Make a summary equation for the reactions of photosynthesis. General equation of plant photosynthesis
The chemical equation for the process of photosynthesis in general can be represented as follows:
6СО 2 + 6Н 2 О + Qlight → С 6 Н 12 О 6 + 6О 2.
Photosynthesis is a process in which the electromagnetic energy of the sun is absorbed by chlorophyll and auxiliary pigments and is converted into chemical energy, the absorption of carbon dioxide from the atmosphere, its reduction into organic compounds and the return of oxygen to the atmosphere.
In the process of photosynthesis, various organic compounds are built from simple inorganic compounds (CO 2, H 2 O). As a result, a rearrangement of chemical bonds occurs: instead of C - O and H - O bonds, C - C and C - H bonds appear, in which electrons occupy a higher energy level. Thus, energy-rich organic substances that feed and receive energy (in the process of breathing) animals and humans are initially created in a green leaf. We can say that almost all living matter on Earth is the result of photosynthetic activity.
The date of the discovery of the process of photosynthesis can be considered 1771. The English scientist J. Priestley drew attention to the change in the composition of the air due to the vital activity of animals. In the presence of green plants, the air again became suitable both for breathing and for burning. Subsequently, the work of a number of scientists (J. Ingenhaus, J. Senebier, T. Saussure, J. B. Boussingot) found that green plants absorb CO2 from the air, from which organic matter is formed with the participation of water in the light. It was this process that in 1877 the German scientist W. Pfeffer called photosynthesis. The law of conservation of energy, formulated by R. Mayer, was of great importance for the disclosure of the essence of photosynthesis. In 1845, R. Mayer put forward the assumption that the energy used by plants is the energy of the Sun, which plants convert into chemical energy during photosynthesis. This position was developed and experimentally confirmed in the studies of the remarkable Russian scientist K.A. Timiryazev.
Photosynthesis includes both light and dark reactions. A number of experiments have been carried out, proving that in the process of photosynthesis, not only reactions occurring with the use of light energy, but also dark ones, which do not require the direct participation of light energy. The following evidence can be given for the existence of dark reactions in the process of photosynthesis:
1) photosynthesis accelerates with increasing temperature. It directly follows from this that some stages of this process are not directly related to the use of light energy. The dependence of photosynthesis on temperature is especially pronounced at high light intensities. Apparently, in this case, the rate of photosynthesis is limited precisely by dark reactions;
2) the efficiency of using light energy in the process of photosynthesis turned out to be higher with intermittent illumination. In this case, for a more efficient use of light energy, the duration of the dark gaps should significantly exceed the duration of the light ones.
Photosynthesis pigments
In order for light to have an effect on the plant organism and, in particular, to be used in the process of photosynthesis, it must be absorbed by photoreceptors-pigments. Pigments are colored substances. Pigments absorb light at a specific wavelength. Unabsorbed areas of the solar spectrum are reflected, which determines the color of the pigments. Thus, the green pigment chlorophyll absorbs red and blue rays, while green rays are mainly reflected. The visible part of the solar spectrum includes wavelengths from 400 to 700 nm. Substances that absorb the entire visible spectrum appear black.
Pigments concentrated in plastids can be divided into three groups: chlorophylls, carotenoids, phycobilins.
To the group chlorophylls include organic compounds that contain 4 pyrrole rings connected by magnesium atoms and have a green color.
Currently, about ten chlorophylls are known. They differ in chemical structure, color, distribution among living organisms. All higher plants contain chlorophylls a and b. Chlorophyll c is found in diatoms, chlorophyll d in red algae.
The main pigments, without which photosynthesis does not take place, are chlorophyll for green plants and bacteriochlorophyll for bacteria. For the first time, an accurate understanding of the green leaf pigments of higher plants was obtained thanks to the works of the largest Russian botanist M.S. Colors (1872-1919). He developed a new chromatographic method for separating substances and isolated the leaf pigments in their pure form.
Chromatographic separation of substances is based on their different adsorption capacity. This method has been widely used. M.S. The color passed the extract from the sheet through a glass tube filled with a powder - chalk or sucrose (chromatographic column). The individual components of the mixture of pigments differed in the degree of adsorption and moved at different speeds, as a result of which they were concentrated in different zones of the column. By dividing the column into separate portions (zones) and using the appropriate solvent system, each pigment could be isolated. It turned out that the leaves of higher plants contain chlorophyll a and chlorophyll b, as well as carotenoids (carotene, xanthophyll, etc.). Chlorophylls, like carotenoids, are insoluble in water, but readily soluble in organic solvents. Chlorophylls a and b differ in color: chlorophyll a is blue-green and chlorophyll b is yellow-green. The content of chlorophyll a in the leaf is approximately three times higher than that of chlorophyll b.
Carotenoids are yellow and orange pigments of aliphatic structure, isoprene derivatives. Carotenoids are found in all higher plants and in many microorganisms. These are the most common pigments with a variety of functions. Oxygen-containing carotenoids are called xanthophylls. The main representatives of carotenoids in higher plants are two pigments - carotene (orange) and xanthophyll (yellow). Unlike chlorophylls, carotenoids do not absorb red rays, nor do they have the ability to fluoresce. Like chlorophyll, carotenoids in chloroplasts and chromatophores are in the form of water-insoluble complexes with proteins. Carotenoids, absorbing certain parts of the solar spectrum, transfer the energy of these rays to chlorophyll molecules. Thus, they promote the use of rays that are not absorbed by chlorophyll.
Phycobilins- red and blue pigments found in cyanobacteria and some algae. Studies have shown that red algae and cyanobacteria, along with chlorophyll a, contain phycobilins. The chemical structure of phycobilins is based on four pyrrole groups.
Phycobilins are represented by pigments: phycocyanin, phycoerythrin and allophycocyanin. Phycoerythrin is an oxidized phycocyanin. Phycobilins form strong compounds with proteins (phycobilin proteins). The connection between phycobilins and proteins is destroyed only by acid.
Phycobilins absorb rays in the green and yellow parts of the solar spectrum. This is the part of the spectrum that lies between the two main absorption lines of chlorophyll. Phycoerythrin absorbs rays with a wavelength of 495-565 nm, and phycocyanin - 550-615 nm. Comparison of the absorption spectra of phycobilins with the spectral composition of light in which photosynthesis takes place in cyanobacteria and red algae shows that they are very close. This suggests that phycobilins absorb light energy and, like carotenoids, transfer it to the chlorophyll molecule, after which it is used in the process of photosynthesis. The presence of phycobilins in algae is an example of the adaptation of organisms in the process of evolution to the use of areas of the solar spectrum that penetrate the seawater (chromatic adaptation). As you know, red rays corresponding to the main absorption line of chlorophyll are absorbed when passing through the water column. Green rays penetrate deeply, which are absorbed not by chlorophyll, but by phycobilins.
Chlorophyll properties
All chlorophylls are pyrrole magnesium salts. In the center of the chlorophyll molecule are magnesium and four pyrrole rings connected to each other by methane bridges.
According to the chemical structure, chlorophylls are esters of a dicarboxylic organic acid - chlorophyllin and two alcohols - phytol and methyl.
The most important part of the chlorophyll molecule is the central nucleus. It consists of four pyrrole five-membered rings connected by carbon bridges and forming a large porphyrin core with nitrogen atoms in the middle bonded to a magnesium atom. The chlorophyll molecule has an additional cyclopentanone ring that contains carbonyl and carboxyl groups linked by an ether bond with methyl alcohol. The presence in the porphyrin core of a system of ten double bonds and magnesium conjugated in a circle determines the green color characteristic of chlorophyll.
Chlorophyll b differs from chlorophyll a only in that instead of a methyl group in the second pyrrole ring it has an aldehyde group COH. Chlorophyll is blue-green in color, and chlorophyll b is light green. They are adsorbed in different layers of the chromatogram, which indicates different chemical and physical properties. According to modern concepts, the biosynthesis of chlorophyll b proceeds through chlorophyll a.
