The light phase of photosynthesis. Photosynthesis process: briefly and understandable for children

Photosynthesis is a combination of the processes of formation of light energy into the energy of chemical bonds of organic substances with the participation of photosynthetic coloring substances.

This type of nutrition is characteristic of plants, prokaryotes and certain types of single-cell eukaryotes.

With natural synthesis, carbon and water in interaction with light are converted into glucose and free oxygen:

6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2

Modern plant physiology under the concept of photosynthesis understands a photometrophic function, which is a set of processes of absorption, transformation and use of luminous energy quanta in different non-repproductive reactions, including the conversion of carbon dioxide to the organic.

Phase

Photosynthesis in plants occurs in the leaves through chloroplasts - semi-autonomous two-grained organelles related to class class. With a flat form of sheet plates, high-quality absorption and full use of light energy and carbon dioxide are provided. Water necessary for natural synthesis comes from roots through water tissue. Gas exchange occurs with the help of diffusion through the dysstrian and partly through the cuticle.

Chloroplasts are filled with colorless stroma and permeated with lamellas, which when connected to each other, form thylacides. It is in them and photosynthesis occurs. Cyanobacteria are chloroplasts themselves, therefore the apparatus for natural synthesis in them is not highlighted in separate organella.

Photosynthesis proceeds with the participation of pigmentswhich are usually served chlorophylls. Some organisms contain another pigment - carotenoid or ficobilin. Prokaryotes have a pigment bacterio-chlorophyll, and these organisms do not excrete oxygen at the end of natural synthesis.

Photosynthesis takes place two phases - light and dark. Each of them is characterized by certain reactions and interacting substances. Consider a Read more photosynthesis phase process.

Light

The first phase of photosynthesis It is characterized by the formation of high-energy products that are ATP, cellular source of energy, and NADF, reducing agent. At the end of the stage, oxygen is formed as a by-product. The light stage occurs necessarily with sunlight.

The photosynthesis process takes place in tylakoid membranes with the participation of electron carriers, ATP-synthetase and chlorophyll (or other pigment).

The functioning of electrochemical chains, according to which electron transmission and partially hydrogen protons occurs, is formed in complex complexes formed by pigments and enzymes.

Light phase process description:

1. In case of sunlight on the leaf plates of plant organisms, the electron of chlorophyll in the structure of the plates occurs;
2. In the active state, the particles come out of the pigment molecule and fall on the outer side of the thylacide, charged negatively. This happens simultaneously with the oxidation and subsequent restoration of the chlorophyll molecules, which select the next electrons from the water entered into the leaves;
3. Then there is a photo and for the formation of ions, which give electrons and are converted to OH radicals that can participate in reactions and in the future;
4. Then these radicals are connected, forming water molecules and free oxygen, entering the atmosphere;
5. The thylacoid membrane acquires a positive charge due to the hydrogen ion, and on the other - negative at the expense of electrons;
6. With the achievement of a 200 mV difference between the sides of the membrane, the protons pass through the ATP-synthetase enzyme, which leads to the transformation of ADP in ATP (phosphorylation process);
7. With nuclear hydrogen released from water, the NADF + is restored in NADF · H2;

Whereas free oxygen in the reaction process enters the atmosphere, ATP and NADF · H2 are involved in the dark phase of natural synthesis.

Norma

Mandatory component for this stage - carbon dioxidewhich plants are constantly absorbed from the external environment through the dust in the leaves. The processes of the dark phase are held in the stroma of chloroplast. Since at this stage is not required a lot of solar energy and will be sufficiently obtained during the light phase ATP and NADF · H2, the reactions in the organisms can occur during the day, and at night. The processes at this stage occur faster than on the previous one.

