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Photosynthesis
Photosynthesis
is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities (energy transformation). This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water – hence the name photosynthesis, from the Greek φῶς, phōs, "light", and σύνθεσις, synthesis, "putting together".[1][2][3] In most cases, oxygen is also released as a waste product. Most plants, most algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis
Photosynthesis
is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies all of the organic compounds and most of the energy necessary for life on Earth.[4] 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 of water is used in the creation of two further compounds that serve as short-term stores of energy, enabling its transfer to drive other reactions: these compounds are reduced nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP), the "energy currency" of cells. In plants, algae and cyanobacteria, long-term energy storage in the form of sugars is produced by a subsequent sequence of light-independent reactions called the Calvin cycle; some bacteria use different mechanisms, such as the reverse Krebs cycle, to achieve the same end. In the Calvin cycle, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, such as ribulose bisphosphate (RuBP).[5] Using the ATP and NADPH
NADPH
produced by the light-dependent reactions, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose. The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or hydrogen sulfide, rather than water, as sources of electrons.[6] Cyanobacteria
Cyanobacteria
appeared later; the excess oxygen they produced contributed directly to the oxygenation of the Earth,[7] which rendered the evolution of complex life possible. Today, the average rate of energy capture by photosynthesis globally is approximately 130 terawatts,[8][9][10] which is about three times the current power consumption of human civilization.[11] Photosynthetic organisms also convert around 100–115 thousand million metric tonnes of carbon into biomass per year.[12][13]

Contents

1 Overview 2 Photosynthetic membranes and organelles 3 Light-dependent reactions

3.1 Z scheme 3.2 Water
Water
photolysis

4 Light-independent reactions

4.1 Calvin cycle 4.2 Carbon concentrating mechanisms

4.2.1 On land 4.2.2 In water

5 Order and kinetics 6 Efficiency 7 Evolution

7.1 Symbiosis
Symbiosis
and the origin of chloroplasts 7.2 Cyanobacteria
Cyanobacteria
and the evolution of photosynthesis

8 Discovery

8.1 Development of the concept 8.2 C3 : C4 photosynthesis research

9 Factors

9.1 Light
Light
intensity (irradiance), wavelength and temperature 9.2 Carbon dioxide
Carbon dioxide
levels and photorespiration

10 See also 11 References 12 Further reading

12.1 Books 12.2 Papers

13 External links

Overview

Photosynthesis
Photosynthesis
changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.

Photosynthetic organisms are photoautotrophs, which means that they are able to synthesize food directly from carbon dioxide and water using energy from light. However, not all organisms that use light as a source of energy carry out photosynthesis; photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon.[4] In plants, algae, and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis and is by far the most common type of photosynthesis used by living organisms. Although there are some differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms. There are also many varieties of anoxygenic photosynthesis, used mostly by certain types of bacteria, which consume carbon dioxide but do not release oxygen. Carbon dioxide
Carbon dioxide
is converted into sugars in a process called carbon fixation; photosynthesis captures energy from sunlight to convert carbon dioxide into carbohydrate. Carbon fixation
Carbon fixation
is an endothermic redox reaction. In general outline, photosynthesis is the opposite of cellular respiration; in the latter, glucose and other compounds are oxidized to produce carbon dioxide and water, and to release chemical energy (an exothermic reaction) to drive the organism's metabolism. The two processes, reduction of carbon dioxide to carbohydrate and then later oxidation of the carbohydrate, are distinct: photosynthesis and cellular respiration take place through a different sequence of chemical reactions and in different cellular compartments. The general equation for photosynthesis as first proposed by Cornelius van Niel is therefore:[14]

CO2 + 2H2A + photons → [​CH2O​] + 2A + H2O carbon dioxide + electron donor + light energy → carbohydrate + oxidized electron donor + water

Since water is used as the electron donor in oxygenic photosynthesis, the equation for this process is:

CO2 + 2H2O + photons → [CH2O] + O2 + H2O carbon dioxide + water + light energy → carbohydrate + oxygen + water

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:

CO2 + H2O + photons → [CH2O] + O2 carbon dioxide + water + light energy → carbohydrate + oxygen

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:[15] The equation for this reaction is:

CO2 + (AsO3− 3) + photons → (AsO3− 4) + CO[16] carbon dioxide + arsenite + light energy → arsenate + carbon monoxide (used to build other compounds in subsequent reactions)

Photosynthesis
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, 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.[17] Some organisms employ even more radical variants of photosynthesis. Some archea 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 and does not release oxygen, and seems to have evolved separately from the more common types of photosynthesis.[18][19] Photosynthetic membranes and organelles

Chloroplast
Chloroplast
ultrastructure: 1. outer membrane 2. intermembrane space 3. inner membrane (1+2+3: envelope) 4. stroma (aqueous fluid) 5. thylakoid lumen (inside of thylakoid) 6. thylakoid membrane 7. granum (stack of thylakoids) 8. thylakoid (lamella) 9. starch 10. ribosome 11. plastidial DNA 12. plastoglobule (drop of lipids)

