Have you ever wondered how many living organisms 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 - the main reason for such a phenomenon as stuffiness in the room. It takes place when there are many people in it, and the room is not aired for a long time. In addition, production facilities, private automobile and public transport fill the air with toxic substances.
In view of the foregoing, a quite logical question arises: how, then, have we not yet suffocated if all life is a source of poisonous carbon dioxide? Savior of all living things in this situation is photosynthesis. What is this process and what is its need?
Its result is carbon balance adjustment and air oxygen saturation. 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 several stages.
Definition of a concept
According to the scientific definition, organic substances in the process of photosynthesis are converted to organic at the cellular level in autotrophic organisms due to exposure to sunlight.
In a more understandable language, photosynthesis is a process in which the following occurs:
- The plant is saturated with moisture. The source of moisture can be water from the ground or humid tropical air.
- Chlorophyll (a special substance that is contained in the plant) reacts to the effects of solar energy.
- The formation of food necessary for representatives of the flora, which they themselves are not able to obtain in a heterotrophic way, but are themselves its producer. In other words, plants feed on what they themselves produce. This is the result of photosynthesis.
Stage one
Almost 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 photosynthesis of the leaf is especially common in nature. Since the latter is quite simple in structure and has a relatively large surface, which means that the amount of energy needed for the savior process will be much larger.
When light is absorbed by chlorophyll, the latter is in a state of excitement and transmits its energy messages to other organic molecules of the plant. The greatest amount of such energy goes to the participants of the photosynthesis process.
Stage Two
The formation of photosynthesis in the second stage does not require the participation of light. It consists in the formation of chemical bonds using poisonous carbon dioxide, which is formed from air masses and water. Also, there is a synthesis of many substances that provide vital activity of representatives of the flora. Those are starch, glucose.
In plants, such organic elements act as a source of nutrition for individual parts of the plant, while simultaneously ensuring the normal course of life processes. Representatives of the fauna that consume plants for food also receive such substances. 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 ensure the appropriate conditions for photosynthesis. For the process under consideration, light is primarily required. We are talking about both artificial and sunlight. In nature, usually the activity of plants is characterized by intensity in spring and summer, that is, when there is a need for a large amount of solar energy. You can not say about the autumn season, when there is less light, the day is 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, chlorophylls will resume their activity and the active production of oxygen and other nutrients that are of vital importance will begin.
Photosynthesis conditions include not only the presence of light. Moisture should also be enough. After all, the plant first absorbs moisture, and then the reaction begins with the participation of solar energy. The result of this process is plant food.
Only in the presence of green matter does photosynthesis occur. What are chlorophylls, we have already said 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 work. Green substances have the ability to absorb many sunlight.
A significant role is played by oxygen. For the photosynthesis process to be successful, plants need a lot of it, since it contains only 0.03% carbon dioxide. So, from 20,000 m 3 of air you can get 6 m 3 of acid. It is the latter substance - 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 course of the light stage
The light stage of photosynthesis has another name - photochemical. The main participants at this stage are:
- energy of sun;
- various pigments.
With the first component, everything is clear, this is sunlight. But not everyone knows what pigments are. They are green, yellow, red or blue. Chlorophylls of groups “A” and “B” belong to green, and phycobilins, respectively, to yellow and red / blue. Among the participants in this stage of the process, only chlorophyll “A” exhibit photochemical activity. The rest has a complementary role, the essence of which is the collection of light quanta and their transportation to the photochemical center.
Since chlorophyll is endowed with the ability to efficiently absorb solar energy at a specific wavelength, the following photochemical systems have been identified:
- Photochemical center 1 (green substances of group “A”) - pigment 700 is included in the composition, absorbing light rays, the length of which is approximately 700 nm. This pigment has a fundamental role in creating the products of the light stage of photosynthesis.
- Photochemical center 2 (green substances of group “B”) - pigment 680 is included in the composition, which absorbs light rays, the length of which is 680 nm. He plays the role of the second plan, which consists in the function of replenishing electrons lost by the photochemical center 1. Achieved thanks to the hydrolysis of the liquid.
For 350–400 pigment molecules that concentrate the light fluxes in photosystems 1 and 2, there is only one pigment molecule, which is chemically active — group A chlorophyll.
What's happening?
1. The light energy absorbed by the plant affects the pigment 700 contained in it, which changes from a normal state to an excitation state. The pigment loses an electron, resulting in the formation of a so-called electron hole. Further, a pigment molecule that has lost an electron can act as its acceptor, that is, the side receiving the electron, and return to its shape.
2. The process of liquid decomposition in the photochemical center of the light-absorbing pigment 680 of the photosystem 2. During the decomposition of water, electrons are formed that are initially accepted by a substance such as cytochrome C550 and are denoted by the letter Q. Then, from cytochrome, the electrons enter the carrier chain and are transported to the photochemical center 1 for replenishment of the electron hole, which was the result of the penetration of light quanta and the recovery process of pigment 700.
There are times 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 having a negative charge combines with special iron-sulfur proteins and is transferred along one of the chains to pigment 700 or enters another chain of carriers and reunites with a constant acceptor.
In the first embodiment, cyclic transportation of an electron of the closed type takes place, in the second - non-cyclic.
Both processes fall at the first stage of photosynthesis under the catalysis of the same chain of electron carriers. But it is worth noting that during photophosphorylation of the cyclic type, the initial and at the same time the final point of transportation is chlorophyll, while non-cyclic transportation implies the transition of the green substance of group “B” to chlorophyll “A”.
