Have you ever wondered how many living organisms there are on the planet?! And after all, they all need to inhale oxygen in order to generate energy and exhale carbon dioxide. It is carbon dioxide that is the main cause of such a phenomenon as stuffiness in the room. It takes place when there are a lot of people in it, and the room is not ventilated for a long time. In addition, industrial facilities, private automobile and public transport fill the air with toxic substances.
In view of the above, a logical question arises: how did we not suffocate then, if all life is a source of poisonous carbon dioxide? The savior of all living beings in this situation is photosynthesis. What is this process and why is it necessary?
Its result is the adjustment of the balance of carbon dioxide and the saturation of the air with oxygen. Such a process is known only to representatives of the world of flora, that is, plants, since it occurs only in their cells.
Photosynthesis itself is an extremely complex procedure, depending on certain conditions and occurring in severalstages.
Definition of concept
According to the scientific definition, organic substances are converted into organic substances during photosynthesis at the cellular level in autotrophic organisms due to exposure to sunlight.
To put it more simply, photosynthesis is the process by which the following occurs:
- The plant is saturated with moisture. The source of moisture can be water from the ground or moist tropical air.
- Chlorophyll (a special substance found in plants) reacts to solar energy.
- The formation of the food necessary for representatives of the flora, which they are not able to get on their own in a heterotrophic way, but they themselves are its producer. In other words, plants eat what they produce. This is the result of photosynthesis.
Stage one
Practically every plant contains a green substance, thanks to which it can absorb light. This substance is nothing more than chlorophyll. Its location is chloroplasts. But chloroplasts are located in the stem part of the plant and its fruits. But leaf photosynthesis is especially common in nature. Since the latter is quite simple in its structure and has a relatively large surface, which means that the amount of energy required for the rescue process to proceed will be much larger.
When light is absorbed by chlorophyll, the latter is in a state of excitation and itstransmits energy messages to other organic molecules of the plant. The largest amount of such energy goes to the participants in the process of photosynthesis.
Stage Two
The formation of photosynthesis at the second stage does not require the mandatory participation of light. It consists in the formation of chemical bonds using poisonous carbon dioxide formed from air masses and water. There is also a synthesis of many substances that ensure the vital activity of representatives of the flora. These are starch, glucose.
In plants, such organic elements act as a source of nutrition for individual parts of the plant, while ensuring the normal course of life processes. Such substances are also obtained by representatives of the fauna that eat plants for food. The human body is saturated with these substances through food, which is included in the daily diet.
What? Where? When?
In order for organic substances to become organic, it is necessary to provide appropriate conditions for photosynthesis. For the process under consideration, first of all, light is needed. We are talking about artificial and sunlight. In nature, plant activity is usually characterized by intensity in spring and summer, that is, when there is a need for a large amount of solar energy. What can not be said about the autumn season, when there is less and less light, the day is getting shorter. As a result, the foliage turns yellow, and then completely falls off. But as soon as the first spring rays of the sun shine, green grass will rise, they will immediately resume their activities.chlorophylls, and the active production of oxygen and other vital nutrients will begin.
The conditions for photosynthesis include more than just light. Moisture should also be sufficient. After all, the plant first absorbs moisture, and then a reaction begins with the participation of solar energy. Plant food is the result of this process.
Only in the presence of green matter does photosynthesis occur. What are chlorophylls, we have already told above. They act as a kind of conductor between light or solar energy and the plant itself, ensuring the proper course of their life and activity. Green substances have the ability to absorb many of the sun's rays.
Oxygen also plays a significant role. In order for the photosynthesis process to be successful, plants need a lot of it, since it contains only 0.03% carbonic acid. So, from 20,000 m3 of air, you can get 6 m3 of acid. It is the latter substance that is the main source material for glucose, which, in turn, is a substance necessary for life.
There are two stages of photosynthesis. The first is called light, the second is dark.
What is the mechanism of the light stage flow
The light stage of photosynthesis has another name - photochemical. The main participants at this stage are:
- solar energy;
- variety of pigments.