Fluorescence is the property of many bodies under the influence of incident light, in turn, to emit light: in this case, the wavelength of the emitted light is usually greater than the wavelength of the exciting light. One of the most important properties of chlorophylls is their pronounced ability to fluorescence, which is intense in solution and inhibited in chlorophyll contained in leaf tissues, in plastids. If you look at a chlorophyll solution in the rays of light passing through it, then it seems emerald green, if you look at it in the rays of reflected light, then it acquires a red color - this is a phenomenon of fluorescence.
Chlorophylls differ in absorption spectra, while in chlorophyll b, compared with chlorophyll a, the absorption band in the red region of the spectrum is slightly shifted towards short-wavelength rays, and in the blue-violet region the absorption maximum is shifted towards long-wavelength (red) rays.
Photosynthetic phosphorylation was discovered by D. Arnon with colleagues and other researchers in experiments with isolated chloroplasts of higher plants and with cell-free preparations from various photosynthetic bacteria and algae. During photosynthesis, two types of photosynthetic phosphorylation occur: cyclic and non-cyclic. In both types of photophosphorylation, ATP synthesis from ADP and inorganic phosphate occurs at the stage of electron transfer from cytochrome b6 to cytochrome f.
The synthesis of ATP is carried out with the participation of the ATP-ase complex, "mounted" into the protein-lipid membrane of the thylakoid from its outer side. According to Mitchell's theory, just as in the case of oxidative phosphorylation in mitochondria, the electron transport chain in the thylakoid membrane functions as a "proton pump", creating a concentration gradient of protons. However, in this case, the transfer of electrons that occurs during the absorption of light causes them to move from outside to inside the thylakoid, and the resulting transmembrane potential (between the inner and outer surface of the membrane) is opposite to that formed in the mitochondrial membrane. Electrostatic and proton gradient energy is used to synthesize ATP by ATP synthetase.
In non-cyclic photophosphorylation, electrons from water and compound Z to photosystem 2 and then to photosystem 1 are directed to intermediate X and then used to reduce NADP + to NADPH; their journey ends here. During cyclic photophosphorylation, electrons from photosystem 1 to compound X are directed again to cytochrome b6 and from it further to cytochrome Y, participating at this last stage of their path in the synthesis of ATP from ADP and inorganic phosphate. Thus, during acyclic photophosphorylation, the movement of electrons is accompanied by the synthesis of ATP and NADPH. During cyclic photophosphorylation, only ATP synthesis occurs, and NADPH is not formed. ATP formed during photophosphorylation and respiration is used not only in the reduction of phosphoglyceric acid to carbohydrate, but also in other synthetic reactions - in the synthesis of starch, proteins, lipids, nucleic acids, and pigments. It also serves as a source of energy for the processes of movement, transport of metabolites, maintenance of ionic balance, etc.
The role of plastoquinones in photosynthesis
In chloroplasts, five forms of plastoquinones are discovered, designated by the letters A, B, C, D and E, which are derivatives of benzoquinone. For example, plastoquinone A is 2, 3-dimethyl-5-solanesyl benzoquinone. Plastoquinones are very similar in structure to ubiquinones (coenzymes Q), which play an important role in the process of electron transfer during respiration. The important role of plastoquinones in the process of photosynthesis follows from the fact that if they are extracted from chloroplasts with petroleum ether, the photolysis of water and photophosphorylation cease, but resume after the addition of plastoquinones. What are the details of the functional relationship of various pigments and electron carriers involved in the process of photosynthesis - cytochromes, ferredoxin, plastocyanin and plastoquinones - should be shown in further studies. In any case, whatever the details of this process, it is now obvious that the light phase of photosynthesis leads to the formation of three specific products: NADPH, ATP, and molecular oxygen.
What compounds are formed as a result of the third, dark stage of photosynthesis?
Significant results shedding light on the nature of the primary products formed during photosynthesis were obtained using the isotopic technique. In these studies, barley plants, as well as the unicellular green algae Chlorella and Scenedesmus, received carbon dioxide as a carbon source containing 14C labeled radioactive carbon. After extremely short irradiation of the experimental plants, which excluded the possibility of secondary reactions, the distribution of isotopic carbon in various products of photosynthesis was investigated. It was found that the first product of photosynthesis is phosphoglyceric acid; at the same time, with very short-term irradiation of plants, along with phosphoglyceric acid, an insignificant amount of phosphoenolpyruvic and malic acids is formed. For example, in experiments with the unicellular green alga Sceriedesmus, after photosynthesis, which lasted five seconds, 87% of the isotopic carbon was found in phosphoglyceric acid, 10% in phosphoenolpyruvic acid, and 3% in malic acid. Apparently, phosphoenolpyruvic acid is a product of the secondary conversion of phosphoglyceric acid. With longer photosynthesis, lasting 15-60 seconds, radioactive carbon 14C is also found in glycolic acid, triose phosphates, sucrose, aspartic acid, alanine, serine, glycocol, and also in proteins. The latest labeled carbon is found in glucose, fructose, succinic, fumaric and citric acids, as well as in some amino acids and amides (threonine, phenylalanine, tyrosine, glutamine, asparagine). Thus, experiments with the assimilation of carbon dioxide by plants containing labeled carbon showed that the first product of photosynthesis is phosphoglyceric acid.
What substance does carbon dioxide add to in the process of photosynthesis?
The works of M. Calvin, carried out with the help of radioactive carbon 14C, showed that in most plants the compound to which CO2 is attached is ribulose diphosphate. By attaching CO2, it gives two molecules of phosphoglyceric acid. The latter is phosphoorylated with the participation of ATP with the formation of diphosphoglyceric acid, which is reduced with the participation of NADPH and forms phosphoglyceric aldehyde, which is partially converted into phosphodioxyacetone. Due to the synthetic action of the enzyme aldolase, phosphoglyceric aldehyde and phosphodioxyacetone combine to form a molecule of fructose diphosphate, from which sucrose and various polysaccharides are further synthesized. Ribulose diphosphate is a CO2 acceptor, formed as a result of a series of enzymatic transformations of phosphoglycerol aldehyde, phosphodioxyacetone and fructose diphosphate. In this case, erythrosophosphate, sedoheptulose phosphate, xylulose phosphate, ribose phosphate and ribulose phosphate arise as intermediate products. Enzyme systems that catalyze all these transformations are found in chlorella cells, spinach leaves and other plants. According to M. Calvin, the process of formation of phosphoglyceric acid from ribulose diphosphate and CO2 is cyclical. The assimilation of carbon dioxide with the formation of phosphoglyceric acid occurs without the participation of light and chlorophyll and is a dark process. The hydrogen in the water is ultimately used to reduce phosphoglyceric acid to phosphoglyceric aldehyde. This process is catalyzed by the enzyme phosphoglyceric aldehyde dehydrogenase and requires the participation of NADPH as a source of hydrogen. Since this process stops immediately in the dark, it is obvious that the reduction of NADP is carried out by hydrogen formed during photolysis of water.
Calvin's equation for photosynthesis
The total equation of the Calvin cycle is as follows:
6CO2 + 12NADPH + 12H + + 18ATP + 11H2O = fructose-b-phosphate + 12NADP + + 18ADP + 17P inorg
Thus, the synthesis of one hexose molecule requires six CO2 molecules. To convert one CO2 molecule, you need two NADPH molecules and three ATP molecules (1: 1.5). Since the ratio of formed NADPH: ATP is 1: 1 during noncyclic photophosphorylation, the additional required amount of ATP is synthesized during cyclic photophosphorylation.
The carbon pathway during photosynthesis was studied by Calvin at relatively high CO2 concentrations. At lower concentrations, approaching atmospheric (0.03%), a significant amount of phosphoglycolic acid is formed in the chloroplast under the action of ribulose diphosphate carboxylase. The latter, in the process of transport through the chloroplast membrane, is hydrolyzed by a specific phosphatase, and the formed glycolic acid moves from the chloroplast to the subcellular structures associated with it - peroxisomes, where, under the action of the glycolate oxidase enzyme, it is oxidized to glyoxylic acid HOC-COOH. The latter, by transamination, forms glycine, which, moving into the mitochondria, is converted here into serine.
