query: when do the light reactions of photosynthesis occur

pos: Light-dependent reactions the green color of leaves. The light-dependent reactions begin in photosystem II. When a chlorophyll "a" molecule within the reaction center of PSII absorbs a photon, an electron in this molecule attains a higher energy level. Because this state of an electron is very unstable, the electron is transferred from one to another molecule creating a chain of redox reactions, called an electron transport chain (ETC). The electron flow goes from PSII to cytochrome b6f to PSI. In PSI, the electron gets the energy from another photon. The final electron acceptor is NADP. In oxygenic photosynthesis, the first electron donor

pos: Light-dependent reactions the green color of leaves. The light-dependent reactions begin in photosystem II. When a chlorophyll "a" molecule within the reaction center of PSII absorbs a photon, an electron in this molecule attains a higher energy level. Because this state of an electron is very unstable, the electron is transferred from one to another molecule creating a chain of redox reactions, called an electron transport chain (ETC). The electron flow goes from PSII to cytochrome b6f to PSI. In PSI, the electron gets the energy from another photon. The final electron acceptor is NADP. In oxygenic photosynthesis, the first electron donor

neg: Light-independent reactions 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

neg: Light-independent reactions 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

neg: Light-dependent reactions up two protons to become plastoquinol. Plastoquinol is then released into the membrane as a mobile electron carrier. This is the second core process in photosynthesis. The initial stages occur within "picoseconds", with an efficiency of 100%. The seemingly impossible efficiency is due to the precise positioning of molecules within the reaction center. This is a solid-state process, not a chemical reaction. It occurs within an essentially crystalline environment created by the macromolecular structure of PS II. The usual rules of chemistry (which involve random collisions and random energy distributions) do not apply in solid-state environments. When the chlorophyll passes

neg: Photosynthesis 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

neg: Chloroplast sheath cells are specialized for each stage of photosynthesis. In mesophyll cells, chloroplasts are specialized for the light reactions, so they lack RuBisCO, and have normal grana and thylakoids, which they use to make ATP and NADPH, as well as oxygen. They store in a four-carbon compound, which is why the process is called " photosynthesis". The four-carbon compound is then transported to the bundle sheath chloroplasts, where it drops off and returns to the mesophyll. Bundle sheath chloroplasts do not carry out the light reactions, preventing oxygen from building up in them and disrupting RuBisCO activity. Because of this,

neg: Photosystem II Photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem, enzymes capture photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol. The energized electrons are replaced by oxidizing water to form hydrogen ions and molecular oxygen. By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated

neg: Photosynthesis 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

neg: Photoinhibition reactions. Some researchers prefer to define the term “photoinhibition” so that it contains all reactions that lower the quantum yield of photosynthesis when a plant is exposed to light. In this case, the term "dynamic photoinhibition" comprises phenomena that reversibly down-regulate photosynthesis in the light and the term "photodamage" or "irreversible photoinhibition" covers the concept of photoinhibition used by other researchers. The main mechanism of dynamic photoinhibition is non-photochemical quenching of excitation energy absorbed by PSII. Dynamic photoinhibition is acclimation to strong light rather than light-induced damage, and therefore "dynamic photoinhibition" may actually protect the plant against "photoinhibition". Photoinhibition may

neg: Fractionation of carbon isotopes in oxygenic photosynthesis 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

neg: Chlorophyll a chemical energy but is not the only pigment that can be used for photosynthesis. All oxygenic photosynthetic organisms use chlorophyll "a", but differ in accessory pigments like chlorophylls "b". Chlorophyll "z" can also be found in very small quantities in the green sulfur bacteria, an anaerobic photoautotroph. These organisms use bacteriochlorophyll and some chlorophyll "a" but do not produce oxygen. Anoxygenic photosynthesis is the term applied to this process, unlike oxygenic photosynthesis where oxygen is produced during the light reactions of photosynthesis. The molecular structure of chlorophyll "a" consists of a chlorin ring, whose four nitrogen atoms surround a central

neg: Hill reaction 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

neg: Grow light lumens. Therefore, when it comes to measuring the amount of light available to plants for photosynthesis, biologists often measure the amount of photosynthetically active radiation (PAR) received by a plant. PAR designates the spectral range of solar radiation from 400 to 700 nanometers, which generally corresponds to the spectral range that photosynthetic organisms are able to use in the process of photosynthesis. The irradiance of PAR can be expressed in units of energy flux (W/m), which is relevant in energy-balance considerations for photosynthetic organisms. However, photosynthesis is a quantum process and the chemical reactions of photosynthesis are more dependent on

