On currently Two types of pigments have been discovered in living organisms that can perform the function of photosynthetic antennas. These pigments absorb quanta visible light and provide further storage of radiation energy in the form of the energy of the electrochemical gradient of H + on biological membranes. Less common is the case in which the vitamin A derivative, retinal, serves as the antenna; In the vast majority of organisms, chlorophylls play the role of antennas. In accordance with this, non-chlorophyll and chlorophyll photosynthesis are distinguished.

Non-chlorophyll photosynthesis

The system of chlorophyll-free photosynthesis is characterized by significant simplicity of organization, and therefore is assumed to be the evolutionarily primary mechanism for storing energy electromagnetic radiation. The efficiency of chlorophyll-free photosynthesis as an energy conversion mechanism is relatively low (only one H + is transferred per absorbed quantum).

Discovery in halophilic archaea

Dieter Oesterhelt and Walther Stoeckenius identified a representative of halophilic archaea in the “purple membranes” Halobacterium salinarium(former name N. halobium) a protein that was later named bacteriorhodopsin. Evidence was soon accumulated indicating that bacteriorhodopsin is a light-dependent generator of a proton gradient. In particular, photophosphorylation was demonstrated on artificial vesicles containing bacteriorhodopsin and mitochondrial ATP synthase, photophosphorylation in intact cells H. salinarium, a light-induced drop in pH of the environment and suppression of respiration, all of these effects correlated with the absorption spectrum of bacteriorhodopsin. Thus, irrefutable evidence of the existence of chlorophyll-free photosynthesis was obtained.

Mechanism

The photosynthetic apparatus of extreme halobacteria is the most primitive currently known; it lacks an electron transport chain. Cytoplasmic membrane halobacteria is a coupling membrane containing two main components: a light-dependent proton pump (bacteriorhodopsin) and ATP synthase. The operation of such a photosynthetic apparatus is based on the following energy transformations:

1. The chromophore of bacteriorhodopsin, retinal, absorbs light quanta, which leads to conformational changes in the structure of bacteriorhodopsin and proton transport from the cytoplasm to the periplasmic space. In addition, an additional contribution to the electrical component of the gradient is made by the active light-dependent import of the chloride anion, which is provided by halorhodopsin [ ] . Thus, as a result of the work of bacteriorhodopsin, the energy solar radiation is transformed into the energy of the electrochemical gradient of protons on the membrane.
2. During the operation of ATP synthase, the energy of the transmembrane gradient is transformed into the energy of ATP chemical bonds. Thus, chemiosmotic coupling occurs.

With the chlorophyll-free type of photosynthesis (as well as with the implementation of cyclic flows in electron transport chains), the formation of reducing equivalents (reduced ferredoxin or NAD(P)H) necessary for the assimilation of carbon dioxide does not occur. Therefore, during chlorophyll-free photosynthesis, there is no assimilation of carbon dioxide, but only the storage of solar energy in the form of ATP (photophosphorylation).

Meaning

The main way for halobacteria to obtain energy is the aerobic oxidation of organic compounds (carbohydrates and amino acids are used during cultivation). In case of oxygen deficiency, in addition to non-chlorophyll photosynthesis, anaerobic nitrate respiration or fermentation of arginine and citrulline can serve as energy sources for halobacteria. However, the experiment showed that chlorophyll-free photosynthesis can also serve as the only source of energy under anaerobic conditions when anaerobic respiration and fermentation are suppressed, provided that retinal is added to the medium, the synthesis of which requires oxygen.

Chlorophyll photosynthesis

Chlorophyll photosynthesis differs from bacteriorhodopsin photosynthesis by its significantly greater efficiency of energy storage. For each absorbed quantum of radiation, at least one H + is transferred against the gradient, and in some cases the energy is stored in the form of reduced compounds (ferredoxin, NADP).

Anoxygenic

Anoxygenic (or oxygen-free) photosynthesis occurs without the release of oxygen. Purple and green bacteria, as well as heliobacteria, are capable of anoxygenic photosynthesis.

With anoxygenic photosynthesis, it is possible to:

1. Light-dependent cyclic electron transport, not accompanied by the formation of reducing equivalents and leading exclusively to the storage of light energy in the form of ATP. With cyclic light-dependent electron transport, there is no need for exogenous electron donors. The need for reducing equivalents is met non-photochemically, usually through exogenous organic compounds.
2. Light-dependent non-cyclic electron transport, accompanied by the formation of reducing equivalents and the synthesis of ADP. In this case, there is a need for exogenous electron donors, which are necessary to fill the electron vacancy in the reaction center. Both organic and inorganic reducing agents can be used as exogenous electron donors. Among inorganic compounds, the most commonly used are various reduced forms of sulfur (hydrogen sulfide, molecular sulfur, sulfites, thiosulfates, tetrathionates, thioglycolates), and molecular hydrogen can also be used.

Oxygenic

Oxygenic (or oxygenic) photosynthesis is accompanied by the release of oxygen as a by-product. In oxygenic photosynthesis, noncyclic electron transport occurs, although under certain physiological conditions, exclusively cyclic electron transport occurs. An extremely weak electron donor - water - is used as an electron donor in a non-cyclic flow.

Oxygenic photosynthesis is much more widespread. Characteristic of higher plants, algae, many protists and cyanobacteria.

Stages

Photosynthesis is a process with an extremely complex spatiotemporal organization.

The spread of characteristic times of various stages of photosynthesis is 19 orders of magnitude: the rate of absorption of light quanta and energy migration is measured in the femtosecond interval (10−15 s), the rate of electron transport has characteristic times of 10−10−10−2 s, and processes associated with growth plants are measured in days (10 5 −10 7 s).

Also, a large variation in size is characteristic of structures that ensure photosynthesis occurs: from the molecular level (10 −27 m 3) to the level of phytocenoses (10 5 m 3).

In photosynthesis, individual stages can be distinguished, differing in nature and characteristic rates of processes:

• Photophysical;
• Photochemical;
• Chemical:
  • Electron transport reactions;
  • "Dark" reactions or carbon cycles during photosynthesis.