This transformation is accompanied by the formation of CO2 and NH3: 2 glycine + H2O = serine + CO2 + NH3 + 2H + + 2-.
However, ammonia is not released into the external environment, but binds in the form of glutamine. Thus, peroxisomes and mitochondria take part in the process of so-called photorespiration - the process of oxygen absorption and CO2 release stimulated by light. This process is associated with the conversion of glycolic acid and its oxidation to CO2. As a result of intense photorespiration, the productivity of plants can significantly (up to 30%) decrease.
Other possibilities of CO2 assimilation during photosynthesis
The assimilation of CO2 in the process of photosynthesis occurs not only by carboxylation of ribulose diphosphate, but also by carboxylation of other compounds. For example, it has been shown that in sugar cane, corn, sorghum, millet, and a number of other plants, the enzyme phosphoenolpyruvate carboxylase, which synthesizes oxaloacetic acid from phosphoenolpyruvate, CO2, and water, plays a particularly important role in the process of photosynthetic fixation. Plants in which phosphoglyceric acid is the first product of CO2 fixation are usually called C3 plants, and those in which oxaloacetic acid is synthesized as C4 plants. The above-mentioned process of photorespiration is characteristic of C3 plants and is a consequence of the inhibitory effect of oxygen on ribulose diphosphate carboxylase.
Photosynthesis in bacteria
In photosynthetic bacteria, CO2 fixation occurs with the participation of ferredoxin. Thus, from the photosynthetic bacterium Chromatium, an enzyme system was isolated and partially purified, which, with the participation of ferredoxin, catalyzes the reductive synthesis of pyruvic acid from CO2 and acetyl coenzyme A:
Acetyl-CoA + CO2 + ferredoxin reduced = pyruvate + ferredoxin oxidized. + CoA
Similarly, with the participation of ferredoxin in acellular enzyme preparations isolated from photosynthetic bacteria Chlorobium thiosulfatophilum, a-ketoglutaric acid is synthesized by carboxylation of succinic acid:
Succinyl-CoA + CO2 + ferredoxin recovered = a-ketoglutarate + CoA + ferredoxin is oxidized.
In some microorganisms containing bacteriochlorophyll, the so-called purple sulfur bacteria, photosynthesis also occurs in the light. However, in contrast to the photosynthesis of higher plants, in this case, the reduction of carbon dioxide is carried out by hydrogen sulfide. The overall equation of photosynthesis in purple bacteria can be represented as follows:
Light, bacteriochlorophyll: CO2 + 2H2S = CH2O + H2O + 2S
Thus, in this case, photosynthesis is also a coupled redox process under the influence of light energy absorbed by bacteriochlorophyll. From the above equation, it can be seen that as a result of photosynthesis, purple bacteria release free sulfur, which accumulates in them in the form of granules.
Studies carried out using the isotopic technique with the anaerobic photosynthetic purple bacterium Chromatium showed that with very short photosynthesis times (30 seconds), about 45% of CO2 carbon is included in aspartic acid, and about 28% - in phosphoglyceric acid. Apparently, the formation of phosphoglyceric acid precedes the formation of aspartic acid, and the earliest product of photosynthesis in Chromatium, as in higher plants and unicellular green algae, is ribulose diphosphate. The latter, under the action of ribulose diphosphate carboxylase, adds CO2 to form phosphoglyceric acid. This acid in Chromatium, in accordance with the Calvin scheme, can be partially converted to phosphorylated sugars, and mainly converted to aspartic acid. The formation of aspartic acid occurs by the conversion of phosphoglyceric acid to phosphoenolpyruvic acid, which, undergoing carboxylation, gives oxaloacetic acid; the latter, by transamination, gives aspartic acid.
Photosynthesis is the source of organic matter on Earth
The process of photosynthesis, which occurs with the participation of chlorophyll, is currently the main source of the formation of organic matter on Earth.
Photosynthesis for hydrogen production
It should be noted that unicellular photosynthetic algae release gaseous hydrogen under anaerobic conditions. Isolated chloroplasts of higher plants, illuminated in the presence of the hydrogenase enzyme catalyzing the reaction 2H + + 2- = H2, also release hydrogen. Thus, photosynthetic production of hydrogen as fuel is possible. This issue, especially in the context of the energy crisis, attracts a lot of attention.
A new type of photosynthesis
V. Stokenius discovered a fundamentally new type of photosynthesis. It turned out that the bacteria Halobacterium halobium living in concentrated solutions of sodium chloride, the protein-lipid membrane surrounding the protoplasm contains the chromoprotein bacteriorhodopsin, which is similar to rhodopsin, the visual purpura of the eyes of animals. In bacteriorhodopsin, retinal (the aldehyde form of vitamin A) is bound to a protein with a molecular weight of 26534, it consists of 247 amino acid residues. By absorbing light, bacteriorhodopsin participates in the process of converting light energy into chemical energy of high-energy ATP bonds. Thus, an organism that does not contain chlorophyll is able, with the help of bacteriorhodopsin, to use light energy to synthesize ATP and provide the cell with energy.
General equation of photosynthesis: 6CO 2 + 6 H 2 O ––– (light, chloroplasts) –––> C 6 H 12 O 6 + 6 O 2. In the course of this process, the carbohydrate glucose (C 6 H 12 O 6), an energy-rich substance, is formed from substances poor in energy - carbon dioxide and water - and molecular oxygen is also formed. This phenomenon was described very figuratively by the Russian scientist, plant physiologist - K.A. Timiryazev.
The equation of photosynthesis corresponds to two partial reactions:
1) light reaction or energy conversion - the process of localization in chloroplast tilakoids. ]
2) dark reaction or transformation of substances - the process of localization in the stroma of the chloroplast. 
3.Leaf as an organ of photosynthesis. The leaf is an organ of photosynthesis that absorbs and stores solar energy and exchanges gas with the atmosphere. On average, a leaf absorbs 80-85% of photosynthetically active radiation (PAR) and 25% of infrared energy. Photosynthesis consumes 1.5-2% of the absorbed PAR, the rest of the energy is spent on water evaporation - transpiration. The sheet is flat and thin. The architectonics of plants is of great importance for the effective capture of light - the spatial arrangement of organs, those leaves are located on the plant without obscuring each other. Features that ensure the efficiency of photosynthesis: 1) the presence of an integumentary tissue-epidermis, which protects the leaf from excessive loss of water. The cells of the lower and upper epidermis are devoid of chloroplasts and have large vacuoles. how lenses focus light on deeper chlorophyll tissue. The lower and upper epidermis have stomata through which CO2 diffuses into the leaf. 2) the presence of a specialized photosynthetic tissue, chlorenchyme. The main chlorophyll-bearing tissue is the palisade parenchyma, which is located on the illuminated part of the leaf. Each cell of the palisade parenchyma contains 30-40 chloroplasts. 3) the presence of a highly developed system of veins of the pathways, which ensures a rapid outflow of assimilates and the supply of photosynthetic cells with water and essential minerals. Depending on the external conditions at the cat, the formation and functioning of the leaves occurs, their anatomical structure may change.
4.Chloroplast structure and function. Chloroplasts are plastids of higher plants in which the process of photosynthesis takes place, i.e., the use of the energy of light rays for the formation of organic substances from inorganic substances (carbon dioxide and water) with the simultaneous release of oxygen into the atmosphere. Chloroplasts have the shape of a biconvex lens, their size is about 4-6 microns. They are found in the parenchymal cells of leaves and other green parts of higher plants. Their number in a cell varies between 25-50.
Outside, the chloroplast is covered with a membrane consisting of two lipoprotein membranes, external and internal. Both membranes have a thickness of about 7 nm, they are separated from each other by an intermembrane space of about 20-30 nm. The inner membrane of chloroplasts, like other plastids, forms folded invaginations into the matrix or stroma. In the mature chloroplast of higher plants, two types of internal membranes are visible. These are membranes that form flat, extended lamellae of the stroma, and membranes of thylakoids, flat disc-shaped vacuoles or sacs.
The main function of chloroplasts is to capture and convert light energy.
