Diffusion biology. Diffusion. Application of diffusion in technology and in everyday life
In the school curriculum in the course of physics (approximately in the seventh grade), students learn that diffusion is a process that is the mutual penetration of particles of one substance between particles of another substance, as a result of which concentrations are equalized throughout the occupied volume. This is a rather difficult definition to understand. To understand what simple diffusion is, the law of diffusion, its equation, it is necessary to study in detail the materials on these issues. However, if a general idea is enough for a person, then the data below will help to obtain elementary knowledge.
Physical phenomenon - what is it
Due to the fact that many people confuse or do not know at all what a physical phenomenon is and how it differs from a chemical one, as well as what kind of phenomena diffusion belongs to, it is necessary to understand what a physical phenomenon is. So, as everyone knows, physics is an independent science belonging to the field of natural science, which studies the general natural laws about the structure and movement of matter, and also studies matter itself. Accordingly, a physical phenomenon is such a phenomenon, as a result of which no new substances are formed, but only a change in the structure of the substance occurs. The difference between a physical phenomenon and a chemical one lies precisely in the fact that no new substances are obtained as a result. Thus, diffusion is a physical phenomenon.
Definition of the term diffusion
As you know, there can be many formulations of a concept, but the general meaning should not change. And diffusion is no exception. The generalized definition is as follows: diffusion is a physical phenomenon, which is the mutual penetration of particles (molecules, atoms) of two or more substances to a uniform distribution over the entire volume occupied by these substances. As a result of diffusion, no new substances are formed, therefore it is precisely a physical phenomenon. Simple diffusion is called diffusion, as a result of which particles move from the region of highest concentration to the region of lower concentration, which is due to thermal (chaotic, Brownian) motion of particles. In other words, diffusion is a process of mixing particles of different substances, and the particles are distributed evenly throughout the volume. This is a very simplified definition, but the most understandable.
Types of diffusion
Diffusion can be fixed both when observing gaseous and liquid substances, and solid ones. Therefore, it includes several types:
- Quantum diffusion is the process of diffusion of particles or point defects (local disturbances in the crystal lattice of a substance), which is carried out in solids. Local violations are violations at a certain point in the crystal lattice.
- Colloidal - diffusion occurring throughout the entire volume of the colloidal system. A colloidal system is a medium in which particles, bubbles, drops of another medium, differing in aggregate state and composition from the first, are distributed. Such systems, as well as the processes occurring in them, are studied in detail in the course of colloid chemistry.
- Convective - the transfer of microparticles of one substance by macroparticles of the medium. A special branch of physics called hydrodynamics deals with the study of the motion of continuous media. From there you can get knowledge about the states of the flow.
- Turbulent diffusion is the process of transferring one substance to another, due to the turbulent movement of the second substance (typical for gases and liquids).
The statement is confirmed that diffusion can proceed both in gases and liquids, and in solids.
What is Fick's law?
The German scientist, physicist Fick, deduced a law showing the dependence of the particle flux density through a single area on a change in the concentration of a substance per unit length. This law is the law of diffusion. The law can be formulated as follows: the flow of particles, which is directed along the axis, is proportional to the derivative of the number of particles with respect to the variable plotted along the axis relative to which the direction of the flow of particles is determined. In other words, the flow of particles moving in the direction of the axis is proportional to the derivative of the number of particles with respect to the variable, which is plotted along the same axis as the flow. Fick's law allows you to describe the process of transfer of matter in time and space.
Diffusion equation
When flows are present in a substance, the substance itself is redistributed in space. In this regard, there are several equations that describe this redistribution process from a macroscopic point of view. The diffusion equation is differential. It stems from general equation the transfer of matter, which is also called the continuity equation. In the presence of diffusion, Fick's law is used, which is described above. The equation has the following form:
dn/dt=(d/dx)*(D*(dn/dx)+q.
Diffusion methods
The diffusion method, or rather the method of its implementation in solid materials, has been widely used in recent years. This is due to the advantages of the method, one of which is the simplicity of the equipment used and the process itself. The essence of the method of diffusion from solid sources is the deposition of films doped with one or more elements on semiconductors. There are several other methods for implementing diffusion, in addition to the solid source method:
- in a closed volume (ampoule method). Minimal toxicity is an advantage of the method, but its high cost, due to the disposability of the ampoule, is a significant drawback;
- in an open volume (thermal diffusion). The possibility of using many elements due to high temperatures is excluded, as well as lateral diffusion are big disadvantages of this method;
- in a partially closed volume (box method). This is an intermediate method between the two described above.
In order to learn more about the methods and features of diffusion, it is necessary to study additional literature devoted specifically to these issues.
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Introduction
The relevance of the work. Diffusion is a fundamental phenomenon of nature. It underlies the transformations of matter and energy. Its manifestations take place at all levels of organization of natural systems on our planet, starting from the level elementary particles, atoms and molecules, and ending with the geosphere. It is widely used in engineering Everyday life.
The essence of diffusion is the movement of particles of the medium, leading to the transfer of substances and the equalization of concentrations or to the establishment of an equilibrium distribution of particles of a given type in the medium. The diffusion of molecules and atoms is due to their thermal motion.
Diffusion is also a fundamental process underlying the functioning of living systems at any level of organization, from the level of elementary particles (electron diffusion) to biosphere level(circulation of substances in the biosphere).
It plays a huge role in nature, in human life and in technology. Diffusion processes can have both positive and negative effects on the life of humans and animals. An example of a positive impact is the maintenance of a homogeneous composition of atmospheric air near the Earth's surface. Diffusion plays an important role in various fields of science and technology, in processes occurring in animate and inanimate nature. It influences the flow chemical reactions.
With the participation of diffusion or in violation and change of this process, negative phenomena can occur in nature and human life, such as extensive pollution of the environment by products of human technical progress.
Objective: To study the features of diffusion in gases, liquids and solids and to find out the use of diffusion by man and the manifestation of diffusion in nature, to consider the influence of diffusion processes on the ecological balance in nature and the influence of man on diffusion processes.
Essence of diffusion
Demonstrates diffusion in gases by spraying deodorant in the corner of the classroom. The spread of odor is explained by the movement of molecules. This movement is continuous and erratic. Colliding with the molecules of gases that make up the air, the deodorant molecules change their direction of movement many times and, moving randomly, scatter throughout the room.
The process of penetration of particles (molecules, atoms, ions) of one substance between particles of another substance due to chaotic motion is called diffusion(from lat. diffusio - spreading, spreading, scattering). Thus, diffusion is the result of the chaotic movement of all particles of matter, of any mechanical action.
The movement of particles during diffusion is completely random, all directions of displacement are equally probable,
Since particles move in gases, liquids, and solids, diffusion is possible in these substances. Diffusion is the transfer of a substance due to the spontaneous alignment of an inhomogeneous concentration of atoms or molecules of various types. If portions of various gases are let into the vessel, then after a while all gases are uniformly mixed: the number of molecules of each type per unit volume of the vessel becomes constant, the concentration levels out. Diffusion is explained as follows. First, between the two bodies, the interface between the two media is clearly visible (Fig. 1a). Then, due to their movement, individual particles of substances located near the boundary exchange places.
The boundary between substances blurs (Fig. 1b). Having penetrated between the particles of another substance, the particles of the first begin to exchange places with the particles of the second, which are in ever deeper layers. The interface between substances becomes even more vague. Due to the continuous and random movement of particles, this process eventually leads to the fact that the solution in the vessel becomes homogeneous (Fig. 1c).