Main articles: Chloroplast
Chloroplast
and Thylakoid 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.[20] However, the membrane may be tightly folded into cylindrical sheets called thylakoids,[21] or bunched up into round vesicles called intracytoplasmic membranes.[22] 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.[21] In plants and algae, photosynthesis takes place in organelles called chloroplasts. A typical plant cell contains about 10 to 100 chloroplasts. The chloroplast is enclosed by a membrane. This membrane is composed of a phospholipid inner membrane, a phospholipid outer membrane, and an intermembrane space. Enclosed by the membrane is an aqueous fluid called the stroma. Embedded within the stroma are stacks of thylakoids (grana), which are the site of photosynthesis. The thylakoids appear as flattened disks. The thylakoid itself is enclosed by the thylakoid membrane, and within the enclosed volume is a lumen or thylakoid space. Embedded in the thylakoid membrane are integral and peripheral membrane protein complexes of the photosynthetic system. Plants
Plants
absorb light primarily using the pigment chlorophyll. The green part of the light spectrum is not absorbed but is reflected which is the reason that most plants have a green color. Besides chlorophyll, plants also use pigments such as carotenes and xanthophylls.[23] Algae also use chlorophyll, but various other pigments are present, such as phycocyanin, carotenes, and xanthophylls in green algae, phycoerythrin in red algae (rhodophytes) and fucoxanthin in brown algae and diatoms resulting in a wide variety of colors. These pigments are embedded in plants and algae in complexes called antenna proteins. In such proteins, the pigments are arranged to work together. Such a combination of proteins is also called a light-harvesting complex. Although all cells in the green parts of a plant have chloroplasts, the majority of those are found in specially adapted structures called leaves. Certain species adapted to conditions of strong sunlight and aridity, such as many Euphorbia
Euphorbia
and cactus species, have their main photosynthetic organs in their stems. The cells in the interior tissues of a leaf, called the mesophyll, can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf. The 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. Light-dependent reactions

Light-dependent reactions
Light-dependent reactions
of photosynthesis at the thylakoid membrane

Main article: Light-dependent reactions 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 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
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 (O2) 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:[24]

2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH
NADPH
+ 2 H+ + 3 ATP + O2

Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with absorption peaks in violet-blue and red light. In red algae, the action spectrum is blue-green light, which allows these algae to use the blue end of the spectrum to grow in the deeper waters that filter out the longer wavelengths (red light) used by above ground green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms. Z scheme

The "Z scheme"

In 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 electron-acceptor molecule, pheophytin. As the electrons are shuttled through an electron transport chain (the so-called Z-scheme shown in the diagram), it initially functions to generate a chemiosmotic potential by pumping proton cations (H+) across the membrane and into the thylakoid space. An ATP synthase
ATP synthase
enzyme uses that chemiosmotic potential to make ATP during photophosphorylation, whereas NADPH
NADPH
is a product of the terminal redox reaction in the Z-scheme. The electron enters a chlorophyll molecule in Photosystem
Photosystem
I. There it is further excited by the light absorbed by that photosystem. The electron is then passed along a chain of electron acceptors to 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
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, the electron is passed down the electron acceptor molecules and returns to photosystem I, from where it was emitted, hence the name cyclic reaction. Water
Water
photolysis Main articles: Photodissociation and Oxygen
Oxygen
evolution The NADPH
NADPH
is the main reducing agent produced by chloroplasts, which then goes on to provide a source of energetic electrons in other cellular reactions. Its production leaves chlorophyll in photosystem I with a deficit of electrons (chlorophyll has been oxidized), which must be balanced by some other reducing agent that will supply the missing electron. The excited electrons lost from chlorophyll from photosystem I are supplied from the electron transport chain by plastocyanin. However, since photosystem II is the first step of the Z-scheme, an external source of electrons is required to reduce its oxidized chlorophyll a molecules. The source of electrons in green-plant and cyanobacterial photosynthesis is water. Two water molecules are oxidized by four successive charge-separation reactions by photosystem II to yield a molecule of diatomic oxygen and four hydrogen ions; the electrons yielded are transferred to a redox-active tyrosine residue that then reduces the oxidized chlorophyll a (called P680) that serves as the primary light-driven electron donor in the photosystem II reaction center. That photo receptor is in effect reset and is then able to repeat the absorption of another photon and the release of another photo-dissociated electron. The oxidation of water is catalyzed in photosystem II by a redox-active structure that contains four manganese ions and a calcium ion; this oxygen-evolving complex binds two water molecules and contains the four oxidizing equivalents that are used to drive the water-oxidizing reaction (Dolai's S-state diagrams).[25] Photosystem
Photosystem
II is the only known biological enzyme that carries out this oxidation of water. The hydrogen ions released contribute to the transmembrane chemiosmotic potential that leads to ATP synthesis. Oxygen
Oxygen
is a waste product of light-dependent reactions, but the majority of organisms on Earth use oxygen for cellular respiration, including photosynthetic organisms.[26][27] Light-independent reactions Calvin cycle Main articles: Calvin cycle, Carbon fixation, and Light-independent reactions In the light-independent (or "dark") reactions, the enzyme RuBisCO captures CO2 from the atmosphere and, in a process called the Calvin-Benson cycle, it uses the newly formed NADPH
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[24]:128

3 CO2 + 9 ATP + 6 NADPH
NADPH
+ 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O

Overview of the Calvin cycle
Calvin cycle
and carbon fixation

Carbon fixation
Carbon fixation
produces the intermediate three-carbon sugar product, which is then converted to 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 passed through a food chain. The fixation or reduction of carbon dioxide is a process in which carbon dioxide combines with a five-carbon sugar, ribulose 1,5-bisphosphate, to yield two molecules of a three-carbon compound, glycerate 3-phosphate, also known as 3-phosphoglycerate. Glycerate 3-phosphate, in the presence of ATP and NADPH
NADPH
produced during the light-dependent stages, is reduced to glyceraldehyde 3-phosphate. This product is also referred to as 3-phosphoglyceraldehyde (PGAL) or, more generically, as triose phosphate. Most (5 out of 6 molecules) of the glyceraldehyde 3-phosphate produced is used to regenerate ribulose 1,5-bisphosphate so the process can continue. The triose phosphates not 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. Carbon concentrating mechanisms On land

