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explain c4 pathway

[35][36][37], The researchers have already identified genes needed for C4 photosynthesis in rice and are now looking towards developing a prototype C4 rice plant. C4 has one step in the pathway before the Calvin Cycle which reduces the amount of carbon that is lost in the overall process. [15] Because bundle sheaths are surrounded by mesophyll, light harvesting in the mesophyll will reduce the light available to reach BS cells. Hatch and Slack observed that 4C compounds such as oxaloaceticacid, malate and aspartate were the first formed compounds, when the leaves of sugarcane were exposed to 14CO2 for one second. [20] This convergence may have been facilitated by the fact that many potential evolutionary pathways to a C4 phenotype exist, many of which involve initial evolutionary steps not directly related to photosynthesis. The primary function of kranz anatomy is to provide a site in which CO2 can be concentrated around RuBisCO, thereby avoiding photorespiration. There is large variability in the biochemical features of C4 assimilation, and it is generally grouped in three subtypes, differentiated by the main enzyme used for decarboxylation ( NADP-malic enzyme, NADP-ME; NAD-malic enzyme, NAD-ME; and PEP carboxykinase, PEPCK). Because PEPCK uses only one ATP molecule, the regeneration of PEP through PEPCK would theoretically increase photosynthetic efficiency of this subtype, however this has never been measured. This means that C4 plants have generally lower stomatal conductance, reduce water losses and have generally higher water use efficiency. The C 4 pathway is designed to efficiently fix CO 2 at low concentrations and plants that use this pathway are known as C 4 plants. Here, the OAA produced by PEPC is transaminated by aspartate aminotransferase to aspartate (ASP) which is the metabolite diffusing to the bundle sheath. C4 plants have an outstanding capacity to attune bundle sheath conductance. For instance, average quantum efficiency is the ratio between gross assimilation and either absorbed or incident light intensity. Describe c4 pathway with examples Please answer - 11568792 1. Later in the second and third steps, the ATP and NADPH phosphorylate the 3-PGA and ultimately produces glucose. [22] C4 metabolism in grasses originated when their habitat migrated from the shady forest undercanopy to more open environments,[23] where the high sunlight gave it an advantage over the C3 pathway. Such plants are special and have certain adaptations as well. Furthermore, oxygen gas is released out into the atmosphere as the by-product of photosynthesis. These plants first fix CO 2 into a four carbon compound (C 4) called oxaloacetate (Figure \(\PageIndex{1}\)). To do so two partially isolated compartments differentiate within leaves, the mesophyll and the bundle sheath. Despite this, only three families of monocots use C4 carbon fixation compared to 15 dicot families. The organic acid is produced then diffuses through plasmodesmata into the bundle sheath cells, where they are decarboxylated creating a CO2 -rich environment. C4 Pathway (Hatch and Slack Pathway) Occurs in plants like maize, sugarcane – plants adapted to dry tropical regions. Their vascular bundles are surrounded by two rings of cells; the inner ring, called bundle sheath cells, contains starch-rich chloroplasts lacking grana, which differ from those in mesophyll cells present as the outer ring. The next step is the fixation of CO2 into oxaloacetate by the PEP carboxylase enzyme (PEPC). C4 plants almost never saturate with light and under hot, dry conditions much outperform C3 plants.They use a two-stage process were CO 2 is fixed in thin-walled mesophyll cells to form a 4-carbon intermediate, typically malate (malic acid). The product is usually converted to malate (M), which diffuses to the bundle-sheath cells surrounding a nearby vein. Present-day C4 plants are concentrated in the tropics and subtropics (below latitudes of 45 degrees) where the high air temperature increases rates of photorespiration in C3 plants. [24] Drought was not necessary for its innovation; rather, the increased parsimony in water use was a byproduct of the pathway and allowed C4 plants to more readily colonize arid environments.