Fig.1. Explanation of the phenomenon of diffusion.
Diffusion in nature
With the help of diffusion, various gaseous substances spread in the air: for example, the smoke of a fire spreads over long distances.
The result of this phenomenon may be the equalization of the temperature in the room during ventilation. In the same way, air pollution occurs with harmful industrial products and vehicle exhaust gases. The natural combustible gas we use at home is colorless and odorless. In the event of a leak, it is impossible to notice it, therefore, at distribution stations, the gas is mixed with a special substance that has a sharp, unpleasant odor that is easily felt by a person.
Due to the phenomenon of diffusion, the lower layer of the atmosphere - the troposphere - consists of a mixture of gases: nitrogen, oxygen, carbon dioxide and water vapor. In the absence of diffusion, stratification would occur under the action of gravity: at the bottom there would be a layer of heavy carbon dioxide, above it - oxygen, above - nitrogen - inert gases.
In the sky, we also observe this phenomenon. Scattering clouds are also an example of diffusion, and how exactly F. Tyutchev said about this: “Clouds are melting in the sky ...”
In liquids, diffusion proceeds more slowly than in gases, but this process can be accelerated by heating. For example, in order to quickly pickle cucumbers, they are poured with hot brine. We know that sugar dissolves more slowly in cold tea than in hot tea.
In the summer, watching the ants, I always thought about how they, in the world that is huge for them, find out the way home. It turns out that this mystery is also opened by the phenomenon of diffusion. Ants mark their path with droplets of odorous liquid.
Thanks to diffusion, insects find their food. Butterflies, fluttering between plants, always find their way to a beautiful flower. The bees, having found a sweet object, storm it with their swarm.
And the plant grows, blooms for them, too, thanks to diffusion. After all, we say that a plant breathes and exhales air, drinks water, and receives various microadditives from the soil.
Carnivores also find their prey by diffusion. Sharks smell blood at a distance of several kilometers, as well as piranha fish.
The ecology of the environment is deteriorating due to emissions into the atmosphere, into the water of chemical and other harmful substances, and this all spreads and pollutes vast territories. But trees release oxygen and absorb carbon dioxide through diffusion.
The mixing of fresh water with salt water at the confluence of rivers into the sea is based on the principle of diffusion. The diffusion of solutions of various salts in the soil contributes to the normal nutrition of plants.
In all the examples given, we observe the mutual penetration of molecules of substances, i.e. diffusion. This process is based on many physiological processes in humans and animals: such as respiration, absorption, etc. In general, diffusion is of great importance in nature, but this phenomenon is also harmful in relation to environmental pollution.
2.1 Diffusion in flora
K.A. Timiryazev said: “Whether we talk about the nutrition of the root due to substances in the soil, whether we talk about the air nutrition of the leaves due to the atmosphere or the nutrition of one organ due to another, neighboring one, everywhere we will resort to the same reasons for explanation. : diffusion".
Indeed, the role of diffusion is very important in the plant kingdom. For example, the large development of the leaf crown of trees is explained by the fact that diffusion exchange through the surface of the leaves performs not only the function of respiration, but also partly of nutrition. Currently, foliar top dressing of fruit trees is widely practiced by spraying their crowns.
Diffuse processes play an important role in supplying natural water bodies and aquariums with oxygen. Oxygen enters the deeper layers of water in stagnant waters due to diffusion through their free surface. Therefore, any restrictions on the free surface of water are undesirable. So, for example, leaves or duckweed covering the surface of the water can completely stop the access of oxygen to the water and lead to the death of its inhabitants. For the same reason, narrow-necked vessels are unsuitable for use as an aquarium.
In the process of metabolism, when complex nutrients or their elements are broken down into simpler ones, the energy necessary for the life of the body is released.
2.2 The role of diffusion in plant nutrition.
The main role in diffusion processes in living organisms is played by cell membranes, which have selective permeability. The passage of substances through the membrane depends on:
Molecule sizes;
Electric charge;
From the presence and number of water molecules;
From the solubility of these particles in fats;
From the structure of the membrane.
There are two forms of diffusion: a) dialysis is the diffusion of solute molecules; b) osmosis is the diffusion of a solvent through a semi-permeable membrane. Soil solutions contain mineral salts and organic compounds. Water from the soil enters the plant by osmosis through the semi-permeable membranes of the root hairs. The concentration of water in the soil is higher than inside the root hairs, so there is diffusion from the zone with a higher concentration to the zone with a lower concentration. Then the concentration of water in these cells becomes higher than in the overlying ones - root pressure arises, causing an upward flow of juice through the roots and stem, and the loss of water by the leaves ensures further absorption of water.
Mineral substances enter the plant: a) by diffusion; b) sometimes by active transfer against the concentration gradient, accompanied by energy consumption. There are also turgor pressure is the pressure exerted by the contents of the cell on the cell wall. It is almost always lower than the osmotic pressure of the sap cell, because. outside is not pure water, but a saline solution. Turgor pressure value:
Preservation of the form of a plant organism;
Ensuring growth in young plant cells;
Preservation of plant elasticity (demonstration of cactus and aloe plants);
Shaping in the absence of reinforcing fabric (demonstration of a tomato);
Application of diffusion in medicine.
More than 30 years ago, the German doctor William Kolf used the "artificial kidney" device. Since then, it has been used: for emergency chronic care for acute intoxication; to prepare patients with chronic renal failure for kidney transplantation; for long-term (10-15 years) life support of patients with chronic kidney disease.
The use of the device "artificial kidney" is becoming more of a therapeutic procedure, the device is used both in the clinic and at home. With the help of the device, the recipient was prepared for the world's first successful kidney transplantation, carried out in 1965 by Academician B.V. Petrovsky.
The device is a hemodialyzer in which the blood is in contact with a saline solution through a semi-permeable membrane. Due to the difference in osmotic pressures, ions and molecules of metabolic products (urea, uric acid), as well as various toxic substances to be removed from the body, pass through the membrane from the blood into the saline solution. The device is a system of flat channels separated by thin cellophane membranes, through which blood and dialysate slowly move in opposite directions - a saline solution enriched gas mixture CO 2 + O 2 The device is connected to the patient's circulatory system using catheters inserted into the vena cava (blood entry into the dialysate) and cubital (outlet) veins. Dialysis lasts 4-6 hours. This achieves blood purification from nitrogenous wastes in case of insufficient kidney function, i.e. blood chemistry is regulated.
Biology teacher: The following message will help you understand and understand the forms of diffusion, osmosis and dialysis.
Application of diffusion in technology and in everyday life
Diffusion finds wide application in industry and everyday life. Diffusion welding of metals is based on the phenomenon of diffusion. The method of diffusion welding without the use of solders, electrodes and fluxes connects metals, non-metals, metals and non-metals, plastics. The parts are placed in a closed welding chamber with a strong vacuum, squeezed and heated to 800 degrees. In this case, intense mutual diffusion of atoms occurs in the surface layers of the contacting materials. Diffusion welding is mainly used in the electronic and semiconductor industries, precision engineering.
A diffusion apparatus is used to extract soluble substances from solid ground material. Such apparatuses are mainly used in sugar beet production, where they are used to obtain sugar juice from beet chips heated together with water.
