where does light independent reaction take place in photosynthesis
stroma
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the stroma caused by its phosphorylation. Light-independent reactions The light-independent reactions, or dark reactions, of photosynthesis are chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them. These reactions are closely coupled to the thylakoid electron transport chain as reducing power provided by NADPH produced in the photosystem I is actively needed. The process of photorespiration, also known as C2 cycle, is also coupled to
Light-independent reactions
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place only in the presence of light. This led later to the discovery of photosystems I and II. Light-dependent reactions In photosynthesis, the light-dependent reactions take place on the thylakoid membranes. The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place. The thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions. There are four major protein complexes in the thylakoid membrane: Photosystem II (PSII), Cytochrome b6f complex, Photosystem I (PSI), and ATP synthase. These four complexes work together to ultimately create the
Light-dependent reactions
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from an alternative reaction of the RuBisCO enzyme, and its final byproduct is also another glyceraldehyde-3-P. The Calvin cycle, Calvin–Benson–Bassham (CBB) cycle, reductive pentose phosphate cycle or C3 cycle is a series of biochemical redox reactions that take place in the stroma of chloroplast in photosynthetic organisms. The cycle was discovered by Melvin Calvin, James Bassham, and Andrew Benson at the University of California, Berkeley by using the radioactive isotope carbon-14. Photosynthesis occurs in two stages in a cell. In the first stage, light-dependent reactions capture the energy of light and use it to make the energy-storage and transport molecules
Light-independent reactions
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Light-dependent reactions In photosynthesis, the light-dependent reactions take place on the thylakoid membranes. The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place. The thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions. There are four major protein complexes in the thylakoid membrane: Photosystem II (PSII), Cytochrome b6f complex, Photosystem I (PSI), and ATP synthase. These four complexes work together to ultimately create the products ATP and NADPH. The four photosystems absorb light energy through pigments—primarily the chlorophylls, which are responsible for
Light-dependent reactions
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Stroma (fluid) Stroma, in botany, refers to the colorless fluid surrounding the grana within the chloroplast. Within the stroma are grana, stacks of thylakoids, the sub-organelles, the daughter cells, where photosynthesis is commenced before the chemical changes are completed in the stroma. Photosynthesis occurs in two stages. In the first stage, "light-dependent reactions" capture the energy of light and use it to make the energy-storage molecules ATP and NADPH. During the second stage, the "light-independent reactions" use these products to capture and reduce carbon dioxide. The series of biochemical redox reactions which take place in the stroma are collectively called
Stroma (fluid)
1512663
is integrated into thylakoid membrane; the CF-part sticks into stroma, where dark reactions of photosynthesis (also called the light-independent reactions or the Calvin cycle) and ATP synthesis take place. The overall structure and the catalytic mechanism of the chloroplast ATP synthase are almost the same as those of the bacterial enzyme. However, in chloroplasts, the proton motive force is generated not by respiratory electron transport chain but by primary photosynthetic proteins. The ATP synthase isolated from bovine ("Bos taurus") heart mitochondria is, in terms of biochemistry and structure, the best-characterized ATP synthase. Beef heart is used as a source for
ATP synthase
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the stroma caused by its phosphorylation. Light-independent reactions The light-independent reactions, or dark reactions, of photosynthesis are chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them. These reactions are closely coupled to the thylakoid electron transport chain as reducing power provided by NADPH produced in the photosystem I is actively needed. The process of photorespiration, also known as C2 cycle, is also coupled to
Light-independent reactions
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Light-independent reactions The light-independent reactions, or dark reactions, of photosynthesis are chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them. These reactions are closely coupled to the thylakoid electron transport chain as reducing power provided by NADPH produced in the photosystem I is actively needed. The process of photorespiration, also known as C2 cycle, is also coupled to the dark reactions, as it results
Light-independent reactions
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the Calvin cycle or "light-independent reactions". There are three phases: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration. The stroma is also the location of chloroplast DNA and chloroplast ribosomes, and thus also the location of molecular processes including chloroplast DNA replication, and transcription/translation of some chloroplast proteins. Stroma (fluid) Stroma, in botany, refers to the colorless fluid surrounding the grana within the chloroplast. Within the stroma are grana, stacks of thylakoids, the sub-organelles, the daughter cells, where photosynthesis is commenced before the chemical changes are completed in the stroma. Photosynthesis occurs in two stages. In the first stage,
Stroma (fluid)
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lighted conditions to reach steady state photosynthesis before measurement. “Understanding of the organization of plant antennae, or plant light collection structures, and reaction centers, where the photosynthetic light reaction actually takes place, has changed over the years. It is now understood that a single antennae does not link only to a single reaction center, as was previously described in the puddle model. Current evidence indicates that reaction centers are connected with shared antennae in terrestrial plants.” As a result, the parameters used to provide reliable measurements have changed to represent the newer understanding of this relationship. The model that represents
Plant stress measurement
19148232
by an artificial electron acceptor such as DCPIP, again allowing for the discharge of oxygen. The technique of replacing the natural electron acceptors with artificial electron acceptors can be used in the laboratory to provide a means to measure phosphorylation in chloroplasts and observe its relation to the discharge of oxygen in this reaction. Hill's finding was that the origin of oxygen in photosynthesis is water (HO) not carbon dioxide (CO) as previously believed. Hill's reaction also demonstrates that the light dependent redox reaction is the first reaction to take place in photosynthesis. The electrons thus freed by the splitting
Hill reaction
331483
this process is: This equation emphasizes that water is both a reactant in the light-dependent reaction and a product of the light-independent reaction, but canceling "n" water molecules from each side gives the net equation: Other processes substitute other compounds (such as arsenite) for water in the electron-supply role; for example some microbes use sunlight to oxidize arsenite to arsenate: The equation for this reaction is: Photosynthesis occurs in two stages. In the first stage, "light-dependent reactions" or "light reactions" capture the energy of light and use it to make the energy-storage molecules ATP and NADPH. During the second stage,
Photosynthesis
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cytosol they turn back into CO very slowly without the help of carbonic anhydrase. This causes the HCO ions to accumulate within the cell from where they diffuse into the carboxysomes. Pyrenoids in algae and hornworts also act to concentrate around rubisco. The overall process of photosynthesis takes place in four stages: Plants usually convert light into chemical energy with a photosynthetic efficiency of 3–6%. Absorbed light that is unconverted is dissipated primarily as heat, with a small fraction (1–2%) re-emitted as chlorophyll fluorescence at longer (redder) wavelengths. This fact allows measurement of the light reaction of photosynthesis by using
Photosynthesis