With the first component, everything is clear, it is sunlight. BUTthat's what pigments are, not everyone knows. They are green, yellow, red or blue. Chlorophylls of groups "A" and "B" belong to green, phycobilins to yellow and red / blue, respectively. Photochemical activity among the participants in this stage of the process is shown only by chlorophylls "A". The rest play a complementary role, the essence of which is the collection of light quanta and their transportation to the photochemical center.
Because chlorophyll is endowed with the ability to effectively absorb solar energy at a certain wavelength, the following photochemical systems have been identified:
- Photochemical center 1 (green substances of group "A") - the composition includes pigment 700, which absorbs light rays, the length of which is approximately 700 nm. This pigment plays a fundamental role in creating products of the light stage of photosynthesis.
- Photochemical center 2 (green substances of group "B") - the composition includes pigment 680, which absorbs light rays, the length of which is 680 nm. He has a secondary role, which consists in the function of replenishing the electrons lost by the photochemical center 1. It is achieved due to the hydrolysis of the liquid.
For 350–400 pigment molecules that concentrate light fluxes in photosystems 1 and 2, there is only one molecule of pigment, which is photochemically active - chlorophyll of group “A”.
What's going on?
1. The light energy absorbed by the plant affects the pigment 700 contained therein, which changes from the normal state to the excited state. Pigment loseselectron, resulting in the formation of the so-called electron hole. Further, the pigment molecule that has lost an electron can act as its acceptor, that is, the side that receives the electron, and return to its shape.
2. The process of liquid decomposition in the photochemical center of the light-absorbing pigment 680 of photosystem 2. During the decomposition of water, electrons are formed, which are initially accepted by a substance such as cytochrome C550 and are denoted by the letter Q. Then, from the cytochrome, the electrons enter the carrier chain and are transported to photochemical center 1 to replenish the electron hole, which was the result of the penetration of light quanta and the reduction process of pigment 700.
There are cases when such a molecule gets back an electron identical to the previous one. This will result in the release of light energy in the form of heat. But almost always, an electron with a negative charge combines with special iron-sulfur proteins and is transferred along one of the chains to pigment 700, or enters another carrier chain and reunites with a permanent acceptor.
In the first variant, there is a cyclic closed-type electron transport, in the second - non-cyclic.
Both processes are catalyzed by the same chain of electron carriers in the first stage of photosynthesis. But it should be noted that during photophosphorylation of the cyclic type, the initial and at the same time the end point of transportation is chlorophyll, while non-cyclic transportation implies the transition of the green substance of group "B" tochlorophyll "A".
Features of cyclic transportation
Cyclic phosphorylation is also called photosynthetic. As a result of this process, ATP molecules are formed. This transportation is based on the return of electrons in an excited state to pigment 700 through several successive stages, as a result of which energy is released, which takes part in the work of the phosphorylating enzyme system for the purpose of further accumulation in ATP phosphate bonds. That is, energy is not dissipated.
Cyclic phosphorylation is the primary reaction of photosynthesis, which is based on the technology of generating chemical energy on the membrane surfaces of chloroplast thylactoids using the energy of sunlight.
Without photosynthetic phosphorylation, assimilation reactions in the dark phase of photosynthesis are impossible.
The nuances of transportation of non-cyclic type
The process consists in the restoration of NADP+ and the formation of NADPH. The mechanism is based on the transfer of an electron to ferredoxin, its reduction reaction and the subsequent transition to NADP+ with further reduction to NADPH.
As a result, the electrons that lost pigment 700 are replenished thanks to the electrons of water, which decomposes under light rays in the photosystem 2.
The non-cyclic path of electrons, the flow of which also implies light photosynthesis, is carried out through the interaction of both photosystems with each other, links their electron transport chains. Luminousenergy directs the flow of electrons back. When transporting from photochemical center 1 to center 2, electrons lose part of their energy due to accumulation as a proton potential on the membrane surface of thylactoids.
In the dark phase of photosynthesis, the process of creating a proton-type potential in the electron transport chain and its exploitation for the formation of ATP in chloroplasts is almost completely identical to the same process in mitochondria. But features are still present. Thylactoids in this situation are mitochondria turned inside out. This is the main reason that electrons and protons move across the membrane in the opposite direction relative to the transport flow in the mitochondrial membrane. Electrons are transported to the outside, while protons accumulate in the interior of the thylactic matrix. The latter accepts only a positive charge, while the outer membrane of the thylactoide is negative. It follows that the path of the proton-type gradient is opposite to its path in mitochondria.