An essential role in the operation of nuclear reactors is played by neutron diffusion, that is, the propagation of neutrons in matter, accompanied by a multiple change in the direction and speed of their movement as a result of collisions with atomic nuclei. The diffusion of neutrons in a medium is similar to the diffusion of atoms and molecules in gases and obeys the same laws.
As a result of the diffusion of carriers in semiconductors, an electric current arises. The movement of charge carriers in semiconductors is due to the inhomogeneity of their concentration. To create, for example, a semiconductor diode, indium is melted into one of the surfaces of germanium. Due to the diffusion of indium atoms deep into the germanium single crystal, a p-n transition is formed in it, through which a significant current can flow with minimal resistance.
The phenomenon of diffusion is based on the process of metallization - covering the surface of an article with a layer of metal or alloy to impart physical, chemical and mechanical properties to it, different from the properties of the material being metallized. It is used to protect products from corrosion, wear, increase contact electrical conductivity, for decorative purposes, for example, carburizing is used to increase the hardness and heat resistance of steel parts. It consists in the fact that steel parts are placed in a box with graphite powder, which is installed in a thermal furnace. Due to diffusion, carbon atoms penetrate into the surface layer of the parts. The penetration depth depends on the temperature and the exposure time of the parts in the thermal furnace.
Human influence on the course of diffusion in nature.
Unfortunately, as a result of the development of human civilization, it turns out Negative influence on nature and the processes that take place in it. The diffusion process plays an important role in the pollution of rivers, seas and oceans. For example, you can be sure that detergents drained into sewers, for example, in Odessa, will end up off the coast of Turkey due to diffusion and existing currents. The annual discharge of industrial and domestic wastewater in the world is estimated at tens of trillions of tons. An example of the negative impact of man on the processes of diffusion in nature are large-scale accidents that occurred in the basins of different water bodies. As a result of this phenomenon, oil and products of its processing spread over the surface of the water and, as a result, diffusion processes are disturbed, for example: oxygen does not enter the water column, and fish die without oxygen.
Due to the phenomenon of diffusion, the air is polluted with waste from various factories, because of it, harmful human waste penetrates the soil, water, and then has a harmful effect on the life and functioning of animals and plants. The area of land polluted by emissions from industrial enterprises, etc. is increasing. Over 2,000 hectares of land are occupied by industrial and domestic waste dumps. One of the currently difficult issues to solve is the issue of industrial waste disposal, including toxic ones.
An urgent problem is air pollution by exhaust gases, products of processing of harmful substances emitted into the atmosphere by various factories. Chimneys of enterprises emit carbon dioxide, nitrogen oxides and sulfur into the atmosphere. Currently, the total amount of gas emissions into the atmosphere exceeds 40 billion tons per year. An excess of carbon dioxide in the atmosphere is dangerous for the living world of the Earth, disrupts the carbon cycle in nature, and leads to the formation of acid rain. The diffusion process plays an important role in the pollution of rivers, seas and oceans. The annual discharge of industrial and domestic wastewater in the world is approximately 10 trillion tons.
Some medical studies have shown a relationship between the incidence of the respiratory system and the upper respiratory tract and the state of the air. There is a direct relationship between the indicator of the level of respiratory diseases and the volume of emissions of harmful substances into the atmosphere. These examples of diffusion have a detrimental effect on various processes occurring in nature.
Pollution of water bodies leads to the fact that life disappears in them, and the water used for drinking has to be purified, which is very expensive. In addition, chemical reactions occur in polluted water with the release of heat. The temperature of the water rises, while the oxygen content in the water decreases, which is bad for aquatic organisms. Due to rising water temperatures, many rivers now do not freeze in winter. To reduce the emission of harmful gases from industrial pipes, pipes of thermal power plants, special filters are installed. Such filters are installed, for example, at a thermal power plant in the Leninsky district of Chelyabinsk, but their installation is very expensive. To prevent pollution of water bodies, it is necessary to ensure that garbage, food waste, manure, and various chemicals are not thrown near the coast.
Considering global warming, it is important to investigate the change in diffusion rate depending on the increase in ambient temperature.
Experimental part.
I experience. Observation of the penetration of particles of one substance between the molecules of another substance .
Target : study the diffusion of solids and draw a conclusion about the rate of diffusion.
Devices and materials : gelatin, potassium permanganate, copper sulfate, Petria dish, tweezers, heating device.
:
Gelatin serves as a solid solution. In order to prepare a solution, it is necessary to dip 1 spoon of gelatin in cold water for 2 hours so that the powder swells, then heat the mixture and dissolve the gelatin without boiling, then pour it into a Petria dish (Fig. 3). When the gelatin had cooled, in the middle, with a quick movement, a crystal of potassium permanganate was introduced into one glass with tweezers, and copper sulphate in the other. And now we can observe the result of diffusion.
Here we observed the penetration of particles of potassium permanganate and copper sulphate between gelatin molecules. After 24 hours, no diffusion of potassium permanganate was observed (Fig. 4), since potassium permanganate is a strong oxidizing agent.
Thus, diffusion in solids proceeds more slowly. If strong oxidizing agents enter the environment, they lead to its destruction.
II experience. Observation of the dissolution of gouache pieces in water, at a constant temperature (at t = 22 ° C)
They took a piece of orange gouache and a vessel with clean water at a temperature of 22 °C. They put a piece of gouache in the vessel (Fig. 1) and began to observe what was happening. After 10 minutes, the water in the vessel begins to turn into the color of gouache (solid) (Fig. 2). Water is a good solvent. Under the action of water molecules, the bonds between the molecules of gouache solids are destroyed. 25 minutes have passed since the beginning of the experiment. The color of the water becomes more intense (Fig. 3). Water molecules penetrate between gouache molecules, breaking the forces of attraction. 45 minutes have passed since the beginning of the experiment (Fig. 4). Simultaneously with the forces of attraction between the molecules, repulsive forces begin to act and, as a result, the crystal lattice of a solid substance (gouache) is destroyed. The process of dissolving gouache is over. The duration of the experiment is 2 hours 50 minutes. The water was completely dyed in the color of gouache.
Thus, the phenomenon of diffusion is a long process, which results in the dissolution of solids.
W experience.The study of the dependence of the rate of diffusion on temperature and penetration into food.
Target : study how temperature affects the rate of diffusion.
Devices and materials : thermometers - 2 pcs, clock - 1 pc, glass - 1 pc, iodine, potatoes, magnetic stirrer.
Description of experience and results : they took a glass, put iodine in it and closed the glass with half-cut potatoes at t = 22 ° C. After 15 min from the beginning of the experiment, the diffusion process is not active. Started the heating process after 4 min. The diffusion process began, after 1 min, we see the penetration of iodine into the potato, after 2 min.
From this experience, it can be concluded that the rate of diffusion is affected by temperature: the higher the temperature, the higher the rate of diffusion, which negatively affects food.
Thus, the air is polluted with waste from various factories, vehicle exhaust gases penetrate food, and then have a harmful effect on the life and functioning of humans, animals and plants.
IV experience.The study of the dependence of the rate of diffusion of gaseous substances into water at a constant temperature
Target : to study the rate of diffusion of gaseous substances into water at a constant temperature and draw a conclusion about the rate of diffusion.
Devices and materials : thermometers - 1 pc, clock - 1 pc, flask - 1 pc, water, iodine.