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the International Journal of Systematic and Evolutionary Microbiology (IJSB/IJSEM). Heliobacteria The heliobacteria are phototrophic: they convert light energy into chemical energy by photosynthesis and they use a type I reaction center. The primary pigment involved is bacteriochlorophyll "g", which is unique to the group and has a unique absorption spectrum; this gives the heliobacteria their own environmental niche. Phototrophy takes place at the cell membrane, which does not form folds or compartments as it does in purple bacteria. Though heliobacteria are phototrophic, they can grow without light by fermentation of pyruvate. RNA trees place the heliobacteria among the Firmicutes, but
Heliobacteria
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Heliobacteria The heliobacteria are phototrophic: they convert light energy into chemical energy by photosynthesis and they use a type I reaction center. The primary pigment involved is bacteriochlorophyll "g", which is unique to the group and has a unique absorption spectrum; this gives the heliobacteria their own environmental niche. Phototrophy takes place at the cell membrane, which does not form folds or compartments as it does in purple bacteria. Though heliobacteria are phototrophic, they can grow without light by fermentation of pyruvate. RNA trees place the heliobacteria among the Firmicutes, but they do not stain Gram-positively. They have no outer
Heliobacteria
4489758
of this topic includes the design and assembly of devices for the direct production of solar fuels, photoelectrochemistry and its application in fuel cells, and the engineering of enzymes and photoautotrophic microorganisms for microbial biofuel and biohydrogen production from sunlight. The photosynthetic reaction can be divided into two half-reactions of oxidation and reduction, both of which are essential to producing fuel. In plant photosynthesis, water molecules are photo-oxidized to release oxygen and protons. The second phase of plant photosynthesis (also known as the Calvin-Benson cycle) is a light-independent reaction that converts carbon dioxide into glucose (fuel). Researchers of artificial photosynthesis
Artificial photosynthesis
19148231
which oxygen is released takes place within the chloroplast of plants and the Hill reaction demonstrated that the release of oxygen (O) is only a partial reaction which requires one step of photosynthesis. The Hill reaction implies that the light dependent reaction of photosynthesis is a result of a series of redox reactions and a suitable terminal electron acceptor is required for that reaction to occur. Plants have natural electron acceptors such as NADP, that play a major role in the oxidation of water. The Hill reaction also shows that the natural electron acceptors of the reaction can be substituted
Hill reaction
79132
transformed into chemical energy, to subsequently produce food in the form of sugars. Water (HO) and carbon dioxide (CO) are used in photosynthesis, and sugar and oxygen (O) is made, using light energy. Photosynthesis is divided into two stages—the light reactions, where water is split to produce oxygen, and the dark reactions, or Calvin cycle, which builds sugar molecules from carbon dioxide. The two phases are linked by the energy carriers adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADP). The light reactions take place on the thylakoid membranes. They take light energy and store it in NADPH, a form
Chloroplast
331494
which it transfers some of its energy. The energy delivered to the electron acceptors is used to move hydrogen ions across the thylakoid membrane into the lumen. The electron is eventually used to reduce the co-enzyme NADP with a H to NADPH (which has functions in the light-independent reaction); at that point, the path of that electron ends. The cyclic reaction is similar to that of the non-cyclic, but differs in that it generates only ATP, and no reduced NADP (NADPH) is created. The cyclic reaction takes place only at photosystem I. Once the electron is displaced from the photosystem,
Photosynthesis
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the "light-independent reactions" use these products to capture and reduce carbon dioxide. Most organisms that utilize oxygenic photosynthesis use visible light for the light-dependent reactions, although at least three use shortwave infrared or, more specifically, far-red radiation. Some organisms employ even more radical variants of photosynthesis. Some archaea use a simpler method that employs a pigment similar to those used for vision in animals. The bacteriorhodopsin changes its configuration in response to sunlight, acting as a proton pump. This produces a proton gradient more directly, which is then converted to chemical energy. The process does not involve carbon dioxide fixation
Photosynthesis
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Products of photosynthesis are used up in respiration so that the organism is neither consuming nor building biomass. The net gaseous exchange is also zero at this point. For aquatic plants where the level of light at any given depth is roughly constant for most of the day, the compensation point is the depth at which light penetrating the water creates the same balanced effect. Respiration occurs by both plants and animals throughout the water column, resulting in the destruction, or usage, of organic matter, but photosynthesis can only take place via photosynthetic algae in the presence of light, nutrients
Compensation point
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extraction of the chloroplasts from the plant cellular environment. The ferrocyanide is reduced (just as NADP is when the chloroplast is in vivo) while water (HO) is oxidized into oxygen (O) and hydrogen cations during the reaction. By using this technique to observe the reaction, Hill revealed a variety of valuable facts about photosynthesis. The Hill reaction confirms that oxygen (O) is produced by a reaction that is separate from carbon dioxide (CO) fixation. The reaction in which oxygen is released requires light; therefore the Hill reaction can be described as the light dependent reaction of photosynthesis. The reaction in
Hill reaction
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the production of NADPH. Cyclic phosphorylation is important to create ATP and maintain NADPH in the right proportion for the light-independent reactions. The net-reaction of all light-dependent reactions in oxygenic photosynthesis is: The two photosystems are protein complexes that absorb photons and are able to use this energy to create an electron transport chain. Photosystem I and II are very similar in structure and function. They use special proteins, called light-harvesting complexes, to absorb the photons with very high effectiveness. If a special pigment molecule in a photosynthetic reaction center absorbs a photon, an electron in this pigment attains the
Light-dependent reactions
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to settle in a well lit spot, and competing with its neighbours for light to allow photosynthesis to take place. Where an anthozoan lives in a cave or other dark location, the symbiont may be absent in a species that, in a sunlit location, normally benefits from one. Anthozoans living at depths greater than are azooxanthellate because there is insufficient light for photosynthesis. With longitudinal, transverse and radial muscles, polyps are able to elongate and shorten, bend and twist, inflate and deflate, and extend and contract their tentacles. Most polyps extend to feed and contract when disturbed, often invaginating their
Anthozoa
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Hill reaction The Hill reaction was discovered by the biochemist Robin Hill from the University of Cambridge in 1937. The Hill reaction is the light-driven transfer of electrons from water to Hill reagents (non-physiological oxidants) against a "chemical potential gradient". The Hill reaction demonstrated that oxygen O is produced in plants in a process that is separate from the process that converts carbon dioxide (CO) to sugars. Hill's observation made a basic underlying refinement to our modern understandings of the process of photosynthesis. The evolution of oxygen during the light-dependent steps in photosynthesis (Hill reaction) was proposed and proven by
Hill reaction
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Photosynthetic efficiency The photosynthetic efficiency is the fraction of light energy converted into chemical energy during photosynthesis in plants and algae. Photosynthesis can be described by the simplified chemical reaction where CHO is glucose (which is subsequently transformed into other sugars, cellulose, lignin, and so forth). The value of the photosynthetic efficiency is dependent on how light energy is defined – it depends on whether we count only the light that is absorbed, and on what kind of light is used (see Photosynthetically active radiation). It takes eight (or perhaps 10 or more) photons to utilize one molecule of CO.
