Photosynthesis is the process in which plants use the energy from the sunlight to make glucose, which is sugar. The plants then use the glucose as food. The equation for photosynthesis is: 6CO2 (Carbon dioxide) +6H2O (Water) –> (Sunlight) C6H12O6 (Glucose)+6O2 (Oxygen). Plants, algae, and cyanobacteria are photosynthetic beings An overview of photosynthesis Introduction. Photosynthesis is the ultimate source of all of humankind's food and oxygen, whereas fossilized The site of photosynthesis in plants. In land plants, the principal organs of photosynthesis are the leaves (Figure 2 Photosynthetic electron and proton Essay on Photosynthesis Words2 Pages Photosynthesis is a biochemical process in which plant, algae, and some bacteria harness the energy of light to produce food. Nearly all living things depend on energy produced from photosynthesis for their nourishment, making it vital to life on Earth
Photosynthesis: Essay on Photosynthesis ( Words)
Matthew P. Johnson; Photosynthesis. Essays Biochem 31 October ; 60 3 : — Photosynthesis sustains virtually all life on planet Earth providing the oxygen we breathe and the food we eat; it forms the basis of global food chains and meets the majority of humankind's current energy needs through fossilized photosynthetic fuels. The process of photosynthesis in plants is based on two reactions that are carried out by separate parts of the chloroplast. The light reactions occur in the chloroplast thylakoid membrane and involve the splitting of water into oxygen, protons and electrons.
The protons and electrons are then transferred through the thylakoid membrane to create the energy storage molecules adenosine triphosphate ATP photosynthesis essay nicotinomide—adenine dinucleotide phosphate NADPH.
The ATP and NADPH are then utilized by the enzymes of the Calvin—Benson cycle the dark reactionswhich converts CO 2 into carbohydrate in the chloroplast stroma. The basic principles of solar energy capture, photosynthesis essay, energy, electron and proton transfer and the biochemical basis of carbon fixation are explained and their significance is discussed.
It is the biochemical process that sustains the biosphere as the basis for the food chain. The oxygen produced as a by-product of photosynthesis allowed the formation of the ozone layer, the evolution of aerobic respiration and thus complex multicellular life.
Oxygenic photosynthesis involves the conversion of water and CO 2 into complex organic molecules such as carbohydrates and oxygen, photosynthesis essay. In the light reactions, photosynthesis essay, water is split using light into oxygen, protons photosynthesis essay electrons, and in the dark reactions, the protons and electrons are used to reduce CO 2 to carbohydrate given here by the general photosynthesis essay CH 2 O.
The two processes can be summarized thus:. The positive sign of the standard free energy change of the reaction Δ G ° given above means that the reaction requires energy an endergonic reaction. The energy required is provided by absorbed solar photosynthesis essay, which is converted into the chemical bond energy of the products Box 1.
By facilitating conversion of solar energy into chemical energy, photosynthesis acts as the primary energy input into the global food chain, photosynthesis essay. Nearly all living organisms use the complex organic compounds derived from photosynthesis as a source of photosynthesis essay. The breakdown of these organic compounds occurs via the process of aerobic respiration, which of course also requires the oxygen produced by photosynthesis.
Unlike photosynthesis, aerobic respiration is an exergonic process negative Δ G ° with the energy released being used photosynthesis essay the organism to power biosynthetic processes that allow growth and renewal, mechanical work such as muscle contraction or flagella rotation and facilitating changes in chemical concentrations within the cell e, photosynthesis essay. accumulation of nutrients and expulsion of waste. Photosynthesis and respiration are thus seemingly the reverse of one another, with the important caveat that both oxygen formation during photosynthesis and its utilization during respiration result in its liberation or incorporation respectively into water rather than CO 2.
In addition, glucose is one of several possible products of photosynthesis with amino acids and lipids also being synthesized rapidly from the primary photosynthetic products. The consideration of photosynthesis and respiration as opposing processes helps us to appreciate their role in shaping our environment.
The fixation of CO 2 by photosynthesis and its release during breakdown of organic molecules during respiration, decay and combustion of organic matter and photosynthesis essay fuels can be visualized as the global carbon cycle Figure 1.
The relationship between respiration, photosynthesis and global CO 2 and O 2 levels. Oxygenic photosynthesis is thought to have evolved only once during Earth's history in the cyanobacteria. Cyanobacteria themselves are thought to have evolved from simpler photosynthetic bacteria that use either organic or inorganic compounds such a hydrogen sulfide as a source of electrons rather than water and thus do not produce oxygen.
In land plants, photosynthesis essay, the principal organs of photosynthesis are the leaves Figure 2 A. Leaves have evolved to expose the largest possible area of green tissue to light and entry of CO 2 to the leaf is controlled by small holes in the lower epidermis called stomata Figure 2 B. The size of the stomatal openings is variable and regulated by a pair of guard cells, which respond to the turgor pressure water content of the leaf, photosynthesis essay, thus when the leaf is hydrated, the stomata can open to allow CO 2 in.