At the first stage, light quanta are absorbed by pigments, their transition to an excited state and energy transfer to other molecules of the photosystem. At the second stage, charges are separated in the reaction center, electrons are transferred along the photosynthetic electron transport chain, which ends in the synthesis of ATP and NADPH. The first two stages are collectively called the light-dependent stage of photosynthesis. The third stage occurs without the mandatory participation of light and includes biochemical reactions of the synthesis of organic substances using the energy accumulated in the light-dependent stage. Most often, such reactions are considered to be the Calvin cycle and gluconeogenesis, the formation of sugars and starch from carbon dioxide in the air.

Spatial localization

Sheet

Plant photosynthesis occurs in chloroplasts: semi-autonomous double-membrane organelles belonging to the class of plastids. Chloroplasts can be contained in the cells of stems, fruits, and sepals, but the main organ of photosynthesis is the leaf. The leaf has formed during evolution and is anatomically adapted to absorb light energy and assimilate carbon dioxide. Flat leaf shape providing great attitude surface to volume, allows you to more fully use the energy of sunlight. The water necessary to maintain turgor and photosynthesis is delivered to the leaves from the root system through the xylem of a developed network of conducting bundles (leaf veins) and the stem. Loss of water through evaporation through the stomata and, to a lesser extent, through the cuticle (transpiration) serves as the driving force for vascular transport. However, excess transpiration is undesirable and, during the course of evolution, plants have developed various adaptations aimed at reducing water loss. The outflow of assimilates, necessary for the functioning of the Calvin cycle, occurs through the phloem of vascular bundles (veins) and the phloem of the stem. During intense photosynthesis, carbohydrates can polymerize and at the same time starch grains are formed in chloroplasts. Gas exchange (intake of carbon dioxide and release of oxygen) is carried out by diffusion through the stomata, some of the gases move through the cuticle.

Since carbon dioxide deficiency significantly increases the loss of assimilates during photorespiration, it is necessary to maintain a high concentration of carbon dioxide in the intercellular space, which is possible with open stomata. However, maintaining stomata open when high temperature leads to an increase in transpiration water losses - water losses by evaporation, which leads to water deficiency and also reduces the productivity of photosynthesis. This conflict is resolved in accordance with the principle of adaptive compromise. In addition, the primary absorption of carbon dioxide at night, at low temperatures, in plants with CAM photosynthesis allows one to avoid high transpiration losses of water.

Photosynthesis at the tissue level

At the tissue level, photosynthesis in higher plants is provided by specialized tissue - chlorenchis And my . Chlorenchyma is located near the surface of the plant body, where it receives a sufficient amount of light energy. Usually chlorenchyma is located directly under the epidermis. In plants growing in conditions of increased insolation, one or two layers of transparent cells (hypodermis) may be located between the epidermis and chlorenchyma, providing light scattering. In some shade-loving plants, the epidermis is also rich in chloroplasts (for example, wood sorrel). Often the mesophyll chlorenchyma of a leaf is differentiated into palisade (columnar) and spongy, but can also consist of homogeneous cells. Subject to differentiation, palisade chlorenchyma is richest in chloroplasts.

Chloroplasts

The internal space of the chloroplast is filled with colorless contents (stroma) and permeated by membranes (lamellae), which, connecting with each other, form thylakoids, which, in turn, are grouped into stacks called grana. The intrathylakoid space is separated and does not communicate with the rest of the stroma, it is also assumed that inner space all thylakoids communicate with each other. The light stages of photosynthesis are confined to membranes; autotrophic fixation of CO 2 occurs in the stroma.

Chloroplasts have their own DNA, RNA, ribosomes (70s type), and protein synthesis occurs (although this process is controlled from the nucleus). They are not synthesized again, but are formed by dividing the previous ones. All this made it possible to consider them the descendants of free cyanobacteria that became part of the eukaryotic cell during the process of symbiogenesis.

Photosynthetic membranes of prokaryotes

Photochemical essence of the process

Photosystem I

Light-harvesting complex I contains approximately 200 chlorophyll molecules.

In the reaction center of the first photosystem there is a dimer of chlorophyll a with an absorption maximum at 700 nm (P 700). After excitation by a light quantum, it restores the primary acceptor - chlorophyll a, which is the secondary acceptor (vitamin K 1 or phylloquinone), after which the electron is transferred to ferredoxin, which restores NADP using the enzyme ferredoxin-NADP reductase.

The plastocyanin protein, reduced in the b 6 f complex, is transported to the reaction center of the first photosystem from the side of the intrathylakoid space and transfers an electron to the oxidized P 700.

Cyclic and pseudocyclic electron transport

In addition to the complete non-cyclic electron path described above, a cyclic and pseudo-cyclic path has been discovered.

The essence of the cyclic pathway is that ferredoxin, instead of NADP, reduces plastoquinone, which transfers it back to the b 6 f complex. This results in a larger proton gradient and more ATP, but no NADPH.

In the pseudocyclic pathway, ferredoxin reduces oxygen, which is further converted into water and can be used in photosystem II. In this case, NADPH is also not formed.

Dark phase

In the dark stage, with the participation of ATP and NADP, CO 2 is reduced to glucose (C 6 H 12 O 6). Although light is not required for this process, it is involved in its regulation.

C 3 photosynthesis, Calvin cycle

In the second stage, FHA is restored in two stages. First, it is phosphorylated by ATP under the action of phosphoroglycerokinase with the formation of 1,3-diphosphoglyceric acid (DPGA), then, under the influence of triosephosphate dehydrogenase and NADPH, the acyl-phosphate group of DPGA is dephosphorylated and reduced to an aldehyde and glyceraldehyde-3-phosphate - phosphorylated carbohydrate (PHA) is formed.

The third stage involves 5 PHA molecules, which, through the formation of 4-, 5-, 6- and 7-carbon compounds, are combined into 3 5-carbon ribulose-1,5-biphosphate, which requires 3ATP.