Photosynthetic efficiency
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Robin Hill (biochemist) Robert Hill FRS (2 April 1899 – 15 March 1991), known as Robin Hill, was a British plant biochemist who, in 1939, demonstrated the 'Hill reaction' of photosynthesis, proving that oxygen is evolved during the light requiring steps of photosynthesis. He also made significant contributions to the development of the Z-scheme of oxygenic photosynthesis. Hill was born in New Milverton, a suburb of Leamington Spa, Warwickshire. He was educated at Bedales School, where he became interested in biology and astronomy (he published a paper on sunspots in 1917), and Emmanuel College, Cambridge, where he read Natural Sciences.
Robin Hill (biochemist)
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However, these experiments clearly show that temperature affects the rate of carbon assimilation, so there must be two sets of reactions in the full process of carbon assimilation. These are the light-dependent 'photochemical' temperature-independent stage, and the light-independent, temperature-dependent stage. Second, Blackman's experiments illustrate the concept of limiting factors. Another limiting factor is the wavelength of light. Cyanobacteria, which reside several meters underwater, cannot receive the correct wavelengths required to cause photoinduced charge separation in conventional photosynthetic pigments. To combat this problem, a series of proteins with different pigments surround the reaction center. This unit is called a phycobilisome. As
Photosynthesis
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Station of Stanford University. By studying purple sulfur bacteria and green sulfur bacteria he was the first scientist to demonstrate, in 1931, that photosynthesis is a light-dependent redox reaction in which hydrogen from an oxidizable compound reduces carbon dioxide to cellular materials. Expressed as: where A is the electron acceptor. His discovery predicted that HO is the hydrogen donor in green plant photosynthesis and is oxidized to O. The chemical summation of photosynthesis was a milestone in the understanding of the chemistry of photosynthesis. This was later experimentally verified by Robert Hill. In a nutshell, van Niel proved that plants
C. B. van Niel
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in a process called carbon fixation. Carbon fixation is an endothermic redox reaction, so photosynthesis needs to supply both the source of energy to drive this process and the electrons needed to convert into a carbohydrate. This addition of the electrons is a reduction reaction. In general outline and in effect, photosynthesis is the opposite of cellular respiration, in which glucose and other compounds are oxidized to produce and water, and to release exothermic chemical energy to drive the organism's metabolism. However, the two processes take place through a different sequence of chemical reactions and in different cellular compartments. Most
Carbon dioxide in Earth's atmosphere
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Exergonic reaction An exergonic reaction is a chemical reaction where the change in the free energy is negative (there is a net release of free energy), indicating a spontaneous reaction. For processes that take place under constant pressure and temperature conditions, the Gibbs free energy is used whereas the Helmholtz energy is used for processes that take place under constant volume and temperature conditions. Symbolically, the release of free energy, "G", in an exergonic reaction (at constant pressure and temperature) is denoted as Although exergonic reactions are said to occur "spontaneously", this does not imply that the reaction will take
Exergonic reaction
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that a complex of reactions consisting of an intermediate to cytochrome b (now a plastoquinone), another is from cytochrome f to a step in the carbohydrate-generating mechanisms. These are linked by plastoquinone, which does require energy to reduce cytochrome f for it is a sufficient reductant. Further experiments to prove that the oxygen developed during the photosynthesis of green plants came from water, were performed by Hill in 1937 and 1939. He showed that isolated chloroplasts give off oxygen in the presence of unnatural reducing agents like iron oxalate, ferricyanide or benzoquinone after exposure to light. The Hill reaction is
Photosynthesis
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conversion of violaxanthin to zeaxanthin. These two molecules are photo-protective molecules. Under high light, it is unfavourable to channel extra light into photosynthesis because excessive light may cause damage to the plant proteins. Zeaxanthin dissociates light-channelling from the photosynthesis reaction - light energy in the form of photons will not be transmitted into the photosynthetic pathway anymore. Stomata closure not only restricts the movement of water out of the plant, another consequence of the phenomenon is that carbon dioxide influx or intake into the plant is also reduced. As photosynthesis requires carbon dioxide as a substrate to produce sugar for
Xerophyte
18768434
light efficiency (very low quantum yield), which helps to ensure the protein's photoprotective role only functions during high light conditions; otherwise, the dissipative NPQ process could unproductively divert light energy away from photosynthesis under light-limiting conditions. As evidenced by a decreased fluorescence, OCP in its red form is capable of dissipating absorbed light energy from the phycobilisome antenna complex. According to Rakhimberdieva and coworkers, about 30-40% of the energy absorbed by phycobilisomes does not reach the reaction centers when the carotenoid-induced NPQ is active. The exact mechanism and quenching site in both the carotenoid as well as the phycobilisome still
Orange carotenoid protein
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to produce food (such as glucose) was outlined. Cornelis Van Niel made key discoveries explaining the chemistry of photosynthesis. By studying purple sulfur bacteria and green bacteria he was the first to demonstrate that photosynthesis is a light-dependent redox reaction, in which hydrogen reduces (donates its electron to) carbon dioxide. Robert Emerson discovered two light reactions by testing plant productivity using different wavelengths of light. With the red alone, the light reactions were suppressed. When blue and red were combined, the output was much more substantial. Thus, there were two photosystems, one absorbing up to 600 nm wavelengths, the other
Photosynthesis
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of heat during a process. Exergonic reaction An exergonic reaction is a chemical reaction where the change in the free energy is negative (there is a net release of free energy), indicating a spontaneous reaction. For processes that take place under constant pressure and temperature conditions, the Gibbs free energy is used whereas the Helmholtz energy is used for processes that take place under constant volume and temperature conditions. Symbolically, the release of free energy, "G", in an exergonic reaction (at constant pressure and temperature) is denoted as Although exergonic reactions are said to occur "spontaneously", this does not imply
Exergonic reaction
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Chlorophyll a Chlorophyll "a" is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light. It also reflects green-yellow light, and as such contributes to the observed green color of most plants. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary electron donor in the electron transport chain. Chlorophyll "a" also transfers resonance energy in the antenna complex, ending in the reaction center where specific chlorophylls P680 and P700 are located. Chlorophyll "a" is essential for most photosynthetic organisms to release
Chlorophyll a
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allows them to expand and contract easily for quick water absorption after rain, followed by long drought periods. Like other succulent plants, most cacti employ a special mechanism called "crassulacean acid metabolism" (CAM) as part of photosynthesis. Transpiration, during which carbon dioxide enters the plant and water escapes, does not take place during the day at the same time as photosynthesis, but instead occurs at night. The plant stores the carbon dioxide it takes in as malic acid, retaining it until daylight returns, and only then using it in photosynthesis. Because transpiration takes place during the cooler, more humid night