Description of experience and results : water of the same mass and the same temperature (22 ° C) was poured into the flask, then vegetable oil (5 ml) was poured into another flask. Vegetable oil in our experience imitated oil. The flasks were covered with adhesive tape with iodine glued to it. The observation was taken after 45 minutes.
The water, covered with a film of vegetable oil, is very weakly colored, it can be judged that it is more difficult for oxygen molecules to penetrate into the water: fish and other aquatic inhabitants lack oxygen and may even die.
Output : the presence of various substances on the water surface disrupts diffusion processes and can lead to undesirable environmental consequences.
Conclusion
We see how great is the importance of diffusion in inanimate nature, and the existence of living organisms would be impossible if this phenomenon did not exist. Unfortunately, we have to deal with the negative manifestation of this phenomenon, but there are many more positive factors and therefore we are talking about the great importance of diffusion in nature.
Nature makes extensive use of the possibilities inherent in the process of diffusion penetration, plays an important role in the absorption of nutrition and oxygenation of the blood. In the flames of the Sun, in the life and death of distant stars, in the air we breathe, everywhere we see the manifestation of the omnipotent and universal diffusion.
Thus, diffusion is of great importance in the life processes of humans, animals and plants. Due to diffusion, oxygen from the lungs penetrates into the human blood, and from the blood into tissues. But, unfortunately, as a result of their activities, people often have a negative impact on natural processes in nature.
Studying diffusion, its role in the ecological balance of nature and the factors influencing its course in nature, I came to the conclusion that it is necessary to draw public attention to environmental problems.
Literature
Alekseev S.V., Gruzdeva M.V., Muravyov A.G., Gushchina E.V. Workshop on ecology. M. AO MDS, 1996
Ilchenko V.R. Crossroads of physics, chemistry and biology. M: "Enlightenment", 1986
Kirillova I.G. A book for reading in physics. M. "Enlightenment", 1986
Peryshkin A.V. Physics textbook Grade 7. M. "Enlightenment", 2005
Prokhorov A.M. Physical encyclopedic Dictionary. 1995
Ryzhenkov A.P. Physics. Human. Environment. M: Enlightenment, 1996
Chuyanov V.A. Encyclopedic Dictionary of a Young Physicist. 1999
Shakhmaev N.M. and others. Physics 7.M.: Mnemozina, 2007.
Encyclopedia for children.V.19. Ecology: In 33 volumes / Ch. ed. Volodin V. A. - M.: Avanta +, 2004 - 448 p.
The article shows the role of diffuse processes in wounds sutured in the traditional way and in the way proposed by the authors. Theoretically substantiated the improvement of diffuse processes in wounds in the treatment of hardware method.
The problem of wound healing of various etiologies is one of the main branches of medicine that have not lost their significance at the present time. Treatment of this pathology in the shortest possible time without purulent complications is possible only with sufficient provision of medical institutions with modern effective wound healing drugs.
In the wound process, the local and general reaction of the body is directly dependent on the severity and characteristics of damage to tissues and organs. Local and general reactive processes during regeneration processes are in direct and inverse relationship being interdependent and mutually influencing. The basis of wound healing is the ability to control the course of the wound process. This problem is invariably in the field of view of scientists and practicing surgeons.
A large number of used methods of wound treatment belong to the pharmacological group. At the same time, a large number of technical devices for the treatment of wounds were proposed. However, the most common method of suturing wounds is a circular vertical suture.
The human skin, consisting of collagen proteins, is an ideal natural membrane that performs numerous metabolic and protective functions. These processes are mainly due to diffusion. Diffusion (from Latin diffusio - spreading, spreading), mutual penetration of contiguous substances into each other due to the movement of particles of a substance.
Diffusion is a process at the molecular level and is determined by the random nature of the movement of individual molecules. The diffusion rate is therefore proportional to the average velocity of the molecules. Diffusion occurs in the direction of decreasing concentration of the substance and leads to a uniform distribution of the substance over the entire volume it occupies (to equalization of the chemical potential of the substance).
The role of diffuse processes in the pathogenesis and treatment of the wound process is very high. So, for example, in skin transplantation, the thickness of the flaps plays a huge role in the healing of burn wounds, since it has a positive effect on diffuse processes between the graft and the wound surface.
However, the significance of diffuse processes in the wound is practically not studied. The edges of the wound are conductive systems in which diffuse processes should take place under normal conditions. This process is shown schematically in Figure 1.
On the schematic drawing it can be seen that the surgical wound (1), sutured with traditional circular vertical sutures according to the classification of Golikov A.N., has certain disadvantages. Surgical suture (2), which is a means for approaching the edges of the wound, provides complete ischemia (5) of tissues, which leads to the formation of "silent areas" for the passage of diffuse processes, which leads to deformation (4) of the diffusion vector (3). As a result, the traditionally used surgical suture leads to the artificial formation of tissue areas that are not involved in the regeneration processes. Moreover, in unfavorable cases, these "tissue defects" are the sources of the formation of foci of the infectious process. Because, in the end, the tissue, deprived of access to nutrients, oxygen, etc., becomes necrotic, which ends with the formation of a scar. Otherwise, necrotic tissue masses are a favorable breeding ground for pathogens.
The security document of the National Institute of Intellectual Property of the Republic of Kazakhstan No. 13864 dated 15.08.2007 was obtained for the hardware method. The main principle of the proposed method is the tight closing of the wound edges to each other using physical and mechanical techniques. A nylon fishing line of sufficient length is applied along the edge of the wound, creating a “ligature arc”, which is fixed with its ends to the ends of the apparatus of the author's design.
The author's apparatus in assembled form has the shape of a frame, in the form of a quadrangular parallelogram, the sides of which are rods, and the ends are movable bars located and fixed to the bars with two nuts at both ends of the pins, holes of the same diameter are drilled on the movable bars for the rods and fixing the threads ligatures (Fig. 2).
regeneration processes. The effectiveness of the apparatus method has been proven experimentally and clinically.
Thus, a rationale for the effectiveness of the proposed hardware method in comparison with traditional methods of suturing wounds has been theoretically proposed. This is due to an increase in pressure on the wound area, which (due to the design features of the device) leads to a local increase in the diffusion rate.
Literature
- Golikov A.N. Healing of a granulating wound closed with sutures. - Moscow: 1951. - 160 p.
- Waldorf H., Fewres J. Wound healing // Adv. Derm. - 1995. No. 10. - P. 77–96.
- Abaturova E.K., Baimatov V.N., Batyrshina G.I. Influence of biostimulants on the wound process // Morphology. - 2002. - T. 121, No. 2–3. – S.6.
- Kochnev O.S., Izmailov G.S. Methods for suturing wounds. - Kazan: 1992. - 160 p.
- Kiselev S.I. The value of donor skin resources in the choice of rational surgical tactics in patients with deep burns: Abstract of the thesis. … Candidate of Medical Sciences. Ryazan, 1971. 17 p.
Zharalardy emdeu biology syndagy diffusion
Tuyin Makalada әdettegi әdіspen zhane maқala avtorlarymen ұsynylyp otyrғan apparatuses аdіstің zhalalardy emdeudegі diffusion processer turaly aitylgyn. Zharalarda diffusion of the processterdin apparatty adistin zhaksargany theory zhuzinde daleldip korsetildі.
