It is better to explain such a voluminous material as photosynthesis in two paired lessons - then the integrity of the perception of the topic is not lost. The lesson must begin with the history of the study of photosynthesis, the structure of chloroplasts and laboratory work on the study of leaf chloroplasts. After this, it is necessary to move on to the study of the light and dark phases of photosynthesis. When explaining the reactions occurring in these phases, it is necessary to draw up a general diagram:
As you explain, you need to draw diagram of the light phase of photosynthesis.
1. The absorption of a quantum of light by a chlorophyll molecule, which is located in the grana thylakoid membranes, leads to the loss of one electron and transfers it to an excited state. Electrons are transferred along the electron transport chain, resulting in the reduction of NADP + to NADP H.
2. The place of the released electrons in chlorophyll molecules is taken by the electrons of water molecules - this is how water undergoes decomposition (photolysis) under the influence of light. The resulting hydroxyls OH– become radicals and combine in the reaction 4 OH – → 2 H 2 O +O 2, leading to the release of free oxygen into the atmosphere.
3. Hydrogen ions H+ do not penetrate the thylakoid membrane and accumulate inside, charging it positively, which leads to an increase in the electrical potential difference (EPD) across the thylakoid membrane.
4. When the critical REF is reached, protons rush out through the proton channel. This stream of positively charged particles is used to produce chemical energy using a special enzyme complex. Formed as a result ATP molecules pass into the stroma, where they participate in carbon fixation reactions.
5. Hydrogen ions released to the surface of the thylakoid membrane combine with electrons, forming atomic hydrogen, which is used to restore the NADP + transporter.
The sponsor of the article is the Aris group of companies. Production, sales and rental scaffolding(frame facade LRSP, frame high-rise A-48, etc.) and tour towers (PSRV "Aris", PSRV "Aris Compact" and "Aris-Dachnaya", platforms). Clamps for scaffolding, construction fencing, wheel supports for towers. You can find out more about the company, view the product catalog and prices, contacts on the website, which is located at: http://www.scaffolder.ru/.
After considering this issue, analyzing it again according to the diagram, we invite students to fill out the table.
Table. Reactions of light and dark phases of photosynthesis
After filling out the first part of the table, you can proceed to the analysis dark phase of photosynthesis.
In the stroma of the chloroplast, pentoses are constantly present - carbohydrates, which are five-carbon compounds that are formed in the Calvin cycle (carbon dioxide fixation cycle).
1. Joins pentose carbon dioxide, an unstable six-carbon compound is formed, which breaks down into two molecules of 3-phosphoglyceric acid (PGA).
2. PGA molecules accept one phosphate group from ATP and are enriched with energy.
3. Each of the FHAs attaches one hydrogen atom from two carriers, turning into a triose. Trioses combine to form glucose and then starch.
4. Triose molecules combining to form different combinations, form pentoses and re-enter the cycle.
Total reaction of photosynthesis:
Scheme. Photosynthesis process
Test
1. Photosynthesis occurs in organelles:
a) mitochondria;
b) ribosomes;
c) chloroplasts;
d) chromoplasts.
2. The chlorophyll pigment is concentrated in:
a) chloroplast membrane;
b) stroma;
c) grains.
3. Chlorophyll absorbs light in the region of the spectrum:
a) red;
b) green;
c) purple;
d) in the entire region.
4. Free oxygen during photosynthesis is released during the breakdown of:
a) carbon dioxide;
b) ATP;
c) NADP;
d) water.
5. Free oxygen is formed in:
a) dark phase;
b) light phase.
6. In the light phase of photosynthesis, ATP:
a) synthesized;
b) splits.
7. In the chloroplast, the primary carbohydrate is formed in:
a) light phase;
b) dark phase.
8. NADP in the chloroplast is necessary:
1) as a trap for electrons;
2) as an enzyme for the formation of starch;
3) how component chloroplast membranes;
4) as an enzyme for photolysis of water.
9. Photolysis of water is:
1) accumulation of water under the influence of light;
2) dissociation of water into ions under the influence of light;
3) release of water vapor through stomata;
4) injection of water into the leaves under the influence of light.