neg: Chloroplast 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

neg: Glyceraldehyde 3-phosphate pathways. Furthermore, it is a participant in and a product of the pentose phosphate pathway. During plant photosynthesis, 2 equivalents of glycerate 3-phosphate (GP; also known as 3-phosphoglycerate) are produced by the first step of the light-independent reactions when ribulose 1,5-bisphosphate (RuBP) and carbon dioxide are catalysed by the rubisco enzyme. The GP is converted to D-glyceraldehyde 3-phosphate (G3P) using the energy in ATP and the reducing power of NADPH as part of the Calvin cycle. This returns ADP, phosphate ions Pi, and NADP+ to the light-dependent reactions of photosynthesis for their continued function. RuBP is regenerated for the Calvin

neg: Photosynthesis 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

neg: Light curve (botany) 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

neg: Stroma (fluid) 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

neg: Photosynthesis 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,

neg: Chloroplast 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

neg: Light-dependent reactions 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

neg: Light-dependent reactions 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

neg: Photosynthesis light, oxidize cytochrome f, chlorophyll a (and other pigments) will absorb another light, but will reduce this same oxidized cytochrome, stating the two light reactions are in series. In 1893, Charles Reid Barnes proposed two terms, "photosyntax" and "photosynthesis", for the biological process of "synthesis of complex carbon compounds out of carbonic acid, in the presence of chlorophyll, under the influence of light". Over time, the term "photosynthesis" came into common usage as the term of choice. Later discovery of anoxygenic photosynthetic bacteria and photophosphorylation necessitated redefinition of the term. After WWII at late 1940 at the University of California,

neg: Oxygen evolution 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

neg: Photosynthesis that leads to the ultimate reduction of NADP to NADPH. In addition, this creates a proton gradient (energy gradient) across the chloroplast membrane, which is used by ATP synthase in the synthesis of ATP. The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis, which releases a dioxygen (O) molecule as a waste product. The overall equation for the light-dependent reactions under the conditions of non-cyclic electron flow in green plants is: Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory

neg: Photogeochemistry 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

neg: Photosynthesis 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

neg: Fractionation of carbon isotopes in oxygenic photosynthesis + 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

neg: Fractionation of carbon isotopes in oxygenic photosynthesis Calvin cycle during the day, when stomata are closed to prevent water loss, and the light reactions can drive the necessary ATP and NADPH production. This pathway differs from C4 photosynthesis because CAM plants separate carbon by storing fixed CO in vesicles at night, then transporting it for use during the day. Thus, CAM plants temporally concentrate CO to improve Rubsico efficiency, whereas C4 plants spatially concentrate CO in bundle sheath cells. The distribution of plants which use CAM photosynthesis includes epiphytes (e.g., orchids, bromeliads) and xerophytes (e.g., succulents, cacti). In Crassulacean acid metabolism, isotopic fractionation combines the effects of

neg: Dioxygen in biological reactions Dioxygen in biological reactions Dioxygen () plays an important role in the energy metabolism of living organisms. Free oxygen is produced in the biosphere through photolysis (light-driven oxidation and splitting) of water during photosynthesis in cyanobacteria, green algae, and plants. During oxidative phosphorylation in cellular respiration, oxygen is reduced to water, thus closing the biological water-oxygen redox cycle. In nature, free oxygen is produced by the light-driven splitting of water during oxygenic photosynthesis. Green algae and cyanobacteria in marine environments provide about 70% of the free oxygen produced on earth. The remainder is produced by terrestrial plants, although for example,

neg: KaiB of the Kai oscillator can be shifted in response to environmental changes. However, unlike phase-shifting mechanisms characterized in eukaryotic organisms, photopigments do not appear to play a role in entrainment of the cyanobacterial clock. Instead, identified input mechanisms rely on biochemical changes that track photosynthetic reactions performed by the cyanobacterium, reactions that exhibit rate increases proportional to ambient light intensity. CikA and LdpA, for example, sense the redox state of the intracellular environment and relay changes to the Kai oscillator. In addition, KaiA and KaiC appear to directly detect metabolites of photosynthesis – specifically quinone and ATP – and adjust

neg: Light-dependent reactions 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

neg: Soil fertility may occur under anaerobic conditions (flooding) in the presence of denitrifying bacteria. Nutrient cations, including potassium and many micronutrients, are held in relatively strong bonds with the negatively charged portions of the soil in a process known as cation exchange. In 2008 the cost of phosphorus as fertilizer more than doubled, while the price of rock phosphate as base commodity rose eight-fold. Recently the term peak phosphorus has been coined, due to the limited occurrence of rock phosphate in the world. Photosynthesis is the process whereby plants use light energy to drive chemical reactions which convert CO into sugars. As