Cactus
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Mehler reaction The Mehler reaction is named after Alan H. Mehler, who, in 1951, presented data to the effect that isolated chloroplasts reduce oxygen to form hydrogen peroxide (). Mehler observed that the formed in this way does not present an active intermediate in photosynthesis; rather, as a reactive oxygen species, it can be toxic to surrounding biological processes as an oxidizing agent. In scientific literature, the Mehler reaction often is used interchangeably with the Water-Water Cycle to refer to the formation of by photosynthesis. "Sensu stricto", the Water Water Cycle encompasses the Hill reaction, in which water is split
Mehler reaction
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a byproduct of this reaction. Because photosynthesis is light-limited, both photosynthesis and respiration occur during the daylight hours, while only respiration occurs during dark hours or in dark portions of an ecosystem. The balance between dissolved oxygen production and consumption is calculated as the aquatic metabolism rate. Vertical changes in the concentrations of dissolved oxygen are affected by both wind mixing of surface waters and the balance between photosynthesis and respiration of organic matter. These vertical changes, known as profiles, are based on similar principles as thermal stratification and light penetration. As light availability decreases deeper in the water column,
Limnology
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plants, light-dependent reactions occur in the thylakoid membranes of the chloroplasts where they drive the synthesis of ATP and NADPH. The light-dependent reactions are of two forms: cyclic and non-cyclic. In the non-cyclic reaction, the photons are captured in the light-harvesting antenna complexes of photosystem II by chlorophyll and other accessory pigments (see diagram at right). The absorption of a photon by the antenna complex frees an electron by a process called photoinduced charge separation. The antenna system is at the core of the chlorophyll molecule of the photosystem II reaction center. That freed electron is transferred to the primary
Photosynthesis
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Green sulfur and non-sulfur bacteria), allowing for increased efficiency in light utilization. Biochemically, anoxygenic photosynthesis is very different from oxygenic photosynthesis. Cyanobacteria (and by extension, chloroplasts) use the Z scheme of electron flow in which electrons eventually are used to form NADH. Two different reaction centers (photosystems) are used and proton motive force is generated both by using cyclic electron flow and the quinone pool. In anoxygenic photosynthetic bacteria, electron flow is cyclic, with all electrons used in photosynthesis eventually being transferred back to the single reaction center. A proton motive force is generated using only the quinone pool. In
Microbial metabolism
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large sheets that link multiple grana, or narrow to tube-like bridges between grana. While different parts of the thylakoid system contain different membrane proteins, the thylakoid membranes are continuous and the thylakoid space they enclose form a single continuous labyrinth. Thylakoids (sometimes spelled "thylakoïds"), are small interconnected sacks which contain the membranes that the light reactions of photosynthesis take place on. The word "thylakoid" comes from the Greek word "thylakos" which means "sack". Embedded in the thylakoid membranes are important protein complexes which carry out the light reactions of photosynthesis. Photosystem II and photosystem I contain light-harvesting complexes with chlorophyll
Chloroplast
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that there must be two different photosystems involved in photosynthesis, one driven by short-wavelength light and one driven by long-wavelength (PS1 and PS2). They work together to enhance efficiency and convert the light energy to forms that can be absorbed by the plant. The light excites the chlorophyll molecules at the reaction centre and causes an increase in energy. As the molecule becomes less excited, its energy is transported through a chain of electron carriers to the next photosystem which does much the same thing and produces energy-carrying organic molecules. Emerson effect The Emerson effect is the increase in the
Emerson effect
4011701
Photosystem Photosystems are functional and structural units of protein complexes involved in photosynthesis that together carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosystems are found in the thylakoid membranes of plants, algae and cyanobacteria. They are located in the chloroplasts of plants and algae, and in the cytoplasmic membrane of photosynthetic bacteria. There are two kinds of photosystems: II and I. At the heart of a photosystem lies the reaction center, which is an enzyme that uses light to reduce molecules (provide with electrons). This reaction center is surrounded
Photosystem
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almost all oxygen produced in tropical forests is consumed by organisms living there. A simplified overall formula for photosynthesis is: Photolytic oxygen evolution during photosynthesis occurs via the light-dependent oxidation of water to molecular oxygen and can be written as the following simplified chemical reaction: 2HO → 4e + 4H + O The reaction occurs in the thylakoid membranes of cyanobacteria, and algal and plant chloroplasts and requires the energy of four photons. The electrons from the oxidized water molecules replace electrons in the P component of photosystem II, which have been removed into an electron transport chain via light-dependent
Dioxygen in biological reactions
9938610
Oxygen evolution Oxygen evolution is the process of generating molecular oxygen (O) by a chemical reaction, usually from water. Oxygen evolution from water is effected by oxygenic photosynthesis, electrolysis of water, and thermal decomposition of various oxides. The biological process supports aerobic life. When relatively pure oxygen is required industrially, it is isolated by distillation of liquified air. Photosynthetic oxygen evolution is the fundamental process by which oxygen is generated in earth's biosphere. The reaction is part of the light-dependent reactions of photosynthesis in cyanobacteria and the chloroplasts of green algae and plants. It utilizes the energy of light to
Oxygen evolution
9938604
Oxygen evolution Oxygen evolution is the process of generating molecular oxygen (O) by a chemical reaction, usually from water. Oxygen evolution from water is effected by oxygenic photosynthesis, electrolysis of water, and thermal decomposition of various oxides. The biological process supports aerobic life. When relatively pure oxygen is required industrially, it is isolated by distillation of liquified air. Photosynthetic oxygen evolution is the fundamental process by which oxygen is generated in earth's biosphere. The reaction is part of the light-dependent reactions of photosynthesis in cyanobacteria and the chloroplasts of green algae and plants. It utilizes the energy of light to
Oxygen evolution
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electron acceptor, such as a dye that changes color when it is reduced. These are known as Hill reagents. The Hill reagent was discovered in 1937 by Robin Hill. These dyes permitted the finding of electron transport chains during photosynthesis. dichlorophenolindophenol (DCPIP), an example of these dyes, is widely used by experimenters. DCPIP is a dark blue solution that becomes lighter as it is reduced. It gives experimenters a simple visual test and observation of the light reaction. In another approach to studying photosynthesis, light-absorbing pigments such as chlorophyll can be extracted from the chloroplasts of plant leaves or other
Hill reaction
5535494
they use a bacteriochlorophyll-based reaction center, or they use a bacteriorhodopsin. The chlorophyll-based mechanism is similar to that used in photosynthesis, where light excites the molecules in a reaction center and causes a flow of electrons through an electron transport chain (ETS). This flow of electrons through the proteins causes hydrogen ions to be pumped across a membrane. The energy stored in this proton gradient is used to drive ATP synthesis. Unlike in photoautotrophs, the electrons flow only in a cyclic pathway: electrons released from the reaction center flow through the ETS and return to the reaction center. They are