Finally, two PHAs are required for glucose synthesis. To form one of its molecules, 6 cycle revolutions, 6 CO 2, 12 NADPH and 18 ATP are required.

C 4 photosynthesis

The difference between this mechanism of photosynthesis and the usual one is that the fixation of carbon dioxide and its use are divided in space, between different cells of the plant.

At a low concentration of CO 2 dissolved in the stroma, ribulose biphosphate carboxylase catalyzes the oxidation reaction of ribulose-1,5-biphosphate and its breakdown into 3-phosphoglyceric acid and phosphoglycolic acid, which is forced to be used in the process of photorespiration.

To increase CO2 concentration, type 4 C plants changed their leaf anatomy. The Calvin cycle is localized in the sheath cells of the vascular bundle; in the mesophyll cells, under the action of PEP carboxylase, phosphoenolpyruvate is carboxylated to form oxaloacetic acid, which is converted into malate or aspartate and transported to the sheath cells, where it is decarboxylated to form pyruvate, which is returned to the mesophyll cells.

With 4, photosynthesis is practically not accompanied by losses of ribulose-1,5-biphosphate from the Calvin cycle, and therefore is more efficient. However, it requires not 18, but 30 ATP for the synthesis of 1 glucose molecule. This is justified in the tropics, where the hot climate requires keeping the stomata closed, which prevents the entry of CO 2 into the leaf, as well as with a ruderal life strategy.

Photosynthesis via the C4 pathway is carried out by about 7,600 plant species, all of which are flowering plants: many cereals (61% of species, including cultivated plants - corn, sugar cane and sorghum, etc.), Cloveaceae (the largest share in the families Chenopoaceae - 40% of species, Amaranthaceae - 25%), some Sedgeaceae, Asteraceae, Brassicas, Euphorbiaceae.

photosynthesis itself

The energy obtained by humanity by burning fossil fuels (coal, oil, natural gas, peat) is also stored in the process of photosynthesis.

Photosynthesis serves as the main input of inorganic carbon into the biogeochemical cycle.

Photosynthesis is the basis for the productivity of agriculturally important plants.

Most of the free oxygen in the atmosphere is of biogenic origin and is a by-product of photosynthesis. The formation of an oxidizing atmosphere (oxygen catastrophe) completely changed the state of the earth's surface, made the appearance of respiration possible, and later, after the formation of the ozone layer, allowed life to exist on land.

History of the study

The first experiments in the study of photosynthesis were carried out by Joseph Priestley in the 1780s, when he drew attention to the “spoilage” of air in a sealed vessel with a burning candle (the air ceased to support combustion, and the animals placed in it suffocated) and its “correction” by plants. Priestley concluded that plants produce oxygen, which is necessary for respiration and combustion, but did not notice that plants need light for this. This was soon shown by Jan Ingenhaus.

Later it was found that in addition to releasing oxygen, plants absorb carbon dioxide and, with the participation of water, synthesize organic matter in the light. Based on the law of conservation of energy, Robert Mayer postulated that plants convert the energy of sunlight into the energy of chemical bonds. V. Pfeffer called this process photosynthesis.

Chlorophylls were first isolated in P. J. Pelletier and J. Caventou. M. S. Tsvet managed to separate the pigments and study them separately using the chromatography method he created. The absorption spectra of chlorophyll were studied by K. A. Timiryazev, who, developing Mayer’s principles, showed that it is the absorbed rays that make it possible to increase the energy of the system, creating instead of weak ones C-O connections and O-H high-energy C-C (before this, it was believed that photosynthesis uses yellow rays that are not absorbed by leaf pigments). This was done thanks to the method he created for accounting for photosynthesis based on absorbed CO 2: during experiments on illuminating a plant with light of different wavelengths ( different color) it turned out that the intensity of photosynthesis coincides with the absorption spectrum of chlorophyll.

The redox essence of photosynthesis (both oxygenic and anoxygenic) was postulated by Cornelis van Niel, who in 1931 proved that purple bacteria and green sulfur bacteria carry out anoxygenic photosynthesis. The redox nature of photosynthesis meant that oxygen in oxygenic photosynthesis is formed entirely from water, which was experimentally confirmed in A.P. Vinogradov in experiments with an isotope label. Robert Hill found that the process of water oxidation (and oxygen release) and CO 2 assimilation can be separated. In - gg.

The history of the discovery of an amazing and vitally important phenomenon such as photosynthesis is deeply rooted in the past. More than four centuries ago, in 1600, the Belgian scientist Jan Van Helmont performed a simple experiment. He placed a willow twig in a bag containing 80 kg of earth. The scientist recorded the initial weight of the willow, and then watered the plant exclusively with rainwater for five years. Imagine Jan Van Helmont's surprise when he re-weighed the willow. The weight of the plant increased by 65 kg, and the mass of the earth decreased by only 50 grams! Where did the plant get 64 kg 950 g nutrients remained a mystery to the scientist!

The next significant experiment on the path to the discovery of photosynthesis belonged to the English chemist Joseph Priestley. The scientist put a mouse under the hood, and five hours later the rodent died. When Priestley placed a sprig of mint with the mouse and also covered the rodent with a cap, the mouse remained alive. This experiment led the scientist to the idea that there is a process opposite to breathing. Jan Ingenhouse in 1779 established the fact that only green parts of plants are capable of releasing oxygen. Three years later, Swiss scientist Jean Senebier proved that carbon dioxide, under the influence of sunlight, decomposes in green plant organelles. Just five years later, French scientist Jacques Boussingault, conducting laboratory research, discovered the fact that the absorption of water by plants also occurs during the synthesis of organic substances. The epochal discovery was made in 1864 by the German botanist Julius Sachs. He was able to prove that the volume of carbon dioxide consumed and oxygen released occurs in a 1:1 ratio.

Photosynthesis is one of the most significant biological processes

Speaking scientific language, photosynthesis (from ancient Greek φῶς - light and σύνθεσις - connection, binding) is a process in which organic substances are formed from carbon dioxide and water in the light. The main role in this process belongs to photosynthetic segments.