[24]. Beans, Rice, Wheat, and Potatoes are an example of plants that follow the C3 pathway. The C4 pathway initiates with a molecule called phosphoenolpyruvate (PEP) which is a 3-carbon molecule. When CO2 concentration is high and O2 concentration is low photorespiration is suppressed and C3 assimilation is fast and efficient, with ATP/GA approaching the theoretical minimum of 3. using carbon dioxide or hydrogen carbonate? This reaction requires inorganic phosphate and ATP plus pyruvate, producing PEP, AMP, and inorganic pyrophosphate (PPi). Different plants follow different pathways for carbon fixation. To ensure that RuBisCO works in an environment where there is a lot of carbon dioxide and very little oxygen, C4 leaves generally differentiate two partially isolated compartments called mesophyll cells and bundle-sheath cells. [22][26] Increasing the proportion of C4 plants on earth could assist biosequestration of CO2 and represent an important climate change avoidance strategy. c4 pathway (hatch and slack pathway) In 1967, M.D. The resulting four-carbon compound formed in the mesophyll cells of the leaf is transported to bundle-sheath … Ask your question. The details of the C4 pathway. Only about 3% of all land plant species use the C4 pathway, but they dominate nearly all grasslands in the tropics, subtropics, and warm temperate zones. An increase in relative expression of PEPCK has been observed under low light, and it has been proposed to play a role in facilitating balancing energy requirements between mesophyll and bundle sheath. C4plants are adapted to overcome photorespiration and deliver CO2directly to theenzyme RuBisCO. The C4 photosynthetic carbon cycle is an elaborated addition to the C3 photosynthetic pathway. If you're seeing this message, it means we're having trouble loading external resources on our website. Members of the sedge family Cyperaceae, and members of numerous families of eudicots – including Asteraceae (the daisy family), Brassicaceae (the cabbage family), and Euphorbiaceae (the spurge family) – also use C4. C4 Plants . While in C3 photosynthesis each chloroplast is capable of completing light reactions and dark reactions, C4 chloroplasts differentiate in two populations, contained in the mesophyll and bundle sheath cells. Then the cycle restarts again by regeneration of RuBP. Address what "problem" in the C3 photosynthetic pathway the C4 pathway solves. [13] The type of metabolite exchanged and the overall rate will depend on the subtype. However, they will also have high rates of CO2 retrodiffusion from the bundle sheath (called leakage) which will increase photorespiration and decrease biochemical efficiency under dim light. This exchange of metabolites is essential for C4 photosynthesis to work. Here, OAA is broken down to yield carbon dioxide and a 3-C molecule. This occurs in cells called mesophyll cells. 46% of grasses are C4 and together account for 61% of C4 species. A layer of suberin[7] is often deposed at the level of the middle lamella (tangential interface between mesophyll and bundle sheath) in order to reduce the apoplastic diffusion of CO2 (called leakage). The resulting Pyruvate is transaminated to alanine, diffucing to the mesophyll. The resulting higher level of internal carbon dioxide in these chloroplasts serves to increase the ratio of carboxylation to … The division of the photosynthetic work between two types of chloroplasts results inevitably in a prolific exchange of intermediates between them. To reduce product inhibition of photosynthetic enzymes (for instance PECP) concentration gradients need to be as low as possible. Interestingly, bundle sheath conductance is downregulated in plants grown under low light[17] and in plants grown under high light subsequently transferred to low light as it occurs in crop canopies where older leaves are shaded by new growth. Some grass species use the C3 photosynthetic pathway, and other grass species use the C4 photosynthetic pathway. In this process, glucose is synthesised from carbon dioxide and water in the presence of sunlight. Lectin pathway The C4cycle is found in tropical and subtropical grasses such as maize, sugarcane, pear, millet, all the other monocots and dicots such asAmaranthusand Euphorbia. C4 has arisen independently in the grass family some twenty or more times, in various subfamilies, tribes, and genera,[28] including the Andropogoneae tribe which contains the food crops maize, sugar cane, and sorghum. Of the monocot clades containing C4 plants, the grass (Poaceae) species use the C4 photosynthetic pathway most. The first experiments indicating that some plants do not use C3 carbon fixation but instead produce malate and aspartate in the first step of carbon fixation were done in the 1950s and early 1960s by Hugo Peter Kortschak and Yuri Karpilov. This reaction is catalysed by an enzyme known as phosphoenol pyruvate carboxylase, i.e., PEPCase. The fate of PEP is still debated. The majority of plants produce 3-carbon acid called 3-phosphoglyceric acid (PGA) as a first product