The granular membranes contain a green pigment, chlorophyll. It is here that the light reactions of photosynthesis take place - the absorption of light rays by chlorophyll and the conversion of light energy into the energy of excited electrons. Electrons excited by light, that is, having excess energy, give up their energy to decompose water and synthesize ATP. When water decomposes, oxygen and hydrogen are formed. Oxygen is released into the atmosphere, and hydrogen is bound by the protein ferredoxin.
Chloroplasts have a certain autonomy in the cell system. They have their own ribosomes and a set of substances that determine the synthesis of a number of chloroplast's own proteins. There are also enzymes whose work leads to the formation of lipids that make up the lamellae and chlorophyll. Thanks to all this, chloroplasts are able to independently build their own structures. Another very important function is the assimilation of carbon dioxide in the chloroplast or, as they say, the fixation of carbon dioxide, that is, the inclusion of its carbon in the composition of organic compounds
5.Pigments of the photosynthetic apparatus (general characteristic) The ability of plants to carry out photosynthesis is associated with the presence of pigments in them. The most important of them is the magnesium-containing porphyrin pigment - chlorophyll.
In nature, there are five different types of chlorophyll, which differ slightly in their molecular structure. Chlorophyll a is present in all algae and higher plants; chlorophyll b - in green, charovy and euglepids and in higher plants; chlorophyll c - in brown algae, golden algae, diatoms and dinoflagellates; chlorophyll d - in red algae; chlorophyll e was found only once, apparently, it is chlorophyll c; finally, various types of bacteriochlorophyll are found in photosynthetic bacteria. Blue-green and red algae are characterized by the presence of biliproteins: phycocyanin and phycoerythrin. Chlorophyll a is the best studied. Its molecule consists of four pyrrole rings, the nitrogen of which is associated with a magnesium atom, and a monoatomic unsaturated alcohol phytol is attached to one of the rings.
The chlorophyll molecule is embedded in the membrane - immersed in a hydrophobic phytol chain in its lipid part. A pure chlorophyll a solution has an absorption maximum at 663 nm. In an intact, undamaged, normally functioning cell, chlorophyll is also characterized by absorption maxima at 672 and 683 nm. The high efficiency of light absorption by chlorophylls is due to the presence of a large number of conjugated double bonds in their molecule.
The process of converting the sun's radiant energy into chemical energy using the latter in the synthesis of carbohydrates from carbon dioxide. This is the only way to capture solar energy and use it for life on our planet.
The capture and conversion of solar energy is carried out by a variety of photosynthetic organisms (photoautotrophs). These include multicellular organisms (higher green plants and their lower forms - green, brown and red algae) and unicellular (euglena, dinoflagellates and diatoms). A large group of photosynthetic organisms are prokaryotes - blue-green algae, green and purple bacteria. About half of the photosynthetic work on Earth is done by higher green plants, and the remaining half is mainly single-celled algae.
The first ideas about photosynthesis were formed in the 17th century. Later, as new data appeared, these representations changed many times. [show] .
Development of ideas about photosynthesis
The study of photosynthesis began in 1630, when van Helmont showed that plants themselves form organic matter, and do not receive them from the soil. Weighing the pot of soil in which the willow grew and the tree itself, he showed that within 5 years the weight of the tree increased by 74 kg, while the soil lost only 57 g. Van Helmont concluded that the rest of the food the plant got from water that was poured over the tree. We now know that the main material for synthesis is carbon dioxide, which is extracted by the plant from the air.
In 1772, Joseph Priestley showed that a mint sprout "corrects" air "tainted" by a burning candle. Seven years later, Jan Ingenhuis discovered that plants can only "fix" bad air by being exposed to light, and the ability of plants to "fix" the air is proportional to the clarity of the day and the length of time the plants are exposed to the sun. In the dark, plants emit air that is "harmful to animals."
The next important step in the development of knowledge about photosynthesis was the experiments of Saussure, carried out in 1804. Weighing the air and plants before and after photosynthesis, Saussure found that the increase in dry mass of a plant exceeded the mass of carbon dioxide absorbed from the air. Saussure concluded that the other substance involved in the increase in mass was water. Thus, 160 years ago, the process of photosynthesis was imagined as follows:
H 2 O + CO 2 + hv -> C 6 H 12 O 6 + O 2
Water + Carbonic acid + Solar energy ----> Organic matter + Oxygen
Ingenhus suggested that the role of light in photosynthesis is to break down carbon dioxide; in this case, oxygen is released, and the released "carbon" is used to build plant tissues. On this basis, living organisms were divided into green plants, which can use solar energy to "assimilate" carbon dioxide, and other organisms that do not contain chlorophyll, which cannot use light energy and are unable to assimilate CO 2.
This principle of dividing the living world was violated when S. N. Vinogradsky in 1887 discovered chemosynthetic bacteria - chlorophyll-free organisms capable of assimilating (i.e. converting into organic compounds) carbon dioxide in the dark. It was also disturbed when, in 1883, Engelmann discovered purple bacteria that carry out a kind of photosynthesis that is not accompanied by the release of oxygen. At one time this fact was not properly appreciated; meanwhile, the discovery of chemosynthetic bacteria assimilating carbon dioxide in the dark shows that the assimilation of carbon dioxide cannot be considered a specific feature of photosynthesis alone.
After 1940, thanks to the use of tagged carbon, it was established that all cells - plant, bacterial and animal - are capable of assimilating carbon dioxide, that is, incorporating it into the molecules of organic substances; only the sources from which they draw the energy necessary for this are different.
Another major contribution to the study of the process of photosynthesis was made in 1905 by Blackman, who discovered that photosynthesis consists of two sequential reactions: a rapid light response and a series of slower, light-independent stages, which he called the tempo response. Using high-intensity light, Blackman showed that photosynthesis proceeds at the same rate both under intermittent illumination with flashes of only a fraction of a second and under continuous illumination, despite the fact that in the former case, the photosynthetic system receives half the energy. The intensity of photosynthesis decreased only with a significant increase in the dark period. In further studies, it was found that the rate of the dark reaction increases significantly with increasing temperature.
The next hypothesis regarding the chemical basis of photosynthesis was put forward by van Niel, who in 1931 experimentally showed that in bacteria photosynthesis can occur under anaerobic conditions, without the release of oxygen. Van Niel suggested that, in principle, the process of photosynthesis is similar in bacteria and in green plants. In the latter, light energy is used for photolysis of water (H 2 0) with the formation of a reducing agent (H), which is determined by the way involved in the assimilation of carbon dioxide, and an oxidizing agent (OH), a hypothetical precursor of molecular oxygen. In bacteria, photosynthesis is generally the same, but the hydrogen donor is Н 2 S or molecular hydrogen, and therefore oxygen is not released.
Modern concepts of photosynthesis
According to modern concepts, the essence of photosynthesis is the conversion of the radiant energy of sunlight into chemical energy in the form of ATP and reduced nicotinamide adenine dinucleotide phosphate (NADP · H).
Currently, it is generally accepted that the process of photosynthesis consists of two stages, in which photosynthetic structures take an active part. [show] and light-sensitive cell pigments.
Photosynthetic structures
Bacteria photosynthetic structures are presented in the form of invagination of the cell membrane, forming lamellar organelles of the mesosome. Isolated mesosomes, obtained by the destruction of bacteria, are called chromatophores; a photosensitive apparatus is concentrated in them.
In eukaryotes The photosynthetic apparatus is located in special intracellular organelles - chloroplasts, containing the green pigment chlorophyll, which gives the plant a green color and plays an important role in photosynthesis, capturing the energy of sunlight. Chloroplasts, like mitochondria, also contain DNA, RNA and an apparatus for protein synthesis, that is, they have the potential for self-reproduction. Chloroplasts are several times larger than mitochondria in size. The number of chloroplasts ranges from one in algae to 40 per cell in higher plants.
In addition to chloroplasts, green plant cells also contain mitochondria, which are used to generate energy at night through respiration, as in heterotrophic cells.
Chloroplasts are spherical or flattened. They are surrounded by two membranes - outer and inner (Fig. 1). The inner membrane is stacked in the form of stacks of flattened vesicular discs. This stack is called a grain.