10. Under the influence of light quanta:
1) chlorophyll is converted into NADP;
2) an electron leaves the chlorophyll molecule;
3) the chloroplast increases in volume;
4) chlorophyll is converted into ATP.
LITERATURE
Bogdanova T.P., Solodova E.A. Biology. Handbook for high school students and applicants to universities. – M.: LLC “AST-Press School”, 2007.
Photosynthesis is a set of processes for the synthesis of organic compounds from inorganic ones due to the conversion of light energy into energy chemical bonds. Phototrophic organisms include green plants, some prokaryotes - cyanobacteria, purple and green sulfur bacteria, and plant flagellates.
Research into the process of photosynthesis began in the second half of the 18th century. An important discovery was made by the outstanding Russian scientist K. A. Timiryazev, who substantiated the doctrine of the cosmic role of green plants. Plants absorb sunlight and convert light energy into the energy of chemical bonds of organic compounds synthesized by them. Thus, they ensure the preservation and development of life on Earth. The scientist also theoretically substantiated and experimentally proved the role of chlorophyll in the absorption of light during photosynthesis.
Chlorophylls are the main photosynthetic pigments. They are similar in structure to hemoglobin, but contain magnesium instead of iron. Iron content is necessary to ensure the synthesis of chlorophyll molecules. There are several chlorophylls that differ in their chemical structure. Mandatory for all phototrophs is chlorophyll a . Chlorophyllb found in green plants chlorophyll c – in diatoms and brown algae. Chlorophyll d characteristic of red algae.
Green and purple photosynthetic bacteria have special bacteriochlorophylls . Bacterial photosynthesis has much in common with plant photosynthesis. It differs in that in bacteria the hydrogen donor is hydrogen sulfide, and in plants it is water. Green and purple bacteria do not have photosystem II. Bacterial photosynthesis is not accompanied by the release of oxygen. The overall equation for bacterial photosynthesis is:
6C0 2 + 12H 2 S → C 6 H 12 O 6 + 12S + 6H 2 0.
Photosynthesis is based on the redox process. It is associated with the transfer of electrons from compounds that supply electrons-donors to compounds that accept them - acceptors. Light energy is converted into the energy of synthesized organic compounds (carbohydrates).
There are special structures on the membranes of chloroplasts - reaction centers that contain chlorophyll. In green plants and cyanobacteria there are two photosystems – first (I) And second (II) , which have different reaction centers and are interconnected through an electron transfer system.
Two phases of photosynthesis
The process of photosynthesis consists of two phases: light and dark.
Occurs only in the presence of light on the internal membranes of mitochondria in the membranes of special structures - thylakoids . Photosynthetic pigments capture light quanta (photons). This leads to the “excitation” of one of the electrons of the chlorophyll molecule. With the help of carrier molecules, the electron moves to the outer surface of the thylakoid membrane, acquiring a certain potential energy.
This electron in photosystem I can return to its energy level and restore it. NADP (nicotinamide adenine dinucleotide phosphate) may also be transmitted. By interacting with hydrogen ions, electrons restore this compound. Reduced NADP (NADP H) supplies hydrogen to reduce atmospheric CO 2 to glucose.
Similar processes occur in photosystem II . Excited electrons can be transferred to photosystem I and restore it. The restoration of photosystem II occurs due to electrons supplied by water molecules. Water molecules split (photolysis of water) into hydrogen protons and molecular oxygen, which is released into the atmosphere. The electrons are used to restore photosystem II. Water photolysis equation:
2Н 2 0 → 4Н + + 0 2 + 2е.
When electrons from the outer surface of the thylakoid membrane return to the previous energy level, energy is released. It is stored in the form of chemical bonds of ATP molecules, which are synthesized during reactions in both photosystems. The process of ATP synthesis with ADP and phosphoric acid is called photophosphorylation . Some of the energy is used to evaporate water.
During the light phase of photosynthesis, energy-rich compounds are formed: ATP and NADP H. During the breakdown (photolysis) of water molecules, molecular oxygen is released into the atmosphere.