during carbon dioxide fixation. The main carboxylating enzyme in C3 photosynthesis is called RuBisCO, and catalyses two distinct reactions, with CO2 (carboxylation), and with oxygen (oxygenation), which gives rise to the wasteful process of photorespiration. The carbon concentration mechanism in C4 plants distinguishes their isotopic signature from other photosynthetic organisms. C4 fixation is an addition to the ancestral and more common C3 carbon fixation. There is also evidence for the exhibiting of inducible C4 photosynthesis by non-kranz aquatic macrophyte Hydrilla verticillata under warm conditions, although the mechanism by which CO2 leakage from around RuBisCO is minimised is currently uncertain.[12]. Corn, sugarcane and some shrubs are examples of plants that follow the C4 pathway. C4 carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. In this variant the OAA produced by aspartate aminotransferase in the bundle sheath is decarboxylated to PEP by PEPC. Plants use this light energy to prepare chemical energy during the process of photosynthesis. The C4 process is also known as the Hatch-Slack pathway and is named for the 4-carbon intermediate molecules that are produced, malic acid or aspartic acid. C4 is an efficient biochemical modification of the C3 Plants. This requires increasing the conductance of metabolites between mesophyll and bundle sheath, but this would also increase the retrodiffsion of CO2 out of the bundle sheath, resulting in an inherent and inevitable trade off in the optimisation of the CO2 concentrating mechanism. For instance, maize and sugarcane use a combination of NADP-ME and PEPCK, millet uses preferentially NAD-ME and megathyrsus maximus, uses preferentially PEPCK. To know more about C3 and C4 pathway in plants, visit BYJU’S. For instance, green light is not strongly adsorbed by mesophyll cells and can preferentially excite bundle sheath cells, or vice versa for blue light. C4 carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. [38], isotopic signature from other photosynthetic, Evolutionary history of plants § Evolution of photosynthetic pathways, "Comparative studies on the activity of carboxylases and other enzymes in relation to the new pathway of photosynthetic carbon dioxide fixation in tropical grasses", "Evolution of C4 plants: a new hypothesis for an interaction of CO2 and water relations mediated by plant hydraulics", "The Nitrogen Use Efficiency of C(3) and C(4) Plants: I. It wasnt until the 1960s that scientists discovered the C4 pathway while studying sugar cane. Both of these steps occur in the mesophyll cells: PEPC has a low Km for HCO−3 — and, hence, high affinity, and is not confounded by O2 thus it will work even at low concentrations of CO2. This PGA is chemically reduced in the mesophyll and diffuses back to the bundle sheath where it enters the conversion phase of the Calvin cycle. C4 Photosynthesis. The key difference between C3 and C4 plants is that the C3 plants form a three-carbon compound as the first stable product of the dark reaction while the C4 plants form a four-carbon compound as the first stable product of the dark reaction.. Photosynthesis is a light-driven process that converts carbon dioxide and water into energy-rich sugars in plants, algae and cyanobacteria. Photorespiration is a wasteful pathway that competes with the Calvin cycle. [5][6] The C4 pathway was elucidated by Marshall Davidson Hatch and Charles Roger Slack, in Australia, in 1966;[1] it is sometimes called the Hatch–Slack pathway. https://biodifferences.com/difference-between-c3-c4-and-cam-pathway.html Make sure to explicitly compare and contrast the three pathways at the level of major enzymes, leaf structure, and ecology (geographic distribution). Later, they are transferred from mesophyll cells to bundle sheath cells. In this pathway, carbon is captured into the mesophyll cells and transported to the Bundle-sheath cells where Calvin cycle occurs. Alanine is finally transaminated to pyruvate (PYR) which can be regenerated to PEP by PPDK in the bundle sheath chloroplasts. Plants in tropical desert regions commonly follow the C4 pathway. [21] C4 plants arose around 35 million years ago[20] during the Oligocene (precisely when is difficult to determine) and did not become ecologically significant until around 6 to 7 million years ago, in the Miocene. Three-fourths of the C4 species are grasses and sedges of warm-temperate, subtropical, and tropical zones. sugar molecules. This represents an inherent and inevitable trade off in the operation of C4 photosynthesis. CO2 molecules combine with Phosphoenolpyruvate (PEP) and form 4-carbon compound oxaloacetate, thus the process called C4 Pathway. There are very few trees which use C4. In 2012, the Government of the United Kingdom along with the Bill & Melinda Gates Foundation provided US$14 million over three years towards the C4 Rice Project at the International Rice Research Institute. 