds. They lack C dicarboxylic acid cycles, and therefore have higher carbon dioxide compensation points than CAM or C plants. C plants have a carbon isotope signature of − 24 to − 33 ‰. Other autotrophic pathways Of the five other autotrophic pathways, two are known only in bacteria, two only in archaea, and one in both bacteria and archaea. Reductive citric acid cycle The reductive citric acid cycle is the oxidative citric acid cycle run in reverse. It has been found in anaerobic and microaerobic bacteria. It was proposed in 1966 by Evans, Buchanan and Arnon who were working with the anoxygenic photosynthetic green sulfur bacterium that they called Chlorobium thiosulfatophilum. The reductive citric acid cycle is sometimes called the Arnon - Buchanan cycle. Reductive acetyl CoA pathway The reductive acetyl CoA pathway operated in strictly anaerobic bacteria ( acetogens ) and archaea ( methanogens ). The pathway was proposed in 1965 by Ljungdahl and Wood. They were working with the gram - positive acetic acid producing bacterium Clostridium thermoaceticum, which is now named Moorella thermoacetica. Hydrogenotrophic methanogenesis, which is only found in certain archaea and accounts for 80 % of global methanogenesis, is also based on the reductive acetyl CoA pathway. The pathway is often referred to as the Wood -- Ljungdahl pathway. 3 - hydroxypropionate and two related cycles The 3 - hydroxypropionate cycle is utilized only by green nonsulfur bacteria. It was proposed in 2002 for the anoxygenic photosynthetic Chloroflexus aurantiacus. None of the enzymes that participate in the 3 - hydroxypropionate cycle are especially oxygen sensitive. A variant of the 3 - hydroxypropionate pathway was found to operate in aerobic extreme thermoacidophile archaeon Metallosphaera sedula. This pathway, called the 3 - hydroxypropionate / 4 - hydroxybutyrate cycle. And yet another variant of the 3 - hydroxypropionate pathway is the dicarboxylate / 4 - hydroxybutyrate cycle. It was discovered in anaerobic archaea. It was proposed in 2008 for the hyperthermophile archeon Ignicoccus hospitalis. Chemosynthesis Chemosynthesis is carbon fixation driven by the oxidation of inorganic substances ( e.g., hydrogen gas or hydrogen sulfide ). Sulfur - and hydrogen - oxidizing bacteria often use the Calvin cycle or the reductive citric acid cycle. Non-autotrophic pathways Although almost all heterotrophs can not synthesize complete organic molecules from carbon dioxide, some carbon dioxide is incorporated in their metabolism. Notably pyruvate carboxylase consumes carbon dioxide ( as bicarbonate ions ) as part of gluconeogenesis, and carbon dioxide is consumed in various anaplerotic reactions. Carbon isotope discrimination Some carboxylases, particularly RuBisCO, preferentially bind the lighter carbon stable isotope carbon - 12 over the heavier carbon - 13. This is known as carbon isotope discrimination and results in carbon - 12 to carbon - 13 ratios in the plant that are higher than in the free air. Measurement of this ratio is important in the evaluation of water use efficiency in plants, and also in assessing the possible or likely sources of carbon in global carbon cycle studies. References ^ Jump up to : Geider, R.J., et al., `` Primary productivity of planet earth : biological determinants and physical constraints in terrestrial and aquatic habitats '', Global Change Biol. 2001, 7, 849 -- 882. doi : 10.1046 / j. 1365 - 2486.2001. 