The next feature can be called a large pH level in the potential of protons.
The third feature is the presence of only two conjugation sites in the thylactoid chain and, as a result, the ratio of the ATP molecule to protons is 1:3.
Conclusion
In the first stage, photosynthesis is the interaction of light energy (artificial and non-artificial) with a plant. Green substances react to the rays - chlorophylls, most of which are found in leaves.
The formation of ATP and NADPH is the result of such a reaction. These products are essential for dark reactions to occur. Therefore, the light stage is an obligatory process, without which the second stage - the dark stage - will not take place.
Dark stage: essence and features
Dark photosynthesis and its reactions are the procedure of carbon dioxide into substances of organic origin with the production of carbohydrates. The implementation of such reactions occurs in the stroma of the chloroplast and the products of the first stage of photosynthesis - light take an active part in them.
The mechanism of the dark stage of photosynthesis is based on the process of carbon dioxide assimilation (also called photochemical carboxylation, the Calvin cycle), which is characterized by cyclicity. Consists of three phases:
- Carboxylation - addition of CO2.
- Recovery phase.
- Ribulose diphosphate regeneration phase.
Ribulophosphate, a sugar with five carbon atoms, is phosphorylated by ATP, resulting in ribulose diphosphate, which is further carboxylated by combining with CO2 product with six carbons, which instantly decompose when interacting with a water molecule, creating two molecular particles of phosphoglyceric acid. Then this acid undergoes a course of complete reduction during the implementation of an enzymatic reaction, for which the presence of ATP and NADP is required to form a sugar with three carbons - a three-carbon sugar, triose or aldehydephosphoglycerol. When two such trioses condense, a hexose molecule is obtained, which can become an integral part of the starch molecule and be debugged in reserve.
This phase ends with the absorption of one CO molecule during the process of photosynthesis2 and the use of three ATP molecules and four H atoms. Hexose phosphate lends itself to the reactions of the pentose phosphate cycle, resulting in ribulose phosphate is regenerated, which can recombine with another carbonic acid molecule.
Reactions of carboxylation, restoration, regeneration cannot be called specific exclusively for the cell in which photosynthesis takes place. You can’t say what a “homogeneous” course of processes is either, since the difference still exists - during the recovery process, NADPH is used, and not OVERH.
The addition of CO2 by ribulose diphosphate is catalyzed by ribulose diphosphate carboxylase. The reaction product is 3-phosphoglycerate, which is reduced by NADPH2 and ATP to glyceraldehyde-3-phosphate. The reduction process is catalyzed by glyceraldehyde-3-phosphate dehydrogenase. The latter is easily converted to dihydroxyacetone phosphate. fructose bisphosphate is formed. Some of its molecules take part in the regenerating process of ribulose diphosphate, closing the cycle, and the second part is used to create carbohydrate reserves in photosynthesis cells, that is, carbohydrate photosynthesis takes place.
Light energy is necessary for phosphorylation and synthesis of organic substancesorigin, and the energy of oxidation of organic substances is necessary for oxidative phosphorylation. That is why vegetation provides life for animals and other organisms that are heterotrophic.
Photosynthesis in a plant cell occurs in this way. Its product is carbohydrates, necessary to create the carbon skeletons of many substances of the representatives of the world of flora, which are of organic origin.
Substances of the nitrogen-organic type are assimilated in photosynthetic organisms due to the reduction of inorganic nitrates, and sulfur - due to the reduction of sulfates to sulfhydryl groups of amino acids. Provides the formation of proteins, nucleic acids, lipids, carbohydrates, cofactors, namely photosynthesis. What is an "assortment" of substances is vital for plants has already been emphasized, but not a word was said about the products of secondary synthesis, which are valuable medicinal substances (flavonoids, alkaloids, terpenes, polyphenols, steroids, organic acids and others). Therefore, without exaggeration, we can say that photosynthesis is the key to the life of plants, animals and people.