The combination of all processes occurring in the dark phase is represented as a peculiar chain of consecutive carbon dioxide transformations received from the external environment:

1. The first reaction in such a chain is the fixation of carbon dioxide. The presence of the enzyme ribf carboxylase contributes to the rapid and smooth flow of the reaction, which results in the formation of a hexagonal compound, disintegrating on 2 phosphoglycerolic acid molecules;
2. Then there is a rather complex cycle, including another number of reactions, upon completion of which phosphoglycerin acid is converted into natural sugar - glucose. This process is called Calvin Cycle;

Together with sugar, fatty acids, amino acids, glycerol and nucleotides are also occurring.

The essence of photosynthesis

From the table of comparisons of light and dark phases of natural synthesis, you can briefly describe the essence of each of them. The light phase occurs in chloroplast marins with mandatory inclusion in the reaction of light energy. In reactions, such components are involved as proteins that carry electrons, ATP synthetase and chlorophyll, which, when interacting with water, form free oxygen, ATP and NAPF · H2. For the dark phase occurring in the stroma of chloroplast, the sunlight is not mandatory. The Natural Sugar (glucose) formed at the last stage of ATP and NAPF · H2 in the interaction with carbon dioxide.

As can be seen from the foregoing, photosynthesis appears quite complex and multi-stage phenomenon, including a plurality of reactions in which different substances are involved. As a result of natural synthesis, oxygen is obtained, which is necessary for the respiration of living organisms and protect them from ultraviolet radiation by the formation of the ozone layer.

Photosynthesis - synthesis of organic compounds from inorganic due to light energy (HV). Total photosynthesis equation:

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

Photosynthesis proceeds with the participation of photosynthetic pigments with a unique property of conversion of solar light into the chemical energy in the form of ATP. Photosynthetic pigments are protein-like substances. The most important of them is a pigment chlorophyll. In eukaryotes, photosynthetic pigments are built into the inner membrane of the plastic, in prokaryotes - in prying the cytoplasmic membrane.

The structure of chloroplast is very similar to the structure of mitochondria. In the inner membrane of thylacoids, the grains contain photosynthetic pigments, as well as the proteins of the electron transfer chain and the ATP-synthetase enzyme molecule.

The process of photosynthesis consists of two phases: light and dark.

Light phase Photosynthesis proceeds only in the light in the tylacoid membrane. In this phase, the absorption of the light quanta, the formation of the ATP molecule and the photo and the water is absorbed.

Under the action of the light quantum (HV), chlorophyll loses electrons, moving to the excited state:

Chl → Chl + E -

These electrons are transmitted by carriers to the outer, i.e. Tylacoid membrane surface facing the matrix, where they accumulate.

At the same time inside Tylacoids, the water is a photo of water, i.e. her decomposition under the action of light

2H 2 O → O 2 + 4H + + 4e -

The resulting electrons are transmitted by carriers to chlorophyll molecules and restore them: chlorophyll molecules are returned to a stable state.

The hydrogen protons formed during the photolisis of water are accumulated inside the thylacoid, creating a H + -rerevoire. As a result, the inner surface of the thylacide membrane is charged positively (due to H +), and the outer-negative (due to E -). As they accumulate on both sides of the membrane oppositely charged particles, the potential difference increases. When the critical amount of potential difference is reached, the power of the electric field begins to push protons through the ATP-synthetase channel. The energy released is used to phosphorylation Molecules ADP:

ADP + F → ATP

The formation of ATP in the process of photosynthesis under the action of light energy is called photo phosphaeling.

Hydrogen ions, found ourselves on the outer surface of the thylacoid membrane, are found there with electrons and form atomic hydrogen, which binds to a molecule-carrier of hydrogen NADF (nicotinyndaenindinucleotidphosphate):

2H + + 4e - + Nadf + → Nadf H 2

Thus, during the light phase of photosynthesis, three processes occur: the formation of oxygen due to water decomposition, the synthesis of ATP, the formation of hydrogen atoms in the form of NADF H 2. Oxygen diffuses into the atmosphere, ATP and NADF H 2 are involved in the process of the dark phase.