neg: Butanol fuel this process and electricity is used as the energetic component. The process they developed effectively separates the light and dark reactions that occur during photosynthesis. Solar panels are used to convert sunlight to electrical energy which is then converted using the microorganism to a chemical intermediate. The team is now in the process of scaling up the operation and believes this process will be more efficient than the biologic process. In late 2012, a new discovery made the alternative fuel butanol more attractive to the biofuel industry. Scientist Hao Feng found a method that could significantly reduce the cost of

neg: Photosynthesis 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

neg: Photoassimilate particles - namely viroids - to accomplish long ranged movement and consequently infection of an entire plant. Photoassimilate In botany, a photoassimilate is one of a number of biological compounds formed by assimilation using light-dependent reactions. This term is most commonly used to refer to the energy-storing monosaccharides produced by photosynthesis in the leaves of plants. Only NADPH, ATP and water are made in the "light" reactions. Monosaccharides, though generally more complex sugars, are made in the "dark" reactions.The term "light" reaction can be confusing as some "dark" reactions require light to be active. Photoassimilate movement through plants from "source

neg: Photoassimilate Photoassimilate In botany, a photoassimilate is one of a number of biological compounds formed by assimilation using light-dependent reactions. This term is most commonly used to refer to the energy-storing monosaccharides produced by photosynthesis in the leaves of plants. Only NADPH, ATP and water are made in the "light" reactions. Monosaccharides, though generally more complex sugars, are made in the "dark" reactions.The term "light" reaction can be confusing as some "dark" reactions require light to be active. Photoassimilate movement through plants from "source to sink" using xylem and phloem is of biological significance. This movement is mimicked by many infectious

neg: Chloroplast big problem, since O is produced by the initial light reactions of photosynthesis, causing issues down the line in the Calvin cycle which uses RuBisCO. plants evolved a way to solve this—by spatially separating the light reactions and the Calvin cycle. The light reactions, which store light energy in ATP and NADPH, are done in the mesophyll cells of a leaf. The Calvin cycle, which uses the stored energy to make sugar using RuBisCO, is done in the bundle sheath cells, a layer of cells surrounding a vein in a leaf. As a result, chloroplasts in mesophyll cells and bundle

neg: Light-dependent reactions 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

neg: Ecology is the primary input of energy into the planet's ecosystems. Light is composed of electromagnetic energy of different wavelengths. Radiant energy from the sun generates heat, provides photons of light measured as active energy in the chemical reactions of life, and also acts as a catalyst for genetic mutation. Plants, algae, and some bacteria absorb light and assimilate the energy through photosynthesis. Organisms capable of assimilating energy by photosynthesis or through inorganic fixation of HS are autotrophs. Autotrophs — responsible for primary production — assimilate light energy which becomes metabolically stored as potential energy in the form of biochemical enthalpic

neg: Plant perception (physiology) auxin redistribution occurs in a way to produce differential growth away from gravity. For perception to happen, the plant must sense, perceive and translate the direction of gravity. Without gravity, proper orientation will not occur and the plant will not effectively grow. The root will not be able to uptake nutrients or water, and the shoot will not grow towards the sky to maximize photosynthesis. Plants do not have a brain or neuronal network, but reactions within signalling pathways may provide a biochemical basis for learning and memory in addition to computation and problem solving. Controversially, the brain is used

neg: Etiolation cell to expand. Chloroplasts that have not been exposed to light are called etioplasts (see also plastids). De-etiolation, is a series of physiological and biochemical changes a plant shoot undergoes when emerging from the ground or in response to light after a period of insufficient light exposure. This process is known informally as greening. These changes that are triggered in the plants shoots or already formed leaves and stems occur in preparation for photosynthesis. Some of the changes that occur include: This process is regulated by the exposure of various photoreceptor pigments to light. Phytochrome A and phytochrome B both

neg: Plastoquinone the cell membrane. One example of how it does this is by reacting with superoxides to form hydrogen peroxide and plastosemiquinone. The prefix "plasto-" means either plastid or chloroplast, alluding to its location within the cell. The role that plastoquinone plays in photosynthesis, more specifically in the light-dependent reactions of photosynthesis, is that of a mobile electron carrier through the membrane of the thylakoid. Plastoquinone is reduced when it accepts two electrons from photosystem II and two hydrogen cations (H) from the stroma of the chloroplast, thereby forming plastoquinol (PQH). It transfers the electrons further down the electron transport chain

neg: Light curve (botany) 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 RuBisCo and the availability of carbon dioxide. The point on the curve where these two differing slopes meet is called the light saturation point and is where the light-dependent reactions are producing more