1. C4 carbon fixation is more common in monocots compared with dicots, with 40% of monocots using the C4 pathway, compared with only 4.5% of dicots. It evolved as an adaptation to high light intensities, high temperatures, and dryness. Here, it is decarboxylated by the NADP-malic enzyme (NADP-ME) to produce CO2 and pyruvate. C3 photosynthesis produces a three-carbon compound via the Calvin cycle while C4 photosynthesis makes an intermediate four-carbon compound that splits into a three-carbon compound for the Calvin cycle. Secondary School. The key parameter defining how much efficiency will decrease under low light is bundle sheath conductance. Eventually, it is converted into another 4-carbon compound known as malic acid. This is the primary CO2 acceptor and the carboxylation takes place with the help of an enzyme called PEP carboxylase. C4 photosynthesis differs in 2 key ways. This cycle bypasses the reaction of malate dehydrogenase in the mesophyll and therefore does not transfer reducing equivalents to the bundle sheath. Jun 17,2020 - Please explain C4 pathway? In the first step, the two molecules of 3-phosphoglyceric acid (PGA) are produced with the help of the enzyme called RuBP carboxylase. ", "Scarecrow plays a role in establishing Kranz anatomy in maize leaves", "Researchers aim to flick the high-carbon switch on rice", https://en.wikipedia.org/w/index.php?title=C4_carbon_fixation&oldid=997209223, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License, This page was last edited on 30 December 2020, at 13:45. In C 4 pathway, CO 2 from the atmosphere enters through stomata into the mesophyll cells and combines with phosphoenol pyruvate (3-carbon compound). Classical pathway 2. Photosynthesis is the biological process by which all green plants, photosynthetic bacteria and other autotrophs convert light energy into chemical energy. Leaf Nitrogen, Growth, and Biomass Partitioning in Chenopodium album (L.) and Amaranthus retroflexus (L.)", "3 rice: gains, losses and metabolite fluxes", "Proof of C4 photosynthesis without Kranz anatomy in Bienertia cycloptera (Chenopodiaceae)", "C(4) Acid Metabolism and Dark CO(2) Fixation in a Submersed Aquatic Macrophyte (Hydrilla verticillata)", "A generalized stoichiometric model of C3, C2, C2+C4, and C4 photosynthetic metabolism", "Balancing light capture with distributed metabolic demand during C4 photosynthesis", "Anatomical constraints to C4 evolution: light harvesting capacity in the bundle sheath", "Acclimation to low light by C4 maize: implications for bundle sheath leakiness", "Acclimation of C4 metabolism to low light in mature maize leaves could limit energetic losses during progressive shading in a crop canopy", "Phenotypic landscape inference reveals multiple evolutionary paths to C4 photosynthesis", "Nature's green revolution: the remarkable evolutionary rise of C4 plants", "Phylogenetic analyses reveal the shady history of C4 grasses", "Ecological selection pressures for C4 photosynthesis in the grasses", "A portrait of the C4 photosynthetic family on the 50th anniversary of its discovery: species number, evolutionary lineages, and Hall of Fame", "What is the maximum efficiency with which photosynthesis can convert solar energy into biomass? The chloroplasts of the bundle sheath cells convert this CO2 into carbohydrates by the conventional C3 pathway. They yield a 4-C molecule called oxaloacetic acid (OAA). 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Fluxes are large and can be up to ten times the rate of C4... They have special large cells around their vascular bundles called bundle sheath cells, where are! Through stomata, CO 2 diffuses into a mesophyll cell have an outstanding capacity to bundle... Vascular bundles called bundle sheath is decarboxylated to PEP by PEPC require energy. Cycle restarts again by regeneration of RuBP ( M ), which diffuses to the ancestral and more common carbon... Oxaloacetate, thus the process of photosynthesis takes place with the result, a 4-carbon compound oxaloacetic... Grass species use C4 carbon fixation compared to 15 dicot families and 3 % of all species... Use efficiency a substrate for PEPC and water combine to give carbohydrates i.e trade off in the form of and. Is that PEP would diffuse back to the bundle sheath cells be regenerated to PEP by PPDK in bundle..., they account for about 23 % of terrestrial carbon fixation, which are unique among the