Speaking figuratively, a plant leaf can be compared to a laboratory, the windows of which overlook sunny side. It is in it that the formation of organic substances occurs. This process is the basis for the existence of all life on Earth.

Many will reasonably ask the question: what do people who live in a city breathe, where you can’t even find a tree or a blade of grass during the day with fire? The answer is very simple. The fact is that the share land plants accounts for only 20% of the oxygen released by plants. Seaweed plays a leading role in the production of oxygen in the atmosphere. They account for 80% of the oxygen produced. Speaking in the language of numbers, both plants and algae annually release 145 billion tons (!) of oxygen into the atmosphere! It’s not for nothing that the world’s oceans are called “the lungs of the planet.”

General formula photosynthesis looks like this:

Water + Carbon dioxide + Light → Carbohydrates + Oxygen

Why do plants need photosynthesis?

As we have learned, photosynthesis is necessary condition existence of man on Earth. However, this is not the only reason why photosynthetic organisms actively produce oxygen into the atmosphere. The fact is that both algae and plants annually form more than 100 billion organic substances (!), which form the basis of their life activity. Remembering the experiment of Jan Van Helmont, we understand that photosynthesis is the basis of plant nutrition. It has been scientifically proven that 95% of the harvest is determined by organic substances obtained by the plant during the process of photosynthesis, and 5% by those mineral fertilizers which the gardener adds to the soil.

Modern summer residents pay the main attention to soil nutrition of plants, forgetting about its air nutrition. It is unknown what kind of harvest gardeners could get if they were careful about the process of photosynthesis.

However, neither plants nor algae could produce oxygen and carbohydrates so actively if they did not have an amazing green pigment - chlorophyll.

The Mystery of the Green Pigment

The main difference between plant cells and the cells of other living organisms is the presence of chlorophyll. By the way, it is he who is responsible for the fact that plant leaves are colored precisely green color. This complex organic compound has one amazing property: It can absorb sunlight! Thanks to chlorophyll, the process of photosynthesis also becomes possible.

Two stages of photosynthesis

Speaking in simple language, photosynthesis is a process in which water and carbon dioxide absorbed by a plant in the light with the help of chlorophyll form sugar and oxygen. Thus, inorganic substances amazingly become organic. The sugar obtained as a result of conversion is a source of energy for plants.

Photosynthesis has two stages: light and dark.

Light phase of photosynthesis

It is carried out on thylakoid membranes.

Thylakoids are membrane-bounded structures. They are located in the stroma of the chloroplast.

The order of events in the light stage of photosynthesis is:

1. Light hits the chlorophyll molecule, which is then absorbed by the green pigment and causes it to become excited. An electron that is part of a molecule is transferred to more high level, participates in the synthesis process.
2. Water splits, during which protons are converted into hydrogen atoms under the influence of electrons. Subsequently, they are spent on the synthesis of carbohydrates.
3. At the final stage of the light stage, ATP (Adenosine triphosphate) is synthesized. This is an organic substance that plays the role of a universal energy accumulator in biological systems.

Dark phase of photosynthesis

The place where the dark phase occurs is the stroma of chloroplasts. It is during the dark phase that oxygen is released and glucose is synthesized. Many will think that this phase received this name because the process occurring within this stage occurs exclusively at night. In fact, this is not entirely true. Glucose synthesis occurs around the clock. The fact is that it is at this stage that light energy is no longer consumed, which means it is simply not needed.

The importance of photosynthesis for plants

We have already determined the fact that plants need photoynthesis no less than we do. It is very easy to talk about the scale of photosynthesis in terms of numbers. Scientists have calculated that land plants alone store as much solar energy as could be consumed by 100 megacities within 100 years!

Plant respiration is the opposite process of photosynthesis. The meaning of plant respiration is to release energy during the process of photosynthesis and direct it to the needs of plants. In simple terms, yield is the difference between photosynthesis and respiration. The more photosynthesis and the lower the respiration, the greater the harvest, and vice versa!

Photosynthesis is an amazing process that makes possible life on the ground!

Plants obtain water and minerals from their roots. The leaves provide organic nutrition to the plants. Unlike roots, they are not in the soil, but in the air, therefore they provide not soil, but air nutrition.

From the history of studying aerial nutrition of plants

Knowledge about plant nutrition accumulated gradually.

About 350 years ago, the Dutch scientist Jan Helmont first experimented with the study of plant nutrition. IN clay pot With soil, he grew willow, adding only water. The scientist carefully weighed the fallen leaves. After five years, the mass of the willow together with fallen leaves increased by 74.5 kg, and the mass of the soil decreased by only 57 g. Based on this, Helmont came to the conclusion that all substances in the plant are formed not from soil, but from water. The opinion that a plant increases in size only due to water persisted until late XVIII century.

In 1771, the English chemist Joseph Priestley studied carbon dioxide, or, as he called it, “spoiled air” and made a remarkable discovery. If you light a candle and cover it with a glass cover, then after it burns a little, it will go out.

A mouse under such a hood begins to suffocate. However, if you place a mint branch under the cap with the mouse, the mouse does not suffocate and continues to live. This means that plants “correct” the air spoiled by the breathing of animals, that is, they convert carbon dioxide into oxygen.

In 1862, the German botanist Julius Sachs proved through experiments that green plants not only produce oxygen, but also create organic substances that serve as food for all other organisms.

Photosynthesis

The main difference between green plants and other living organisms is the presence in their cells of chloroplasts containing chlorophyll. Chlorophyll has the property of trapping Sun rays, the energy of which is necessary to create organic substances. The process of formation of organic matter from carbon dioxide and water using solar energy is called photosynthesis (Greek pbo1os light). During the process of photosynthesis, not only organic substances - sugars - are formed, but oxygen is also released.

Schematically, the process of photosynthesis can be depicted as follows:

Water is absorbed by the roots and moves through the conductive system of the roots and stem to the leaves. Carbon dioxide - component air. It enters the leaves through open stomata. The absorption of carbon dioxide is facilitated by the structure of the leaf: the flat surface of the leaf blades, which increases the area of ​​contact with air, and the presence of a large number of stomata in the skin.