neg: Chemical reaction and many others. The biochemical reactions that occur in living organisms are collectively known as metabolism. Among the most important of its mechanisms is the anabolism, in which different DNA and enzyme-controlled processes result in the production of large molecules such as proteins and carbohydrates from smaller units. Bioenergetics studies the sources of energy for such reactions. An important energy source is glucose, which can be produced by plants via photosynthesis or assimilated from food. All organisms use this energy to produce adenosine triphosphate (ATP), which can then be used to energize other reactions. Chemical reactions are central to chemical

neg: Limnology 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,

neg: Thylakoid 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

neg: MELiSSA can be used by crewmembers can be achieved by two means: physiochemically or biologically. Physiochemical processes such as the Sabatier reaction would result in high efficiencies however a large amount of energy is required in terms of temperature and pressure. Whereas biologically, using photosynthesis, efficiencies are lower, however ambient temperatures and pressures can be used. Photosynthesis is the process whereby plants convert light energy into chemical energy of sugars and other organic compounds. The chemical reactions utilise carbon and water with the by-product of oxygen, released into the atmosphere. MELiSSA is partly based on these photosynthetic reactions: recycling carbon dioxide

neg: Photosynthesis light reactions reduces photorespiration and increases fixation and, thus, the photosynthetic capacity of the leaf. plants can produce more sugar than plants in conditions of high light and temperature. Many important crop plants are plants, including maize, sorghum, sugarcane, and millet. Plants that do not use PEP-carboxylase in carbon fixation are called C plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle. Over 90% of plants use carbon fixation, compared to 3% that use carbon fixation; however, the evolution of in over 60 plant lineages makes it a striking example

neg: Thermodynamic free energy force’ for chemical change. Why do chemical reactions occur, and why do they stop at certain points? Chemists called the ‘force’ that caused chemical reactions affinity, but it lacked a clear definition." During the entire 18th century, the dominant view with regard to heat and light was that put forth by Isaac Newton, called the "Newtonian hypothesis", which states that light and heat are forms of matter attracted or repelled by other forms of matter, with forces analogous to gravitation or to chemical affinity. In the 19th century, the French chemist Marcellin Berthelot and the Danish chemist Julius Thomsen had

neg: Light-independent reactions 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

neg: Photosynthesis 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

neg: Artificial photosynthesis 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

neg: Electromagnetic radiation to damaging levels. However, in plant tissues that conduct photosynthesis, carotenoids act to quench electronically excited chlorophyll produced by visible light in a process called non-photochemical quenching, in order to prevent reactions that would otherwise interfere with photosynthesis at high light levels. Limited evidence indicate that some reactive oxygen species are created by visible light in skin, and that these may have some role in photoaging, in the same manner as ultraviolet A. As frequency increases into the ultraviolet, photons now carry enough energy (about three electron volts or more) to excite certain doubly bonded molecules into permanent chemical rearrangement.

neg: Photosynthesis the newly formed NADPH and releases three-carbon sugars, which are later combined to form sucrose and starch. The overall equation for the light-independent reactions in green plants is Carbon fixation produces the intermediate three-carbon sugar product, which is then converted into the final carbohydrate products. The simple carbon sugars produced by photosynthesis are then used in the forming of other organic compounds, such as the building material cellulose, the precursors for lipid and amino acid biosynthesis, or as a fuel in cellular respiration. The latter occurs not only in plants but also in animals when the energy from plants is

neg: Stroma (fluid) 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,

neg: Photosynthesis thus "recycled" often condense to form hexose phosphates, which ultimately yield sucrose, starch and cellulose. The sugars produced during carbon metabolism yield carbon skeletons that can be used for other metabolic reactions like the production of amino acids and lipids. In hot and dry conditions, plants close their stomata to prevent water loss. Under these conditions, will decrease and oxygen gas, produced by the light reactions of photosynthesis, will increase, causing an increase of photorespiration by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and decrease in carbon fixation. Some plants have evolved mechanisms to increase the concentration in the leaves under

neg: Fractionation of carbon isotopes in oxygenic photosynthesis characterization of food chains. Oxygenic photosynthesis is a metabolic pathway facilitated by autotrophs, including plants, algae, and cyanobacteria. This pathway converts inorganic carbon dioxide from the atmosphere or aquatic environment into carbohydrates, using water and energy from light, then releases molecular oxygen as a product. Organic carbon contains less of the stable isotope Carbon-13, or C, relative to the initial inorganic carbon from the atmosphere or water because photosynthetic carbon fixation involves several fractionating reactions with kinetic isotope effects. These reactions undergo a kinetic isotope effect because they are limited by overcoming an activation energy barrier. The lighter isotope has