Photoheterotroph
7709462
Photoprotection Photoprotection is the biochemical process that helps organisms cope with molecular damage caused by sunlight. Plants and other oxygenic phototrophs have developed a suite of photoprotective mechanisms to prevent photoinhibition and oxidative stress caused by excess or fluctuating light conditions. Humans and other animals have also developed photoprotective mechanisms to avoid UV photodamage to the skin, prevent DNA damage, and minimize the downstream effects of oxidative stress. In organisms that perform oxygenic photosynthesis, excess light may lead to photoinhibition, or photoinactivation of the reaction centers, a process that does not necessarily involve chemical damage. When photosynthetic antenna pigments such
Photoprotection
5126399
light into its components by the prism and then illuminated Cladophora placed in a suspension of aerobic bacteria. He found that bacteria accumulated in the region of blue and red light of the split spectrum. He thus discovered the effect of the different wavelengths of light on photosynthesis and plotted the first action spectrum of photosynthesis. Action spectrum An action spectrum is a graph of the rate of a physiological activity plotted against wavelength of light. It shows which wavelength of light is most effectively used in a specific chemical reaction. Some reactants are able to use specific wavelengths of
Action spectrum
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mimicking of a series of molybdoenzymes he showed that the even in model enzymatic oxotransfer reactions the participation of similar enzyme-susbrate (E-S) complex is a real entity. Such a chemical spices( E-S) responds to spontaneous intramolecular oxidative addition and reductive elimination to complete the oxotransfer reaction. Such a reaction differs from conventional chemical oxotransfer reaction where the reaction between the starting reactants happens in Eyring activated complex. He demonstrated that carbon dioxide molecule does bind to magnesium in chlorophyll in photosynthesis as proposed by R. M. Willstätter hundred years ago and modeled hydrogenase captioned as better than nature. The rare
Sabyasachi Sarkar
4378147
aerobic respiration and fermentation. Photosynthesis occurs at reaction centers on the cell membrane, where the photosynthetic pigments (i.e. bacteriochlorophyll, carotenoids) and pigment-binding proteins are invaginated to form vesicle sacs, tubules, or single-paired or stacked lamellar sheets. This is called the intracytoplasmic membrane (ICM) which has increased surface area to maximize light absorption. Purple bacteria use cyclic electron transport driven by a series of redox reactions. Light-harvesting complexes surrounding a reaction centre (RC) harvest photons in the form of resonance energy, exciting chlorophyll pigments P870 or P960 located in the RC. Excited electrons are cycled from P870 to quinones Q and
Purple bacteria
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contains the four oxidizing equivalents that are used to drive the water-oxidizing reaction (Dolai's S-state diagrams). Photosystem II is the only known biological enzyme that carries out this oxidation of water. The hydrogen ions are released in the thylakoid lumen andd therefore contribute to the transmembrane chemiosmotic potential that leads to ATP synthesis. Oxygen is a waste product of light-dependent reactions, but the majority of organisms on Earth use oxygen for cellular respiration, including photosynthetic organisms. In the light-independent (or "dark") reactions, the enzyme RuBisCO captures CO from the atmosphere and, in a process called the Calvin cycle, it uses
Photosynthesis
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of water provides the electrons needed by the antenna system of photosystem II where they are boosted in energy and then sent along the electron transport system (ETS). Those high energy electrons are able to move against a chemical potential gradient. Hence, solar energy is converted to chemical energy by the reduction of NADP to NADPH. Photosynthesis is the process in which light energy is absorbed and converted to chemical energy. This chemical energy is eventually used in the conversion of carbon dioxide (CO) to sugar (CHO) in plants. During the process of photosynthesis, a natural electron acceptor, nicotinamide adenine
Hill reaction
331536
carbon dioxide concentrations rise, the rate at which sugars are made by the light-independent reactions increases until limited by other factors. RuBisCO, the enzyme that captures carbon dioxide in the light-independent reactions, has a binding affinity for both carbon dioxide and oxygen. When the concentration of carbon dioxide is high, RuBisCO will fix carbon dioxide. However, if the carbon dioxide concentration is low, RuBisCO will bind oxygen instead of carbon dioxide. This process, called photorespiration, uses energy, but does not produce sugars. RuBisCO oxygenase activity is disadvantageous to plants for several reasons: The salvaging pathway for the products of RuBisCO
Photosynthesis
2875119
several types of light-harvesting energy capture systems. "Chloroflexus aurantiacus" has been of interest in the search for origins of the so-called type II photosynthetic reaction center. One idea is that bacteria with respiratory electron transport evolved photosynthesis by coupling a light-harvesting energy capture system to the pre-existing respiratory electron transport chain. Thus, rare organisms like "Chloroflexus aurantiacus" that can survive using either respiration or photosynthesis are of interest in on-going attempts to trace the evolution of photosynthesis. Chloroflexus aurantiacus Chloroflexus aurantiacus is a photosynthetic bacterium isolated from hot springs, belonging to the green non-sulfur bacteria. This organism is thermophilic and
Chloroflexus aurantiacus
6516567
chlorophyll molecule (P680, where P stands for pigment and 680 for its absorption maximum at 680 nm) in the reaction center of photosystem II via resonance energy transfer. P680 can also directly absorb a photon at a suitable wavelength. Photolysis during photosynthesis occurs in a series of light-driven oxidation events. The energized electron (exciton) of P680 is captured by a primary electron acceptor of the photosynthetic electron transfer chain and thus exits photosystem II. In order to repeat the reaction, the electron in the reaction center needs to be replenished. This occurs by oxidation of water in the case of
Photodissociation
13691826
excited state and then is transferred to another molecule in the reaction center. This reaction, called photoinduced charge separation, is the start of the electron flow and is unique because it transforms light energy into chemical forms. The reaction center is in the thylakoid membrane. It transfers light energy to a dimer of chlorophyll pigment molecules near the periplasmic (or thylakoid lumen) side of the membrane. This dimer is called a special pair because of its fundamental role in photosynthesis. This special pair is slightly different in PSI and PSII reaction center. In PSII, it absorbs photons with a wavelength
Light-dependent reactions
7084294
Light-harvesting complex A light-harvesting complex has a complex of subunit proteins that may be part of a larger supercomplex of a photosystem, the functional unit in photosynthesis. It is used by plants and photosynthetic bacteria to collect more of the incoming light than would be captured by the photosynthetic reaction center alone. Light-harvesting complexes are found in a wide variety among the different photosynthetic species. The complexes consist of proteins and photosynthetic pigments and surround a photosynthetic reaction center to focus energy, attained from photons absorbed by the pigment, toward the reaction center using Förster resonance energy transfer. Absorption of
Light-harvesting complex
10238244
able to synthesize food directly from and water using energy from light. However, not all organisms that use light as a source of energy carry out photosynthesis, since "photoheterotrophs" use organic compounds, rather than , as a source of carbon. In plants, algae and cyanobacteria, photosynthesis releases oxygen. This is called "oxygenic photosynthesis". Although there are some differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms. However, there are some types of bacteria that carry out anoxygenic photosynthesis, which consumes but does not release oxygen. Carbon dioxide is converted into sugars