Overview of C4 carbon fixation

In hot and dry conditions, plants close their stomata to prevent water loss. Under these conditions, CO2 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 CO2 concentration in the leaves under these conditions.[28] Main article: C4 carbon fixation Plants
Plants
that use the C4 carbon fixation
C4 carbon fixation
process chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP carboxylase, creating the four-carbon organic acid oxaloacetic acid. Oxaloacetic acid
Oxaloacetic acid
or malate synthesized by this process is then translocated to specialized bundle sheath cells where the enzyme RuBisCO
RuBisCO
and other Calvin cycle
Calvin cycle
enzymes are located, and where CO2 released by decarboxylation of the four-carbon acids is then fixed by RuBisCO
RuBisCO
activity to the three-carbon 3-phosphoglyceric acids. The physical separation of RuBisCO
RuBisCO
from the oxygen-generating light reactions reduces photorespiration and increases CO2 fixation and, thus, the photosynthetic capacity of the leaf.[29] C4 plants can produce more sugar than C3 plants in conditions of high light and temperature. Many important crop plants are C4 plants, including maize, sorghum, sugarcane, and millet. Plants
Plants
that do not use PEP-carboxylase in carbon fixation are called C3 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 C3 carbon fixation, compared to 3% that use C4 carbon fixation;[30] however, the evolution of C4 in over 60 plant lineages makes it a striking example of convergent evolution.[28] Main article: CAM photosynthesis Xerophytes, such as cacti and most succulents, also use PEP carboxylase to capture carbon dioxide in a process called Crassulacean acid metabolism (CAM). In contrast to C4 metabolism, which spatially separates the CO2 fixation to PEP from the Calvin cycle, CAM temporally separates these two processes. CAM plants have a different leaf anatomy from C3 plants, and fix the CO2 at night, when their stomata are open. CAM plants store the CO2 mostly in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate, which is then reduced to malate. Decarboxylation
Decarboxylation
of malate during the day releases CO2 inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate
3-phosphoglycerate
by RuBisCO. Sixteen thousand species of plants use CAM.[31] In water Cyanobacteria
Cyanobacteria
possess carboxysomes, which increase the concentration of CO2 around RuBisCO
RuBisCO
to increase the rate of photosynthesis. An enzyme, carbonic anhydrase, located within the carboxysome releases CO2 from the dissolved hydrocarbonate ions (HCO− 3). Before the CO2 diffuses out it is quickly sponged up by RuBisCO, which is concentrated within the carboxysomes. HCO− 3 ions are made from CO2 outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the cytosol they turn back into CO2 very slowly without the help of carbonic anhydrase. This causes the HCO− 3 ions to accumulate within the cell from where they diffuse into the carboxysomes.[32] Pyrenoids in algae and hornworts also act to concentrate CO2 around rubisco.[33] Order and kinetics The overall process of photosynthesis takes place in four stages:[13]

Stage Description Time scale

1 Energy transfer in antenna chlorophyll (thylakoid membranes) femtosecond to picosecond

2 Transfer of electrons in photochemical reactions (thylakoid membranes) picosecond to nanosecond

3 Electron
Electron
transport chain and ATP synthesis (thylakoid membranes) microsecond to millisecond

4 Carbon fixation
Carbon fixation
and export of stable products millisecond to second

Efficiency Main article: Photosynthetic efficiency Plants
Plants
usually convert light into chemical energy with a photosynthetic efficiency of 3–6%.[34] Absorbed light that is unconverted is dissipated primarily as heat, with a small fraction (1–2%)[35] re-emitted as chlorophyll fluorescence at longer (redder) wavelengths. This fact allows measurement of the light reaction of photosynthesis by using chlorophyll fluorometers.[36] Actual plants' photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature and proportion of carbon dioxide in the atmosphere, and can vary from 0.1% to 8%.[37] By comparison, solar panels convert light into electric energy at an efficiency of approximately 6–20% for mass-produced panels, and above 40% in laboratory devices. The efficiency of both light and dark reactions can be measured but the relationship between the two can be complex.[38] For example, the ATP and NADPH
NADPH
energy molecules, created by the light reaction, can be used for carbon fixation or for photorespiration in C3 plants.[38] Electrons may also flow to other electron sinks.[39][40][41] For this reason, it is not uncommon for authors to differentiate between work done under non-photorespiratory conditions and under photorespiratory conditions.[42][43][44] Chlorophyll
Chlorophyll
fluorescence of photosystem II can measure the light reaction, and Infrared
Infrared
gas analyzers can measure the dark reaction.[45] It is also possible to investigate both at the same time using an integrated chlorophyll fluorometer and gas exchange system, or by using two separate systems together.[46] Infrared
Infrared
gas analyzers and some moisture sensors are sensitive enough to measure the photosynthetic assimilation of CO2, and of ΔH2O using reliable methods[47] CO2 is commonly measured in μmols/m2/s−1, parts per million or volume per million and H20 is commonly measured in mmol/m2/s−1 or in mbars.[47] By measuring CO2 assimilation, ΔH2O, leaf temperature, barometric pressure, leaf area, and photosynthetically active radiation or PAR, it becomes possible to estimate, “A” or carbon assimilation, “E” or transpiration, “gs” or stomatal conductance, and Ci or intracellular CO2.[47] However, it is more common to used chlorophyll fluorescence for plant stress measurement, where appropriate, because the most commonly used measuring parameters FV/FM and Y(II) or F/FM’ can be made in a few seconds, allowing the measurement of larger plant populations.[44] Gas exchange systems that offer control of CO2 levels, above and below ambient, allow the common practice of measurement of A/Ci curves, at different CO2 levels, to characterize a plant’s photosynthetic response.[47] Integrated chlorophyll fluorometer – gas exchange systems allow a more precise measure of photosynthetic response and mechanisms.[45][46] While standard gas exchange photosynthesis systems can measure Ci, or substomatal CO2 levels, the addition of integrated chlorophyll fluorescence measurements allows a more precise measurement of CC to replace Ci.[46][48] The estimation of CO2 at the site of carboxylation in the chloroplast, or CC, becomes possible with the measurement of mesophyll conductance or gm using an integrated system.[45][46][49] Photosynthesis
Photosynthesis
measurement systems are not designed to directly measure the amount of light absorbed by the leaf. But analysis of chlorophyll-fluorescence, P700- and P515-absorbance and gas exchange measurements reveal detailed information about e.g. the photosystems, quantum efficiency and the CO2 assimilation rates. With some instruments even wavelength-dependency of the photosynthetic efficiency can be analyzed.[50] A phenomenon known as quantum walk increases the efficiency of the energy transport of light significantly. In the photosynthetic cell of an algae, bacterium, or plant, there are light-sensitive molecules called chromophores arranged in an antenna-shaped structure named a photocomplex. When a photon is absorbed by a chromophore, it is converted into a quasiparticle referred to as an exciton, which jumps from chromophore to chromophore towards the reaction center of the photocomplex, a collection of molecules that traps its energy in a chemical form that makes it accessible for the cell's metabolism. The exciton's wave properties enable it to cover a wider area and try out several possible paths simultaneously, allowing it to instantaneously "choose" the most efficient route, where it will have the highest probability of arriving at its destination in the minimum possible time. Because that quantum walking takes place at temperatures far higher than quantum phenomena usually occur, it is only possible over very short distances, due to obstacles in the form of destructive interference that come into play. These obstacles cause the particle to lose its wave properties for an instant before it regains them once again after it is freed from its locked position through a classic "hop". The movement of the electron towards the photo center is therefore covered in a series of conventional hops and quantum walks.[51][52][53] Evolution