In contrast, when water is scarce, the guard cells lose turgor pressure and close, preventing the escape of water from the leaf via transpiration. A The model plant Arabidopsis thaliana. B Basic structure of a leaf shown in cross-section. Chloroplasts are shown as green dots within the cells, photosynthesis essay.
Photosynthesis essay An electron micrograph of an Arabidopsis chloroplast within the leaf. D Close-up region of the chloroplast showing the stacked structure of the thylakoid membrane.
The chloroplast has a complex structure Figure 2 C, D with two outer membranes the envelopephotosynthesis essay, which are colourless and do not participate in photosynthesis, enclosing an aqueous space the stroma wherein sits a third membrane known as the thylakoid, which in turn encloses a single continuous aqueous space called the lumen.
The light reactions of photosynthesis involve light-driven electron and proton transfers, photosynthesis essay, which occur in the thylakoid membrane, whereas the dark reactions involve the fixation of CO 2 into carbohydrate, via the Calvin—Benson cycle, which occurs in the stroma Figure 3.
The light and dark reactions are therefore mutually photosynthesis essay on one another. The photosynthesis essay reactions of photosynthesis take place in the thylakoid membrane, whereas the dark reactions are located in the chloroplast stroma.
The light-driven electron transfer reactions of photosynthesis begin with the splitting of water by Photosystem II PSII. PSII is a chlorophyll—protein complex embedded in the thylakoid membrane that uses light to oxidize water to oxygen and reduce the electron acceptor plastoquinone to plastoquinol, photosynthesis essay.
Plastoquinol in turn carries the electrons derived from water to another thylakoid-embedded protein complex called cytochrome b 6 f cyt b 6 f, photosynthesis essay. cyt b 6 f oxidizes plastoquinol to plastoquinone and reduces a small water-soluble electron carrier protein plastocyanin, which resides in the lumen, photosynthesis essay. A second light-driven reaction is then carried out by another chlorophyll protein complex called Photosystem I PSI. PSI oxidizes plastocyanin and reduces another soluble electron carrier protein ferredoxin that resides in the stroma.
This scheme is known as the linear electron transfer pathway or Z-scheme Photosynthesis essay 4. Generally, electrons are transferred from redox couples with low potentials good reductants to those with higher potentials good oxidants e, photosynthesis essay.
during respiratory electron transfer in mitochondria since this photosynthesis essay is exergonic photosynthesis essay Box 2, photosynthesis essay. However, photosynthetic electron transfer also involves two endergonic steps, which occur at PSII and at PSI and require an energy input in the form of light. The light energy is used to excite an electron within a chlorophyll molecule residing in PSII or PSI to a higher energy level; this excited chlorophyll is then able to reduce the subsequent acceptors in the chain, photosynthesis essay.
The oxidized chlorophyll is then reduced by water in the case of PSII and plastocyanin in the case of PSI. The water-splitting reaction at PSII and plastoquinol oxidation at cyt b 6 f result in the release of protons into the lumen, resulting in a build-up of protons in this compartment relative to the stroma.
The difference in the proton concentration between the two sides of the membrane is called a proton gradient. The proton gradient is a store of free energy similar to a gradient of ions in a battery that is utilized by a molecular mechanical motor ATP photosynthesis essay, which resides in the thylakoid membrane Figure 4. This exergonic reaction is used to power the endergonic synthesis of ATP from ADP and inorganic phosphate P i.
This process of photophosphorylation is thus essentially similar to oxidative phosphorylation, which occurs in the inner mitochondrial membrane during respiration. An alternative electron transfer pathway exists in plants and algae, photosynthesis essay, known as cyclic electron flow. Cyclic electron flow involves the recycling of electrons from ferredoxin to plastoquinone, with the photosynthesis essay that there photosynthesis essay no net production of NADPH; however, since protons are still transferred into the lumen by oxidation of plastoquinol by cyt b 6 fATP can still be formed, photosynthesis essay.
Photosynthesis begins with the absorption of light by pigments molecules located in the thylakoid membrane. The most well-known of these is chlorophyll, but there are also carotenoids and, in cyanobacteria and some algae, bilins, photosynthesis essay.
These pigments all have in common within their chemical structures an alternating series of carbon single and double bonds, which form a conjugated photosynthesis essay π—electron system Figure 6. The chemical structures of the chlorophyll and carotenoid pigments present in the thylakoid membrane. Note the presence in each of a conjugated system of carbon—carbon double bonds that is responsible for light absorption.
The variety of pigments present within each type of photosynthetic organism reflects the photosynthesis essay environment in which it lives; plants on land contain chlorophylls a and b and carotenoids such as β-carotene, lutein, photosynthesis essay, zeaxanthin, violaxanthin, antheraxanthin and neoxanthin Figure 6. Light, photosynthesis essay, or electromagnetic radiation, has the properties of both a wave and a stream of particles light quanta.