Reactions take place in the internal environment of chloroplasts. They can occur both in the presence of light and without it. Organic substances are synthesized (C0 2 is reduced to glucose) using the energy that was formed in the light phase.
The process of carbon dioxide reduction is cyclical and is called Calvin cycle . Named after the American researcher M. Calvin, who discovered this cyclic process.
The cycle begins with the reaction of atmospheric carbon dioxide with ribulose biphosphate. The process is catalyzed by an enzyme carboxylase . Ribulose biphosphate is a five-carbon sugar combined with two phosphoric acid units. A number of chemical transformations occur, each of which is catalyzed by its own specific enzyme. How is the end product of photosynthesis formed? glucose , and ribulose biphosphate is also reduced.
The overall equation for the process of photosynthesis is:
6C0 2 + 6H 2 0 → C 6 H 12 O 6 + 60 2
Thanks to the process of photosynthesis, light energy from the Sun is absorbed and converted into the energy of chemical bonds of synthesized carbohydrates. Energy is transferred through food chains to heterotrophic organisms. During photosynthesis, carbon dioxide is absorbed and oxygen is released. All atmospheric oxygen is of photosynthetic origin. Over 200 billion tons of free oxygen are released annually. Oxygen protects life on Earth from ultraviolet radiation by creating an ozone shield in the atmosphere.
The process of photosynthesis is ineffective, since only 1-2% is converted into synthesized organic matter. solar energy. This is due to the fact that plants do not absorb light enough, part of it is absorbed by the atmosphere, etc. Most of the sunlight is reflected from the surface of the Earth back into space.
- synthesis of organic compounds from inorganic ones using light energy (hv). The overall equation for photosynthesis is:
6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2
Photosynthesis occurs with the participation of photosynthetic pigments that have unique property converting the energy of sunlight into chemical bond energy in the form of ATP. Photosynthetic pigments are protein-like substances. The most important of them is the pigment chlorophyll. In eukaryotes, photosynthetic pigments are embedded in the inner membrane of plastids; in prokaryotes, they are embedded in invaginations of the cytoplasmic membrane.
The structure of the chloroplast is very similar to the structure of the mitochondrion. The inner membrane of the grana thylakoids contains photosynthetic pigments, as well as electron transport chain proteins and ATP synthetase enzyme molecules.
The process of photosynthesis consists of two phases: light and dark.
Light phase Photosynthesis occurs only in the light in the grana thylakoid membrane. In this phase, chlorophyll absorbs light quanta, produces an ATP molecule, and photolysis of water.
Under the influence of a light quantum (hv), chlorophyll loses electrons, passing into an excited state:
Chl → Chl + e -
These electrons are transferred by carriers to the outside, i.e. the surface of the thylakoid membrane facing the matrix, where they accumulate.
At the same time, photolysis of water occurs inside the thylakoids, i.e. its decomposition under the influence of light
2H 2 O → O 2 +4H + + 4e —
The resulting electrons are transferred by carriers to chlorophyll molecules and restore them: the chlorophyll molecules return to a stable state.
Hydrogen protons formed during photolysis of water accumulate inside the thylakoid, creating an H + reservoir. As a result inner surface The thylakoid membrane is charged positively (due to H +), and the outer membrane is charged negatively (due to e -). As oppositely charged particles accumulate on both sides of the membrane, the potential difference increases. When the critical value of the potential difference is reached, the force electric field begins to push protons through the ATP synthetase channel. The energy released in this case is used to phosphorylate ADP molecules:
ADP + P → ATP
The formation of ATP during photosynthesis under the influence of light energy is called photophosphorylation.
Hydrogen ions, once on the outer surface of the thylakoid membrane, meet electrons there and form atomic hydrogen, which binds to the hydrogen carrier molecule NADP (nicotinamide adenine dinucleotide phosphate):
2H + + 4e - + NADP + → NADP H 2
Thus, during the light phase of photosynthesis, three processes occur: the formation of oxygen due to the decomposition of water, the synthesis of ATP, and the formation of hydrogen atoms in the form of NADP H2. Oxygen diffuses into the atmosphere, ATP and NADP H2 participate in the processes of the dark phase.