Life
Life
timeline

view • discuss • edit

-4500 — – -4000 — – -3500 — – -3000 — – -2500 — – -2000 — – -1500 — – -1000 — – -500 — – 0 —

water

Single-celled life

photosynthesis

Eukaryotes

Multicellular life

Land life

Dinosaurs    

Mammals

Flowers

 

Earliest Earth (−4540)

Earliest water

Earliest life

LHB meteorites

Earliest oxygen

Atmospheric oxygen

Oxygen
Oxygen
crisis

Earliest sexual reproduction

Ediacara biota

Cambrian explosion

Earliest humans

P h a n e r o z o i c

P r o t e r o z o i c

A r c h e a n

H a d e a n

Pongola

Huronian

Cryogenian

Andean

Karoo

Quaternary

Axis scale: million years Orange labels: ice ages. Also see: Human
Human
timeline and Nature timeline

Main article: Evolution
Evolution
of photosynthesis Early photosynthetic systems, such as those in green and purple sulfur and green and purple nonsulfur bacteria, are thought to have been anoxygenic, and used various other molecules as electron donors rather than water. Green and purple sulfur bacteria are thought to have used hydrogen and sulfur as electron donors. Green nonsulfur bacteria used various amino and other organic acids as an electron donor. Purple nonsulfur bacteria used a variety of nonspecific organic molecules. The use of these molecules is consistent with the geological evidence that Earth's early atmosphere was highly reducing at that time.[54] Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old.[55][56] More recent studies, reported in March 2018, also suggest that photosynthesis may have begun about 3.4 billion years ago.[57][58] The main source of oxygen in the Earth's atmosphere
Earth's atmosphere
derives from oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, became important during the Paleoproterozoic era around 2 billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen (O 2) in the photosynthetic reaction center. Symbiosis
Symbiosis
and the origin of chloroplasts

Plant
Plant
cells with visible chloroplasts (from a moss, Plagiomnium affine)

Several groups of animals have formed symbiotic relationships with photosynthetic algae. These are most common in corals, sponges and sea anemones. It is presumed that this is due to the particularly simple body plans and large surface areas of these animals compared to their volumes.[59] In addition, a few marine mollusks Elysia viridis
Elysia viridis
and Elysia chlorotica
Elysia chlorotica
also maintain a symbiotic relationship with chloroplasts they capture from the algae in their diet and then store in their bodies. This allows the mollusks to survive solely by photosynthesis for several months at a time.[60][61] Some of the genes from the plant cell nucleus have even been transferred to the slugs, so that the chloroplasts can be supplied with proteins that they need to survive.[62] An even closer form of symbiosis may explain the origin of chloroplasts. Chloroplasts have many similarities with photosynthetic bacteria, including a circular chromosome, prokaryotic-type ribosome, and similar proteins in the photosynthetic reaction center.[63][64] The endosymbiotic theory suggests that photosynthetic bacteria were acquired (by endocytosis) by early eukaryotic cells to form the first plant cells. Therefore, chloroplasts may be photosynthetic bacteria that adapted to life inside plant cells. Like mitochondria, chloroplasts possess their own DNA, separate from the nuclear DNA of their plant host cells and the genes in this chloroplast DNA resemble those found in cyanobacteria.[65] DNA in chloroplasts codes for redox proteins such as those found in the photosynthetic reaction centers. The CoRR Hypothesis proposes that this Co-location is required for Redox
Redox
Regulation.[clarification needed] Cyanobacteria
Cyanobacteria
and the evolution of photosynthesis The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geological record indicates that this transforming event took place early in Earth's history, at least 2450–2320 million years ago (Ma), and, it is speculated, much earlier.[66][67] Because the Earth's atmosphere
Earth's atmosphere
contained almost no oxygen during the estimated development of photosynthesis, it is believed that the first photosynthetic cyanobacteria did not generate oxygen.[68] Available evidence from geobiological studies of Archean
Archean
(>2500 Ma) sedimentary rocks indicates that life existed 3500 Ma, but the question of when oxygenic photosynthesis evolved is still unanswered. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, revealing an already-diverse biota of blue-green algae. Cyanobacteria
Cyanobacteria
remained the principal primary producers of oxygen throughout the Proterozoic
Proterozoic
Eon (2500–543 Ma), in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation.[citation needed] Green algae
Green algae
joined blue-green algae as the major primary producers of oxygen on continental shelves near the end of the Proterozoic, but it was only with the Mesozoic (251–65 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did the primary production of oxygen in marine shelf waters take modern form. Cyanobacteria
Cyanobacteria
remain critical to marine ecosystems as primary producers of oxygen in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae.[69] Discovery Although some of the steps in photosynthesis are still not completely understood, the overall photosynthetic equation has been known since the 19th century. Jan van Helmont began the research of the process in the mid-17th century when he carefully measured the mass of the soil used by a plant and the mass of the plant as it grew. After noticing that the soil mass changed very little, he hypothesized that the mass of the growing plant must come from the water, the only substance he added to the potted plant. His hypothesis was partially accurate — much of the gained mass also comes from carbon dioxide as well as water. However, this was a signaling point to the idea that the bulk of a plant's biomass comes from the inputs of photosynthesis, not the soil itself. Joseph Priestley, a chemist and minister, discovered that, when he isolated a volume of air under an inverted jar, and burned a candle in it, the candle would burn out very quickly, much before it ran out of wax. He further discovered that a mouse could similarly "injure" air. He then showed that the air that had been "injured" by the candle and the mouse could be restored by a 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 CO2 but also to the incorporation of water. Thus, the basic reaction by which photosynthesis is used to produce food (such as glucose) was outlined. Cornelis Van Niel
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 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 up to 700 nm. The former is known as PSII, the latter is PSI. PSI contains only chlorophyll "a", PSII contains primarily chlorophyll "a" with most of the available chlorophyll "b", among other pigment. These include phycobilins, which are the red and blue pigments of red and blue algae respectively, and fucoxanthol for brown algae and diatoms. The process is most productive when the absorption of quanta are equal in both the PSII and PSI, assuring that input energy from the antenna complex is divided between the PSI and PSII system, which in turn powers the photochemistry.[13]