Each grain is made up of separate layers, arranged like columns of coins. Layers of protein molecules alternate with layers containing chlorophyll, carotenes and other pigments, as well as special forms of lipids (containing galactose or sulfur, but only one fatty acid). These surfactant lipids appear to be adsorbed between individual layers of molecules and serve to stabilize a structure composed of alternating layers of protein and pigments. Such a layered (lamellar) grana structure most likely facilitates the transfer of energy during photosynthesis from one molecule to a nearby one.
In algae there is no more than one grain in each chloroplast, and in higher plants - up to 50 grains, which are interconnected by membrane bridges. The aqueous medium between the grains is the chloroplast stroma, which contains enzymes that carry out "dark reactions"
The vesicular structures that make up the grana are called tylactoids. In the range of 10 to 20 tylactoids.
The elementary structural and functional unit of photosynthesis of tylactoid membranes, containing the necessary light-trapping pigments and components of the energy transformation apparatus, is called a quantum-some, which consists of about 230 chlorophyll molecules. This particle has a mass of about 2 x 10 6 daltons and dimensions of about 17.5 nm.
Stages of photosynthesis |
||
Light stage (or energy) |
Dark stage (or metabolic) |
|
Location of the reaction |
In the quantosomes of the tylactoid membranes, it proceeds in the light. |
It is carried out outside the tilactoids, in the aquatic environment of the stroma. |
Starter Products |
Light energy, water (H 2 O), ADP, chlorophyll |
CO 2, ribulose diphosphate, ATP, NADPH 2 |
The essence of the process |
Photolysis of water, phosphorylation In the light stage of photosynthesis, light energy is transformed into chemical energy ATP, and energy-poor electrons of water are converted into energy-rich electrons NADP · H 2. A by-substance formed during the light stage is oxygen. The reactions of the light stage are called "light reactions". |
Carboxylation, hydrogenation, dephosphorylation In the dark stage of photosynthesis, "dark reactions" occur in which reductive synthesis of glucose from CO 2 is observed. Without the energy of the light stage, the dark stage is impossible. |
End products |
О 2, ATP, NADPH 2 Energy-rich light reaction products - ATP and NADP · H2 is then used in the dark stage of photosynthesis. |
|
The relationship between the light and dark stages can be expressed by the diagram
The process of photosynthesis is endergonic, i.e. is accompanied by an increase in free energy, therefore it requires a significant amount of energy supplied from the outside. The overall equation of photosynthesis: 6CO 2 + 12H 2 O ---> C 6 H 12 O 62 + 6H 2 O + 6O 2 + 2861 kJ / mol. |
||
Terrestrial plants absorb the water necessary for the process of photosynthesis through the roots, and aquatic plants receive it by diffusion from the environment. Carbon dioxide, necessary for photosynthesis, diffuses into the plant through small holes on the surface of the leaves - the stomata. Since carbon dioxide is consumed in the process of photosynthesis, its concentration in the cell is usually somewhat lower than in the atmosphere. Oxygen released during photosynthesis diffuses out of the cell, and then out of the plant through the stomata. Sugars formed during photosynthesis also diffuse into those parts of the plant where their concentration is lower.
Plants need a lot of air to carry out photosynthesis, since it contains only 0.03% carbon dioxide. Consequently, from 10,000 m 3 of air, 3 m 3 of carbon dioxide can be obtained, from which about 110 g of glucose is formed in the process of photosynthesis. Plants usually grow better with higher carbon dioxide levels in the air. Therefore, in some greenhouses, the CO 2 content in the air is adjusted to 1-5%.
The mechanism of the light (photochemical) stage of photosynthesis |
Solar energy and various pigments are involved in the implementation of the photochemical function of photosynthesis: green - chlorophylls a and b, yellow - carotenoids and red or blue - phycobilins. Among this complex of pigments, only chlorophyll a is photochemically active. The rest of the pigments play an auxiliary role, being only collectors of light quanta (a kind of light-collecting lenses) and their conductors to the photochemical center.
Based on the ability of chlorophyll to efficiently absorb solar energy of a certain wavelength in the membranes of tylactoids, functional photochemical centers or photosystems were identified (Fig. 3):
- photosystem I (chlorophyll a) - contains pigment 700 (P 700) absorbing light with a wavelength of about 700 nm, plays a major role in the formation of products of the light stage of photosynthesis: ATP and NADP · H 2
- photosystem II (chlorophyll b) - contains pigment 680 (P 680), which absorbs light with a wavelength of 680 nm, plays an auxiliary role by replenishing electrons lost by photosystem I due to photolysis of water
For 300-400 molecules of light-harvesting pigments in photosystems I and II, there is only one molecule of photochemically active pigment - chlorophyll a.
Light quantum absorbed by the plant
- transfers the P 700 pigment from the ground state to the excited one - P * 700, in which it easily loses an electron with the formation of a positive electron hole in the form of P 700 + according to the scheme:
P 700 ---> P * 700 ---> P + 700 + e -
After that, a pigment molecule that has lost an electron can serve as an electron acceptor (capable of accepting an electron) and pass into the reduced form
- causes decomposition (photooxidation) of water in the photochemical center P 680 of photosystem II according to the scheme
Н 2 О ---> 2Н + + 2е - + 1 / 2O 2
The photolysis of water is called the Hill reaction. The electrons produced by the decomposition of water are initially accepted by a substance designated Q (sometimes called cytochrome C 550 at the maximum absorption, although it is not a cytochrome). Then, from substance Q through a chain of carriers, similar in composition to the mitochondrial, electrons are supplied to photosystem I to fill the electron hole formed as a result of absorption by the system of light quanta and restore the P + 700 pigment
If such a molecule simply receives back the same electron, then light energy will be released in the form of heat and fluorescence (this is due to the fluorescence of pure chlorophyll). However, in most cases, the released negatively charged electron is accepted by special iron-sulfur proteins (FeS-center), and then
- or transported along one of the carrier chains back to P + 700, filling the electron hole
- or via another carrier chain through ferredoxin and flavoprotein to a permanent acceptor - NADP · H 2
In the first case, a closed cyclic transport of an electron occurs, and in the second, a non-cyclic one.
Both processes are catalyzed by the same electron carrier chain. However, during cyclic photophosphorylation, electrons return from chlorophyll a back to chlorophyll a, whereas in acyclic photophosphorylation, electrons pass from chlorophyll b to chlorophyll a.
| Cyclic (photosynthetic) phosphorylation | Non-cyclic phosphorylation |
As a result of cyclic phosphorylation, ATP molecules are formed. The process is associated with the return through a series of successive stages of excited electrons to P 700. The return of excited electrons to P 700 leads to the release of energy (during the transition from a high to a low energy level), which, with the participation of the phosphorylating enzyme system, accumulates in the phosphate bonds of ATP, and is not dissipated in the form of fluorescence and heat (Fig. 4). This process is called photosynthetic phosphorylation (as opposed to oxidative phosphorylation by mitochondria); Photosynthetic phosphorylation- the primary reaction of photosynthesis - the mechanism of the formation of chemical energy (synthesis of ATP from ADP and inorganic phosphate) on the chloroplast tylactoid membrane using the energy of sunlight. Required for the dark reaction of CO 2 assimilation |
As a result of non-cyclic phosphorylation, NADP + is reduced with the formation of NADP · H. The process is associated with the transfer of an electron to ferredoxin, its reduction and its further transition to NADP +, followed by its reduction to NADP · H |
In tilactoids, both processes take place, although the second is more complex. It is associated (interconnected) with the operation of photosystem II. |
|
Thus, the lost Р 700 electrons are replenished by the electrons of water decomposed by light in photosystem II.
a+ to the ground state, are formed, apparently, upon excitation of chlorophyll b... These high-energy electrons are transferred to ferredoxin and then via flavoprotein and cytochromes to chlorophyll a... At the last stage, ADP is phosphorylated to ATP (Fig. 5).