Dark phase photosynthesis occurs in the chloroplast matrix both in the light and in the dark and represents a series of sequential transformations of CO 2 coming from the air in the Calvin cycle. Dark phase reactions are carried out using the energy of ATP. In the Calvin cycle, CO 2 bonds with hydrogen from NADP H 2 to form glucose.
In the process of photosynthesis, in addition to monosaccharides (glucose, etc.), monomers of other organic compounds are synthesized - amino acids, glycerol and fatty acids. Thus, thanks to photosynthesis, plants provide themselves and all living things on Earth with the necessary organic substances and oxygen.
Comparative characteristics photosynthesis and respiration of eukaryotes is given in the table:
| Sign | Photosynthesis | Breath |
|---|---|---|
| Reaction equation | 6CO 2 + 6H 2 O + Light energy → C 6 H 12 O 6 + 6O 2 | C 6 H 12 O 6 + 6O 2 → 6H 2 O + Energy (ATP) |
| Starting materials | Carbon dioxide, water | |
| Reaction products | Organic matter, oxygen | Carbon dioxide, water |
| Importance in the cycle of substances | Synthesis of organic substances from inorganic substances | Decomposition of organic substances to inorganic ones |
| Conversion of energy | Conversion of light energy into the energy of chemical bonds of organic substances | Conversion of the energy of chemical bonds of organic substances into the energy of high-energy bonds of ATP |
| Key Stages | Light and dark phase (including Calvin cycle) | Incomplete oxidation (glycolysis) and complete oxidation (including Krebs cycle) |
| Location of the process | Chloroplast | Hyaloplasm (incomplete oxidation) and mitochondria (complete oxidation) |
Photosynthesis — unique system processes of creating, with the help of chlorophyll and light energy, organic substances from inorganic ones and the release of oxygen into the atmosphere, implemented on a huge scale on land and in water.
All processes of the dark phase of photosynthesis occur without direct consumption of light, but high-energy substances (ATP and NADP.H), formed with the participation of light energy, play a large role in them during the light phase of photosynthesis. During the dark phase, the energy of macroenergetic bonds of ATP is converted into the chemical energy of organic compounds of carbohydrate molecules. This means that the energy of sunlight is, as it were, conserved in chemical bonds between atoms of organic substances, which is of great importance in the energy of the biosphere and specifically for the life activity of the entire living population of our planet.
Photosynthesis occurs in the chloroplasts of the cell and is the synthesis of carbohydrates in chlorophyll-bearing cells, which occurs with the consumption of energy from sunlight. There are light and temp phases of photosynthesis. The light phase, with the direct consumption of light quanta, provides the synthesis process with the necessary energy in the form of NADH and ATP. Dark phase - without the participation of light, but through a numerous series chemical reactions (Calvin cycle) provides the formation of carbohydrates, mainly glucose. The importance of photosynthesis in the biosphere is enormous.
On this page there is material on the following topics:
Photosynthesis light and dark phases abstract
Dark phase of photosynthesis test solve
Light phase and dark processes
Report on the topic of the dark phase of photosynthesis
The light reactions of photosynthesis occur in
Questions about this material:
DEFINITION: Photosynthesis is the process of formation of organic substances from carbon dioxide and water, in light, with the release of oxygen.
Brief explanation of photosynthesisThe process of photosynthesis involves:
1) chloroplasts,
3) carbon dioxide,
5) temperature.
U higher plants photosynthesis occurs in chloroplasts - oval-shaped plastids (semi-autonomous organelles) containing the pigment chlorophyll, thanks to the green color of which parts of the plant also have a green color.
In algae, chlorophyll is contained in chromatophores (pigment-containing and light-reflecting cells). In brown and red algae that live at considerable depths, where it is difficult to reach sunlight, there are other pigments.
If you look at the food pyramid of all living things, photosynthetic organisms are at the very bottom, among the autotrophs (organisms that synthesize organic substances from inorganic ones). Therefore, they are a source of food for all life on the planet.