Melvin Calvin
Melvin Calvin
works in his photosynthesis laboratory.

Robert Hill thought that a complex of reactions consisting of an intermediate to cytochrome b6 (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[70] is as follows:

2 H2O + 2 A + (light, chloroplasts) → 2 AH2 + O2

where A is the electron acceptor. Therefore, in light, the electron acceptor is reduced and oxygen is evolved. Samuel Ruben and Martin Kamen used radioactive isotopes to determine that the oxygen liberated in photosynthesis came from the water. Melvin Calvin
Melvin Calvin
and Andrew Benson, along with James Bassham, elucidated the path of carbon assimilation (the photosynthetic carbon reduction cycle) in plants. The carbon reduction cycle is known as the Calvin cycle, which ignores the contribution of Bassham and Benson. Many scientists refer to the cycle as the Calvin-Benson Cycle, Benson-Calvin, and some even call it the Calvin-Benson-Bassham (or CBB) Cycle. Nobel Prize-winning scientist Rudolph A. Marcus
Rudolph A. Marcus
was able to discover the function and significance of the electron transport chain. Otto Heinrich Warburg
Otto Heinrich Warburg
and Dean Burk
Dean Burk
discovered the I-quantum photosynthesis reaction that splits the CO2, activated by the respiration.[71] Louis N.M. Duysens and Jan Amesz discovered that chlorophyll a will absorb one 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. Development of the concept In 1893, Charles Reid Barnes
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.[72] C3 : C4 photosynthesis research After WWII at late 1940 at the University of California, Berkeley, the details of photosynthetic carbon metabolism were sorted out by the chemists Melvin Calvin, Andrew Benson, James Bassham and a score of students and researchers utilizing the carbon-14 isotope and paper chromatography techniques.[73] The pathway of CO2 fixation by the algae Chlorella in a fraction of a second in light resulted in a 3 carbon molecule called phosphoglyceric acid (PGA). For that original and ground-breaking work, a Nobel Prize
Nobel Prize
in Chemistry was awarded to Melvin Calvin
Melvin Calvin
in 1961. In parallel, plant physiologists studied leaf gas exchanges using the new method of infrared gas analysis and a leaf chamber where the net photosynthetic rates ranged from 10 to 13 u mole CO2/square metere.sec., with the conclusion that all terrestrial plants having the same photosynthetic capacities that were light saturated at less than 50% of sunlight.[74][75] Later in 1958-1963 at Cornell University, field grown maize was reported to have much greater leaf photosynthetic rates of 40 u mol CO2/square meter.sec and was not saturated at near full sunlight.[76][77] This higher rate in maize was almost double those observed in other species such as wheat and soybean, indicating that large differences in photosynthesis exist among higher plants. At the University of Arizona, detailed gas exchange research on more than 15 species of monocot and dicot uncovered for the first time that differences in leaf anatomy are crucial factors in differentiating photosynthetic capacities among species.[78][79] In tropical grasses, including maize, sorghum, sugarcane, Bermuda grass and in the dicot amaranthus, leaf photosynthetic rates were around 38−40 u mol CO2/square meter.sec., and the leaves have two types of green cells, i. e. outer layer of mesophyll cells surrounding a tightly packed cholorophyllous vascular bundle sheath cells. This type of anatomy was termed Kranz anatomy in the 19th century by the botanist Gottlieb Haberlandt while studying leaf anatomy of sugarcane.[80] Plant
Plant
species with the greatest photosynthetic rates and Kranz anatomy showed no apparent photorespiration, very low CO2 compensation point, high optimum temperature, high stomatal resistances and lower mesophyll resistances for gas diffusion and rates never saturated at full sun light.[81] The research at Arizona was designated Citation Classic by the ISI 1986.[79] These species was later termed C4 plants as the first stable compound of CO2 fixation in light has 4 carbon as malate and aspartate.[82][83][84] Other species that lack Kranz anatomy were termed C3 type such as cotton and sunflower, as the first stable carbon compound is the 3-carbon PGA acid. At 1000 ppm CO2 in measuring air, both the C3 and C4 plants had similar leaf photosynthetic rates around 60 u mole CO2/square meter.sec. indicating the suppression of photorespiration in C3 plants.[78][79] Factors

The leaf is the primary site of photosynthesis in plants.

There are three main factors affecting photosynthesis and several corollary factors. The three main are:

Light
Light
irradiance and wavelength Carbon dioxide
Carbon dioxide
concentration Temperature.

Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount of leaf area a plant has to capture light (shading by other plants is a major limitation of photosynthesis), rate at which carbon dioxide can be supplied to the chloroplasts to support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis.[85] Light
Light
intensity (irradiance), wavelength and temperature See also: PI (photosynthesis-irradiance) curve

Absorbance spectra of free chlorophyll a (green) and b (red) in a solvent. The action spectra of chlorophyll molecules are slightly modified in vivo depending on specific pigment-protein interactions.