Electrons Required to Return Chlorophyll v its ground state is supplied, probably, by OH - ions, formed during the dissociation of water. Some of the water molecules dissociate into Н + and ОН - ions. As a result of the loss of electrons, OH - ions are converted into radicals (OH), which subsequently give molecules of water and gaseous oxygen (Fig. 6).
This aspect of the theory is confirmed by the results of experiments with water and CO 2 labeled with 18 0 [show] .
According to these results, all of the oxygen gas released during photosynthesis comes from water, not CO 2. Water splitting reactions have not yet been studied in detail. It is clear, however, that the implementation of all sequential reactions of non-cyclic photophosphorylation (Fig. 5), including the excitation of one chlorophyll molecule a and one chlorophyll molecule b, should lead to the formation of one NADP molecule · H, two or more ATP molecules from ADP and F n and to the release of one oxygen atom. This requires at least four quanta of light - two for each chlorophyll molecule.
Non-cyclic electron flow from H 2 O to NADP · Н 2, which occurs during the interaction of two photosystems and electron transport chains connecting them, is observed contrary to the values of redox potentials: E ° for 1 / 2O2 / H2O = +0.81 V, and E ° for NADP / NADP · H = -0.32 V. The energy of light reverses the flow of electrons. It is essential that during the transfer from photosystem II to photosystem I, part of the electron energy is accumulated in the form of a proton potential on the tylactoid membrane, and then into ATP energy.
The mechanism of the formation of the proton potential in the electron transport chain and its use for the formation of ATP in chloroplasts is similar to that in mitochondria. However, there are some peculiarities in the mechanism of photophosphorylation. Tylactoids are, as it were, mitochondria turned inside out, so the direction of the transfer of electrons and protons through the membrane is opposite to its direction in the mitochondrial membrane (Fig. 6). Electrons move to the outside, and protons are concentrated inside the tylactoid matrix. The matrix is charged positively, and the outer membrane of the tylactoid is negatively charged, that is, the direction of the proton gradient is opposite to its direction in the mitochondria.
Another feature is a significantly larger proportion of pH in the proton potential compared to mitochondria. The tylactoid matrix is highly acidic, so the Δ pH can reach 0.1-0.2 V, while the Δ is about 0.1 V. The total value of Δ μ H +> 0.25 V.
H + -ATP synthetase, designated in chloroplasts as the "CF 1 + F 0" complex, is also oriented in the opposite direction. Its head (F 1) looks outward, towards the chloroplast stroma. Protons are pushed out through CF 0 + F 1 from the matrix to the outside, and ATP is formed in the active center of F 1 due to the energy of the proton potential.
In contrast to the mitochondrial chain, the tylactoid chain apparently has only two conjugation sites; therefore, the synthesis of one ATP molecule requires three protons instead of two, i.e., the ratio is 3 H + / 1 mol of ATP.
So, at the first stage of photosynthesis, during light reactions, ATP and NADP are formed in the chloroplast stroma · H - products required for dark reactions.
Mechanism of the dark stage of photosynthesis |
Dark reactions of photosynthesis are the process of incorporating carbon dioxide into organic matter with the formation of carbohydrates (photosynthesis of glucose from CO 2). Reactions take place in the chloroplast stroma with the participation of the products of the light stage of photosynthesis - ATP and NADP · H2.
Assimilation of carbon dioxide (photochemical carboxylation) is a cyclical process also called the pentose phosphate photosynthetic cycle or Calvin cycle (Fig. 7). It can be divided into three main phases:
- carboxylation (fixation of CO 2 with ribulose diphosphate)
- reduction (formation of triose phosphates during the reduction of 3-phosphoglycerate)
- regeneration of ribulose diphosphate
Ribulose 5-phosphate (a sugar containing 5 carbon atoms with a phosphate residue at carbon at position 5) is phosphorylated by ATP, resulting in ribulose diphosphate. This latter substance is carboxylated by addition of CO 2, apparently to an intermediate six-carbon product, which, however, immediately cleaves with the addition of a water molecule, forming two molecules of phosphoglyceric acid. Then phosphoglyceric acid is reduced during an enzymatic reaction, which requires the presence of ATP and NADP · H with the formation of phosphoglycerol aldehyde (three-carbon sugar - triose). As a result of the condensation of two such trioses, a hexose molecule is formed, which can be incorporated into a starch molecule and thus stored in reserve.
To complete this phase of the cycle, 1 CO2 molecule is absorbed in the process of photosynthesis and 3 ATP molecules and 4 H atoms (attached to 2 NAD molecules · H). Ribulose phosphate is regenerated from hexose phosphate by certain reactions of the pentose phosphate cycle (Fig. 8), which can again attach to itself another molecule of carbon dioxide.
None of the described reactions - carboxylation, restoration or regeneration - can be considered specific only for the photosynthesizing cell. The only difference found in them is that for the reduction reaction, during which phosphoglyceric acid is converted into phosphoglyceric aldehyde, NADP is required · H, not OVER · H as usual.
The fixation of CO 2 by ribulose diphosphate is catalyzed by the enzyme ribulose diphosphate carboxylase: Ribulose diphosphate + CO 2 -> 3-Phosphoglycerate Next, 3-phosphoglycerate is reduced using NADP · H 2 and ATP to glyceraldehyde-3-phosphate. This reaction is catalyzed by an enzyme called glyceraldehyde-3-phosphate dehydrogenase. Glyceraldehyde-3-phosphate readily isomerized to dihydroxyacetone phosphate. Both triose phosphates are used in the formation of fructose bisphosphate (a reverse reaction catalyzed by fructose bisphosphate aldolase). Part of the molecules of the formed fructose bisphosphate participate, together with triose phosphates, in the regeneration of ribulose diphosphate (close the cycle), and the other part is used for storing carbohydrates in photosynthetic cells, as shown in the diagram.
It is estimated that 12 NADPH is required to synthesize one glucose molecule from CO 2 in the Calvin cycle. · H + H + and 18 ATP (12 ATP molecules are spent on the reduction of 3-phosphoglycerate, and 6 molecules - in the reactions of ribulose diphosphate regeneration). The minimum ratio is 3 ATP: 2 NADP · H 2.
One can notice the generality of the principles underlying photosynthetic and oxidative phosphorylation, and photophosphorylation is, as it were, inverse oxidative phosphorylation:
The energy of light is the driving force behind the phosphorylation and synthesis of organic substances (S-H 2) during photosynthesis and, conversely, the energy of oxidation of organic substances during oxidative phosphorylation. Therefore, it is plants that provide life for animals and other heterotrophic organisms:
Carbohydrates, formed during photosynthesis, are used to build the carbon skeletons of numerous organic substances in plants. Organo-nitrogen substances are assimilated by photosynthetic organisms by the reduction of inorganic nitrates or atmospheric nitrogen, and sulfur - by the reduction of sulfates to sulfhydryl groups of amino acids. Photosynthesis ultimately ensures the construction of not only essential for life proteins, nucleic acids, carbohydrates, lipids, cofactors, but also numerous products of secondary synthesis, which are valuable medicinal substances (alkaloids, flavonoids, polyphenols, terpenes, steroids, organic acids, etc. .).
Chlorophyll-free photosynthesis
Chlorophyll-free photosynthesis was found in salt-loving bacteria with a violet light-sensitive pigment. This pigment turned out to be a protein called bacteriorhodopsin, which, like the visual purpura of the retina, rhodopsin, contains a derivative of vitamin A, retinal. Bacteriorhodopsin, built into the membrane of salt-loving bacteria, forms a proton potential on this membrane in response to the absorption of light by retinal, which is converted into ATP. Thus, bacteriorhodopsin is a chlorophyll-free converter of light energy.
Photosynthesis and the external environment
Photosynthesis is only possible in the presence of light, water and carbon dioxide. The efficiency of photosynthesis is not more than 20% in cultivated plant species, and usually it does not exceed 6-7%. In the atmosphere, about 0.03% (vol.) CO 2, with an increase in its content to 0.1%, the intensity of photosynthesis and plant productivity increase, therefore it is advisable to feed the plants with hydrocarbons. However, the content of CO 2 in the air above 1.0% has a detrimental effect on photosynthesis. For a year, only terrestrial plants assimilate 3% of the total СО 2 of the Earth's atmosphere, that is, about 20 billion tons. The carbohydrates synthesized from СО 2 accumulate up to 4 · 10 18 kJ of light energy. This corresponds to the power plant's capacity of 40 billion kW. A byproduct of photosynthesis, oxygen, is vital for higher organisms and aerobic microorganisms. Preserving vegetation means preserving life on Earth.