neg: Principle of maximum work to at least the time of Albertus Magnus in 1250. According to Nobelist and chemical engineering professor Ilya Prigogine: “as motion was explained by the Newtonian concept of force, chemists wanted a similar concept of ‘driving force’ for chemical change? Why do chemical reactions occur, and why do they stop at certain points? Chemists called the ‘force’ that caused chemical reactions affinity, but it lacked a clear definition. During the entire 18th century, the dominant view in regard to heat and light was that put forward by Isaac Newton, called the “Newtonian hypothesis”, which stated that light and heat are

neg: Photoinhibition cause coral bleaching. Photoinhibition Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term as light-induced damage to PSII. In living organisms, photoinhibited PSII centres are continuously repaired via degradation and synthesis of the D1 protein of the photosynthetic reaction center of PSII. Photoinhibition is also used in a wider sense, as dynamic photoinhibition, to describe all reactions that decrease the efficiency of photosynthesis when plants are exposed to light. The first measurements of photoinhibition

neg: Photoinhibition Photoinhibition Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term as light-induced damage to PSII. In living organisms, photoinhibited PSII centres are continuously repaired via degradation and synthesis of the D1 protein of the photosynthetic reaction center of PSII. Photoinhibition is also used in a wider sense, as dynamic photoinhibition, to describe all reactions that decrease the efficiency of photosynthesis when plants are exposed to light. The first measurements of photoinhibition were published in

neg: Annihilation quark flavors.) Antiprotons can and do annihilate with neutrons, and likewise antineutrons can annihilate with protons, as discussed below. Reactions in which proton-antiproton annihilation produces as many as nine mesons have been observed, while production of thirteen mesons is theoretically possible. The generated mesons leave the site of the annihilation at moderate fractions of the speed of light, and decay with whatever lifetime is appropriate for their type of meson. Similar reactions will occur when an antinucleon annihilates within a more complex atomic nucleus, save that the resulting mesons, being strongly interacting, have a significant probability of being absorbed by

neg: PI curve 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

neg: Photodissociation Photodissociation Photodissociation, photolysis, or photodecomposition is a chemical reaction in which a chemical compound is broken down by photons. It is defined as the interaction of one or more photons with one target molecule. Photodissociation is not limited to visible light. Any photon with sufficient energy can affect the chemical bonds of a chemical compound. Since a photon's energy is inversely proportional to its wavelength, electromagnetic waves with the energy of visible light or higher, such as ultraviolet light, x-rays and gamma rays are usually involved in such reactions. Photolysis is part of the light-dependent reactions of photosynthesis. The general

neg: Elysia chlorotica further study on several similar species showed these sea slugs do just as well when they are deprived of light. Sven Gould from Heinrich-Heine University in Düsseldorf and his colleagues showed that even when photosynthesis was blocked, the slugs could survive without food for a long time, and seemed to fare just as well as food-deprived slugs exposed to light. They starved six specimens of "P. ocellatus" for 55 days, keeping two in the dark, treating two with chemicals that inhibited photosynthesis, and providing two with appropriate light. All survived and all lost weight at about the same rate. The

neg: Chemical reaction 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

neg: Photosynthesis water, and the availability of suitable temperatures for carrying out photosynthesis. The process of photosynthesis provides the main input of free energy into the biosphere, and is one of four main ways in which radiation is important for plant life. The radiation climate within plant communities is extremely variable, with both time and space. In the early 20th century, Frederick Blackman and Gabrielle Matthaei investigated the effects of light intensity (irradiance) and temperature on the rate of carbon assimilation. These two experiments illustrate several important points: First, it is known that, in general, photochemical reactions are not affected by temperature.

neg: Photochemistry Photochemistry Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible light (400–750 nm) or infrared radiation (750–2500 nm). In nature, photochemistry is of immense importance as it is the basis of photosynthesis, vision, and the formation of vitamin D with sunlight. Photochemical reactions proceed differently than temperature-driven reactions. Photochemical paths access high energy intermediates that cannot be generated thermally, thereby overcoming large activation barriers in a short period of time, and allowing reactions otherwise

neg: Dephosphorylation psilocybin's effect on the change in free energy is currently available. The first protein complex of the photosynthesis component light-dependent reactions is referred to as photosystem II. The complex utilizes an enzyme to capture photons of light, providing the greater photosynthesis process with all of the electrons needed to produce ATP. Photosystem II is particularly temperature sensitive, and desphosphorylation has been implicated as a driver of plasticity in responding to varied temperature. Accelerated protein dephosphorylation in photosynthetic thylakoid membranes occurs at elevated temperatures, directly impacting the desphosphorylation of key proteins within the photosystem II complex. Excessive dephosphorylation of the membrane

neg: Dioxygen in biological reactions 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