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.[86] 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.

At constant temperature, the rate of carbon assimilation varies with irradiance, increasing as the irradiance increases, but reaching a plateau at higher irradiance. At low irradiance, increasing the temperature has little influence on the rate of carbon assimilation. At constant high irradiance, the rate of carbon assimilation increases as the temperature is increased.

These two experiments illustrate several important points: First, it is known that, in general, photochemical reactions are not affected by temperature. 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.[clarification needed] Carbon dioxide
Carbon dioxide
levels and photorespiration

Photorespiration

As 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
RuBisCO
will fix carbon dioxide. However, if the carbon dioxide concentration is low, RuBisCO
RuBisCO
will bind oxygen instead of carbon dioxide. This process, called photorespiration, uses energy, but does not produce sugars. RuBisCO
RuBisCO
oxygenase activity is disadvantageous to plants for several reasons:

One product of oxygenase activity is phosphoglycolate (2 carbon) instead of 3-phosphoglycerate
3-phosphoglycerate
(3 carbon). Phosphoglycolate cannot be metabolized by the Calvin-Benson cycle
Calvin-Benson cycle
and represents carbon lost from the cycle. A high oxygenase activity, therefore, drains the sugars that are required to recycle ribulose 5-bisphosphate and for the continuation of the Calvin-Benson cycle. Phosphoglycolate is quickly metabolized to glycolate that is toxic to a plant at a high concentration; it inhibits photosynthesis. Salvaging glycolate is an energetically expensive process that uses the glycolate pathway, and only 75% of the carbon is returned to the Calvin-Benson cycle
Calvin-Benson cycle
as 3-phosphoglycerate. The reactions also produce ammonia (NH3), which is able to diffuse out of the plant, leading to a loss of nitrogen.

A highly simplified summary is:

2 glycolate + ATP → 3-phosphoglycerate
3-phosphoglycerate
+ carbon dioxide + ADP + NH3

The salvaging pathway for the products of RuBisCO
RuBisCO
oxygenase activity is more commonly known as photorespiration, since it is characterized by light-dependent oxygen consumption and the release of carbon dioxide. See also

Environment portal Ecology
Ecology
portal Earth sciences portal Metabolism
Metabolism
portal

Jan Anderson (scientist) Artificial photosynthesis Calvin-Benson cycle Carbon fixation Cellular respiration Chemosynthesis Integrated fluorometer Light-dependent reaction Organic reaction Photobiology Photoinhibition Photosynthetic reaction center Photosynthetically active radiation Photosystem Photosystem
Photosystem
I Photosystem
Photosystem
II Quantum biology Radiosynthesis Red edge Vitamin
Vitamin
D Hill reaction

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among species in relation to characteristics of leaf anatomy and CO2 diffusion resistances". Crop Sci. 5 (6): 517–521. doi:10.2135/cropsci1965.0011183x000500060010x.  ^ a b c El-Sharkawy MA, Hesketh JD (1986). "Citation Classic- Photosynthesis
Photosynthesis
among species in relation to characteristics of leaf anatomy and CO2 diffusion resistances" (PDF). Curr. Cont./Agr.Biol.Environ. 27: 14. [permanent dead link] ^ Haberlandt G (1904). Physiologische Pflanzanatomie. Leipzig: Engelmann.  ^ El-Sharkawy MA (1965). Factors Limiting Photosynthetic Rates of Different Plant
Plant
Species (Ph.D. thesis). The University of Arizona, Tucson, USA.  ^ Karpilov YS (1960). "The distribution of radioactvity in carbon-14 among the products of photosynthesis in maize". Proc. Kazan Agric. Inst. 14: 15–24.  ^ Kortschak HP, Hart CE, Burr GO (1965). " Carbon dioxide
Carbon dioxide
fixation in sugarcane leaves". Plant
Plant
Physiol. 40 (2): 209–213. doi:10.1104/pp.40.2.209.  ^ Hatch MD, Slack CR (1966). " Photosynthesis
Photosynthesis
by sugar-cane leaves. A new carboxylation reaction and the pathway of sugar formation". Biochem. J. 101: 103–111. doi:10.1042/bj1010103.  ^ Chapin FS, Matson PA, Mooney HA (2002). Principles of Terrestrial Ecosystem
Ecosystem
Ecology. New York: Springer. pp. 97–104. ISBN 978-0-387-95443-1.  ^ Jones HG (2014). Plants
Plants
and Microclimate: a Quantitative Approach to Environmental Plant
Plant
Physiology (Third ed.). Cambridge: Cambridge University Press. ISBN 978-0-521-27959-8. 

Further reading Books

Bidlack JE, Stern KR, Jansky S (2003). Introductory plant biology. New York: McGraw-Hill. ISBN 0-07-290941-2.  Blankenship RE (2014). Molecular Mechanisms of Photosynthesis
Photosynthesis
(2nd ed.). John Wiley & Sons. ISBN 978-1-4051-8975-0.  Govindjee, Beatty JT, Gest H, Allen JF (2006). Discoveries in Photosynthesis. Advances in Photosynthesis
Photosynthesis
and Respiration. 20. Berlin: Springer. ISBN 1-4020-3323-0.  Reece JB, et al. (2013). Campbell Biology. Benjamin Cummings. ISBN 978-0321775658. 

Papers

Gupta RS, Mukhtar T, Singh B (Jun 1999). "Evolutionary relationships among photosynthetic prokaryotes (Heliobacterium chlorum, Chloroflexus aurantiacus, cyanobacteria, Chlorobium tepidum and proteobacteria): implications regarding the origin of photosynthesis". Molecular Microbiology. 32 (5): 893–906. doi:10.1046/j.1365-2958.1999.01417.x. PMID 10361294.  Rutherford AW, Faller P (Jan 2003). " Photosystem
Photosystem
II: evolutionary perspectives". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 358 (1429): 245–53. doi:10.1098/rstb.2002.1186. PMC 1693113 . PMID 12594932. 

