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Explain the difference between C3, C4, and CAM plants

the first detectable molecule after carbon dioxide fixation is a C4 molecule composed of four carbon atoms.

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Photosynthesis: carbon fixation by the 6

Rubisco (ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase) enables net carbon fixation through the carboxylation of RuBP. However, some characteristics of Rubisco make it surprisingly inefficient and compromise photosynthetic productivity. For example, Rubisco catalyses a wasteful reaction with oxygen that leads to the release of previously fixed CO(2) and NH(3) and the consumption of energy during photorespiration. Furthermore, Rubisco is slow and large amounts are needed to support adequate photosynthetic rates. Consequently, Rubisco has been studied intensively as a prime target for manipulations to ‘supercharge’ photosynthesis and improve both productivity and resource use efficiency. The catalytic properties of Rubiscos from diverse sources vary considerably, suggesting that changes in turnover rate, affinity, or specificity for CO(2) can be introduced to improve Rubisco performance in specific crops and environments. While attempts to manipulate plant Rubisco by nuclear transformation have had limited success, modifying its catalysis by targeted changes to its catalytic large subunit via chloroplast transformation have been much more successful. However, this technique is still in need of development for most major food crops including maize, wheat, and rice. Other bioengineering approaches for improving Rubisco performance include improving the activity of its ancillary protein, Rubisco activase, in addition to modulating the synthesis and degradation of Rubisco’s inhibitory sugar phosphate ligands. As the rate-limiting step in carbon assimilation, even modest improvements in the overall performance of Rubisco pose a viable pathway for obtaining significant gains in plant yield, particularly under stressful environmental conditions.

The difference between C3, C4, and CAM plants are their process of light and dark reactions

Light Reactions
Calvin Cycle Reactions
- the organelles that carry on photosynthesis
a double membrane surrounds a fluid-filled area called the stroma.
a third membrane system within the stroma forms flattened sacs called
Stacks of thylakoid (plural, grana)
a pigment that is found in the thylakoids
absorbs solar energy to be used in photosynthesis
Thylakoid Membrane
contains complexes that convert solar energy into a chemical form useable by the enzymes in the stroma
enzyme rich area in which carbon dioxide is reduced to a carbohydrate

This carbohydrate is the only source of energy for most organisms on Earth.
Electrons are removed from water and energized by solar energy
Photosynthetic Pigments
Chlorophylls and Carotenoids
Other types of Photosynthesis
C3 Photosynthesis
Occurs where temperature and rainfall tend to be moderate.
the first detectable molecule after carbon dioxide fixation is a C3 molecule composed of three carbon atoms.

SciCombinator - Concepts - C3 carbon fixation

The number of humans on earth is increasing, generating concerns about food security and spurring efforts throughout the world to increase the productivity of crops. If a way could be found to increase the yield of crops by, say, 20%, it would have immense impact on global food supplies. Fortunately, evolution has already crafted such a mechanism, known as C4 photosynthesis. The C4 pathway is in effect a turbocharger for the more conventional C3 pathway. Just as a turbocharger improves performance of an engine by forcing more air into the manifold, C4 improves photosynthetic performance by forcing CO2 into the standard C3 photosynthetic apparatus. The added efficiency of this mechanism is obvious at a global level. Only about 3% of flowering plant species use the C4 pathway, but this relative handful of species account for 23% of the carbon fixed (primary productivity) in the world. The pathway occurs in several of the world’s major crops, notably maize (corn) and sorghum, and in many of the species in use as biofuels, most importantly sugar cane; all of these are grasses in the family Poaceae. If a major C3 crop such as rice could be bred to use the C4 pathway, the economic impact would be immense.

In a C3 leaf, mesophyll cells are arranged in parallel rows with well formed chloroplasts.
C4 Photosynthesis
Occurs in plants in hot & dry conditions.

The most talked about articles on the subject of C3 carbon fixation

Utilization of CO2 for production of energy-rich carbon compounds using solar light as an energy source has been a very attractive research field because it can solve serious global problems, i.e., energy crisis, depletion of carbon resources, and global warming. Exhaust gases discharged from heavy industries include relatively low concentrations of CO2. As a typical example, exhaust gas from fire power plants includes only 3%–13% CO2 with N2 as the main component; however, most research on photochemical and electrochemical reduction of CO2 have been conducted using pure CO2 to achieve high reaction rates of the active reaction intermediates with CO2. This is problematic because condensation of CO2, achieved by adsorption and desorption processes with amines and MOFs or separation with filters, is a highly energy-consuming process. If low concentrations of CO2 can be directly utilized, a highly promising technology can be developed. To the best of our knowledge, there has been only one report of a visible-light driven photocatalytic reduction system for low concentrations of CO2, of which catalyst was integrated into MOF as CO2 adsorption active sites. Although the MOF system could reduce even 5% concentration of CO2 with about 1.3 times higher efficiency compared to that of the corresponding homogeneous system without MOF, its photocatalysis is not satisfactory because of low durability (TONHCOOH = 33.3) and low selectivity of CO2 reduction (71% with H2 evolution; TONH2 = 14.5). In natural photosynthesis, plants have acquired elaborate systems during the evolutionary process to solve the above-mentioned problem, i.e., the Hatch–Slack cycle for concentration of CO2 and the Calvin cycle for CO2 reductive fixation. A novel photocatalytic system with a different working principle for CO2 condensation is required for the development of artificial photosynthesis research.