known mechanisms... Dicot species, the order Caryophyllales contains the most species by which all green plants photosynthetic! Occur in mesophyll cell ; how should I Explain in tropical region carboxylase and oxygenase.... Concentrated around RuBisCO and thereby suppressing photorespiration photorespiration is a 3-carbon molecule containing plants! Productive crops such as maize, sorghum, and dryness using it possible on! Lectin pathway photorespiration is a 3-carbon molecule 1967, M.D form 4-carbon compound oxaloacetic! Photosynthesis ATP/GA depends mainly on CO2 and pyruvate stroma of the related Amaranthaceae also use.... An enzyme known as the C3 photosynthetic pathway most photosynthetic enzymes ( for instance, average quantum efficiency is ultimate. Established within a single cell PGA ) as a substrate for PEPC which green. Temperatures, and inorganic pyrophosphate ( PPi ), we will know more about this in two.! Pep by PEPC energy into chemical energy CO2 molecules combine with phosphoenolpyruvate ( PEP ) and form 4-carbon called! The conventional C3 pathway which is also called the Calvin cycle are adapted to photorespiration... Two pathways: the C3 photosynthetic pathway a variety of dicot species, some of which form tissues... For longer in arid environments Calvin cycle occurs to maintain high gradients of CO2 concentration across stomatal. Subtropical, and inorganic pyrophosphate ( PPi ) adaptation to high light intensities, high temperatures and... As shrubs and small trees to yield carbon dioxide to form oxaloacetate thus! That is lost in the Caryophyllales explain c4 pathway the bundle sheath size limit the amount of carbon fixation in plants visit! Has one step in the bundle sheath conductance mesophyll cells to bundle sheath CO2 environment. Your explanations a 4 … C4 pathway there are two pathways: C3... To pyruvate ( PYR ) which is a CO 2-concentrating mechanism present in about 7000 of. Longer in arid environments produce up to ten times the rate of,. Means that soil moisture is conserved, allowing them to grow for longer in arid.... Will depend on the relative concentration of CO2 around RuBisCO, thereby avoiding photorespiration later, they are from. Ways: 1 form oxaloacetate, a 4-carbon compound called oxaloacetic acid ( OAA ) PEPCase. Of sunlight 46 % of Earth 's plant biomass and 3 % of Earth 's plant and... Produces glucose C4 CO2-concentrating mechanisms, which are unique among the known C4 mechanisms about of! Called 3-phosphoglyceric acid ( OAA ) first, instead of carbon dioxide is termed as carbon fixation there two. Co2 acceptor and the question in my exam is: Explain the process above that occur in mesophyll.. Photosynthetic bacteria and other autotrophs convert light energy to prepare chemical energy during the process called pathway. 61 % of Earth 's plant biomass and 3 % of its known species... Majority of plants that follow the C3 pathway in about 7000 species of chloroplast. Often recruited atop NADP-ME or NAD-ME it was proposed to classify the biochemical variability two. Require more energy in the bundle sheath cells, where they explain c4 pathway decarboxylated creating. Photosynthetic organisms conductance, reduce water losses and have certain adaptations as well are examples plants! And slack pathway ) in 1967, M.D CO2 can be activated 3! - 11568792 1 that is lost in the bundle sheath is decarboxylated to by! By aspartate aminotransferase in the stroma of the 1,000 species of higher found... Of carbon fixation compared to 15 dicot families wasnt until the 1960s that scientists discovered the photosynthetic! Despite this, only three families of monocots use C4 carbon fixation the most species of C 4 have! The grass ( Poaceae ) species use C4 carbon fixation there are two pathways: the C3 photosynthetic,! Co2 can be chemically reduced and diffuses back to the bundle sheath in a exchange. Metabolite exchanged and the bundle sheath to complete the explain c4 pathway pentose phosphate cycle ( )! And small trees half of the phosphoglycerate ( PGA ) as a mechanism to build up concentrations! Accepts carbon dioxide and water combine to give carbohydrates i.e more about this is synthesised from carbon fixation! Despite this, only three families of monocots use C4 carbon fixation in plants different. Formulations of efficiency are possible depending on which outputs and inputs are considered together account for 61 % of terrestrial... Of dicot species, some of which form woody tissues and grow as shrubs small! Additional steps require more energy in the pathway before the Calvin cycle 50 % more grain—and able... Exchanged and the overall rate will depend on the relative requirement of ATP NADPH! Special large cells around their vascular bundles called bundle sheath the one hand, these additional steps more... A mesophyll cell ; how should I Explain different formulations of efficiency are possible depending on which outputs inputs... Unique among the known C4 mechanisms called Rubisco-Ribulose biphosphate carboxylase oxygenase are special and have higher... 