Sugars formed as a result of photosynthesis are converted into starch. Starch is an organic substance that does not dissolve in water. Kgo can be easily detected using an iodine solution.

Evidence of starch formation in leaves exposed to light

Let us prove that in the green leaves of plants starch is formed from carbon dioxide and water. To do this, consider an experiment that was once carried out by Julius Sachs.

A houseplant (geranium or primrose) is kept in the dark for two days so that all the starch is used up for vital processes. Then several leaves are covered on both sides with black paper so that only part of them is covered. During the day, the plant is exposed to light, and at night it is additionally illuminated using a table lamp.

After a day, the leaves under study are cut off. To find out in which part of the leaf starch is formed, the leaves are boiled in water (to swell the starch grains) and then kept in hot alcohol (the chlorophyll dissolves and the leaf becomes discolored). Then the leaves are washed in water and act on them weak solution Yoda. Thus, areas of leaves that have been exposed to light acquire a blue color from the action of iodine. This means that starch was formed in the cells of the illuminated part of the leaf. Therefore, photosynthesis occurs only in light.

Evidence for the need for carbon dioxide for photosynthesis

To prove that carbon dioxide is necessary for the formation of starch in leaves, indoor plant also pre-conditioned in the dark. One of the leaves is then placed in a flask with a small amount of lime water. The flask is closed with a cotton swab. The plant is exposed to light. Carbon dioxide is absorbed by lime water, so it will not be in the flask. The leaf is cut off and, just as in the previous experiment, examined for the presence of starch. It is aged in hot water and alcohol, treated with iodine solution. However, in this case, the result of the experiment will be different: the sheet is not painted in Blue colour, because it does not contain starch. Therefore, for the formation of starch, in addition to light and water, carbon dioxide is needed.

Thus, we answered the question of what food the plant receives from the air. Experience has shown that it is carbon dioxide. It is necessary for the formation of organic matter.

Organisms that independently create organic substances to build their body are called autotrophamnes (Greek autos - itself, trophe - food).

Evidence of oxygen production during photosynthesis

To prove that during photosynthesis plants external environment release oxygen, consider the experiment with aquatic plant Elodea. Elodea shoots are dipped into a vessel with water and covered with a funnel on top. Place a test tube filled with water at the end of the funnel. The plant is exposed to light for two to three days. In the light, elodea produces gas bubbles. They accumulate at the top of the test tube, displacing water. In order to find out what kind of gas it is, the test tube is carefully removed and a smoldering splinter is introduced into it. The splinter flashes brightly. This means that oxygen has accumulated in the flask, supporting combustion.

The cosmic role of plants

Plants containing chlorophyll are able to absorb solar energy. Therefore K.A. Timiryazev called their role on Earth cosmic. Some of the solar energy stored in organic matter can be stored for a long time. Coal, peat, oil are formed by substances that in distant geological times were created by green plants and absorbed the energy of the Sun. By burning natural combustible materials, a person releases energy stored millions of years ago by green plants.

Photosynthesis (Tests)

1. Organisms that form organic substances only from organic ones:

1.heterotrophs

2.autotrophs

3.chemotrophs

4.mixotrophs

2. During the light phase of photosynthesis, the following occurs:

1.ATP formation

2.glucose formation

3.emission of carbon dioxide

4. formation of carbohydrates

3. During photosynthesis, oxygen is formed, which is released in the process:

1.protein biosynthesis

2.photolysis

3.excitation of the chlorophyll molecule

4.compounds carbon dioxide and water

4. As a result of photosynthesis, light energy is converted into:

1. thermal energy

2.chemical energy of inorganic compounds

3. electrical energy thermal energy

4.chemical energy of organic compounds

5. Respiration in anaerobes in living organisms occurs in the process:

1.oxygen oxidation

2.photosynthesis

3.fermentation

4.chemosynthesis

6. The end products of carbohydrate oxidation in the cell are:

1.ADP and water

2.ammonia and carbon dioxide

3.water and carbon dioxide

4.ammonia, carbon dioxide and water

7. On preparatory stage hydrolysis occurs when carbohydrates are broken down:

1. cellulose to glucose

2. proteins to amino acids

3.DNA to nucleotides

4.fat to glycerol and carboxylic acids

8. Enzymes provide oxygen oxidation:

1.digestive tract and lysosomes

2.cytoplasm

3.mitochondrion

4.plastid

9. During glycolysis, 3 mol of glucose is stored in the form of ATP:

10. Two moles of glucose underwent complete oxidation in the animal cell, and carbon dioxide was released:

11. In the process of chemosynthesis, organisms convert oxidative energy:

1.sulfur compounds

2.organic compounds

3.starch

12. One gene corresponds to information about the molecule:

1.amino acids

2.starch

4.nucleotide

13.The genetic code consists of three nucleotides, which means it:

1. specific

2.redundant

3.universal

4.tripletene

14.V genetic code One amino acid corresponds to 2-6 triplets, this is where it manifests itself:

1.continuity

2.redundancy

3. versatility

4.specificity

15. If the nucleotide composition of DNA is ATT-CHC-TAT, then the nucleotide composition of i-RNA is:
1.TAA-TsGTs-UTA

2.UAA-GTG-AUA

3.UAA-CHTs-AUA

4.UAA-TsGTs-ATA

16. Protein synthesis does not occur on its own ribosomes in:

1.tobacco mosaic virus

2. Drosophila

3.ant

4. Vibrio cholerae

17. Antibiotic:

1. is a protective blood protein

2.synthesizes new protein in the body

3.is a weakened pathogen

4.suppresses protein synthesis of the pathogen

18. The section of the DNA molecule where replication occurs has 30,000 nucleotides (both strands). For replication you will need:

19. How many different amino acids can one t-RNA transport:

1.always one

2.always two

3.always three

4.some can transport one, some can transport several.

