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 captured more fully thanks to flat shape sheet, providing a large 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 performing CAM photosynthesis have developed special mechanisms for active assimilation 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 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.
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 CO 2 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 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 different lengths waves ( different color) 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.,
Photosynthesis is very complex biological process. It has been studied by the science of biology for many years, but, as the history of the study of photosynthesis shows, some stages are still unclear. In scientific reference books, a consistent description of this process takes several pages. The purpose of this article is to describe the phenomenon of photosynthesis, briefly and clearly for children, in the form of diagrams and explanations.
Scientific definition
First, it is important to know what photosynthesis is. In biology, the definition is as follows: this is the process of formation of organic substances (food) from inorganic substances (from carbon dioxide and water) in chloroplasts using light energy.
To understand this definition, we can imagine a perfect factory - any green plant, which is photosynthetic. The “fuel” for this factory is sunlight, plants use water, carbon dioxide and minerals to produce food for almost all life forms on earth. This “factory” is perfect because, unlike other factories, it does not cause harm, but, on the contrary, during production it releases oxygen into the atmosphere and absorbs carbon dioxide. As you can see, certain conditions are required for photosynthesis.
This unique process can be represented as a formula or equation:
sun + water + carbon dioxide = glucose + water + oxygen
Plant leaf structure
In order to characterize the essence of the photosynthesis process, it is necessary to consider the structure of the leaf. If you look under a microscope, you can see transparent cells containing from 50 to 100 green spots. These are chloroplasts, where chlorophyll, the main photosynthetic pigment, is located and in which photosynthesis occurs.
The chloroplast is like a small bag, and inside it there are even smaller bags. They are called thylakoids. Chlorophyll molecules are found on the surface of thylakoids. and are arranged in groups called photosystems. Most plants have two types of photosystems (PS): photosystem I and photosystem II. Only cells that have a chloroplast are capable of photosynthesis.
Description of the light phase
What reactions occur during the light phase of photosynthesis? In the PSII group, the energy of sunlight is transferred to the electrons of the chlorophyll molecule, as a result of which the electron becomes charged, that is, “excited so much” that it jumps out of the photosystem group and is “picked up” by the carrier molecule in the thylakoid membrane. This electron moves from carrier to carrier until it is discharged. It can then be used in another PSI group to replace an electron.
Photosystem II group is missing an electron, and now it is positively charged and requires a new electron. But where can one get such an electron? An area in the group known as the oxygen-evolving complex awaits the carefree water molecule "strolling" around.
A water molecule contains one oxygen atom and two hydrogen atoms. The oxygen evolution complex in PSII has four manganese ions that take electrons from the hydrogen atoms. As a result, the water molecule splits into two positive hydrogen ions, two electrons and one oxygen atom. Water molecules split, and the oxygen atoms are distributed in pairs, forming molecules of oxygen gas, which returns the plant to the air. Hydrogen ions begin to collect in the thylakoid bag, from here the plant can use them, and with the help of electrons, the problem of loss in the PS II complex is solved, which is ready to repeat this cycle many times per second.
Hydrogen ions accumulate in the thylakoid sac, and they begin to look for a way out. Two hydrogen ions, which are always formed during the disintegration of a water molecule, are not all: passing from the PS II complex to the PS I complex, electrons attract other hydrogen ions into the bag. These ions then accumulate in the thylakoid. How can they get out of there?
It turns out that they have a "turnstile" with one output - an enzyme that is used in the production of cellular "fuel" called ATP (adenosine triphosphate). By passing through this "turnstile", hydrogen ions provide the energy needed to recharge already used ATP molecules. ATP molecules are cellular "batteries". They provide energy for reactions inside the cell.
When collecting sugar, one more molecule is needed. It's called NADP (nicotinamide adenine dinucleotide phosphate). NADP molecules are “trucks”, each of them delivers a hydrogen atom to the enzyme of the sugar molecule. The formation of NADP occurs in the PS I complex. While the photosystem (PSII) breaks down water molecules and creates ATP from them, the photosystem (PS I) absorbs light and releases electrons, which will later be needed in the formation of NADP. ATP and NADP molecules are stored in the stroma and will later be used to form sugar.
