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In oxygenic photosynthesis water is the electron donor ..

Since water is used as the electron donor in oxygenic photosynthesis, ..

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Photosynthesis, process by which green plants and certain ..

The main source of in the is , and its first appearance is sometimes referred to as the . Geological evidence suggests that oxygenic photosynthesis, such as that in , became important during the 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 to molecular oxygen () in the .

The source of electrons in green-plant and cyanobacterial photosynthesis is water.

In the perennial herbaceous wintergreen plant (bugle), the photosynthetic apparatus (PSA) is reorganised during winter. The aim of this work was to examine the structural changes in the pigment–protein complexes of PSA. Changes in aggregation of the thylakoid protein complexes were observed including a restructuring of the PSI–PSII megacomplex and the PSII–LHCII supercomplex parallel to changes in the zeaxanthin-dependent protective mechanism.

For photosynthesis in green plants, the electron donor ..

The oxygen released during green plant photosynthesis comes from water, ..

In plant photosynthesis, the photosynthetic electron donor is H2O,which is lysed by photosystem II, resulting in the production of O2.Electrons removed from H2O travel through Photosystem II toPhotosystem I as described in Figure 20 above. Electrons removed fromPhotosystemI reduce ferredoxin directly. Ferredoxin, in turn, passes the electronsto NADP.

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

Are plants using green light for photosynthesis

Since water is most often used as the electron donor in oxygenic photosynthesis, ..

In the , one molecule of the absorbs one and loses one . This electron is passed to a modified form of chlorophyll called , which passes the electron to a molecule, allowing the start of a flow of electrons down an that leads to the ultimate reduction of to . In addition, this creates a across the ; its dissipation is used by for the concomitant synthesis of . The chlorophyll molecule regains the lost electron from a molecule through a process called , which releases a (O2) molecule. The overall equation for the light-dependent reactions under the conditions of non-cyclic electron flow in green plants is:

Not all of light can support photosynthesis. The photosynthetic action spectrum depends on the type of present. For example, in green plants, the resembles the for and with peaks for violet-blue and red light. In red algae, the action spectrum overlaps with the absorption spectrum of for blue-green light, which allows these algae to grow in deeper waters that filter out the longer wavelengths used by green plants. The non-absorbed part of the 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.

In green plant photosynthesis, the electron donor for the light dependent reaction is
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PHOTOSYNTHETIC REACTION CENTERS - Photobiology

All phototrophic bacteria are capable of performing cyclicphotophosphorylationas described above and in Figure 16 and below in Figure 18. Thisuniversalmechanism of cyclic photophosphorylation is referred to as PhotosystemI. Bacterial photosynthesis uses only Photosystem I (PSI), but themore evolved cyanobacteria, as well as algae and plants, have anadditionallight-harvesting system called Photosystem II (PSII). Photosystem IIis used to reduce Photosystem I when electrons are withdrawn from PSIforCO2 fixation. PSII transfers electrons from H2Oandproduces O2, as shown in Figure 20.

Nitrogen fixation and nitrogen metabolism - PEOI

The general scheme for finding electrons for CO2 fixationis to open up Photosystem I and remove the electrons, eventuallygettingthem to NADP which can donate them to the dark reaction. In bacterialphotosynthesisthe process may be quite complex. The electrons are removed fromPhotosystemI at the level of a cytochrome, then moved through an energy-consumingreverseelectron transport system to an iron-sulfur protein, ferredoxin,which reduces NADP to NADPH2. The electrons that replenishPhotosystemI come from the oxidation of an external photosynthetic electrondonor,which may be H2S, other sulfur compounds, H2, orcertain organic compounds.

Lead toxicity in plants - SciELO

Bacteria with only a type I photosystem (PSI), such as green-sulfur bacteria, can be true photoautotrophs. Light energy oxidizes the reaction center chlorophyll, which reduces the the electron carrier NAD+ to make NADH. The oxidized reaction center chlorophyll must then be reduced by electrons from a chemical electron donor, such as hydrogen sulfide (H2S). The oxidized reaction center chlorophyll pulls electrons from H2S down the photosynthetic electron transport chain, which generates a proton gradient to make ATP. Thus green-sulfur bacteria use light energy to produce both ATP and reducing power; both are required for carbon fixation (reduction of CO2 to carbohydrate). However, they are limited by the availability of a suitable electron donor such as H2S.

CSIRO PUBLISHING | Functional Plant Biology

Approximately 2.5-2.7 billion years ago, cyanobacteria evolved a scheme that coupled both types of photosystems with non-cyclic electron flow. In the non-cyclic scheme (often called the Z-scheme), the light-activated PSII gives its electrons to the electron transport chain to drive photophosphorylation. Simultaneously, light-activated PSI gives its electrons to reduce NADP+ to NADPH. The two systems are linked because the oxidized PSI is reduced by the electron transport chain (an electron is transferred from the ETC to PSI). Oxidized PSII regains electrons from oxidizing water molecules to generate oxygen gas. Therefore, in cyanobacteria (and choroplasts), the flow of electrons is from water to PSII, then down the electron transport chain to PSI, and finally to NADP+ to make NADPH (cyanobacteria and chloroplasts use NADP+/NADPH instead of NAD+/NADH). The ability of cyanobacteria to extract electrons from water gave them a huge evolutionary advantage over green-sulfur bacteria, which were restricted to locations that had hydrogen sulfide or other suitable electron donors.

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