00448. x Jump up ^ Swan BK, Martinez - Garcia M, Preston CM, Sczyrba A, Woyke T, Lamy D, Reinthaler T, Poulton NJ, Masland ED, Gomez ML, Sieracki ME, DeLong EF, Herndl GJ, Stepanauskas R ( 2011 ). `` Potential for chemolithoautotrophy among ubiquitous bacteria lineages in the dark ocean ''. Science. 333 ( 6047 ) : 1296 -- 300. Bibcode : 2011Sci... 333.1296 S. doi : 10.1126 / science. 1203690. PMID 21885783. Jump up ^ Brasier M, McLoughlin N, Green O, Wacey D ( 2006 ). `` A fresh look at the fossil evidence for early Archaean cellular life ''. Philos. Trans. R. Soc. Lond. B Biol. Sci. 361 ( 1470 ) : 887 -- 902. doi : 10.1098 / rstb. 2006.1835. PMC 1578727. PMID 16754605. 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BioScience. 38 ( 5 ) : 328 -- 336. doi : 10.2307 / 1310735. JSTOR 1310735. Jump up ^ Sage RF, Meirong L, Monson RK ( 1999 ). `` 16. The Taxonomic Distribution of C4 Photosynthesis ''. In Sage RF, Monson RK. C4 Plant Biology. pp. 551 -- 580. ISBN 0 - 12 - 614440 - 0. Jump up ^ Evans MC, Buchanan BB, Arnon DI ( 1966 ). `` A new ferredoxin - dependent carbon reduction cycle in a photosynthetic bacterium ''. Proc. Natl. Acad. Sci. U.S.A. 55 ( 4 ) : 928 -- 34. Bibcode : 1966PNAS... 55... 928E. doi : 10.1073 / pnas. 55.4. 928. PMC 224252. PMID 5219700. Jump up ^ Ljungdahl L, Wood HG ( 1965 ). `` Incorporation of C - 14 from carbon dioxide into sugar phosphates, carboxylic acids, and amino acids by Clostridium thermoaceticum ''. J. Bacteriol. 89 : 1055 -- 64. PMC 277595. PMID 14276095. Jump up ^ Ljungdahl LG ( 2009 ). `` A life with acetogens, thermophiles, and cellulolytic anaerobes ''. Annu. Rev. Microbiol. 63 : 1 -- 25. doi : 10.1146 / annurev. micro. 091208.073617. PMID 19575555. 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Science. 335 ( 6070 ) : 809 -- 10. Bibcode : 2012Sci... 335... 809S. doi : 10.1126 / science. 1218515. PMID 22344435. Price DC, Chan CX, Yoon HS, Yang EC, Qiu H, Weber AP, Schwacke R, Gross J, Blouin NA, Lane C, Reyes - Prieto A, Durnford DG, Neilson JA, Lang BF, Burger G, Steiner JM, Löffelhardt W, Meuser JE, Posewitz MC, Ball S, Arias MC, Henrissat B, Coutinho PM, Rensing SA, Symeonidi A, Doddapaneni H, Green BR, Rajah VD, Boore J, Bhattacharya D ( 2012 ). `` Cyanophora paradoxa genome elucidates origin of photosynthesis in algae and plants '' ( PDF ). Science. 335 ( 6070 ) : 843 -- 7. Bibcode : 2012Sci... 335... 843P. doi : 10.1126 / science. 1213561. PMID 22344442. Retrieved 10 April 2012. Metabolism, catabolism, anabolism General Metabolic pathway Metabolic network Primary nutritional groups Energy metabolism Aerobic respiration Glycolysis → Pyruvate decarboxylation → Citric acid cycle → Oxidative phosphorylation ( electron transport chain + ATP synthase ) Anaerobic respiration Electron acceptors are other than oxygen Fermentation Glycolysis → Substrate - level phosphorylation ABE Ethanol Lactic acid Specific paths Protein metabolism Protein synthesis Catabolism Carbohydrate metabolism ( carbohydrate catabolism and anabolism ) Human Glycolysis ⇄ Gluconeogenesis Glycogenolysis ⇄ Glycogenesis Pentose phosphate pathway Fructolysis Galactolysis Glycosylation N - linked O - linked Nonhuman Photosynthesis Anoxygenic photosynthesis Chemosynthesis Carbon fixation Xylose metabolism Radiotrophism Lipid metabolism ( lipolysis, lipogenesis ) Fatty acid metabolism Fatty acid degradation ( Beta oxidation ) Fatty acid synthesis Other Steroid metabolism