DIFFUSION INBIOLOGYHealing
Abstract The article shows the role of diffuse processes in wounds sutured in the traditional way and the method proposed by the authors. The diffuse processes in wounds have been justified theoretically.
Esirkepov M.M., Nurmashev B.K., Mukanova U.A.
South Kazakhstan State Medical Academy, Shymkent
MOU Zaozernaya secondary school with in-depth study individual items No. 16
Topic: "Diffusion in animate and inanimate nature."
Completed:
8th grade student Zyabrev Kirill.
Physics teacher: Zavyalova G.M.
Biology teacher: Zyabreva V.F.
Tomsk - 2008
I. Introduction. …………………………………………………………… 3
II. Diffusion in animate and inanimate nature.
1. The history of the discovery of the phenomenon. …………………………………. 4
2. Diffusion, its types. ………………………………………….. 6
3. What does the diffusion rate depend on? ……………………….. 7
4. Diffusion in inanimate nature. ……………………………... 8
5. Diffusion in wildlife. ………………………………… nine
6. Use of diffusion phenomena. …………………………. 16
7. Designing individual diffusion phenomena. …………… 17
III. Conclusion. …………………………………………………... twenty
IV. Used Books. …………………………………. . 21
I. Introduction.
How many amazing and interesting things are happening around us. Distant stars shine in the night sky, a candle burns in the window, the wind carries the aroma of flowering bird cherry, an aging grandmother sees you off with her eyes .... I want to learn a lot, try to explain on my own. After all, many natural phenomena are associated with diffusion processes, which we talked about recently at school. But they said so little!
Work goals :
1. Expand and deepen knowledge about diffusion.
2. Simulate individual diffusion processes.
3. Create additional computer-based material for use in physics and biology lessons.
Tasks:
1. Find the necessary material in the literature, the Internet, study and analyze it.
2. Find out where diffusion phenomena occur in animate and inanimate nature (physics and biology), what significance they have, where they are used by humans.
3. Describe and design the most interesting experiments on this phenomenon.
4. Create animation models of some diffusion processes.
Methods: analysis and synthesis of literature, design, modeling.
My work consists of three parts; the main part consists of 7 chapters. I studied and processed materials from 13 literary sources, including educational, reference, scientific literature and Internet sites, and also prepared a presentation made in the Power Point editor.
II. Diffusion in animate and inanimate nature.
II .one. The history of the discovery of the phenomenon of diffusion.
When observing a suspension of flower pollen in water under a microscope, Robert Brown observed a chaotic movement of particles that arises "not from the movement of a liquid and not from its evaporation." Suspended particles 1 µm or less in size, visible only under a microscope, performed disordered independent movements, describing complex zigzag trajectories. Brownian motion does not weaken with time and does not depend on chemical properties environment; its intensity increases with an increase in the temperature of the medium and with a decrease in its viscosity and particle size. Even qualitatively explain the reasons brownian motion succeeded only 50 years later, when the cause of Brownian motion began to be associated with the impacts of liquid molecules on the surface of a particle suspended in it.
The first quantitative theory of Brownian motion was given by A. Einstein and M. Smoluchowski in 1905-06. based on molecular kinetic theory. It was shown that random walks of Brownian particles are associated with their participation in thermal motion along with the molecules of the medium in which they are suspended. Particles have on average the same kinetic energy, but due to the greater mass they have a lower speed. The theory of Brownian motion explains the random motion of a particle by the action of random forces from molecules and friction forces. According to this theory, the molecules of a liquid or gas are in constant thermal motion, and the impulses of different molecules are not the same in magnitude and direction. If the surface of a particle placed in such a medium is small, as is the case for a Brownian particle, then the impacts experienced by the particle from the surrounding molecules will not be exactly compensated. Therefore, as a result of the “bombardment” by molecules, a Brownian particle begins to move randomly, changing the magnitude and direction of its velocity approximately 1014 times per second. It followed from this theory that by measuring the displacement of a particle over a certain time and knowing its radius and the viscosity of the liquid, one can calculate the Avogadro number.
The conclusions of the theory of Brownian motion were confirmed by the measurements of J. Perrin and T. Svedberg in 1906. Based on these relationships, the Boltzmann constant and the Avogadro constant were experimentally determined. (Avogadro's constant denoted by NA, the number of molecules or atoms in 1 mole of a substance, NA = 6.022.1023 mol-1; name in honor of A. Avogadro.
Boltzmann constant, physical constant k equal to the ratio of the universal gas constant R to the number of Avogadro N A: k = R / N A = 1.3807.10-23 J/K. Named after L. Boltzmann.)
When observing Brownian motion, the position of a particle is fixed at regular intervals. The shorter the time intervals, the more broken the particle's trajectory will look.
The patterns of Brownian motion serve as a clear confirmation of the fundamental provisions of the molecular kinetic theory. It was finally established that the thermal form of the motion of matter is due to the chaotic motion of atoms or molecules that make up macroscopic bodies.
The theory of Brownian motion played an important role in substantiating statistical mechanics; kinetic theory coagulation (mixing) of aqueous solutions. In addition, it also has practical significance in metrology, since Brownian motion is considered as the main factor limiting the accuracy of measuring instruments. For example, the limit of accuracy of readings of a mirror galvanometer is determined by the trembling of the mirror, like a Brownian particle bombarded by air molecules. The laws of Brownian motion determine the random movement of electrons, causing noise in electrical circuits. Dielectric losses in dielectrics are explained by random movements of the dipole molecules that make up the dielectric. Random movements of ions in electrolyte solutions increase their electrical resistance.
Trajectories of Brownian particles (scheme of Perrin's experiment); the dots mark the positions of the particles at regular intervals.
In this way, DIFFUSION, OR BROWNIAN MOVEMENT - this random movement of the smallest particles suspended in a liquid or gas, occurring under the influence of impacts of the molecules of the environment; open
R. Brown in 1827
II. 2. Diffusion, its types.
Distinguish between diffusion and self-diffusion.
by diffusion called the spontaneous penetration of molecules of one substance into the gaps between the molecules of another substance. In this case, the particles are mixed. Diffusion is observed for gases, liquids and solids. For example, a drop of ink is mixed in a glass of water. Or the smell of cologne spreads throughout the room.
Diffusion, like self-diffusion, exists as long as there is a substance density gradient. If the density of any one and the same substance is not the same in different parts of the volume, then the phenomenon of self-diffusion is observed. By self-diffusion called the process of density equalization(or concentration proportional to it) the same substance. Diffusion and self-diffusion occur due to the thermal motion of molecules, which, in non-equilibrium states, creates flows of matter.
The mass flux density is the mass of matter ( dm) diffusing per unit time through a unit area ( dS pl), perpendicular to the axis x :
(1.1)
The phenomenon of diffusion obeys Fick's law
(1.2)
where is the modulus of the density gradient, which determines the rate of density change in the direction of the axis X ;
D- diffusion coefficient, which is calculated from the molecular kinetic theory by the formula
(1.3)
where is the average speed of the thermal motion of molecules;
Mean free path of molecules.
The minus sign indicates that mass transfer occurs in the direction of decreasing density.
Equation (1.2) is called the diffusion equation or Fick's law.
II. 3. Diffusion rate.
When a particle moves in a substance, it constantly collides with its molecules. This is one of the reasons why, under normal conditions, diffusion is slower than normal motion. What does the diffusion rate depend on?