Products of the light phase of photosynthesis:
- oxygen
- NADP*H 2
Night phase scheme
After the light phase, the dark stage of photosynthesis occurs. This phase was first discovered by Calvin. Subsequently, this discovery was called c3 - photosynthesis. In some plant species, a type of photosynthesis is observed - c4.
No sugar is produced during the light phase of photosynthesis. When exposed to light, only ATP and NADP are produced. Enzymes are used in the stroma (the space outside the thylakoid) for sugar production. The chloroplast can be compared to a factory in which teams (PS I and PS II) inside the thylakoid produce trucks and batteries (NADP and ATP) for the work of the third team (special enzymes) of the stroma.
This team forms sugar by adding hydrogen atoms and carbon dioxide molecules through chemical reactions using enzymes located in the stroma. All three teams work during the day, and the “sugar” team works both day and night, until the ATP and NADP that remain after the day shift are used up.
In the stroma, many atoms and molecules are combined with the help of enzymes. Some enzymes are protein molecules that have a special shape that allows them to take on the atoms or molecules they need for a specific reaction. After connection occurs, the enzyme releases a newly formed molecule, and this process is repeated constantly. In the stroma, enzymes pass down the sugar molecules they've collected, rearrange them, charge them with ATP, add carbon dioxide, add hydrogen, then send the three-carbon sugar to another part of the cell where it is converted into glucose and a variety of other substances.
So, the dark phase is characterized by the formation of glucose molecules. And carbohydrates are synthesized from glucose.
Photosynthesis light and dark phases (table)
Role in nature
What is the significance of photosynthesis in nature? We can safely say that life on Earth depends on photosynthesis.
- With its help, plants produce oxygen, which is so necessary for respiration.
- During breathing, carbon dioxide is released. If plants did not absorb it, a greenhouse effect would arise in the atmosphere. With the advent greenhouse effect The climate may change, glaciers may melt, and as a result, many areas of land may be flooded.
- The process of photosynthesis helps fuel all living things and also provides fuel to humanity.
- Thanks to the oxygen released through photosynthesis in the form of an oxygen-ozone screen of the atmosphere, all living things are protected from ultraviolet radiation.
Where does photosynthesis occur?
leaves of green plants
Definition
1) Light phase;
2) Dark phase.
Phases of photosynthesis
Light phase
Dark phase
Result
Where does photosynthesis occur?
Well, to answer the question right away, I will say that photosynthesis occurs in leaves of green plants, or rather in their cells. The main role here is played by chloroplates, special cells without which photosynthesis is impossible. I will note that this process, photosynthesis, seems to me to be amazing property alive.
After all, everyone knows that through photosynthesis, carbon dioxide is absorbed and oxygen is released. Such a phenomenon is simple to understand, and at the same time one of the most complex processes of living organisms, in which a huge number of people take part. different particles and molecules. So that at the end the oxygen that we all breathe is released.
Well, I’ll try to tell you how we get precious oxygen.
Definition
Photosynthesis is the synthesis of organic substances from inorganic substances using sunlight. In other words, sunlight falling on the leaves provides the necessary energy for the process of photosynthesis. As a result, organic matter is formed from inorganic matter and air oxygen is released.
Photosynthesis occurs in 2 phases:
1) Light phase;
2) Dark phase.
I'll tell you a little about the phases of photosynthesis.
Phases of photosynthesis
Light phase- as the name implies, it occurs in the light, on the surface membrane of green leaf cells (scientifically speaking, on the grann membrane). The main participants here will be chlorophyll, special protein molecules (carrier proteins) and ATP synthetase, which is an energy supplier.