The efficiency of photosynthesis
The efficiency of photosynthesis in terms of biomass production can be estimated through the proportion of total solar radiation falling on a certain area over a certain time, which is stored in organic matter of the crop. The productivity of the system can be estimated by the amount of organic dry matter obtained from a unit of area per year, and expressed in units of mass (kg) or energy (mJ) of products obtained per hectare per year.
The biomass yield depends, therefore, on the area of the collector of solar energy (leaves), functioning throughout the year, and the number of days in a year with such illumination conditions when photosynthesis is possible at the maximum rate, which determines the efficiency of the entire process. The results of determining the proportion of solar radiation (in%) available to plants (photosynthetically active radiation, PAR), and knowledge of the main photochemical and biochemical processes and their thermodynamic efficiency make it possible to calculate the probable limiting rates of organic matter formation in terms of carbohydrates.
Plants use light with wavelengths between 400 and 700 nm, which means that photosynthetically active radiation accounts for 50% of all sunlight. This corresponds to an intensity on the Earth's surface of 800-1000 W / m2 for a typical sunny day (on average). The average maximum efficiency of energy conversion during photosynthesis in practice is 5-6%. These estimates are derived from the study of the CO 2 binding process, as well as the accompanying physiological and physical losses. One mole of bound CO 2 in the form of a carbohydrate corresponds to an energy of 0.47 MJ, and the energy of a mole of quanta of red light with a wavelength of 680 nm (the most energy-poor light used in photosynthesis) is 0.176 MJ. Thus, the minimum number of moles of red light quanta required to bind 1 mole of CO 2 is 0.47: 0.176 = 2.7. However, since the transfer of four electrons from water to fix one CO2 molecule requires at least eight quanta of light, the theoretical binding efficiency is 2.7: 8 = 33%. These calculations are made for red light; it is clear that for white light this value will be correspondingly lower.
In the best field conditions, the fixation efficiency in plants reaches 3%, but this is possible only in short periods of growth and, if recalculated for the whole year, it will be somewhere between 1 and 3%.
In practice, on average per year, the efficiency of photosynthetic energy conversion in temperate zones is usually 0.5-1.3%, and for subtropical crops - 0.5-2.5%. The product yield that can be expected at a certain level of sunlight intensity and different photosynthetic efficiency can be easily estimated from the graphs shown in Fig. nine.
The importance of photosynthesis
- The process of photosynthesis is the basis for the nutrition of all living things, and also supplies humanity with fuel, fiber and countless beneficial chemical compounds.
- About 90-95% of the dry weight of the crop is formed from carbon dioxide and water bound from the air during photosynthesis.
- A person uses about 7% of the products of photosynthesis in food, as animal feed, in the form of fuel and building materials.
transformations
absorbed by the body
light energy in
chemical energy
organic
(inorganic)
connections.
The main role is the reduction of CO2 to
carbohydrate level with
use of energy
Sveta.
Development of the doctrine of photosynthesis
Klimant Arkadevich Timiryazev(May 22 (June 3) 1843, Petersburg - 28
April 1920, Moscow) Scientific works
Timiryazev, are devoted to the issue of
decomposition of atmospheric carbon dioxide
green plants under the influence
solar energy. Study of the composition and
optical properties of green pigment
plants (chlorophyll), its genesis,
physical and chemical conditions
decomposition of carbon dioxide, determination
component parts of the sunbeam,
taking part in this phenomenon,
quantification study
between the absorbed energy and
the work performed. Joseph Priestley (March 13
1733 - 6 February 1804) -
British priest, dissenter, naturalist,
philosopher, public figure.
Went down in history first of all
as an outstanding chemist,
discovered oxygen and
carbon dioxide Pierre Joseph Peltier - (March 22, 1788 - July 19
1842) - French chemist and pharmacist, one of the
the founders of the chemistry of alkaloids.
In 1817, together with Joseph Bienneme Cavanto, he
isolated a green pigment from plant leaves, which
they called it chlorophyll. Alexey Nikolaevich Bach
(5 (17) March 1857 - 13 May,
1946) - Soviet biochemist and
plant physiologist. Expressed
thought that CO2 assimilation
in photosynthesis is
coupled redox process,
occurring due to hydrogen and
hydroxyl of water, and oxygen
is released from the water through
intermediate peroxide
connections.
General equation of photosynthesis
6 CO2 + 12 H2OC6H12O6 + 6 O2 + 6 H2O In higher plants, photosynthesis is carried out in
specialized cells of leaf organelles -
chloroplasts.
Chloroplasts are round or disc-shaped
little bodies 1-10 microns long, up to 3 microns thick. Content
there are 20 to 100 of them in cells.
Chemical composition (% on dry basis):
Protein - 35-55
Lipids - 20-30
Carbohydrates - 10
RNA - 2-3
DNA - up to 0.5
Chlorophyll - 9
Carotenoids - 4.5
Chloroplast structure
10. Origin of chloroplasts
Types of chloroplast formation:Division
Budding
Nuclear path
darkness
core
initial
particle
light
prolamillary
body
proplastida
chloroplast
nuclear route diagram
11. Ontogenesis of chloroplasts
12.
Chloroplasts are green plastids thatare found in plant and algae cells.
Chloroplast ultrastructure:
1.the outer membrane
2.intermembrane
space
3.inner membrane
(1 + 2 + 3: shell)
4.stroma (liquid)
5.thylakoid with lumen
6.thylakoid membrane
7.grain (thylakoid stack)
8.thylakoid (lamella)
9.grain starch
10.ribosome
11.plastid DNA
12.plstoglobula (drop of fat)
13. Pigments of photosynthetic plants
chlorophyllsphycobilins
Phycobilins
carotenoids
flavonoid
pigments
14. Chlorophylls
Chlorophyll -green pigment,
conditioning
chloroplast staining
plants in green
Colour. Chemical
structure
chlorophylls -
magnesium complexes
various
tetrapyrroles.
Chlorophylls have
porphyrinic
structure.
15.
ChlorophyllsChlorophyll "a"
(blue-green
bacteria)
Chlorophyll "c"
(brown algae)
Chlorophyll "b"
(higher plants,
green, charovy
seaweed)
Chlorophyll "d"
(red algae)
16. Phycobilins
Phycobilins arepigments,
representing
subsidiary
photosynthetic
pigments that can
transfer energy
absorbed quanta
light on chlorophyll,
expanding the spectrum of action
photosynthesis.
Open tetrapyrrole
structures.
Found in algae.
17. Carotenoids
Structural formula18.
Carotenoids arefat soluble
yellow pigments,
red and orange
colors. Attach
coloring to the majority
orange vegetables and
fruit.
19. Groups of carotenoids:
Carotenes - yellow-orange pigment,unsaturated hydrocarbon
from the group of carotenoids.
Formula C40H56. Insoluble
in water, but dissolves in
organic solvents.
Contained in the leaves of all plants, as well as in
carrot root, rose hips, etc. Is
vitamin A provitamin.
2.
Xanthophylls - plant pigment,
crystallizes in prismatic crystals
yellow color.
1.
20. Flavonoid pigments
Flavonoids are a groupwater-soluble natural
phenolic compounds.
Represent
heterocyclic
oxygenated
connections predominantly
yellow, orange, red
colors. They belong to
compounds С6-С3-С6 series -
their molecules have two
benzene nuclei connected
with each other three carbon
fragment.
Flavone structure
21. Flavonoid pigments:
Anthocyanins are natural substances that color plants;belong to glycosides.
Flavones and flavonols. Play the role of UV absorbers thereby protecting chlorophyll and cytoplasm
from destruction.
22. Stages of photosynthesis
lightImplemented in
chloroplast grains.