20. The section of DNA from which transcription occurs contains 153 nucleotides; this section encodes a polypeptide from:

1.153 amino acids

2.51 amino acids

3.49 amino acids

4,459 amino acids

21. During photosynthesis, oxygen is produced as a result

1.​ photosynthetic water

2.​ decomposition of carbon gas

3.​ reduction of carbon dioxide to glucose

4.​ ATP synthesis

During the process of photosynthesis occurs

1.​ synthesis of carbohydrates and release of oxygen

2.​ water evaporation and oxygen absorption

3. Gas exchange and lipid synthesis

4.​ release of carbon dioxide and protein synthesis

23. During the light phase of photosynthesis, the energy of sunlight is used to synthesize molecules

1. lipids

2.​ proteins

3.​nucleic acid

24. Under the influence of the energy of sunlight, the electron rises to a higher level energy level in a molecule

1.​ squirrel

2.​ glucose

3.​ chlorophyll

4.​ protein biosynthesis

25. A plant cell, like an animal cell, receives energy in the process. .

1.​ oxidation of organic substances

2.​ protein biosynthesis

3. lipid synthesis

4.​nucleic acid synthesis

Photosynthesis occurs in the chloroplasts of plant cells. Chloroplasts contain the pigment chlorophyll, which is involved in the process of photosynthesis and gives plants their green color. It follows that photosynthesis occurs only in the green parts of plants.

Photosynthesis is the process of formation of organic substances from inorganic ones. In particular, the organic substance is glucose, and the inorganic substances are water and carbon dioxide.

Sunlight is also important for photosynthesis to occur. Light energy is stored in the chemical bonds of organic matter. This is the main point of photosynthesis: to bind energy that will later be used to support the life of the plant or animals that eat this plant. Organic matter acts only as a form, a way to store solar energy.

When photosynthesis occurs in cells, various reactions take place in chloroplasts and on their membranes.

Not all of them need light. Therefore, there are two phases of photosynthesis: light and dark. The dark phase does not require light and can occur at night.

Carbon dioxide enters cells from the air through the surface of the plant. The water is coming from the roots along the stem.

As a result of the process of photosynthesis, not only organic matter is formed, but also oxygen. Oxygen is released into the air through the surface of the plant.

The glucose formed as a result of photosynthesis is transferred to other cells, converted into starch (stored), and used for vital processes.

The main organ in which photosynthesis occurs in most plants is the leaf. It is in the leaves that there are many photosynthetic cells that make up photosynthetic tissue.

Since sunlight is important for photosynthesis, leaves usually have large surface. In other words, they are flat and thin. To ensure that light reaches all the leaves of the plants, they are positioned so that they almost do not shade each other.

So, for the process of photosynthesis to take place, you need carbon dioxide, water and light. The products of photosynthesis are organic matter (glucose) and oxygen. Photosynthesis occurs in chloroplasts, which are most abundant in leaves.

Photosynthesis occurs in plants (mainly in their leaves) in the light. This is a process in which the organic substance glucose (one of the types of sugars) is formed from carbon dioxide and water. Next, glucose in the cells is converted into a more complex substance, starch. Both glucose and starch are carbohydrates.

The process of photosynthesis not only produces organic matter, but also produces oxygen as a by-product.

Carbon dioxide and water are inorganic substances, while glucose and starch are organic.

Therefore, it is often said that photosynthesis is the process of formation of organic substances from inorganic substances in the light. Only plants, some single-celled eukaryotes, and some bacteria are capable of photosynthesis. There is no such process in the cells of animals and fungi, so they are forced to absorb from environment organic substances. In this regard, plants are called autotrophs, and animals and fungi are called heterotrophs.

The process of photosynthesis in plants occurs in chloroplasts, which contain green pigment chlorophyll.

So, for photosynthesis to occur, you need:

chlorophyll,

carbon dioxide.

During the process of photosynthesis the following are formed:

organic matter,

oxygen.

Plants are adapted to capture light. For many herbaceous plants the leaves are collected in a so-called basal rosette, when the leaves do not shade each other. Trees are characterized by a leaf mosaic, in which the leaves grow in such a way as to shade each other as little as possible. In plants, leaf blades can turn towards the light due to the bending of the leaf petioles. With all this there are shade-loving plants, which can only grow in the shade.

Waterfor photosynthesisarrivesinto the leavesfrom the rootsalong the stem. Therefore, it is important that the plant receives enough moisture. With a lack of water and some minerals the process of photosynthesis is inhibited.

Carbon dioxidetaken for photosynthesisdirectlyout of thin airleaves. Oxygen, which is produced by the plant during photosynthesis, on the contrary, is released into the air. Gas exchange is facilitated by intercellular spaces (spaces between cells).

Organic substances formed during the process of photosynthesis are partly used in the leaves themselves, but mainly flow into all other organs and are converted into other organic substances, used in energy metabolism, and converted into reserve nutrients.

Photosynthesis

Photosynthesis- the process of synthesis of organic substances using light energy. Organisms that are capable of synthesizing organic substances from inorganic compounds are called autotrophic. Photosynthesis is characteristic only of cells of autotrophic organisms. Heterotrophic organisms are not capable of synthesizing organic substances from inorganic compounds.
Cells of green plants and some bacteria have special structures and complexes chemical substances, which allow them to capture energy from sunlight.

The role of chloroplasts in photosynthesis

Plant cells contain microscopic formations - chloroplasts. These are organelles in which energy and light are absorbed and converted into the energy of ATP and other molecules - energy carriers. The grana of chloroplasts contain chlorophyll, a complex organic substance. Chlorophyll captures light energy for use in the biosynthesis of glucose and other organic substances. The enzymes necessary for the synthesis of glucose are also located in chloroplasts.