neg: Light-dependent reactions removed from an excited chlorophyll molecule and used to reduce NAD to NADH. The electrons removed from P840 must be replaced. This is accomplished by removing electrons from , which is oxidized to sulfur (hence the name "green "sulfur" bacteria"). Purple bacteria and green sulfur bacteria occupy relatively minor ecological niches in the present day biosphere. They are of interest because of their importance in precambrian ecologies, and because their methods of photosynthesis were the likely evolutionary precursors of those in modern plants. The first ideas about light being used in photosynthesis were proposed by Colin Flannery in 1779 who

neg: Plant secondary metabolism to photosynthesis. They do this by transferring some of the light energy they absorb to chlorophylls, which then uses this energy for photosynthesis. Second, they can protect plants which are over-exposed to sunlight. They do this by harmlessly dissipating excess light energy which they absorb as heat. In the absence of carotenoids, this excess light energy could destroy proteins, membranes, and other molecules. Some plant physiologists believe that carotenoids may have an additional function as regulators of certain developmental responses in plants. Tetraterpenes are synthesized from DOXP precursors in plants and some bacteria. Carotenoids involved in photosynthesis are formed in

neg: Thylakoid with known functions, 42% are involved in photosynthesis. The next largest functional groups include proteins involved in protein targeting, processing and folding with 11%, oxidative stress response (9%) and translation (8%). Thylakoid membranes contain integral membrane proteins which play an important role in light harvesting and the light-dependent reactions of photosynthesis. There are four major protein complexes in the thylakoid membrane: Photosystem II is located mostly in the grana thylakoids, whereas photosystem I and ATP synthase are mostly located in the stroma thylakoids and the outer layers of grana. The cytochrome b6f complex is distributed evenly throughout thylakoid membranes. Due

neg: High-nutrient, low-chlorophyll regions production is the process by which autotrophs use light to convert carbon from aqueous carbon dioxide to sugar for cellular growth. Light catalyzes the photosynthetic process and nutrients are incorporated into organic material. For photosynthesis to occur, macronutrients such as nitrate and phosphate must be available in sufficient ratios and bioavailable forms for biological utilization. The molecular ratio of 106(Carbon):16(Nitrogen):1(Phosphorus) was discovered by Redfield, Ketcham, and Richards (RKR) and is known as the Redfield Ratio. Photosynthesis (forward) and respiration (reverse) is represented by the equation: Photosynthesis can be limited by deficiencies of certain macronutrients. However, in the North Pacific, the

neg: Photosynthetic efficiency The Gibbs free energy for converting a mole of CO to glucose is 114 kcal, whereas eight moles of photons of wavelength 600 nm contains 381 kcal, giving a nominal efficiency of 30%. However, photosynthesis can occur with light up to wavelength 720 nm so long as there is also light at wavelengths below 680 nm to keep Photosystem II operating (see Chlorophyll). Using longer wavelengths means less light energy is needed for the same number of photons and therefore for the same amount of photosynthesis. For actual sunlight, where only 45% of the light is in the photosynthetically active

neg: Photosynthetically active radiation metrics such as luminous flux and illuminance is that these measures are based on human perception of brightness, which is strongly green biased and does not accurately describe the quantity of light usable for photosynthesis. The irradiance of PAR can be measured in energy units (W/m), which is relevant in energy-balance considerations for photosynthetic organisms. However, photosynthesis is a quantum process and the chemical reactions of photosynthesis are more dependent on the number of photons than the energy contained in the photons. Therefore, plant biologists often quantify PAR using the number of photons in the 400-700 nm range received by

neg: DCMU effect on photosystem I or other reactions in photosynthesis, such as light absorption or carbon fixation in the Calvin cycle. However, because it absorbs electrons oxidized from water in PS II, the electron "hole" of PS I cannot be satisfied, effectively shutting down "linear" photosynthesis by blocking the reduction of NADP to NADPH. At the same time, it was found that DCMU not only does not inhibit the cyclic photosynthetic pathway, but, under certain circumstances, actually stimulates it. Because of these effects, DCMU is often used to study energy flow in photosynthesis. DCMU DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is an algicide and herbicide

neg: Photosystem II interchange of water molecules in S-states. The arrangement of hydrogen bonding is main criteria of the diagrams. The effect of photon(hv), emission of electron(e) and production of hydrogen ion(H+) from water molecules can be shown by the diagrams in a more specific way of experimental detection. The diagrams almost completely analyze the pathway of water-splitting in photosynthesis. Photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem, enzymes capture photons of light to energize electrons that