During photosynthesis, oxygen is released into the atmosphere. IN upper layers ozone is formed from the atmosphere. The ozone shield protects the Earth's surface from harsh ultraviolet radiation, allowing life to emerge from the sea onto land.
Oxygen is necessary for the respiration of plants and animals. When glucose is oxidized with the participation of oxygen, mitochondria store almost 20 times more energy than without it. This makes the use of food much more efficient, which has led to high level metabolism in birds and mammals.
More detailed description plant photosynthesis process
Progress of photosynthesis:
The process of photosynthesis begins with light hitting chloroplasts - intracellular semi-autonomous organelles containing green pigment. When exposed to light, chloroplasts begin to consume water from the soil, splitting it into hydrogen and oxygen.
Part of the oxygen is released into the atmosphere, the other part goes to oxidative processes in the plant.
Sugar combines with nitrogen, sulfur and phosphorus coming from the soil, in this way green plants produce starch, fats, proteins, vitamins and other complex compounds necessary for their life.
Photosynthesis occurs best under the influence of sunlight, but some plants can be content with artificial lighting.
A complex description of the mechanisms of photosynthesis for the advanced reader
Until the 60s of the 20th century, scientists knew only one mechanism for carbon dioxide fixation - through the C3-pentose phosphate pathway. However, recently a group of Australian scientists was able to prove that in some plants the reduction of carbon dioxide occurs through the C4-dicarboxylic acid cycle.
In plants with the C3 reaction, photosynthesis occurs most actively under conditions of moderate temperature and light, mainly in forests and in dark places. Almost all of these plants include cultivated plants and most vegetables. They form the basis of the human diet.
In plants with the C4 reaction, photosynthesis occurs most actively under conditions high temperature and illumination. Such plants include, for example, corn, sorghum and sugar cane, which grow in warm and tropical climates.
Plant metabolism itself was discovered quite recently, when it was discovered that in some plants that have special tissues for storing water, carbon dioxide accumulates in the form of organic acids and is fixed in carbohydrates only after a day. This mechanism helps plants save water.
How does the process of photosynthesis occur?
The plant absorbs light using a green substance called chlorophyll. Chlorophyll is found in chloroplasts, which are found in stems or fruits. There is a particularly large amount of them in leaves, because due to its very flat structure, the leaf can attract a lot of light, and therefore receive much more energy for the process of photosynthesis.
After absorption, chlorophyll is in an excited state and transfers energy to other molecules of the plant body, especially those directly involved in photosynthesis. The second stage of the photosynthesis process takes place without the mandatory participation of light and consists of obtaining a chemical bond with the participation of carbon dioxide obtained from air and water. At this stage, various very useful substances for life, such as starch and glucose, are synthesized.
These organic substances are used by the plants themselves to nourish its various parts, as well as to maintain normal life functions. In addition, these substances are also obtained by animals by eating plants. People also get these substances by eating foods of animal and plant origin.
Conditions for photosynthesis
Photosynthesis can occur both under the influence of artificial light and sunlight. As a rule, plants “work” intensively in nature in the spring and summer, when there is a lot of necessary sunlight. In autumn there is less light, the days are shortened, the leaves first turn yellow and then fall off. But spring should appear warm sun as green foliage reappears and green "factories" begin to function again to provide the oxygen so essential to life, as well as many other nutrients.
Alternative definition of photosynthesis
Photosynthesis (from ancient Greek photo-light and synthesis - connection, folding, binding, synthesis) is the process of converting light energy into the energy of chemical bonds of organic substances in the light by photoautotrophs with the participation of photosynthetic pigments (chlorophyll in plants, bacteriochlorophyll and bacteriorhodopsin in bacteria ). In modern plant physiology, photosynthesis is more often understood as a photoautotrophic function - a set of processes of absorption, transformation and use of the energy of light quanta in various endergonic reactions, including the conversion of carbon dioxide into organic substances.
Phases of photosynthesis
Photosynthesis is a rather complex process and includes two phases: light, which always occurs exclusively in the light, and dark. All processes occur inside the chloroplasts on special small organs - thylakodia. During the light phase, a quantum of light is absorbed by chlorophyll, resulting in the formation of ATP and NADPH molecules. The water then breaks down, forming hydrogen ions and releasing an oxygen molecule. The question arises, what are these incomprehensible mysterious substances: ATP and NADH?