External links

Find more aboutPhotosynthesisat's sister projects

Definitions from Wiktionary Media from Wikimedia Commons Textbooks from Wikibooks Learning resources from Wikiversity Data from Wikidata

A collection of photosynthesis pages for all levels from a renowned expert (Govindjee) In depth, advanced treatment of photosynthesis, also from Govindjee Science Aid: Photosynthesis
Photosynthesis
Article appropriate for high school science Metabolism, Cellular Respiration and Photosynthesis
Photosynthesis
– The Virtual Library of Biochemistry and Cell Biology Overall examination of Photosynthesis
Photosynthesis
at an intermediate level Overall Energetics of Photosynthesis Photosynthesis
Photosynthesis
Discovery Milestones – experiments and background The source of oxygen produced by photosynthesis Interactive animation, a textbook tutorial Marshall J (2011-03-29). "First practical artificial leaf makes debut". Discovery News.  Photosynthesis
Photosynthesis
Light
Light
Dependent & Light
Light
Independent Stages Khan Academy, video introduction

Library resources about Photosynthesis

Resources in your library

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Botany

History of botany

Subdisciplines

Plant
Plant
systematics Ethnobotany Paleobotany Plant
Plant
anatomy Plant
Plant
ecology Phytogeography

Geobotany Flora

Phytochemistry Plant
Plant
pathology Bryology Phycology Floristics Dendrology

Plant
Plant
groups

Algae Archaeplastida Bryophyte Non-vascular plants Vascular plants Spermatophytes Pteridophyte Gymnosperm Angiosperm

Plant
Plant
morphology (glossary)

Plant
Plant
cells

Cell wall Phragmoplast Plastid Plasmodesma Vacuole

Tissues

Meristem Vascular tissue

Vascular bundle

Ground tissue

Mesophyll

Cork Wood Storage organs

Vegetative

Root Rhizoid Bulb Rhizome Shoot

Stem Leaf

Petiole Cataphyll

Bud Sessility

Reproductive (Flower)

Flower
Flower
development Inflorescence

Umbel Raceme Bract Pedicellate

Flower

Whorl Floral symmetry Floral diagram Floral formula

Receptacle Hypanthium
Hypanthium
(Floral cup) Perianth

Tepal Petal Sepal

Sporophyll Gynoecium

Ovary

Ovule

Stigma

Archegonium Androecium

Stamen Staminode Pollen Tapetum

Gynandrium Gametophyte Sporophyte Plant
Plant
embryo Fruit

Fruit
Fruit
anatomy Berry Capsule Seed

Seed
Seed
dispersal Endosperm

Surface structures

Epicuticular wax Plant
Plant
cuticle Epidermis Stoma Nectary Trichome Prickle

Plant
Plant
physiology Materials

Nutrition Photosynthesis

Chlorophyll

Plant
Plant
hormone Transpiration Turgor pressure Bulk flow Aleurone Phytomelanin Sugar Sap Starch Cellulose

Plant
Plant
growth and habit

Secondary growth Woody plants Herbaceous plants Habit

Vines

Lianas

Shrubs

Subshrubs

Trees Succulent plants

Reproduction

Evolution Ecology

Alternation of generations Sporangium

Spore Microsporangia

Microspore

Megasporangium

Megaspore

Pollination

Pollinators Pollen
Pollen
tube

Double fertilization Germination Evolutionary development Evolutionary history

timeline

Hardiness zone

Plant
Plant
taxonomy

History of plant systematics Herbarium Biological classification Botanical nomenclature

Botanical name Correct name Author citation International Code of Nomenclature for algae, fungi, and plants
International Code of Nomenclature for algae, fungi, and plants
(ICN) - for Cultivated Plants
Plants
(ICNCP)

Taxonomic rank International Association for Plant
Plant
Taxonomy (IAPT) Plant
Plant
taxonomy systems Cultivated plant taxonomy

Citrus taxonomy cultigen

cultivar Group grex

Practice

Agronomy Floriculture Forestry Horticulture

Lists Related topics

Botanical terms Botanists

by author abbreviation

Botanical expedition

Category Portal WikiProject

v t e

Metabolism
Metabolism
map

Carbon Fixation Photo- respiration Pentose Phosphate Pathway Citric Acid Cycle Glyoxylate Cycle Urea Cycle Fatty Acid Synthesis Fatty Acid Elongation Beta Oxidation Peroxisomal Beta Oxidation

Glyco- genolysis Glyco- genesis Glyco- lysis Gluconeo- genesis Decarb- oxylation Fermentation Keto- lysis Keto- genesis feeders to Gluconeo- genesis Direct / C4 / CAM Carbon Intake Light
Light
Reaction Oxidative Phosphorylation Amino Acid Deamination Citrate Shuttle Lipogenesis Lipolysis Steroidogenesis MVA Pathway MEP Pathway Shikimate Pathway Transcription & Replication Translation Proteolysis Glycosy- lation

Sugar Acids Double/Multiple Sugars & Glycans Simple Sugars Inositol-P Amino Sugars & Sialic Acids Nucleotide
Nucleotide
Sugars Hexose-P Triose-P Glycerol P-glycerates Pentose-P Tetrose-P Propionyl -CoA Succinate Acetyl -CoA Pentose-P P-glycerates Glyoxylate Photosystems Pyruvate Lactate Acetyl -CoA Citrate Oxalo- acetate Malate Succinyl -CoA α-Keto- glutarate Ketone Bodies Respiratory Chain Serine
Serine
Group Alanine Branched-chain Amino Acids Aspartate Group Homoserine Group & Lysine Glutamate Group & Proline Arginine Creatine & Polyamines Ketogenic & Glucogenic Amino Acids Amino Acids Shikimate Aromatic Amino Acids & Histidine Ascorbate ( Vitamin
Vitamin
C) δ-ALA Bile Pigments Hemes Cobalamins ( Vitamin
Vitamin
B12) Various Vitamin
Vitamin
B's Calciferols ( Vitamin
Vitamin
D) Retinoids ( Vitamin
Vitamin
A) Quinones ( Vitamin
Vitamin
K) & Carotenoids ( Vitamin
Vitamin
E) Cofactors Vitamins & Minerals Antioxidants PRPP Nucleotides Nucleic Acids Proteins Glycoproteins & Proteoglycans Chlorophylls MEP MVA Acetyl -CoA Polyketides Terpenoid Backbones Terpenoids & Carotenoids ( Vitamin
Vitamin
A) Cholesterol Bile Acids Glycero- phospholipids Glycerolipids Acyl-CoA Fatty Acids Glyco- sphingolipids Sphingolipids Waxes Polyunsaturated Fatty Acids Neurotransmitters & Thyroid Hormones Steroids Endo- cannabinoids Eicosanoids