neg: Autotroph Autotroph An autotroph or producer, is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings, generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). They are the producers in a food chain, such as plants on land or algae in water (in contrast to heterotrophs as consumers of autotrophs). They do not need a living source of energy or organic carbon. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and also create a store of chemical energy. Most autotrophs use water as the reducing

neg: Light-dependent reactions can also synthesize ATP by oxidative phosphorylation, in the manner of other bacteria. The electron transport chain is where the mobile electron carriers are plastoquinone and cytochrome ', while the proton pumps are NADH dehydrogenase, ' and cytochrome ". Cyanobacteria are the only bacteria that produce oxygen during photosynthesis. Earth's primordial atmosphere was anoxic. Organisms like cyanobacteria produced our present-day oxygen-containing atmosphere. The other two major groups of photosynthetic bacteria, purple bacteria and green sulfur bacteria, contain only a single photosystem and do not produce oxygen. Purple bacteria contain a single photosystem that is structurally related to PS II in

neg: Autotroph such as animals, the carbohydrates, fats, and proteins contained in them become energy sources for the heterotrophs. Proteins can be made using nitrates, sulfates, and phosphates in the soil. Autotroph An autotroph or producer, is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings, generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). They are the producers in a food chain, such as plants on land or algae in water (in contrast to heterotrophs as consumers of autotrophs). They do not need a living source of energy

neg: Habitat in oxygen, and are dependent on chemical reactions other than photosynthesis. Boreholes drilled into the rocky seabed have found microbial communities apparently based on the products of reactions between water and the constituents of rocks. These communities have been little studied, but may be an important part of the global carbon cycle. Rock in mines two miles deep also harbour microbes; these live on minute traces of hydrogen produced in slow oxidizing reactions inside the rock. These metabolic reactions allow life to exist in places with no oxygen or light, an environment that had previously been thought to be devoid

neg: Emerson effect Emerson effect The Emerson effect is the increase in the rate of photosynthesis after chloroplasts are exposed to light of wavelength 680 nm (deep red spectrum) and more than 680 nm (far red spectrum). When simultaneously exposed to light of both wavelengths, the rate of photosynthesis is far higher than the sum of the red light and far red light photosynthesis rates. The effect was early evidence that two photosystems, processing different wavelengths, cooperate in photosynthesis. Robert Emerson described the eponymous effect in 1957. In his paper he observed that: When Emerson exposed green plants to differing wavelengths of light,

neg: Chloroplast the pyrenoids when CO is scarce. Pyrenoids can divide to form new pyrenoids, or be produced "de novo". Suspended within the chloroplast stroma is the thylakoid system, a highly dynamic collection of membranous sacks called thylakoids where chlorophyll is found and the light reactions of photosynthesis happen. In most vascular plant chloroplasts, the thylakoids are arranged in stacks called grana, though in certain plant chloroplasts and some algal chloroplasts, the thylakoids are free floating. Using a light microscope, it is just barely possible to see tiny green granules—which were named grana. With electron microscopy, it became possible to see the

neg: George Porter do research at the University of Cambridge supervised by Ronald George Wreyford Norrish where he began the work that ultimately led to them becoming Nobel Laureates. His original research in developing the technique of Flash photolysis to obtain information on short-lived molecular species provided the first evidence of free Radicals. His later research utilised the technique to study the minutiae of the Light-dependent reactions of Photosynthesis, with particular regard to possible applications to a Hydrogen economy, of which he was a strong advocate. He was Assistant Director of the British Rayon Research Association from 1953–4, where he studied the phototendering

neg: C4 carbon fixation C4 carbon fixation The naming "Hatch–Slack pathway" is in honor of Marshall Davidson Hatch and C. R. Slack, who elucidated it in Australia in 1966. The first experiments indicating that some plants do not use 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 P. Kortschak and Yuri Karpilov. The pathway was elucidated by Marshall Davidson Hatch and C. R. Slack, in Australia, in 1966; it is sometimes called the Hatch-Slack pathway. In plants, the first step in the light-independent reactions of photosynthesis involves

neg: Citrus production juice and disease tolerance, and it is taken up largely by the citrus fruit; too little K can lead to splitting and plugging of the fruit. Boron is involved in many enzymatic systems, when it is deficient, the tree suffers in fruit and leaf quality, and the tree loses apical dominance. Copper affects photosynthesis and fruit set. Deficiency causes drooping of shoots, "brown gum" eruptions, and death may occur from the tip. If copper based fungicides are used, this is not usually a problem. Acting as a catalyst for reactions, this element is a cofactor for many enzymes, important for