Avoid the uptake of O2 by rubisco, which would compete with carbon dioxide for the active site on rubisco.
C4 Photosynthesis
C4 plants have a different structure than C3 plants.
Chloroplasts are found in both the mesophyll cells and the bundle sheath cells
the mesophyll cells are arranged concentrically around the bundle sheath cells
the mesophyll cells shield the bundle cells from the oxygen
the Calvin cycle occurs only in the bundle sheath cells
Carbon dioxide is not taken directly from the air
the carbon dioxide is fixed in mesophyll cells producing a C4 molecule.

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  • Photosynthesis: carbon fixation by the C3 and C4 pathways ..

    18/08/2014 · Forget C3 and C4 photosynthesis, give me CAM photosynthesis baby

  • The Path from C3 to C4 Photosynthesis | Plant Physiology

    17/01/2011 · What's the difference in the carbon fixation for a C3 plant and a C4 plant?

  • to identify the carbon fixation steps of photosynthesis

    02/09/2010 · The C4 photosynthetic carbon cycle is an ..

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How does Kranz anatomy relate to C4 photosynthesis?

The C4 photosynthetic pathway accounts for ∼25% of primary productivity on the planet despite being used by only 3% of species. Because C4 plants are higher yielding than C3 plants, efforts are underway to introduce the C4 pathway into the C3 crop rice. This is an ambitious endeavor; however, the C4 pathway evolved from C3 on multiple independent occasions over the last 30 million years, and steps along the trajectory are evident in extant species. One approach toward engineering C4 rice is to recapitulate this trajectory, one of the first steps of which was a change in leaf anatomy. The transition from C3 to so-called “proto-Kranz” anatomy requires an increase in organelle volume in sheath cells surrounding leaf veins. Here we induced chloroplast and mitochondrial development in rice vascular sheath cells through constitutive expression of maize GOLDEN2-LIKE genes. Increased organelle volume was accompanied by the accumulation of photosynthetic enzymes and by increased intercellular connections. This suite of traits reflects that seen in “proto-Kranz” species, and, as such, a key step toward engineering C4 rice has been achieved.

MetaCyc C4 photosynthetic carbon assimilation cycle, …

Traditionally, it was believed that C4 photosynthesis required two types of chlorenchyma cells to concentrate CO2 within the leaf. However, several species have been identified that perform C4 photosynthesis using dimorphic chloroplasts within an individual cell. The goal of this research was to determine how growth under limited light affects leaf structure, biochemistry and efficiency of the single-cell CO2 -concentrating mechanism in Bienertia sinuspersici. Measurements of rates of CO2 assimilation and CO2 isotope exchange in response to light intensity and O2 were used to determine the efficiency of the CO2 -concentrating mechanism in plants grown under moderate and low light. In addition, enzyme assays, chlorophyll content and light microscopy of leaves were used to characterize acclimation to light-limited growth conditions. There was acclimation to growth under low light with a decrease in capacity for photosynthesis when exposed to high light. This was associated with a decreased investment in biochemistry for carbon assimilation with only subtle changes in leaf structure and anatomy. The capture and assimilation of CO2 delivered by the C4 cycle was lower in low-light-grown plants. Low-light-grown plants were able to acclimate to maintain structural and functional features for the performance of efficient single-cell C4 photosynthesis.

What is the major diference between C-3 and C-4 plants?

The C4 photosynthetic pathway evolved to allow efficient CO2 capture by plants where effective carbon supply may be limiting as in hot or dry environments, explaining the high growth rates of C4 plants such as maize. Important crops such as wheat and rice are C3 plants resulting in efforts to engineer them to use the C4 pathway. Here we show the presence of a C4 photosynthetic pathway in the developing wheat grain that is absent in the leaves. Genes specific for C4 photosynthesis were identified in the wheat genome and found to be preferentially expressed in the photosynthetic pericarp tissue (cross- and tube-cell layers) of the wheat caryopsis. The chloroplasts exhibit dimorphism that corresponds to chloroplasts of mesophyll- and bundle sheath-cells in leaves of classical C4 plants. Breeding to optimize the relative contributions of C3 and C4 photosynthesis may adapt wheat to climate change, contributing to wheat food security.

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