First, on the average distance between particle collisions, i.e. free path length. The greater this length, the faster the particle penetrates into the substance.
Secondly, pressure affects speed. The denser the packing of particles in a substance, the more difficult it is for an alien particle to penetrate into such a packing.
Thirdly, the molecular weight of a substance plays an important role in the diffusion rate. The larger the target, the more likely it is to hit, and after a collision, the speed always slows down.
And fourth, temperature. As the temperature rises, the oscillations of the particles increase, and the speed of the molecules increases. However, the speed of diffusion is a thousand times slower than the speed of free movement.
All types of diffusion obey the same laws, are described by the diffusion coefficient D, which is a scalar value and is determined from Fick's first law.
For one-dimensional diffusion 
,
where J is the flux density of atoms or defects of the substance,
D - diffusion coefficient,
N is the concentration of atoms or defects of the substance.
Diffusion is a process at the molecular level and is determined by the random nature of the movement of individual molecules. The diffusion rate is therefore proportional to the average velocity of the molecules. In the case of gases, the average velocity of small molecules is greater, namely, it is inversely proportional to square root from the mass of the molecule and grows with increasing temperature. Diffusion processes in solids at high temperatures often find practical application. For example, certain types of cathode ray tubes (CRTs) use metallic thorium diffused through metallic tungsten at 2000 ºC.
If in a mixture of gases one molecule is four times heavier than another, then such a molecule moves twice as slowly compared to its movement in a pure gas. Accordingly, its diffusion rate is also lower. This difference in diffusion rates between light and heavy molecules is used to separate substances with different molecular weights. An example is the separation of isotopes. If a gas containing two isotopes is passed through a porous membrane, the lighter isotopes penetrate the membrane faster than the heavier ones. For better separation, the process is carried out in several stages. This process has been widely used to separate uranium isotopes (separation of 235U fissile under neutron irradiation from the bulk of 238U). Since this separation method is energy intensive, other, more economical separation methods have been developed. For example, the use of thermal diffusion in a gaseous medium is widely developed. A gas containing a mixture of isotopes is placed in a chamber in which a spatial temperature difference (gradient) is maintained. In this case, heavy isotopes are concentrated over time in the cold region.
Output. Diffuse changes are affected by:
· molecular weight of the substance (the higher the molecular weight, the lower the speed);
· the average distance between particle collisions (the greater the path length, the greater the speed);
· pressure (the larger the packing of particles, the more difficult it is to break through),
· temperature (as the temperature rises, the speed increases).
II.4. Diffusion in inanimate nature.
Did you know that our whole life is built on a strange paradox of nature? Everyone knows that the air we breathe consists of gases of different densities: nitrogen N 2 , oxygen O 2 , carbon dioxide CO 2 and a small amount of other impurities. And these gases should be arranged in layers, according to gravity: the heaviest, CO 2, is at the very surface of the earth, above it - O 2, even higher - N 2. But that doesn't happen. We are surrounded by a homogeneous mixture of gases. Why doesn't the flame go out? After all, the oxygen surrounding it quickly burns out? Here, as in the first case, the alignment mechanism operates. Diffusion prevents imbalance in nature!
Why is the sea salty? We know that rivers make their way through the thickness of rocks, minerals and wash salts into the sea. How is salt mixed with water? This can be explained with a simple experience:
EXPERIENCE DESCRIPTION: Pour an aqueous solution of copper sulfate into a glass vessel. Carefully pour clean water over the solution. We observe the boundary between liquids.
Question: What will happen to these fluids over time, and what will we observe?
Over time, the boundary between the contacting liquids will begin to blur. A vessel with liquids can be placed in a closet and every day you can observe how spontaneous mixing of liquids occurs. In the end, a homogeneous liquid of pale blue color is formed in the vessel, almost colorless in the light.
Copper sulphate particles are heavier than water, but due to diffusion they slowly rise up. The reason is the structure of the liquid. Liquid particles are packed into compact groups - pseudonuclei. They are separated from each other by voids - holes. The nuclei are not stable, their particles are not in equilibrium for long. As soon as the particle imparts energy, the particle breaks away from the nucleus and falls into voids. From there, it easily jumps to another core, and so on.
Molecules of a foreign substance begin their journey through the liquid from holes. On the way, they collide with nuclei, knock particles out of them, and take their place. Moving from one free place to another, they slowly mix with liquid particles. We already know that the diffusion rate is low. Therefore, under normal conditions, this experiment took 18 days, with heating - 2-3 minutes.
Output: In the flames of the Sun, the life and death of distant luminous stars, in the air we breathe, in weather changes, in almost all physical phenomena, we see the manifestation of almighty diffusion!
II.5. Diffusion in wildlife.
Diffusion processes have been well studied at present, their physical and chemical laws have been established, and they are quite applicable to the movement of molecules in a living organism. Diffusion in living organisms is inextricably linked with the plasma membrane of the cell. Therefore, it is necessary to find out how it is arranged, and how the features of its structure are related to the transport of substances in the cell.
The plasma membrane (plasmalemma, cell membrane), a surface, peripheral structure surrounding the protoplasm of plant and animal cells, serves not only as a mechanical barrier, but, most importantly, limits the free two-way flow into and out of the cell of low- and high-molecular substances. Moreover, the plasmalemma acts as a structure that “recognizes” various chemicals and regulates the selective transport of these substances into the cell.
The outer surface of the plasma membrane is covered with a loose fibrous layer of substance 3-4 nm thick - the glycocalyx. It consists of branching chains of complex carbohydrates of membrane integral proteins, between which compounds of proteins with sugars and proteins with fats isolated by the cell can be located. Some cellular enzymes involved in the extracellular breakdown of substances (extracellular digestion, for example, in the intestinal epithelium) are immediately found.
Because the interior of the lipid layer is hydrophobic, it provides a virtually impenetrable barrier to most polar molecules. Due to the presence of this barrier, leakage of the contents of the cells is prevented, however, because of this, the cell was forced to create special mechanisms for the transport of water-soluble substances through the membrane.
The plasma membrane, like other lipoprotein cell membranes, is semipermeable. Water and the gases dissolved in it have the maximum penetrating power. Ion transport can proceed along a concentration gradient, i.e. passively, without energy consumption. In this case, some membrane transport proteins form molecular complexes, channels through which ions pass through the membrane by simple diffusion. In other cases, special membrane carrier proteins selectively bind to one or another ion and transport it across the membrane. This type of transfer is called active transport and is carried out using protein ion pumps. For example, spending 1 ATP molecule, the K-Na pump system pumps out 3 Na ions from the cell in one cycle and pumps 2 K ions against the concentration gradient. In combination with active transport of ions, various sugars, nucleotides and amino acids penetrate through the plasmalemma. Macromolecules, such as proteins, do not pass through the membrane. They, as well as larger particles of the substance, are transported into the cell through endocytosis. During endocytosis, a certain section of the plasmalemma captures, envelops the extracellular material, and encloses it in a membrane vacuole. This vacuole - the endosome - merges in the cytoplasm with the primary lysosome and digestion of the captured material occurs. Endocytosis is formally divided into phagocytosis (absorption of large particles by the cell) and pinocytosis (absorption of solutions). The plasma membrane also takes part in the removal of substances from the cell using exocytosis, a process that is the reverse of endocytosis.