Features of cyclic transportation
Cyclic phosphorylation is also called photosynthetic. As a result of this process, ATP molecules are formed. The basis of such transportation is the return through several successive stages of electrons in an excited state to pigment 700, as a result of which energy is released that takes part in the phosphorylation of the enzyme system with the aim of further accumulation of ATP in phosphate bonds. That is, energy does not dissipate.
Cyclic phosphorylation is the primary reaction of photosynthesis, based on the technology of the formation of chemical energy on the membrane surfaces of chloroplast thylactoids due to the use of solar energy.
Without photosynthetic phosphorylation, assimilation reactions in the dark phase of photosynthesis are impossible.
Nuances of non-cyclic transportation
The process consists in the restoration of NADP + and the formation of NADP * N. The mechanism is based on the electron transfer to ferredoxin, its reduction reaction and the subsequent transition to NADP + with further reduction to NADP * N.
As a result, the electrons that have lost the pigment 700 are replenished due to the electrons of water, which decomposes under light rays in 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, connects their electron-transport chains. Light energy directs the flow of electrons back. When transported from the photochemical center 1 to center 2, the 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 the proton type potential in the electron transport chain and its operation for the formation of ATP in chloroplasts is almost completely identical with the same process in mitochondria. But features are still present. Thylactoids in this situation are mitochondria turned on the wrong side. This is the main reason that electrons and protons move through the membrane in the opposite direction relative to the transport flow in the mitochondrial membrane. Electrons are transported to the outside, and protons accumulate in the inside of the thylactoid matrix. The latter accepts only a positive charge, and the outer membrane of the thylactoid is negative. It follows from this that the path of the proton-type gradient is opposite to its path in the mitochondria.
The next feature can be called a large level of pH in the potential of protons.
The third feature is the presence in the thylactoid chain of only two conjugation sites and, as a consequence, the ratio of the ATP molecule to protons is 1: 3.
Conclusion
At the first stage, photosynthesis is the interaction of light energy (artificial and non-artificial) with the plant. Green substances, chlorophylls, most of which are contained in leaves, react to rays.
The formation of ATP and NADP * N is the result of such a reaction. These products are necessary for the occurrence of dark reactions. Therefore, the light stage is a mandatory process, without which the second stage will not take place - the dark one.
Dark Stage: Essence and Features
Dark photosynthesis and its reactions are a procedure of carbon dioxide in substances of organic origin to produce 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 assimilation of carbon dioxide (also called photochemical carboxylation, Calvin cycle), which is characterized by cyclicality. Consists of three phases:
- Carboxylation - addition of CO 2 .
- The recovery phase.
- The regeneration phase of ribulose diphosphate.
Ribulophosphate - a sugar with five carbon atoms - can be phosphorylated by ATP, resulting in the formation of ribulose diphosphate, which is further carboxylated by combining with a CO 2 product with six carbons, which instantly decompose upon interaction with a water molecule, creating two molecular particles of phosphoglyceric acid acid . Then this acid undergoes a course of complete recovery during the implementation of the enzymatic reaction, for which the presence of ATP and NADP is necessary with the formation of sugar with three carbons - tri-carbon sugar, triose or phosphoglyceric aldehyde. 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 fact that during the photosynthesis process, one CO 2 molecule is absorbed and three ATP molecules and four N atoms are used. The hexose phosphate reacts to the pentose phosphate cycle, resulting in the regeneration of ribulose phosphate, which can reunite with another carbon acid molecule.
The reactions of carboxylation, reduction, and regeneration cannot be called specific only for the cell in which photosynthesis proceeds. You can’t say what a “homogeneous” course of processes is, since a difference still exists - NADP * N is used in the recovery process, and not NAD * N.
The addition of CO2 by ribulose diphosphate undergoes catalysis, which is provided by ribulose diphosphate carboxylase. The reaction product is 3-phosphoglycerate, which is reduced by NADP * H2 and ATP to glyceraldehyde-3-phosphate. The reduction process is catalyzed by glyceraldehyde-3-phosphate dehydrogenase. The latter is easily converted to dihydroxyacetone phosphate. The formation of fructose bisphosphate. Some of its molecules take part in the regeneration process of ribulose diphosphate, closing the cycle, and the second part is used to create carbohydrate reserves in photosynthetic cells, i.e. photosynthesis of carbohydrates takes place.
Light energy is necessary for phosphorylation and synthesis of substances of organic origin, and the oxidation energy of organic substances is necessary for oxidative phosphorylation. That is why vegetation provides life to animals and other organisms that are heterotrophic.
Photosynthesis in a plant cell occurs in this way. Its product is carbohydrates, which are necessary to create carbon skeletons of many substances from the flora that are of organic origin.
Substances of an organic nitrogen type are absorbed in photosynthetic organisms due to the reduction of inorganic nitrates, and sulfur due to the reduction of sulfates to sulfhydryl groups of amino acids. It is photosynthesis that ensures the formation of proteins, nucleic acids, lipids, carbohydrates, cofactors. What is the "assorted" of substances vital for plants has already been emphasized, but not a word has been said about the products of secondary synthesis, which are valuable medicinal substances (flavonoids, alkaloids, terpenes, polyphenols, steroids, organic acids). Therefore, without exaggeration, we can say that photosynthesis is the key to the life of plants, animals and people.