The light phase, like the process of photosynthesis in general, begins with the action of a light quantum on the chlorophyll molecule. As a result of this interaction, chlorophyll comes into an excited state, which is why this very molecule loses an electron, which goes to outer surface membranes. Further, in order to restore the lost electron, the chlorophyll molecule takes it away from the water molecule, which causes its decomposition. We all know that water consists of two hydrogen molecules and one oxygen, and when water decomposes, oxygen enters the atmosphere, and positively charged hydrogen collects on the inner surface of the membrane.
Thus, it turned out that negatively charged electrons are concentrated on one side and positively charged hydrogen protons on the other. From this moment, an ATP synthetase molecule appears, which forms a kind of corridor for the passage of protons to electrons and to reduce this concentration difference, which we discussed below. On this spot light phase it ends and ends with the formation of the energy molecule ATP and the restoration of the specific NADP*H2 transporter molecule.
In other words, the decomposition of water occurred, due to which oxygen was released and an ATP molecule was formed, which will provide energy for the further course of photosynthesis.
Dark phase– oddly enough, this phase can occur both in the light and in the dark. This phase takes place in special organelles of leaf cells that are actively involved in photosynthesis (plastids). This phase includes several chemical reactions that occur with the help of the same ATP molecule synthesized in the first phase and NADPH. In turn, the main roles here belong to water and carbon dioxide. The dark phase requires a continuous supply of energy. Carbon dioxide comes from the atmosphere, hydrogen was formed in the first phase, and the ATP molecule is responsible for the energy. The main result of the dark phase is carbohydrates, that is, the very organic matter that plants need to live.
Result
This is how the very process of formation of organic matter (carbohydrates) from inorganic matter occurs. As a result, plants receive the products they need to live, and we receive oxygen from the air. I will add that this entire process occurs exclusively in green plants, the cells of which contain chloroplasts (“green cells”).
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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 CO 2 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.,
Do you know that every green leaf is a miniature “factory” nutrients and oxygen, which is needed for normal life not only by animals, but also by humans. Photosynthesis is the process of producing these substances from water and carbon dioxide from the atmosphere. This is a very complex chemical process that occurs with the participation of light. Undoubtedly, everyone is interested in how the process of photosynthesis occurs. The process consists of two stages: the first stage is the absorption of light quanta, and the second stage is the use in various chemical reactions their energy.
How does the process of photosynthesis occur?
The plant absorbs light using a green substance called chlorophyll. Chlorophyll is contained in chloroplasts, which are found in fruits and stems. But especially them a large number of is located in the leaves, because the leaf, due to its rather simple structure, can attract a large amount of light, and accordingly, receive much more energy for the photosynthesis process.
Chlorophyll, after absorption, is in an excited state and transfers energy to other molecules of the plant body, especially those that directly take part in photosynthesis. The second stage of the photosynthesis process occurs without the mandatory participation of light and consists of obtaining a chemical bond with the participation of carbon dioxide, which is obtained from water and air. At this stage there is a synthesis of different very useful substances for vital functions, such as glucose and starch.
The plants themselves use these organic substances to nourish their various parts, as well as to maintain normal life functions. In addition, these substances are also obtained by animals that feed on plants. A person obtains these substances by eating foods of plant and animal origin.
Conditions for photosynthesis
The process of photosynthesis can occur not only under the influence of artificial light, but also sunlight. In nature, as a rule, plants intensively carry out their activities in spring-summer period, that is, at a time when a lot of sunlight is needed. Sveta in autumn period less, the day shortens, the leaves turn yellow and then fall off. But as soon as the warm spring sun appears, the green foliage wakes up and the green “factories” resume their work again in order to provide a large amount of nutrients and oxygen, which is so necessary for life.
Where does the process of photosynthesis take place?
Photosynthesis mainly occurs, as we said above, if you remember, in the leaves of plants, for the reason that they have the ability to receive a large amount of light, which is so necessary for the photosynthesis process.
In conclusion, we can summarize and say that a process such as photosynthesis is an integral part of plant life. We hope that our article has helped many people understand what photosynthesis is and why it is necessary.