Diffusion of ions in aqueous solutions is especially important for living organisms. Equally important is the role of diffusion in respiration, photosynthesis, and plant transpiration; in the transfer of oxygen from the air through the walls of the alveoli of the lungs and its entry into the blood of humans and animals. Diffusion of molecular ions through membranes is carried out using an electrical potential inside the cell. Possessing selective permeability, membranes play the role of customs when moving goods across the border: some substances pass through, others delay, and others are generally "expelled" from the cell. The role of membranes in the life of cells is very great. The dying cell loses control over the ability to regulate the concentration of substances across the membrane. The first sign of cell death is the beginning of changes in the permeability and failure of its outer membrane.
In addition to conventional transport - the kinetic process of the transfer of particles of a substance under the action of gradients of electrical or chemical potential, temperature or pressure - active transport also takes place in cellular processes - the movement of molecules and ions against the concentration gradient of substances. This diffusion mechanism is called osmosis. (Osmosis was first observed by A. Nolle in 1748, but the study of this phenomenon was started a century later.) This process is carried out due to different osmotic pressure in an aqueous solution on different sides of a biological membrane. Water often passes freely through the membrane by osmosis, but this membrane can be impervious to substances dissolved in water. It is curious that water flows against the diffusion of this substance, but obeying the general law of the concentration gradient (in this case, water).
Therefore, water tends to move from a more dilute solution, where its concentration is higher, to a more concentrated solution of a substance, in which the water concentration is lower. Not being able to directly suck in and pump out water, the cell does this with the help of osmosis, changing the concentration of solutes in it. Osmosis equalizes the concentration of the solution on both sides of the membrane. From the osmotic pressure of solutions of substances on both sides cell wall and the elasticity of the cell membrane depends on the stress state of the cell membrane, which is called turgor pressure (turgor - from Latin turgere - to be swollen, filled). Usually, the elasticity of animal cell membranes (excluding some intestinal ones) is low, they lack high turgor pressure and remain intact only in isotonic solutions or those that differ little from isotonic ones (the difference between internal pressure and external pressure is less than 0.5-1.0 am). In living plant cells, the internal pressure is always greater than the external pressure, however, the rupture of the cell membrane does not occur due to the presence of a cellulose cell wall. The difference between internal and external pressures in plants (for example, in plants of halophytes - loving salt, mushrooms) reaches 50-100 am. But even so, the margin of safety plant cell is 60-70%. In most plants, the relative elongation of the cell membrane due to turgor does not exceed 5-10%, and the turgor pressure lies in the range of 5-10 am. Thanks to turgor, plant tissues have elasticity and structural strength. (Experiments No. 3, No. 4 confirm this). All processes of autolysis (self-destruction), wilting and aging are accompanied by a drop in turgor pressure.
Considering diffusion in living nature, one cannot fail to mention absorption. Absorption is the process of entry of various substances from the environment through cell membranes into cells, and through them into the internal environment of the body. In plants, this is the process of absorbing water with substances dissolved in it by roots and leaves by osmosis and diffusion; in invertebrates - from the environment or cavity fluid. In primitive organisms, absorption is carried out with the help of pino- and phagocytosis. In vertebrates, absorption can occur both from the abdominal organs - lungs, uterus, Bladder, and from the surface of the skin, from the wound surface, etc. Volatile gases and vapors are absorbed by the skin.
The greatest physiological significance is absorption in the gastrointestinal tract, which occurs mainly in the small intestine. For efficient transport of substances special meaning has a large surface area of the intestine and a constantly high blood flow in the mucous membrane, due to which a high concentration gradient of absorbed compounds is maintained. In humans, the mesenteric blood flow during meals is about 400 ml / min, and at the height of digestion - up to 750 ml / min, with the main share (up to 80%) being the blood flow in the mucous membrane of the digestive organs. Due to the presence of structures that increase the surface of the mucous membrane - circular folds, villi, microvilli, the total area of the suction surface of the human intestine reaches 200 m 2.
Water and salt solutions can diffuse on both sides of the intestinal wall, both in the small and large intestines. Their absorption occurs mainly in the upper sections of the small intestine. Of great importance in the small intestine is the transport of Na + ions, due to which electrical and osmotic gradients are mainly created. The absorption of Na + ions occurs due to both active and passive mechanisms.
If the cell did not have systems for regulating osmotic pressure, then the concentration of dissolved substances inside it would be greater than their external concentrations. Then the concentration of water in the cell would be less than its concentration outside. As a result, there would be a constant influx of water into the cell and its rupture. Fortunately, animal cells and bacteria control the osmotic pressure in their cells by actively pumping out inorganic ions such as Na. Therefore, their total concentration inside the cell is lower than outside. For example, amphibians spend a significant part of their time in water, and the salt content in their blood and lymph is higher than in fresh water. Amphibians continuously absorb water through their skin. Therefore, they produce a lot of urine. A frog, for example, if its cloaca is bandaged, swells like a ball. Conversely, if an amphibian enters salty sea water, it becomes dehydrated and dies very quickly. Therefore, the seas and oceans for amphibians are an insurmountable barrier. Plant cells have rigid walls that prevent them from swelling. Many protozoa avoid bursting from incoming water by using special mechanisms that regularly eject the incoming water.
Thus, the cell is an open thermodynamic system, exchanging matter and energy with the environment, but maintaining a certain constancy of the internal environment. These two properties of a self-regulating system - openness and constancy - are carried out simultaneously, and metabolism (metabolism) is responsible for the constancy of the cell. Metabolism is the regulator that contributes to the preservation of the system, it provides an appropriate response to environmental influences. That's why necessary condition metabolism is the irritability of a living system at all levels, which at the same time acts as a factor in the consistency and integrity of the system.
Membrane can change its permeability under the influence of chemical and physical factors, including as a result of membrane depolarization during the passage of an electrical impulse through the system of neurons and impact on it.
A neuron is a segment of a nerve fiber. If an irritant acts on one end of it, then an electrical impulse occurs. Its value is about 0.01 V for human muscle cells, and it propagates at a speed of about 4 m/s. When the impulse reaches the synapse - a connection of neurons, which can be considered as a kind of relay that transmits a signal from one neuron to another, then the electrical impulse is converted into a chemical impulse by the release of neurotransmitters - specific intermediary substances. When the molecules of such a mediator enter the gap between neurons, the neurotransmitter reaches the end of the gap by diffusion and excites the next neuron.
However, a neuron reacts only if there are special molecules on its surface - receptors that can only bind this mediator and not react to another. This occurs not only on the membrane, but also in any organ, such as a muscle, causing its contraction. Impulse signals through synapses can inhibit or enhance the transmission of others, and therefore neurons perform logical functions (“and”, “or”), which to a certain extent served as N. Wiener’s reason to believe that computational processes in the brain of a living organism and in a computer follow essentially the same pattern. Then the informational approach makes it possible to describe inanimate and living nature in a unified way.
The very process of the effect of the signal on the membrane consists in changing its high electrical resistance, since the potential difference across it is also of the order of 0.01 V. A decrease in resistance leads to an increase in the electric current pulse and the excitation is transmitted further in the form of a nerve impulse, while changing the possibility of passing through membrane of certain ions. Thus, information in the body can be transmitted in combination, by chemical and physical mechanisms, and this ensures the reliability and variety of channels for its transmission and processing in a living system.