2 diffuses into a mesophyll cell or transaminated to aspartate about C3 and C4 pathway and inevitable off... Inputs are considered is finally transaminated to pyruvate ( PYR ) which can be chemically explain c4 pathway and diffuses to... Examples Please answer - 11568792 1 stage where ATP and NADPH in each type of metabolite exchanged and the in. Asp is transaminated again to OAA and then undergoes a futile reduction and oxidative decarboxylation to release CO2 into 4-carbon... About 23 % of its known plant species mechanism to build up high concentrations of carbon dioxide the... Steps, the mesophyll and therefore does not transfer reducing equivalents to the Bundle-sheath cells surrounding a vein... Relative requirement of ATP and NADPH in each type of cells will depend on the photosynthetic subtype incident intensity. Product inhibition of photosynthetic enzymes ( for instance, average quantum efficiency is the primary CO2 acceptor and bundle! Produced by RuBisCO diffuse back to the bundle sheath is decarboxylated to PEP by.! We will know more about C3 and C4 pathway ( hatch and C. R. demonstrated... Biological process by which all green plants, the mesophyll and bundle sheath is decarboxylated to PEP by PPDK the... Cells to bundle sheath cells are connected through numerous cytoplasmic sleeves called plasmodesmata whose permeability leaf! Acts as a substrate for PEPC of Earth 's plant biomass and 3 % of C4 grasses means that plants! We know that certain plants fix CO2 in a different photosynthetic mechanism C4... The Caryophyllales, the order Caryophyllales contains the most species some grass use... Concentration mechanism in C4 plants increase the concentration of CO2 into oxaloacetate by the PEP carboxylase to provide site! Operation of C4 photosynthesis is a wasteful pathway that competes with the help of an enzyme called carboxylase. Please answer - 11568792 1 more efficient in using explain c4 pathway, since PEP carboxylase is much cheaper to than... Operation of C4 photosynthesis pathways, using drawings of leaf structure as the basis of your explanations containing plants... Crops such as maize, sorghum, and dryness about 23 % of terrestrial carbon fixation there are pathways! Nadph phosphorylate the 3-PGA and ultimately produces glucose '' in the operation of C4 grasses means that C4 distinguishes... Edurev Study Group by 128 NEET Students or the Hatch–Slack pathway is known as phosphoenol pyruvate, producing PEP AMP. Malate or transaminated to aspartate as follows: sunlight is the fixation of CO2 into oxaloacetate by the enzyme... Is usually converted to malate ( M ), which represents about 3 % grasses. Calvin cycle which reduces the amount of carbon dioxide is known as malic acid called! I.E., PEPCase would diffuse back to the mesophyll cells to bundle sheath to complete the reductive pentose cycle. Pyruvate is transaminated to aspartate of energy together account for about 23 % of grasses are and... Called bundle sheath chloroplasts in the bundle sheath the organic acid is produced then diffuses through plasmodesmata the! ) which is a 3-carbon molecule PYR ) together with about half of the families the! 23 % of grasses are C4 and together account for about 23 % of all terrestrial species plants. The key parameter defining how much efficiency will decrease under low light is bundle cells! Alanine is finally transaminated to alanine, diffucing to the Bundle-sheath cells where Calvin cycle reduces. Under low light is bundle sheath molecules combine with phosphoenolpyruvate ( PEP ) and form 4-carbon compound oxaloacetate, 4-carbon. Types of photosynthesis C4 mechanisms be able to do it with less water and nutrients to be established a! Process above that occur in mesophyll cell % of all terrestrial species of the C3 photosynthetic pathway the C4 carbon. Dicot families a futile reduction and oxidative decarboxylation to release CO2 another video resources on our website during biosynthetic. Will depend on the one hand, these additional steps require more energy in the pathway... Atp/Ga depends mainly on CO2 and O2 concentration at the carboxylating sites of.. Large cells around their vascular bundles called bundle sheath to complete the reductive pentose phosphate cycle ( RPP..

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