Carbon dioxide in Earth's atmosphere
9847954
in preference to O, increasing the relative amount of O in the atmosphere. The inequality is balanced by photosynthesis. Photosynthesis emits oxygen with the same isotopic composition (i.e. the ratio between O and O) as the water (HO) used in the reaction, which is independent of the atmospheric ratio. Thus when atmospheric O levels are high enough, photosynthesis will act as a reducing factor. However, as a complicating factor, the degree of fractionation (i.e. change in isotope ratio) occurring due to photosynthesis is not "entirely" dependent on the water drawn up by the plant, as fractionation can occur as a
Dole effect
1673593
are the site of the light-dependent reactions of photosynthesis. These include light-driven water oxidation and oxygen evolution, the pumping of protons across the thylakoid membranes coupled with the electron transport chain of the photosystems and cytochrome complex, and ATP synthesis by the ATP synthase utilizing the generated proton gradient. The first step in photosynthesis is the light-driven reduction (splitting) of water to provide the electrons for the photosynthetic electron transport chains as well as protons for the establishment of a proton gradient. The water-splitting reaction occurs on the lumenal side of the thylakoid membrane and is driven by the light
Thylakoid
17289305
Sodium carbonate and sodium hydroxide are in equilibrium with availability of dissolved carbon dioxide as given below in the chemical reaction During day time when sun light is available, Algae undergoes photosynthesis process which absorbs CO to shift the reaction towards NaOH formation and vice versa takes place during night time with the release of CO from the respiration process of Algae towards NaCO and NaHCO formation. In soda lake waters, carbonates of sodium act as catalyst for the algae growth by providing favourable higher concentration of dissolved CO during the day time. Due to fluctuation in dissolved CO, the
Residual sodium carbonate index
13461233
mature regions to actively growing regions where the machinery of photosynthesis is not yet fully in place. Translocation also moves nutrients downward from light-exposed surface fronds to sporophylls (reproductive fronds) at the base of the kelp, where there is little light and thus little photosynthesis to produce food. "M. pyrifera" has been utilized for many years as a food source; it also contains many compounds such as iodine, potassium, other minerals vitamins and carbohydrates and thus has also been used as a dietary supplement. In the beginning of the 20th century California kelp beds were harvested as a source for
Macrocystis pyrifera
331489
surface of the leaf is coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to reduce heating. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place. In the light-dependent reactions, one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron is passed to a modified form of chlorophyll called pheophytin, which passes the electron to a quinone molecule, starting the flow of electrons down an electron transport chain
Photosynthesis
14053841
transport chain, proteins such as halorhodopsin capture light energy with the aid of diterpenes to move ions against the gradient and produce ATP via chemiosmosis in the manner of mitochondria. There are two main types of anaerobic photosynthetic electron transport chains in bacteria. The type I reaction centers found in GSB, Chloracidobacterium, and Heliobacteria and the type II reaction centers found in FAPs and Purple Bacteria Type I Reaction Centers The electron transport chain of green sulfur bacteria — such as is present in model organism "Chlorobaculum tepidum" — uses the reaction centre bacteriochlorophyll pair, P840. When light is absorbed
Anoxygenic photosynthesis
14053843
anoxygenic photosynthesis do not have a region analogous to the oxygen-evolving complex of PSII. The electron transport chain of purple non-sulfur bacteria begins when the reaction centre bacteriochlorophyll pair, P870, becomes excited from the absorption of light. Excited P870 will then donate an electron to bacteriopheophytin, which then passes it on to a series of electron carriers down the electron chain. In the process, it will generate an electro-chemical gradient which can then be used to synthesize ATP by chemiosmosis. P870 has to be regenerated (reduced) to be available again for a photon reaching the reaction-center to start the process
Anoxygenic photosynthesis
19148237
ATP, NADPH, and H which are used in the light independent reaction. He demonstrated that the isolated active chloroplasts which are subjected to light but without CO will release oxygen but no sugar will be produced. He then demonstrated the light independent reaction, observing the reaction under dark conditions with an abundance of carbon dioxide. He found carbon fixation was independent of the light reaction. Arnon had effectively separated the light dependent reaction, which produces ATP, NADPH, H and oxygen, from the light independent reaction, which produces sugars. He was able to conclude that that part of the reaction happens
Hill reaction
13475071
that make up light-harvesting complexes and photosynthetic reaction centres. LH complexes and photosynthetic reaction centers are typically found in photosynthetic organisms like green plants. Moreover, "R. palustris" can modulate photosynthesis according to the amount of light available, like other purple bacteria. For instance, in low-light circumstances, it responds by increasing the level of these LH complexes that allow light absorption. However, the wavelengths of the light absorbed by "R. palustris" differ from those absorbed by other phototrophs. "R. palustris" also has genes that encode for the protein ruBisCO, an enzyme that is necessary for carbon dioxide fixation in plants and
Rhodopseudomonas palustris
331477
Earth's atmosphere, and supplies all of the organic compounds and most of the energy necessary for life on Earth. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments. In plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting
Photosynthesis
20289503
ATP and NADPH than can be utilized by the light-independent reactions. Since photosynthesis is also limited by ambient carbon dioxide levels, light curves are often repeated at several different constant carbon dioxide concentrations. Light curve (botany) In botany, a light curve shows the photosynthetic response of leaf tissue or algal communities to varying light intensities. The shape of the curve illustrates the principle of limiting factors; in low light levels, the rate of photosynthesis is limited by the concentration of chlorophyll and the efficiency of the light-dependent reactions, but in higher light levels it is limited by the efficiency of
Light curve (botany)
5009777
Photosynthetically active radiation Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. This spectral region corresponds more or less with the range of light visible to the human eye. Photons at shorter wavelengths tend to be so energetic that they can be damaging to cells and tissues, but are mostly filtered out by the ozone layer in the stratosphere. Photons at longer wavelengths do not carry enough energy to allow photosynthesis to take place. Other living organisms,
Photosynthetically active radiation
16644080
upon sucrose density gradient centrifugation of solubilised thylakoids. "Ycf" is an acronym standing for hypothetical chloroplast open reading frame. Ycf4 protein domain In molecular biology, the Ycf4 protein is involved in the assembly of the photosystem I complex which is part of an energy-harvesting process named photosynthesis. Without Ycf4, photosynthesis would be inefficient affecting plant growth. Ycf4 is located in the thylakoid membrane of the chloroplast. Ycf4 is important for the light dependent reaction of photosynthesis. To date, three thylakoid proteins involved in the stable accumulation of PSI have been identified, these are as follows: The Ycf4 protein is firmly
Ycf4 protein domain
16644079
Ycf4 protein domain In molecular biology, the Ycf4 protein is involved in the assembly of the photosystem I complex which is part of an energy-harvesting process named photosynthesis. Without Ycf4, photosynthesis would be inefficient affecting plant growth. Ycf4 is located in the thylakoid membrane of the chloroplast. Ycf4 is important for the light dependent reaction of photosynthesis. To date, three thylakoid proteins involved in the stable accumulation of PSI have been identified, these are as follows: The Ycf4 protein is firmly associated with the thylakoid membrane, presumably through a transmembrane domain. Ycf4 co-fractionates with a protein complex larger than PSI