Square Phase Photosynthesis flows in chloroplast matrix both in light and in the dark and is a series of consecutive conversion CO 2 from the air in the Calvin cycle. The reactions of the dark phase due to the energy of ATP. CO 2 Calvin cycle associates with hydrogen from NADF H 2 to form glucose.

In the process of photosynthesis, in addition to monosaccharides (glucose, etc.), monomers of other organic compounds - amino acids, glycerin and fatty acids are synthesized. Thus, thanks to the photosynthesis of the plant provide themselves and all living on Earth necessary organic substances and oxygen.

The comparative characteristic of the photosynthesis and respiration eukaryota is shown in the table:

More precisely: carbon dioxide (CO 2) is bonding to the dark phase.

This multistage process, in nature there are two main ways: C 3-photosynthesis and C 4-photosynthesis. The Latin letter C denotes carbon atom, the number of carbon atoms in the primary organic product of the dark phase of photosynthesis. So in the case of C 3 - the primary product is considered three-carbon phosphoglycerin acid, indicated as FGK. In the case of C 4, the first organic matter with the binding of carbon dioxide is the four-hand-carbon oxaloacetic acid (oxaloacetate).

C 3-photosynthesis is also called Calvin's cycle in honor of the scientist who has studied him. C 4 -Photosynthesis includes a Calvin cycle, however, it consists not only of it and is called a hatch-sabra cycle. In moderate latitudes, C 3-tests are common, in tropical - C 4.

The dark reactions of photosynthesis flow in the stroma of chloroplast.

Calvin cycle

The first calvin cycle reaction is carboxylation of ribulose-1,5-biophosphate (RibF). Carboxylation - This is the addition of CO 2 molecule, resulting in a carboxyl group -COOH. The Ribf is ribose (five-carbon sugar), in which phosphate groups (phosphoric acid formed by phosphoric acid) are attached to the terminal carbon atoms):

Chemical formula RIBF

The reaction is catalyzed by the enzyme ribulose-1,5-bifosfat-carboxylase-oxygenase ( Rubysian). It can catalyze not only the binding of carbon dioxide, but also oxygen, as he says the word "oxygenase" in his title. If Rubisko catalyzes the reaction of the addition of oxygen to the substrate, then the dark phase of photosynthesis is no longer on the path of Calvin cycle, but along the way photocheanThat in principle is harmful to the plant.

CO 2 Catalysis CO 2 to the RIBF occurs in several steps. As a result, an unstable hexagonal organic compound is formed, which immediately disintegrates into two three-carbon molecules. phosphoglycerolic acid (FGK).

Chemical phosphoglycerolic acid formula

Further, FGK for several enzymatic reactions occurring with the considerable energy of ATP and the reducing force of NADF · H 2, turns into phosphoglycerin aldehyde (FGA), also called triosophosphate.

The smaller part of the FGA comes out of the Calvin cycle and is used to synthesize more complex organic substances, for example glucose. She, in turn, can polymerize to the starch. Other substances (amino acids, fatty acids) are formed with the participation of various source substances. Such reactions are observed not only in plant cells. Therefore, if we consider photosynthesis as a unique phenomenon of chlorophyll cells, it ends with a synthesis of FGA, and not glucose.

Most of the FGA molecules remains in the Calvin cycle. A number of transformations occur with it, as a result of which FGA turns into the Ribf. It also uses ATP energy. Thus, the Ribf is regenerated for binding new carbon dioxide molecules.

Cycle Hatch Slaka

Many plants of hot habitats are somewhat more complicated in a challenge of photosynthesis. In the process of evolution, C 4-photosynthesis arose as a more efficient method of binding carbon dioxide, when the amount of oxygen increased in the atmosphere, and Rubisko began to spend money on ineffective photography.