Light phase of photosynthesis

A quantum of red light absorbed by chlorophyll transfers the electron to an excited state. An electron excited by light acquires a large supply of energy, as a result of which it moves to a higher energy level. An electron excited by light can be compared to a stone raised to a height, which also acquires potential energy. He loses it, falling from a height. The excited electron, as if in steps, moves along a chain of complex organic compounds built into the chloroplast. Moving from one step to another, the electron loses energy, which is used for the synthesis of ATP. The electron that wasted energy returns to chlorophyll. A new portion of light energy again excites the chlorophyll electron. It again follows the same path, spending energy on the formation of ATP molecules.
Hydrogen ions and electrons, necessary for the restoration of energy-carrying molecules, are formed by the splitting of water molecules. The breakdown of water molecules in chloroplasts is carried out by a special protein under the influence of light. This process is called photolysis of water.
Thus, the energy of sunlight is directly used by the plant cell to:
1. excitation of chlorophyll electrons, the energy of which is further spent on the formation of ATP and other energy carrier molecules;
2. photolysis of water, supplying hydrogen ions and electrons to the light phase of photosynthesis.
This releases oxygen as a by-product of photolysis reactions.

The stage during which, due to the energy of light, energy-rich compounds are formed - ATP and energy-carrying molecules, called light phase of photosynthesis.

Dark phase of photosynthesis

Chloroplasts contain five-carbon sugars, one of which ribulose diphosphate, is a carbon dioxide acceptor. A special enzyme binds five-carbon sugar with carbon dioxide in the air. In this case, compounds are formed that, using the energy of ATP and other energy carrier molecules, are reduced to a six-carbon glucose molecule.

Thus, the light energy converted during the light phase into the energy of ATP and other energy carrier molecules is used for the synthesis of glucose.

These processes can take place in the dark.
It was possible to isolate chloroplasts from plant cells, which in a test tube, under the influence of light, carried out photosynthesis - they formed new glucose molecules and absorbed carbon dioxide. If the illumination of the chloroplasts was stopped, the synthesis of glucose also stopped. However, if ATP and reduced energy carrier molecules were added to the chloroplasts, then glucose synthesis resumed and could proceed in the dark. This means that light is really only needed to synthesize ATP and charge energy-carrying molecules. Absorption of carbon dioxide and formation of glucose in plants called dark phase of photosynthesis because she can walk in the dark.
Intense lighting, increased content carbon dioxide in the air leads to an increase in the activity of photosynthesis.

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Photosynthesis- the process of synthesis of organic substances using light energy. Organisms that are capable of synthesizing organic substances from inorganic compounds are called autotrophic. Photosynthesis is characteristic only of cells of autotrophic organisms. Heterotrophic organisms are not capable of synthesizing organic substances from inorganic compounds.
The cells of green plants and some bacteria have special structures and complexes of chemicals that allow them to capture energy from sunlight.

The role of chloroplasts in photosynthesis

Plant cells contain microscopic formations - chloroplasts. These are organelles in which energy and light are absorbed and converted into the energy of ATP and other molecules - energy carriers. The grana of chloroplasts contain chlorophyll, a complex organic substance. Chlorophyll captures light energy for use in the biosynthesis of glucose and other organic substances. The enzymes necessary for the synthesis of glucose are also located in chloroplasts.

Light phase of photosynthesis

A quantum of red light absorbed by chlorophyll transfers the electron to an excited state. An electron excited by light acquires a large supply of energy, as a result of which it moves to a higher energy level. An electron excited by light can be compared to a stone raised to a height, which also acquires potential energy. He loses it, falling from a height. The excited electron, as if in steps, moves along a chain of complex organic compounds built into the chloroplast. Moving from one step to another, the electron loses energy, which is used for the synthesis of ATP. The electron that wasted energy returns to chlorophyll. A new portion of light energy again excites the chlorophyll electron. It again follows the same path, spending energy on the formation of ATP molecules.
Hydrogen ions and electrons, necessary for the restoration of energy-carrying molecules, are formed by the splitting of water molecules. The breakdown of water molecules in chloroplasts is carried out by a special protein under the influence of light. This process is called photolysis of water.
Thus, the energy of sunlight is directly used by the plant cell to:
1. excitation of chlorophyll electrons, the energy of which is further spent on the formation of ATP and other energy carrier molecules;
2. photolysis of water, supplying hydrogen ions and electrons to the light phase of photosynthesis.
This releases oxygen as a by-product of photolysis reactions. The stage during which, due to the energy of light, energy-rich compounds are formed - ATP and energy-carrying molecules, called light phase of photosynthesis.

Dark phase of photosynthesis

Chloroplasts contain five-carbon sugars, one of which ribulose diphosphate, is a carbon dioxide acceptor. A special enzyme binds five-carbon sugar with carbon dioxide in the air. In this case, compounds are formed that, using the energy of ATP and other energy carrier molecules, are reduced to a six-carbon glucose molecule. Thus, the light energy converted during the light phase into the energy of ATP and other energy carrier molecules is used for the synthesis of glucose. These processes can take place in the dark.
It was possible to isolate chloroplasts from plant cells, which in a test tube, under the influence of light, carried out photosynthesis - they formed new glucose molecules and absorbed carbon dioxide. If the illumination of the chloroplasts was stopped, the synthesis of glucose also stopped. However, if ATP and reduced energy carrier molecules were added to the chloroplasts, then glucose synthesis resumed and could proceed in the dark. This means that light is really only needed to synthesize ATP and charge energy-carrying molecules. Absorption of carbon dioxide and formation of glucose in plants called dark phase of photosynthesis because she can walk in the dark.
Intense lighting and increased carbon dioxide content in the air lead to increased photosynthesis activity.

Non-chlorophyll photosynthesis

Spatial localization

Plant photosynthesis occurs in chloroplasts: isolated double-membrane organelles of the cell. Chloroplasts can be found in the cells of fruits and stems, but the main organ of photosynthesis, anatomically adapted for its conduct, is the leaf. In the leaf, the palisade parenchyma tissue is richest in chloroplasts. In some succulents with degenerate leaves (such as cacti), the main photosynthetic activity is associated with the stem.