ATP is special organic molecules, which are found in all living organisms, they are often called “energy” currency. It is these molecules that contain high-energy bonds and are the source of energy in any organic synthesis and chemical processes in the body. Well, NADPH is actually a source of hydrogen, it is used directly in the synthesis of high-molecular organic substances - carbohydrates, which occurs in the second, dark phase of photosynthesis using carbon dioxide.
Light phase of photosynthesis
Chloroplasts contain a lot of chlorophyll molecules, and they all absorb sunlight. At the same time, light is absorbed by other pigments, but they cannot carry out photosynthesis. The process itself occurs only in some chlorophyll molecules, of which there are very few. Other molecules of chlorophyll, carotenoids and other substances form special antenna and light-harvesting complexes (LHC). They, like antennas, absorb light quanta and transmit excitation to special reaction centers or traps. These centers are located in photosystems, of which plants have two: photosystem II and photosystem I. They contain special chlorophyll molecules: respectively, in photosystem II - P680, and in photosystem I - P700. They absorb light of exactly this wavelength (680 and 700 nm).
The diagram makes it more clear how everything looks and happens during the light phase of photosynthesis.
In the figure we see two photosystems with chlorophylls P680 and P700. The figure also shows the carriers through which electron transport occurs.
So: both chlorophyll molecules of two photosystems absorb a light quantum and become excited. The electron e- (red in the figure) moves to a higher energy level.
Excited electrons have very high energy; they break off and enter a special chain of transporters, which is located in the membranes of thylakoids - the internal structures of chloroplasts. The figure shows that from photosystem II from chlorophyll P680 an electron goes to plastoquinone, and from photosystem I from chlorophyll P700 to ferredoxin. In the chlorophyll molecules themselves, in place of electrons after their removal, blue holes with a positive charge are formed. What to do?
To compensate for the lack of an electron, the chlorophyll P680 molecule of photosystem II accepts electrons from water, and hydrogen ions are formed. In addition, it is due to the breakdown of water that oxygen is released into the atmosphere. And the chlorophyll P700 molecule, as can be seen from the figure, makes up for the lack of electrons through a system of carriers from photosystem II.
In general, no matter how difficult it may be, this is exactly how the light phase of photosynthesis proceeds, its the main point involves the transfer of electrons. You can also see from the figure that in parallel with electron transport, hydrogen ions H+ move through the membrane, and they accumulate inside the thylakoid. Since there are a lot of them there, they move outward with the help of a special conjugating factor, which in the figure orange color, is pictured on the right and looks like a mushroom.
Finally, we see the final step of electron transport, which results in the formation of the aforementioned NADH compound. And due to the transfer of H+ ions, energy currency is synthesized - ATP (seen on the right in the figure).
So, the light phase of photosynthesis is completed, oxygen is released into the atmosphere, ATP and NADH are formed. What's next? Where is the promised organic matter? And then comes the dark stage, which consists mainly of chemical processes.
Dark phase of photosynthesis
For the dark phase of photosynthesis, carbon dioxide – CO2 – is an essential component. Therefore, the plant must constantly absorb it from the atmosphere. For this purpose, there are special structures on the surface of the leaf - stomata. When they open, CO2 enters the leaf, dissolves in water and reacts with the light phase of photosynthesis.
During the light phase in most plants, CO2 binds to the five-carbon organic compound(which is a chain of five carbon molecules), resulting in two molecules of a three-carbon compound (3-phosphoglyceric acid). Because The primary result is precisely these three-carbon compounds; plants with this type of photosynthesis are called C3 plants.
Further synthesis in chloroplasts occurs rather complexly. It ultimately forms a six-carbon compound, from which glucose, sucrose or starch can subsequently be synthesized. In the form of these organic substances, the plant accumulates energy. In this case, only a small part of them remains in the leaf, which is used for its needs, while the rest of the carbohydrates travel throughout the plant, arriving where energy is most needed - for example, at the growth points.