C 4-tests there are two types of photosynthetic cells. In the chloroplasts of the mesophyll leaves, the light phase of photosynthesis and part of the dark, namely the binding of CO 2 phosphoenolpywatom (FEP). As a result, quadruple organic acid is formed. Next, this acid is transported to the chloroplasts of the cage of the conductive beam. Here, CO 2 molecule is enzymatically cleaved from it, which further enters the Calvin cycle. Three-carbon acid remaining after decarboxylation - pivrograde - Returns to Mesophyll's cells, where turns into FEP again.

Although the hatch-slicer cycle is more energy-efficient version of the dark phase of photosynthesis, but an enzyme binding CO 2 and FPP is a more efficient catalyst than Rubisco. In addition, it does not react with oxygen. CO 2 vehicles using an organic acid into deeper cells to which the inflow of oxygen is difficult leads to the fact that the concentration of carbon dioxide increases here, and rubysically is almost not spent on binding molecular oxygen.

How is the transformation of solar light in the light and dark phases of photosynthesis into the energy of the chemical bonds of glucose? Reply explain the answer.

Answer

In the light phase of photosynthesis, the energy of sunlight is converted into the energy of excited electrons, and then the energy of the excited electrons is converted into the energy of ATP and NADF-H2. In the dark phase of photosynthesis, the energy of ATP and NADF-H2 is converted into the energy of chemical bonds of glucose.

What happens in the light phase of photosynthesis?

Answer

Electrons of chlorophyll, excited by the energy of the light, go through electron-transport chains, their energy is intensified in ATP and NADF-H2. There is a photo of water, oxygen is released.

What basic processes occur in the dark phase of photosynthesis?

Answer

From the carbon dioxide obtained from the atmosphere, and hydrogen obtained in the light phase, due to the energy of ATP obtained in the light phase, glucose is formed.

What is the function of chlorophyll in the plant cell?

Answer

Chlorophyll is involved in the process of photosynthesis: in the light phase, chlorophyll absorbs light, the electron of chlorophyll receives the energy of the light, it takes off and goes through the electro-transport chain.

What role does the electrons of chlorophyll molecules play in photosynthesis?

Answer

Electrons of chlorophyll, excited by sunlight, pass through the electron transport chains and give their energy to the formation of ATP and NADF-H2.

At what stage of photosynthesis is formed free oxygen?

Answer

In the light phase, during photoles of water.

Which phase of photosynthesis is the synthesis of ATP?

Answer

Superior phase.

What substance is the source of oxygen during photosynthesis?

Answer

Water (oxygen is released during water photo gallery).

The speed of photosynthesis depends on the limiting (limiting) factors, among which the light, the concentration of carbon dioxide, temperature is distinguished. Why are these factors limiting for photosynthesis reactions?

Answer

The light is necessary for the excitation of chlorophyll, it supplies energy for the photosynthesis process. Carbon dioxide is needed in the dark phase of photosynthesis, glucose is synthesized from it. The temperature change leads to the denaturation of enzymes, the photosynthesis reaction slows down.

In what exchange reactions in plants carbon dioxide is the source substance for the synthesis of carbohydrates?

Answer

In photosynthesis reactions.

In the leaves of plants intensively proceeds the process of photosynthesis. Does he happen in mature and immature fruits? Reply explain the answer.

Answer

Photosynthesis occurs in green parts of plants in the light. Thus, photosynthesis occurs in the skin of green fruits. Inside the fruits and in the skin of ripe (not green) fruits, photosynthesis does not occur.

Explanation of such a volumetric material, which is photosynthesis, it is better to spend on two paired lessons - then the integrity of the topic perception is not lost. The lesson must begin with the history of the study of photosynthesis, the structure of chloroplasts and the laboratory work on the study of chloroplasts of the sheet. After that, it is necessary to go to the study of the light and dark phases of photosynthesis. When explaining the reactions occurring in these phases, it is necessary to compile a common scheme:

In the course of the explanation it is necessary to draw photosynthesis light phase diagram.

1. Absorption of a chlorophyll molecule light quantum, which is located in the Tylacoid membranes of the Grand, leads to a loss of one electron and translates it into an excited state. Electrons are transferred according to the electron traffic circuit, which leads to the recovery of Nadf + to Nadf N.