Each quantum of light contains a discrete amount of energy that can be calculated by photosynthesis essay Planck's constant, h 6. The frequency ν and wavelength λ of light are related by:. where c is the velocity of light 3. The electrons within the delocalized π system of the pigment have the ability to jump up from the lowest occupied molecular orbital ground state to higher unoccupied molecular electron orbitals excited states via the absorption of photosynthesis essay wavelengths of light in the visible range — nm.
Photons with slightly different energies colours excite each of the vibrational substates of each excited state as shown by variation in the size and colour of the arrows. Upon excitation, the electron in the S 2 state quickly undergoes losses of energy photosynthesis essay heat through molecular vibration and undergoes conversion into the energy of the S 1 state by a process called internal conversion.
The energy of a photosynthesis essay photon is thus rapidly degraded to that of a red photon. Excitation of the molecule with a red photon would lead to promotion of an electron to the S 1 state directly. The energy of the excited electron in the S 1 state can have one of several fates: it could return to the ground state S 0 by emission of the energy as a photon of light fluorescenceor it could be lost as heat due to internal conversion between S 1 and S 0.
Alternatively, if another chlorophyll is nearby, a process known as excitation energy transfer EET can result in the non-radiative photosynthesis essay of energy between the two molecules Figure 9. Two chlorophyll molecules with resonant S 1 states undergo a photosynthesis essay transition resulting in the non-radiative transfer of excitation energy between them. In photosynthetic systems, chlorophylls and carotenoids are found attached to membrane-embedded proteins known as light-harvesting complexes LHCs.
Through careful binding and orientation of the pigment molecules, absorbed energy can be transferred among them by EET. A photosystem consists of numerous LHCs that form an antenna of hundreds of pigment molecules. The acceptor in PSII is plastoquinone and in PSI it is ferredoxin, photosynthesis essay.
If the RC is to go on functioning, the electron deficiency on the special pair must be made good, in PSII the electron donor is water and in PSI it is plastocyanin. Light energy is captured by the antenna pigments and transferred to the special pair of RC chlorophylls which undergo a redox reaction leading to reduction of an acceptor molecule. The oxidized special pair is regenerated by an electron donor.
It is worth asking why photosynthetic organisms bother to have a large antenna of pigments serving an RC rather than more numerous RCs. The answer lies in the fact that the special pair of chlorophylls alone have a rather small spatial and spectral cross-section, meaning that there is a limit to the amount of light they can efficiently absorb.
The amount of light they can practically absorb is around two orders of magnitude smaller than their maximum possible turnover rate, Thus LHCs act to increase the spatial hundreds of pigments and spectral several types of pigments with different light absorption characteristics cross-section of the RC special pair ensuring that its turnover rate runs much closer to capacity.
PSII is a light-driven water—plastoquinone oxidoreductase and is the only enzyme photosynthesis essay Nature that is capable of performing the difficult chemistry of splitting water into protons, electrons and oxygen Figure PSII uses light energy to excite a special pair of chlorophylls, known as P due to their nm absorption peak in the red part of the spectrum. Nonetheless, since water splitting involves four electron chemistry and charge separation only involves transfer of one electron, four separate charge separations turnovers of PSII are required to drive formation of one molecule of O 2 from two molecules of water.
Progressive extraction of electrons from the manganese cluster is driven by the oxidation of P within PSII by light and is known as the S-state cycle Figure After the fourth turnover of P, sufficient positive charge is built up in the manganese cluster to permit the splitting of water into electrons, which regenerate the original state of the manganese cluster, protons, photosynthesis essay, which are released into the lumen and contribute to the proton gradient used for ATP synthesis, and the by-product O 2.
Thus charge separation at P provides the thermodynamic driving force, whereas the manganese cluster acts as a catalyst for the water-splitting reaction. The organization of PSII and its light-harvesting antenna. Protein is shown in grey, with chlorophylls in green and carotenoids in orange. Drawn from PDB code 3JCU. Progressive extraction of photosynthesis essay from the manganese cluster is driven by the oxidation of P within PSII by light.
Each of the electrons given up by the cluster is eventually repaid at the S 4 to S 0 transition when molecular oxygen O 2 is formed.
Photosynthesis (in detail)
, time: 17:52Essays on Photosynthesis. Essay topics and examples of research paper about Photosynthesis
Photosynthesis Essay. Words2 Pages. Photosynthesis. Photosynthesis is the most important part of the lively hood of humans and animals. Without photosynthesis we would not be able to receive energy. We should be more appreciate of An overview of photosynthesis Introduction. Photosynthesis is the ultimate source of all of humankind's food and oxygen, whereas fossilized The site of photosynthesis in plants. In land plants, the principal organs of photosynthesis are the leaves (Figure 2 Photosynthetic electron and proton A net reaction can be written as follows, using glucose as the carbohydrate. For many years after the raw materials and end products of photosynthesis were known, it was thought that carbon and oxygen separated during the process, in such a reaction, carbon would attach to water, and oxygen would be blogger.comted Reading Time: 7 mins
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