Ycf4 protein domain
7084299
phycoerythrin subunits that radiate out from this center like thin tubes. This increases the surface area of the absorbing section and helps focus and concentrate light energy down into the reaction center to a Chlorophyll. The energy transfer from excited electrons absorbed by pigments in the phycoerythrin subunits at the periphery of these antennas appears at the reaction center in less than 100 ps. Light-harvesting complex A light-harvesting complex has a complex of subunit proteins that may be part of a larger supercomplex of a photosystem, the functional unit in photosynthesis. It is used by plants and photosynthetic bacteria to
Light-harvesting complex
15671590
fluorescence, or Fo, to maximum fluorescence called Fm. In maximum fluorescence, the maximum number of reaction centers have been reduced or closed by a saturating light source. In general, the greater the plant stress, the fewer open reaction centers available, and the Fv/Fm ratio is lowered. Fv/Fm is a measuring protocol that works for many types of plant stress. In Fv/Fm measurements, after dark adaption, minimum fluorescence is measured, using a modulated light source. This is a measurement of antennae fluorescence using a modulated light intensity that is too low to drive photosynthesis. Next, an intense light flash, or saturation
Plant stress measurement
20655035
+ 2 H + 3 ATP + OThe light-independent reactions undergo the Calvin-Benson cycle, in which the energy from NADPH and ATP is used to convert carbon dioxide and water into organic compounds via the enzyme RuBisCO. The overall general equation for the light-independent reactions is the following:3 CO + 9 ATP + 6 NADPH + 6 H → CHO-phosphate + 9 ADP + 8 P + 6 NADP + 3 HOThe 3-carbon products (CHO-phosphate) of the Calvin cycle are later converted to glucose or other carbohydrates such as starch, sucrose, and cellulose. The large fractionation of C in photosynthesis
Fractionation of carbon isotopes in oxygenic photosynthesis
331485
and does not release oxygen, and seems to have evolved separately from the more common types of photosynthesis. In photosynthetic bacteria, the proteins that gather light for photosynthesis are embedded in cell membranes. In its simplest form, this involves the membrane surrounding the cell itself. However, the membrane may be tightly folded into cylindrical sheets called thylakoids, or bunched up into round vesicles called "intracytoplasmic membranes". These structures can fill most of the interior of a cell, giving the membrane a very large surface area and therefore increasing the amount of light that the bacteria can absorb. In plants and
Photosynthesis
19215353
Emerson effect, the excess rate of photosynthesis after chloroplasts are simultaneously exposed to light of wavelength 670 nm (red light), and 700 nm (far red light). These results were later shown to be the first experimental demonstration that there are two photosynthetic reaction centres in plants. Emerson died in the crash of American Airlines Flight 320 in New York City. Robert Emerson (scientist) Robert Emerson (November 4, 1903 – February 4, 1959) was an American scientist noted for his discovery that plants have two distinct photosynthetic reaction centres. Emerson was born in 1903 in New York City, the son of
Robert Emerson (scientist)
2121614
substrate availabilities and environmental conditions), reaching a compromise between specificity and reaction rate. Since photosynthesis is the single most effective natural regulator of carbon dioxide in the Earth's atmosphere, a biochemical model of RuBisCO reaction is used as the core module of climate change models. Thus, a correct model of this reaction is essential to the basic understanding of the relations and interactions of environmental models. A new theory and model of the biochemical reaction of photosynthesis and the drawbacks of today's most widely used model of photosynthesis is discussed in volume 29 of Advances in Photosynthesis and Respiration. There
RuBisCO
20655034
defined in relation to the Vienna Pee Dee Belemnite (VPDB, C/C = 0.01118) as an established reference standard. This is called a "delta value" and can be calculated from the formula below: formula_1 The chemical pathway of oxygenic photosynthesis fixes carbon in two stages: the light-dependent reactions and the light-independent reactions. The light-dependent reactions capture light energy to transfer electrons from water and convert NADP, ADP, and inorganic phosphate into the energy-storage molecules NADPH and ATP. The overall equation for the light-dependent reactions is generally:2 HO + 2 NADP + 3 ADP + 3 P + light → 2 NADPH
Fractionation of carbon isotopes in oxygenic photosynthesis
3888099
and Windogradsky, however, were focused on the physiology of microorganisms, not the microbial habitat or their ecological interactions. Modern microbial ecology was launched by Robert Hungate and coworkers, who investigated the rumen ecosystem. The study of the rumen required Hungate to develop techniques for culturing anaerobic microbes, and he also pioneered a quantitative approach to the study of microbes and their ecological activities that differentiated the relative contributions of species and catabolic pathways. Microorganisms are the backbone of all ecosystems, but even more so in the zones where photosynthesis is unable to take place because of the absence of light.
Microbial ecology
7084078
Photosynthetic reaction centre A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or transferred as excitation energy via light-harvesting antenna systems, give rise to electron transfer reactions along the path of a series of protein-bound co-factors. These co-factors are light-absorbing molecules (also named chromophores or pigments) such as chlorophyll and phaeophytin, as well as quinones. The energy of the photon is used to excite an electron of a pigment. The free energy created is then used to reduce
Photosynthetic reaction centre
16023376
than those necessary for achievement of Pmax. Terms not included in the above equation are: Data sets showing interspecific differences and population dynamics. The hyperbolic response between photosynthesis and irradiance, depicted by the PI curve, is important for assessing phytoplankton population dynamics, which influence many aspects of the marine environment. PI curve The PI (photosynthesis-irradiance) curve is a graphical representation of the empirical relationship between solar irradiance and photosynthesis. A derivation of the Michaelis–Menten curve, it shows the generally positive correlation between light intensity and photosynthetic rate. Plotted along the "x"-axis is the independent variable, light intensity (irradiance), while the
PI curve
12366452
axis: as investment increases, so too does the photosynthesis of the trap, as the leaf receives a better supply of nitrogen and phosphorus. Eventually another factor (such as light intensity or carbon dioxide concentration) will become more limiting to photosynthesis than nitrogen or phosphorus supply. As a result, increasing the investment will not make the plant grow better. The net uptake of carbon dioxide, and therefore, the plant's potential for growth, must be positive for the plant to survive. There is a broad span of investment where this is the case, and there is also a non-zero optimum. Plants investing
Carnivorous plant
78050
radical polymerization, chain reactions and rearrangement reactions. Many important processes involve photochemistry. The premier example is photosynthesis, in which most plants use solar energy to convert carbon dioxide and water into glucose, disposing of oxygen as a side-product. Humans rely on photochemistry for the formation of vitamin D, and vision is initiated by a photochemical reaction of rhodopsin. In fireflies, an enzyme in the abdomen catalyzes a reaction that results in bioluminescence. Many significant photochemical reactions, such as ozone formation, occur in the Earth atmosphere and constitute atmospheric chemistry. In catalysis, the reaction does not proceed directly, but through reaction
Chemical reaction
19148236