2. The place of the released electrons in chlorophyll molecules occupy electrons of water molecules - so water under the action of light is exposed to decomposition (photo gallery). The resulting hydroxyls are radicals and are combined in the reaction 4 of it - → 2 H 2 O + O 2, leading to the release of free oxygen into the atmosphere.

3. The hydrogen ions of H + do not penetrate through the tylacoid membrane and accumulate inside, chargeing it positively, which leads to an increase in the difference in electrical potentials (RPP) on the tylacide membrane.

4. Upon reaching a critical rap, the protons rushed along the proton channel outward. This stream of positively charged particles is used to obtain chemical energy using a special enzyme complex. The resulting ATP molecules are moving in stroma, where they are involved in carbon fixation reactions.

5. Hydrogen ions released on the surface of the thylacide membrane are connected to electrons, forming atomic hydrogen, which goes to restore the Nadf + carrier.

Sponsor Publication Articles Group of Companies "Aris". Production, sale and rent of scaffolding (frame facade LRSP, frame high-altitude A - 48, etc.) and the tag (PSRV "Aris", the PSRV "Aris Compact" and "Aris-Dacha", Dance). Clamps for scaffolding, construction fences, wheel supports for steamers. Learn more about the company, see the product catalog and prices, contacts you can on the site, which is located at: http://www.scaffolder.ru/.

After considering this issue, after analyzing it once again on the compiled scheme, we offer students to fill in the table.

Table. Reactions of light and dark phases photosynthesis

After filling in the first part of the table, you can go to the disaster the dark phase of photosynthesis.

In the stroma of chloroplast there are constantly present pentoses - carbohydrates representing five-carbon compounds that are formed in the Calvin cycle (carbon dioxide fixation cycle).

1. The pentose is joined carbon dioxide, an unstable hexagonal compound is formed, which disintegrates into two 3-phosphoglycerolic acid molecules (FGK).

2. FGK molecules are taken from ATP on one phosphate group and enriched with energy.

3. Each of FGK joins one atom of hydrogen from two carriers, turning into triosis. Triosis, combining, form glucose, and then starch.

4. Triosis molecules, combining in different combinations, form pentoses and are again included in the cycle.

Total photosynthesis reaction:

Scheme. Fotosynthesis process

Test

1. Photosynthesis is carried out in organellah:

a) mitochondria;
b) ribosomes;
c) chloroplasts;
d) chromoplasts.

2. Pigment Chlorophyll is concentrated in:

a) the shell of chloroplast;
b) stroma;
c) grans.

3. Chlorophyll absorbs light in the field of spectrum:

a) red;
b) green;
c) purple;
d) in the whole area.

4. Free oxygen at photosynthesis is released during splitting:

a) carbon dioxide;
b) ATP;
c) NADF;
d) water.

5. Free oxygen is formed in:

a) the dark phase;
b) light phase.

6. In the light phase of photosynthesis ATP:

a) synthesized;
b) split.

7. In chloroplast, the primary carbohydrate is formed in:

a) light phase;
b) the dark phase.

8. NADF in chloroplast is necessary:

1) as a trap for electrons;
2) as an enzyme for the formation of starch;
3) as an integral part of the chloroplast membrane;
4) as an enzyme for water photo polyesis.

9. Photoliz of water is:

1) the accumulation of water under the action of light;
2) dissociation of water to ions under the action of light;
3) the release of water vapors through the dust;
4) Water injection into leaves under the action of light.

10. Under the influence of light quanta:

1) chlorophyll turns into NADF;
2) the electron leaves the chlorophyll molecule;
3) chloroplast increases in volume;
4) Chlorophyll turns into ATP.

LITERATURE

Bogdanova TP, Solodova E.A.Biology. Handbook for high school students and entering universities. - M.: LLC "AST-PRESS SCHOOL", 2007.