Leaks if present
light fast< 10 (-5)
sec
dark
Implemented in
colorless protein stroma
chloroplasts.
For the flowing light
not required
Slow ~ 10 (-2) sec
23.
24.
25. Light stage of photosynthesis
During the light stage of photosynthesis,high-energy products: ATP serving in
the cell as a source of energy, and NADPH, which is used
as a reducing agent. As a by-product
oxygen is released.
General equation:
ADP + H3PO4 + H2O + NADP
ATP + NADPH + 1 / 2O2
26.
Absorption spectraPAR: 380 - 710 nm
Carotenoids: 400-550 nm principal
maximum: 480 nm
Chlorophylls:
in the red region of the spectrum
640-700 nm
in blue - 400-450 nm
27. Chlorophyll arousal levels
1st level. Associated with the transition to a higherenergy level of electrons in the system
conjugation of two links
2nd level. Associated with the excitation of unpaired electrons
four nitrogen and oxygen atoms in the porphyrin
ring.
28. Pigment systems
Photosystem IConsists of 200 molecules
chlorophyll "a", 50
molecules of caroinoids and 1
pigment molecules
(P700)
Photosystem II
Consists of 200 molecules
chlorophyll "a670", 200
chlorophyll "b" molecules and
one pigment molecule
(P680)
29. Localization of electron and proton transport reactions in the thylakoid membrane
30. Non-cyclic photosynthetic phosphorylation (Z - scheme, or Govindzhi scheme)
xe
Фg е
Ff e
NADP
Nx
e
FeS
e
ADP
Cit b6
e
II FS
NADPH
ATF
e
I FS
Cit f
e
e
PC
e
P680
hV
О2
e
H2 O
P700
hV
Ff - pheofetin
Px - plastoquinone
FeS - iron sulfur protein
Cyt b6 - cytochrome
PC - Plastocynin
Фg - ferodoxin
x - unknown nature.
compound
31. Photosynthetic phosphorylation
Photosynthetic phosphorylation is a processenergy formation of ATP and NADPH during photosynthesis with
using quanta of light.
Views:
non-cyclic (Z-scheme). Two
pigment systems.
cyclical. Photosystem I participates.
pseudocyclic. Goes as non-cyclic, but not
there is a visible evolution of oxygen.
32. Cyclic photosynthetic phosphorylation
eADP
Фg
e
ATF
Citb6
e
e
Citf
e
P700
hV
e
ADP
ATF
Cyt b6 - cytochrome
Фg - ferodoxin
33. Cyclic and non-cyclic transport of electrons in chloroplasts
34.
Photosynthesis chemistryPhotosynthesis
carried out
by
sequential alternation of two phases:
light,
flowing
with
big
speed and temperature independent;
dark, so named because for
reactions occurring in this phase
no light energy required.
35. Dark stage of photosynthesis
In the dark stage with the participation of ATP and NADPHCO2 is reduced to glucose (C6H12O6).
Although no light is required for this
process, he participates in its regulation.
36.C3-photosynthesis, Calvin cycle
Calvin cycle or reductionthe pentose phosphate cycle consists of three stages:
Carboxylation of RDF.
Recovery. There is a restoration of 3-FGK to
3-FGA.
Regeneration of the RDF acceptor. Carried out in series
reactions of interconversion of phosphorylated sugars with
different number of carbon atoms (triose, tetrose,
pentose, hexose, etc.)
37. General equation of the Calvin cycle
H2CO (P)C = O
HO-C-H + * CO2
H-C-OH
H2CO (P)
RDF
H2 * CO (P)
2 NSON
UNSD
3-FGK
H2 * CO (P)
2nson
COO (R)
1,3-FGK
H2 * CO (P)
2nson
C = O
H
3-FGA
H2 * CO (P)
2C = O
NSON
3-FDA
condensation, or
polymerization
H
H2CO (P)
H2CO (P)
C = O
C = O
C = O
NSON
HOSN
HOSN
HOSN
H * DREAM
NSON
H * DREAM
NSON
NSON
NSON
H2CO (P)
Н2СОН
H2CO (P)
1,6-diphosphate-fructose-6-glucose-6-fructose
phosphate
phosphate
H
C = O
NSON
HOSN
H * DREAM
NSON
Н2СОН
glucose
38.C4-photosynthesis (the Hatch - Slack - Karpilov path)
It is carried out in plants with two types of chloroplast.In addition to RDF, there can be three CO2 acceptors
carbon compound - phosphoenol PVC (FEP)
C4 - the path was first discovered
in tropical cereals. In works
Yu.S. Karpilov, M. Hatch, K. Slack with
using tagged carbon
it was shown that the first
products of photosynthesis in these
plants are organic
acid.
39.
40. Photosynthesis like tolstyankovs
Typical for plantssucculents at night
fix carbon in
organic acids by
predominantly in apple. it
occurs under the influence
enzymes
pyruvate carboxylic acid. it
allows during the day
keep the stomata closed and
thus reduce
transpiration. This type
received the name SAMPhotosynthesis.
41. SAM photosynthesis
In CAM photosynthesis, separation occursassimilation of CO2 and the Calvin cycle is not in
space as in C4, but in time. At night in
vacuoles of cells in a similar
the above mechanism with open
stomata accumulate malate, during the day when
closed stomata are in the Calvin cycle. This
the mechanism allows you to save as much as possible
water, however, is inferior in efficiency to both C4 and
C3.
42.
43.
Photorespiration44. Influence of internal and external factors on photosynthesis
Photosynthesismuch
changes due
influence on him
complex often
interacting
external and internal
factors.
45. Factors affecting photosynthesis
1.Ontogenetic
plant condition.
Maximum
intensity
photosynthesis is observed
during the transition
plants from vegetation to
reproductive phase. Have
aging leaves
intensity
photosynthesis significantly
falls.
46. Factors affecting photosynthesis
2. Light. Photosynthesis does not occur in the dark, sincecarbon dioxide produced by breathing is released from
leaves; with an increase in light intensity,
compensation point at which absorption
carbon dioxide during photosynthesis and its release during
breathing balance each other.
47. Factors affecting photosynthesis
3. Spectrallight composition.
Spectral
composition of solar
light experiences
some
changes in
during the day and in
throughout the year.
48. Factors affecting photosynthesis
4. CO2.Is the main
substrate of photosynthesis and from
its content depends
the intensity of this process.
The atmosphere contains
0.03% by volume; increase
volume of carbon dioxide from 0.1
up to 0.4% increases
the intensity of photosynthesis up to
a certain limit, and
then takes turns
carbon dioxide saturation.
49. Factors affecting photosynthesis
5. Temperature.In plants of moderate
optimal zones
temperature for
photosynthesis
is 20-25; at
tropical - 2035.
50. Factors affecting photosynthesis
6. Water content.Reduction of tissue dehydration by more than 20%
leads to a decrease in the intensity of photosynthesis and to
its further termination, if the loss of water will be
more than 50%.
51. Factors affecting photosynthesis
7. Trace elements.Fe deficiency
causes chlorosis and
affects activity
enzymes. Mn
necessary for
liberation
oxygen and for
assimilation of carbon dioxide
gas. Lack of Cu and
Zn reduces photosynthesis
by 30%
52. Factors affecting photosynthesis
8 contaminantssubstances and
chemical
drugs.
Cause
decline
photosynthesis.
Most
dangerous
substances: NO2,
SO2, weighted
particles.
53. Diurnal course of photosynthesis
At moderate daytime temperatures and sufficienthumidity, the daily course of photosynthesis is approximately
corresponds to a change in the intensity of the solar
insolation. Photosynthesis starting in the morning with sunrise
the sun, reaches a maximum at noon hours,
gradually decreases towards evening and stops with sunset
sun. At elevated temperatures and decreasing
humidity, the maximum of photosynthesis shifts to early
watch.
54. Conclusion
Thus, photosynthesis is the only process onEarth, walking on a grand scale, associated with
converting sunlight energy into chemical energy
connections. This energy stored in green plants
constitutes the basis for the life of all others
heterotrophic organisms on Earth from bacteria to humans.