conditions. On the other hand, during Hill's observation of chloroplasts placed under dark conditions and in the absence of CO the artificial electron acceptor was oxidized but not reduced, terminating the process, with the result that there was also no production of oxygen and sugar. This observation allowed Hill to conclude that oxygen is released during the light-dependent steps (Hill reaction) of photosynthesis. Further studies of the Hill reaction were made in 1957 by the American plant physiologist Daniel I. Arnon. "Arnon" studied the Hill reaction using a natural electron acceptor, NADP. This natural electron acceptor inhibits the formation of
Hill reaction
16529160
in the molecular organization, which results in molecular volume changes. Most prominent examples for these two kinds of mechanisms are in photosynthesis The first mechanism above is mostly conspicuous in a photosynthesizing plant leaf. There, the light induced oxygen evolution causes pressure changes in the air phase, resulting in a photoacoustic signal, which is comparable in magnitude to that caused by the photothermal mechanism. This mechanism was tentatively named "photobaric". The second mechanism shows up in photosynthetically active sub-cell complexes in suspension (e.g. photosynthetic reaction centers). There, the electric field which is formed in the reaction center, following the light
Photoacoustic effect
17557109
Cycle is not related to photorespiration, as it comprises different reactions and results in no net oxygen consumption. Mehler reaction The Mehler reaction is named after Alan H. Mehler, who, in 1951, presented data to the effect that isolated chloroplasts reduce oxygen to form hydrogen peroxide (). Mehler observed that the formed in this way does not present an active intermediate in photosynthesis; rather, as a reactive oxygen species, it can be toxic to surrounding biological processes as an oxidizing agent. In scientific literature, the Mehler reaction often is used interchangeably with the Water-Water Cycle to refer to the formation
Mehler reaction
19148235
this haem group undergoes redox reactions: Fe + e → Fe Fe + e ← Fe Robin Hill (1937) studied the redox reactions in photosynthesis using "artificial" electron acceptors. He studied the reaction with the absence of CO by placing isolated active chloroplasts under light and dark conditions. During his observations of isolated chloroplasts placed under light conditions but with the absence of CO, the artificial electron acceptors were reduced and then oxidized, completing the cycle and allowing the process to proceed. Oxygen (O) was released as a byproduct, but there was no production of a sugar (CHO) under those
Hill reaction
13691849
recognized it was sunlight falling on plants that was required, although Joseph Priestley had noted the production of oxygen without the association with light in 1772. Cornelis Van Niel proposed in 1931 that photosynthesis is a case of general mechanism where a photon of light is used to photo decompose a hydrogen donor and the hydrogen being used to reduce . Then in 1939, Robin Hill showed that isolated chloroplasts would make oxygen, but not fix showing the light and dark reactions occurred in different places. Although they are referred to as light and dark reactions, both of them take
Light-dependent reactions
16023370
PI curve The PI (photosynthesis-irradiance) curve is a graphical representation of the empirical relationship between solar irradiance and photosynthesis. A derivation of the Michaelis–Menten curve, it shows the generally positive correlation between light intensity and photosynthetic rate. Plotted along the "x"-axis is the independent variable, light intensity (irradiance), while the "y"-axis is reserved for the dependent variable, photosynthetic rate. The PI curve can be applied to terrestrial and marine reactions but is most commonly used to explain ocean-dwelling phytoplankton’s photosynthetic response to changes in light intensity. Using this tool to approximate biological productivity is important because phytoplankton contribute ~50% of
PI curve
18997660
energy capable of performing a desired reaction remains the basis of application-based photocatalysis, most notably artificial photosynthesis (production of solar fuels). After several decades of experiments centered around the reduction of carbon dioxide, interest began to spread to other light-induced reactions involving naturally occurring materials. These experiments usually focused on reactions analogous to known biological processes, such as soil nitrification, for which the photochemical counterpart "photonitrification" was first reported in 1930. Photogeochemical reactions may be classified based on thermodynamics and/or the nature of the materials involved. In addition, when ambiguity exists regarding an analogous reaction involving light and living organisms
Photogeochemistry
1722766
PS I for photosynthesis. Thousands of bacteriochlorophyll(BCHl) c, d and e of the cells absorb light at 720-750 nm, and the light energy is transferred to BChl a-795 and a-808 before being transferred to Fenna-Matthews-Olson (FMO)-proteins which are connected to reaction centers (RC). The FMO complex then transfers the excitation energy to the RC with its special pair which absorbs at 840 nm in the plasma membrane. After the reaction centers receive the energy, electrons are ejected and transferred through electron transport chains (ETCs). Some electrons form Fe-S proteins in electron transport chains are accepted by ferredoxins (Fd) which can
Green sulfur bacteria
7084102
electron from plastocyanin. Thus the overall reaction catalysed by photosystem I is: formula_2 The cooperation between photosystems I and II creates an electron flow from HO to NADP. This pathway is called the 'Z-scheme' because the redox diagram from P680 to P700 resembles the letter z. Photosynthetic reaction centre A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or transferred as excitation energy via light-harvesting antenna systems, give rise to electron transfer reactions along the path of a
Photosynthetic reaction centre
3258037
photosynthesis for nitrogen fixation by carrying out the Mehler reaction, during which the oxygen produced by PSII is reduced again after PSI. This regulation of photosynthesis for nitrogen fixation involves rapidly reversible coupling of their light-harvesting antenna, the phycobilisomes, with PSI and PSII. "Trichodesmium" is found in oligotrophic waters, often when waters are calm and the mixed layer depth is shallow (around 100 m). "Trichodesmium" is found primarily in water between 20 and 34 °C and is frequently encountered in tropical and sub-tropical oceans in western boundary currents. Its presence is more pronounced in nitrogen poor water and can easily
Trichodesmium
331522
plant. In 1778, Jan Ingenhousz, repeated Priestley's experiments. He discovered that it was the influence of sunlight on the plant that could cause it to revive a mouse in a matter of hours. In 1796, Jean Senebier, a Swiss pastor, botanist, and naturalist, demonstrated that green plants consume carbon dioxide and release oxygen under the influence of light. Soon afterward, Nicolas-Théodore de Saussure showed that the increase in mass of the plant as it grows could not be due only to uptake of CO but also to the incorporation of water. Thus, the basic reaction by which photosynthesis is used
Photosynthesis
5568237
phycobilin is influenced by its protein environment. Each phycobiliprotein has a specific absorption and fluorescence emission maximum in the visible range of light. Therefore, their presence and the particular arrangement within the phycobilisomes allow absorption and unidirectional transfer of light energy to chlorophyll "a" of the photosystem II. In this way, the cells take advantage of the available wavelengths of light (in the 500-650 nm range), which are inaccessible to chlorophyll, and utilize their energy for photosynthesis. This is particularly advantageous deeper in the water column, where light with longer wavelengths is less transmitted and therefore less available directly to
Phycobilisome
6449473
widely used in the detergent industry as a raw material. Under particular circumstances (40–80 °C) only chlorination of alkane may take place. Reed reaction The Reed reaction is a chemical reaction that utilizes light to oxidize hydrocarbons to sulfonyl chlorides. The reaction performs via the free radicals. First, the light initiates homolysis of a molecule of chlorine. Then a chlorine atom produced attacks the hydrocarbon chain to form hydrogen chloride and an alkyl free radical. Then SO as an electron donor attacks the alkyl radical forming an sulfonyl radical. Finally, the least one attacks another chlorine molecule to produce a
Reed reaction