Sphingolipid metabolism Eicosanoid metabolism Ketosis Reverse cholesterol transport Amino acid Amino acid synthesis Urea cycle Nucleotide metabolism Purine metabolism Nucleotide salvage Pyrimidine metabolism Other Metal metabolism Iron metabolism Ethanol metabolism Metabolism map Carbon Fixation Photo - respiration Pentose Phosphate Pathway Citric Acid Cycle Glyoxylate Cycle Urea Cycle Fatty Acid Synthesis Fatty Acid Elongation Beta Oxidation Peroxisomal Beta Oxidation Glyco - genolysis Glyco - genesis Glyco - lysis Gluconeo - genesis Decarb - oxylation Fermentation Keto - lysis Keto - genesis feeders to Gluconeo - genesis Direct / C4 / CAM Carbon Intake Light Reaction Oxidative Phosphorylation Amino Acid Deamination Citrate Shuttle Lipogenesis Lipolysis Steroidogenesis MVA Pathway MEP Pathway Shikimate Pathway Transcription & Replication Translation Proteolysis Glycosy - lation Sugar Acids Double / Multiple Sugars & Glycans Simple Sugars Inositol - P Amino Sugars & Sialic Acids Nucleotide Sugars Hexose - P Triose - P Glycerol P - glycerates Pentose - P Tetrose - P Propionyl - CoA Succinate Acetyl - CoA Pentose - P P - glycerates Glyoxylate Photosystems Pyruvate Lactate Acetyl - CoA Citrate Oxalo - acetate Malate Succinyl - CoA α - Keto - glutarate Ketone Bodies Respiratory Chain Serine Group Alanine Branched - chain Amino Acids Aspartate Group Homoserine Group & Lysine Glutamate Group & Proline Arginine Creatine & Polyamines Ketogenic & Glucogenic Amino Acids Amino Acids Shikimate Aromatic Amino Acids & Histidine Ascorbate ( Vitamin C ) δ - ALA Bile Pigments Hemes Cobalamins ( Vitamin B ) Various Vitamin B 's Calciferols ( Vitamin D ) Retinoids ( Vitamin A ) Quinones ( Vitamin K ) & Carotenoids ( Vitamin E ) Cofactors Vitamins & Minerals Antioxidants PRPP Nucleotides Nucleic Acids Proteins Glycoproteins & Proteoglycans Chlorophylls MEP MVA Acetyl - CoA Polyketides Terpenoid Backbones Terpenoids & Carotenoids ( Vitamin A ) Cholesterol Bile Acids Glycero - phospholipids Glycerolipids Acyl - CoA Fatty Acids Glyco - sphingolipids Sphingolipids Waxes Polyunsaturated Fatty Acids Neurotransmitters & Thyroid Hormones Steroids Endo - cannabinoids Eicosanoids Major metabolic pathways in metro - style map. Click any text ( name of pathway or metabolites ) to link to the corresponding article. Single lines : pathways common to most lifeforms. Double lines : pathways not in humans ( occurs in e.g. plants, fungi, prokaryotes ). Orange nodes : carbohydrate metabolism. Violet nodes : photosynthesis. Red nodes : cellular respiration. Pink nodes : cell signaling. Blue nodes : amino acid metabolism. Grey nodes : vitamin and cofactor metabolism. Brown nodes : nucleotide and protein metabolism. Green nodes : lipid metabolism. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Carbon_fixation&oldid=811978720 '' Categories : Photosynthesis Carbon Metabolic pathways Hidden categories : Use dmy dates from February 2013 All articles with dead external links Articles with dead external links from November 2016 Articles with permanently dead external links Talk Contents About Wikipedia Català Deutsch Español فارسی Français Galego 한국어 Bahasa Indonesia Italiano 日本 語 Polski Português Română Русский Simple English தமிழ் ไทย Українська Edit links This page was last edited on 25 November 2017, at 04 : 58. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: where does the energy to fix gaseous co2 come from
Answer: sunlight