Light for photosynthesis is more fully captured due to the flat leaf shape, which provides a high surface to volume ratio. Water is delivered from the root through a developed network of vessels (leaf veins). Carbon dioxide enters partly by diffusion through the cuticle and epidermis, but most of it diffuses into the leaf through the stomata and through the leaf through the intercellular space. Plants that carry out CAM photosynthesis have developed special mechanisms for the active assimilation of carbon dioxide.

The internal space of the chloroplast is filled with colorless contents (stroma) and is penetrated by membranes (lamellae), which, when connected to each other, form thylakoids, which in turn are grouped into stacks called grana. The intrathylakoid space is separated and does not communicate with the rest of the stroma; it is also assumed that the internal space of all thylakoids communicates with each other. The light stages of photosynthesis are confined to membranes; autotrophic fixation of CO 2 occurs in the stroma.

Chloroplasts have their own DNA, RNA, ribosomes (70s type), and protein synthesis occurs (although this process is controlled from the nucleus). They are not synthesized again, but are formed by dividing the previous ones. All this made it possible to consider them the descendants of free cyanobacteria that became part of the eukaryotic cell during the process of symbiogenesis.

Photosystem I

Light-harvesting complex I contains approximately 200 chlorophyll molecules.

In the reaction center of the first photosystem there is a dimer of chlorophyll a with an absorption maximum at 700 nm (P700). After excitation by a light quantum, it restores the primary acceptor - chlorophyll a, which restores the secondary one (vitamin K 1 or phylloquinone), after which the electron is transferred to ferredoxin, which reduces NADP using the enzyme ferredoxin-NADP reductase.

The plastocyanin protein, reduced in the b 6 f complex, is transported to the reaction center of the first photosystem from the intrathylakoid space and transfers an electron to the oxidized P700.

Cyclic and pseudocyclic electron transport

In addition to the complete non-cyclic electron path described above, a cyclic and pseudo-cyclic path has been discovered.

The essence of the cyclic pathway is that ferredoxin, instead of NADP, reduces plastoquinone, which transfers it back to the b 6 f complex. This results in a larger proton gradient and more ATP, but no NADPH.

In the pseudocyclic pathway, ferredoxin reduces oxygen, which is further converted into water and can be used in photosystem II. In this case, NADPH is also not formed.

Dark stage

In the dark stage, with the participation of ATP and NADPH, CO 2 is reduced to glucose (C 6 H 12 O 6). Although light is not required for this process, it is involved in its regulation.

C 3 photosynthesis, Calvin cycle

The third stage involves 5 PHA molecules, which, through the formation of 4-, 5-, 6- and 7-carbon compounds, are combined into 3 5-carbon ribulose-1,5-biphosphate, which requires 3ATP.

Finally, two PHAs are required for glucose synthesis. To form one of its molecules, 6 cycle revolutions, 6 CO 2, 12 NADPH and 18 ATP are required.

C 4 photosynthesis

Main articles: Hatch-Slack-Karpilov cycle, C4 photosynthesis

At a low concentration of CO 2 dissolved in the stroma, ribulose biphosphate carboxylase catalyzes the oxidation reaction of ribulose-1,5-biphosphate and its breakdown into 3-phosphoglyceric acid and phosphoglycolic acid, which is forced to be used in the process of photorespiration.

To increase CO2 concentration, type 4 C plants changed their leaf anatomy. The Calvin cycle is localized in the sheath cells of the vascular bundle; in the mesophyll cells, under the action of PEP carboxylase, phosphoenolpyruvate is carboxylated to form oxaloacetic acid, which is converted into malate or aspartate and transported to the sheath cells, where it is decarboxylated to form pyruvate, which is returned to the mesophyll cells.

With 4, photosynthesis is practically not accompanied by losses of ribulose-1,5-biphosphate from the Calvin cycle, and therefore is more efficient. However, it requires not 18, but 30 ATP for the synthesis of 1 glucose molecule. This is justified in the tropics, where the hot climate requires keeping the stomata closed, which prevents the entry of CO 2 into the leaf, as well as with a ruderal life strategy.

photosynthesis itself

Later it was found that in addition to releasing oxygen, plants absorb carbon dioxide and, with the participation of water, synthesize organic matter in the light. Based on the law of conservation of energy, Robert Mayer postulated that plants convert the energy of sunlight into the energy of chemical bonds. W. Pfeffer called this process photosynthesis.

Chlorophylls were first isolated by P. J. Peltier and J. Caventou. M. S. Tsvet managed to separate the pigments and study them separately using the chromatography method he created. The absorption spectra of chlorophyll were studied by K. A. Timiryazev, who, developing Mayer’s principles, showed that it is the absorbed rays that make it possible to increase the energy of the system, creating high-energy C-C bonds instead of weak C-O and O-H bonds (before that it was believed that in photosynthesis uses yellow rays that are not absorbed by leaf pigments). This was done thanks to the method he created for accounting for photosynthesis based on absorbed CO 2: during experiments on illuminating a plant with light of different wavelengths (different colors), it turned out that the intensity of photosynthesis coincides with the absorption spectrum of chlorophyll.

The redox nature of photosynthesis (both oxygenic and anoxygenic) was postulated by Cornelis van Niel. This meant that oxygen in photosynthesis is formed entirely from water, which was experimentally confirmed by A.P. Vinogradov in experiments with an isotope label. Robert Hill found that the process of water oxidation (and oxygen release) and CO 2 assimilation can be separated. W. D. Arnon established the mechanism of the light stages of photosynthesis, and the essence of the CO 2 assimilation process was revealed by Melvin Calvin using carbon isotopes in the late 1940s, for which he was awarded the Nobel Prize.

Other facts

see also

Literature

• Hall D., Rao K. Photosynthesis: Transl. from English - M.: Mir, 1983.
• Plant physiology / ed. prof. Ermakova I. P. - M.: Academy, 2007
• Molecular biology of cells / Albertis B., Bray D. et al. In 3 vols. - M.: Mir, 1994
• Rubin A. B. Biophysics. In 2 vols. - M.: Publishing house. Moscow University and Science, 2004.
• Chernavskaya N. M.,