Major metabolic pathways in metro-style map. Click any text (name of pathway or metabolites) to link to the corresponding article. Single lines: pathways common to most lifeforms. Double lines: pathways not in humans (occurs in e.g. plants, fungi, prokaryotes). Orange nodes: carbohydrate metabolism. Violet nodes: photosynthesis. Red nodes: cellular respiration. Pink nodes: cell signaling. Blue nodes: amino acid metabolism. Grey nodes: vitamin and cofactor metabolism. Brown nodes: nucleotide and protein metabolism. Green nodes: lipid metabolism.

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Ecology: Modelling ecosystems: Trophic components

General

Abiotic component Abiotic stress Behaviour Biogeochemical cycle Biomass Biotic component Biotic stress Carrying capacity Competition Ecosystem Ecosystem
Ecosystem
ecology Ecosystem
Ecosystem
model Keystone species List of feeding behaviours Metabolic theory of ecology Productivity Resource

Producers

Autotrophs Chemosynthesis Chemotrophs Foundation species Mixotrophs Myco-heterotrophy Mycotroph Organotrophs Photoheterotrophs Photosynthesis Photosynthetic efficiency Phototrophs Primary nutritional groups Primary production

Consumers

Apex predator Bacterivore Carnivores Chemoorganotroph Foraging Generalist and specialist species Intraguild predation Herbivores Heterotroph Heterotrophic nutrition Insectivore Mesopredators Mesopredator
Mesopredator
release hypothesis Omnivores Optimal foraging theory Predation Prey switching

Decomposers

Chemoorganoheterotrophy Decomposition Detritivores Detritus

Microorganisms

Archaea Bacteriophage Environmental microbiology Lithoautotroph Lithotrophy Microbial cooperation Microbial ecology Microbial food web Microbial intelligence Microbial loop Microbial mat Microbial metabolism Phage ecology

Food webs

Biomagnification Ecological efficiency Ecological pyramid Energy flow Food chain Trophic level

Example webs

Cold seeps Hydrothermal vents Intertidal Kelp forests Lakes North Pacific Subtropical Gyre Rivers San Francisco Estuary Soil Tide pool

Processes

Ascendency Bioaccumulation Cascade effect Climax community Competitive exclusion principle Consumer-resource systems Copiotrophs Dominance Ecological network Ecological succession Energy quality Energy Systems Language f-ratio Feed conversion ratio Feeding frenzy Mesotrophic soil Nutrient cycle Oligotroph Paradox of the plankton Trophic cascade Trophic mutualism Trophic state index

Defense, counter

Animal
Animal
coloration Antipredator adaptations Camouflage Deimatic behaviour Herbivore
Herbivore
adaptations to plant defense Mimicry Plant
Plant
defense against herbivory Predator avoidance in schooling fish

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Ecology: Modelling ecosystems: Other components

Population ecology

Abundance Allee effect Depensation Ecological yield Effective population size Intraspecific competition Logistic function Malthusian growth model Maximum sustainable yield Overpopulation in wild animals Overexploitation Population cycle Population dynamics Population modeling Population size Predator–prey (Lotka–Volterra) equations Recruitment Resilience Small population size Stability

Species

Biodiversity Density-dependent inhibition Ecological effects of biodiversity Ecological extinction Endemic species Flagship species Gradient analysis Indicator species Introduced species Invasive species Latitudinal gradients in species diversity Minimum viable population Neutral theory Occupancy–abundance relationship Population viability analysis Priority effect Rapoport's rule Relative abundance distribution Relative species abundance Species diversity Species homogeneity Species richness Species distribution Species-area curve Umbrella species

Species interaction

Antibiosis Biological interaction Commensalism Community ecology Ecological facilitation Interspecific competition Mutualism Storage effect

Spatial ecology

Biogeography Cross-boundary subsidy Ecocline Ecotone Ecotype Disturbance Edge effects Foster's rule Habitat
Habitat
fragmentation Ideal free distribution Intermediate Disturbance Hypothesis Island biogeography Landscape ecology Landscape epidemiology Landscape limnology Metapopulation Patch dynamics r/K selection theory Resource selection function Source–sink dynamics

Niche

Ecological niche Ecological trap Ecosystem
Ecosystem
engineer Environmental niche modelling Guild Habitat Marine habitats Limiting similarity Niche apportionment models Niche construction Niche differentiation

Other networks

Assembly rules Bateman's principle Bioluminescence Ecological collapse Ecological debt Ecological deficit Ecological energetics Ecological indicator Ecological threshold Ecosystem
Ecosystem
diversity Emergence Extinction debt Kleiber's law Liebig's law of the minimum Marginal value theorem Thorson's rule Xerosere

Other

Allometry Alternative stable state Balance of nature Biological data visualization Ecocline Ecological economics Ecological footprint Ecological forecasting Ecological humanities Ecological stoichiometry Ecopath Ecosystem
Ecosystem
based fisheries Endolith Evolutionary ecology Functional ecology Industrial ecology Macroecology Microecosystem Natural environment Regime shift Systems ecology Urban ecology Theoretical ecology

List of ecology topics

Authority control

GND: 40459