neg: Hill reaction 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

neg: Gibbs free energy entropy. Thus, a reaction with a positive Gibbs free energy will not proceed spontaneously. However, in biological systems (among others), energy inputs from other energy sources (including the Sun and exothermic chemical reactions) are "coupled" with reactions that are not entropically favored (i.e. have a Gibbs free energy above zero). Taking into account the coupled reactions, the total entropy in the universe increases. This coupling allows endergonic reactions, such as photosynthesis and DNA synthesis, to proceed without decreasing the total entropy of the universe. Thus biological systems do not violate the second law of thermodynamics. The standard Gibbs free energy

neg: Photochemistry 1834, 11 Photochemistry Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible light (400–750 nm) or infrared radiation (750–2500 nm). In nature, photochemistry is of immense importance as it is the basis of photosynthesis, vision, and the formation of vitamin D with sunlight. Photochemical reactions proceed differently than temperature-driven reactions. Photochemical paths access high energy intermediates that cannot be generated thermally, thereby overcoming large activation barriers in a short period of time, and allowing

neg: Malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+) site. However, the inhibitory effect exhibits pH-dependence – existent at a pH of 7 but not a pH of 8. The control of enzyme activity due to pH changes align with the hypothesis that NADP-ME is most active while photosynthesis is in progress: Active light reactions leads to a rise in basicity within the chloroplast stroma, the location of NADP-ME, leading to a diminished inhibitory effect of malate on NADP-ME and thereby promoting a more active state. Conversely, slowed light reactions leads to a rise in acidity within the stroma, promoting the inhibition of NADP-ME by malate. Because the high

neg: Photosynthetic reaction centre 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

neg: Photosynthesis 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

neg: Soil microbiology dependent on oxygen, and the higher the moisture content in the soil, the less oxygen is present for them. Algae can make their own nutrients through photosynthesis. Photosynthesis converts light energy to chemical energy that can be stored as nutrients. For algae to grow, they must be exposed to light because photosynthesis requires light, so algae are typically distributed evenly wherever sunlight and moderate moisture is available. Algae do not have to be directly exposed to the Sun, but can live below the soil surface given uniform temperature and moisture conditions. Algae are also capable of performing nitrogen fixation. Algae

neg: Chemosynthesis (nanotechnology) Chemosynthesis (nanotechnology) In molecular nanotechnology, chemosynthesis is any chemical synthesis where reactions occur due to random thermal motion, a class which encompasses almost all of modern synthetic chemistry. The human-authored processes of chemical engineering are accordingly represented as biomimicry of the natural phenomena above, and the entire class of non-photosynthetic chains by which complex molecules are constructed is described as chemo-. This form of engineering is then contrasted with mechanosynthesis, a hypothetical process where individual molecules are mechanically manipulated to control reactions to human specification. Since photosynthesis and other natural processes create extremely complex molecules to the specifications contained in

neg: Dynamic equilibrium of the elementary reactions by Dynamic equilibrium In chemistry, a dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state. In thermodynamics, a closed system is in thermodynamic equilibrium when reactions occur at such rates that the composition of the mixture does not change with time. Reactions do in fact occur, sometimes vigorously, but to such an extent that changes in composition cannot be observed. Equilibrium constants can

neg: Phototroph live in aquatic environments, and will, using light, oxidize chemical substances such as hydrogen sulfide rather than water. In an ecological context, phototrophs are often the food source for neighboring heterotrophic life. In terrestrial environments, plants are the predominant variety, while aquatic environments include a range of phototrophic organisms such as algae (e.g., kelp), other protists (such as euglena), phytoplankton, and bacteria (such as cyanobacteria). The depth to which sunlight or artificial light can penetrate into water, so that photosynthesis may occur, is known as the photic zone. Cyanobacteria, which are prokaryotic organisms which carry out oxygenic photosynthesis, occupy many

neg: Photophosphorylation intact "Chlorella" cells and interpreting his findings as light-dependent ATP formation. In 1954, Daniel I. Arnon et.al. discovered photophosphorylation "in vitro" in isolated chloroplasts with the help of P. His first review on the early research of photophosphorylation was published in 1956. Photophosphorylation In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Only two sources of energy are available to living organisms: sunlight and reduction-oxidation (redox) reactions. All organisms produce ATP, which is the universal energy currency of life. Commonly in photosynthesis this involves photolysis, or photodissociation, of water

neg: Halobacteriales and assisting in the production of energy from light. The process is unrelated to other forms of photosynthesis involving electron transport; however, and halobacteria are incapable of fixing carbon from carbon dioxide. Halobacteria can exist in salty environments because although they are aerobes they have a separate and different way of creating energy through photosynthesis. Parts of the membranes of halobacteria are purplish in color. These parts conduct photosynthetic reactions with retinal pigment rather than chlorophyll. This allows them to create a proton gradient across the membrane of the cell which can be used to create ATP for their own