The processes of cellular respiration, when ATP molecules are formed in the mitochondria of the cell, providing it with the necessary energy, are closely related to the processes of ordinary respiration of a living organism, which requires oxygen O2 obtained as a result of photosynthesis. The mechanisms of these processes are also based on the laws of diffusion. Essentially, these are the material and energy components that are necessary for a living organism. Photosynthesis is the process of storing solar energy by forming new bonds in the molecules of synthesized substances. The starting materials for photosynthesis are water H 2 O and carbon dioxide CO 2 . These simple inorganic compounds form more complex, energy-rich nutrients. As a side product, but very important for us, molecular oxygen O 2 is formed. An example is a reaction that occurs due to the absorption of light quanta and the presence of the chlorophyll pigment contained in chloroplasts.
The result is one sugar molecule C 6 H 12 O 6 and six oxygen molecules O 2. The process proceeds in stages, first at the stage of photolysis, hydrogen and oxygen are formed by splitting water, and then hydrogen, combining with carbon dioxide, forms a carbohydrate - sugar C 6 H 12 O 6. Essentially, photosynthesis is the conversion of the radiant energy of the Sun into energy. chemical bonds emerging organic matter. Thus, photosynthesis, which produces oxygen O 2 in the light, is the biological process that provides living organisms with free energy. The process of normal respiration as a metabolic process in the body associated with the consumption of oxygen is the reverse of the process of photosynthesis. Both of these processes can go along the following chain:
Solar energy (photosynthesis)
nutrients + (breath)
Energy of chemical bonds.
The end products of respiration serve as starting materials for photosynthesis. Thus, the processes of photosynthesis and respiration are involved in the cycle of substances on Earth. Part of the solar radiation is absorbed by plants and some organisms, which, as we already know, are autotrophs, i.e. self-feeding (food for them - sunlight). As a result of the process of photosynthesis, autotrophs bind atmospheric carbon dioxide and water, forming up to 150 billion tons of organic substances, absorbing up to 300 billion tons of CO 2, and emit about 200 billion tons of free oxygen O 2 annually.
Received organic matter are used as food by humans and herbivores, which, in turn, feed on other heterotrophs. Plant and animal remains are then decomposed into simple inorganic substances, which can again participate in the form of CO 2 and H 2 O in photosynthesis. Part of the resulting energy, including that stored in the form of fossil energy fuel, is used by living organisms, and part is uselessly dissipated into the environment. Therefore, the process of photosynthesis, due to the possibility of providing them with the necessary energy and oxygen, is at a certain stage in the development of the Earth's biosphere a catalyst for the evolution of living things.
Diffusion processes underlie the metabolism in the cell, which means that with their help these processes are carried out at the level of organs. This is how absorption processes are carried out in the root hairs of plants, the intestines of animals and humans; gas exchange in plant stomata, lungs and tissues of humans and animals, excretory processes.
Biologists have been engaged in the structure and study of cells for more than 150 years, starting with Schleiden, Schwann, Purime and Virchow, who in 1855 established the mechanism of cell growth by dividing them. It was found that every organism develops from one cell, which begins to divide and as a result of this, many cells are formed that are noticeably different from each other. But since initially the development of the organism began from the division of the first cell, then at one of the stages of our life cycle we retain a resemblance to a very distant unicellular ancestor, and we can jokingly say that we are more likely descended from an amoeba than from a monkey.
Organs are formed from cells, and the system of cells acquires such qualities that its constituent elements do not have, i.e. individual cells. These differences are due to the set of proteins synthesized by this cell. There are muscle cells, nerve cells, blood cells (erythrocytes), epithelial and others, depending on their functionality. Cell differentiation occurs gradually during the development of the organism. In the process of cell division, their life and death, a continuous replacement of cells occurs throughout the life of the organism.
No molecule in our body stays the same for more than a few weeks or months. During this time, molecules are synthesized, fulfill their role in the life of the cell, are destroyed and replaced by other, more or less identical molecules. The most amazing thing is that living organisms as a whole are much more constant than their constituent molecules, and the structure of cells and the whole body consisting of these cells remains unchanged in this unceasing cycle, despite the replacement of individual components.
Moreover, this is not a replacement of individual parts of the car, but, as S. Rose figuratively compares, the body with a brick building, “from which a crazy bricklayer continuously takes out one brick after another at night and day and inserts new ones in their place. At the same time, the external appearance of the building remains the same, and the material is constantly being replaced. We are born with some neurons and cells, and we die with others. An example is the consciousness, understanding and perception of a child and an old person. All cells have complete genetic information to build all the proteins of a given organism. Storage and transmission of hereditary information is carried out with the help of the cell nucleus.
Output: It is impossible to exaggerate the role of the permeability of the plasma membrane in the vital activity of the cell. Most of the processes associated with providing the cell with energy, obtaining products and getting rid of decay products are based on the laws of diffusion through this semi-permeable living barrier.
Osmosis- in fact, a simple diffusion of water from places with a higher concentration of water to places with a lower concentration of water.
Passive transport- this is the transfer of substances from places with a large value of the electrochemical potential to places with its lower value. The transfer of small water-soluble molecules is carried out using special transport proteins. These are special transmembrane proteins, each of which is responsible for the transport of certain molecules or groups of related molecules.
It is often necessary to ensure that molecules are transported across the membrane against their electrochemical gradient. Such a process is called active transport and is carried out by carrier proteins, the activity of which requires energy expenditure. If a carrier protein is linked to an energy source, a mechanism can be obtained that ensures the active transport of substances across the membrane.
II.6. Application of diffusion.
Man has been using diffusion phenomena since ancient times. Cooking and heating the home are associated with this process. We encounter diffusion during heat treatment of metals (welding, soldering, cutting, coating, etc.); applying a thin layer of metals to the surface of metal products to increase the chemical resistance, strength, hardness of parts and devices, or for protective and decorative purposes (zinc plating, chromium plating, nickel plating).
The natural combustible gas we use at home for cooking is colorless and odorless. Therefore, it would be difficult to immediately notice a gas leak. And in case of leakage due to diffusion, the gas spreads throughout the room. Meanwhile, at a certain ratio of gas to air in a closed room, a mixture is formed that can explode, for example, from a lit match. The gas can also cause poisoning.
To make the flow of gas into the room noticeable, at distribution stations, combustible gas is pre-mixed with special substances that have a sharp unpleasant odor, which is easily felt by a person even at a very low concentration. This precaution allows you to quickly notice the accumulation of gas in the room if a leak occurs.
In modern industry, vacuum forming is used, a method for manufacturing products from sheet thermoplastics. The product of the required configuration is obtained due to the pressure difference that occurs due to rarefaction in the mold cavity, over which the sheet is fixed. It is used, for example, in the production of containers, parts of refrigerators, instrument cases. Due to diffusion in this way, it is possible to weld something that cannot be welded by itself (metal with glass, glass and ceramics, metals and ceramics, and much more).
Due to the diffusion of various uranium isotopes through porous membranes, fuel for nuclear reactors has been obtained. Sometimes nuclear fuel is called nuclear fuel.
Absorption (resorption) of substances when they are introduced into the subcutaneous tissue, into muscles or when applied to the mucous membranes of the eye, nose, skin of the ear canal occurs mainly due to diffusion. This is the basis for the use of many medicinal substances, and absorption in the muscles is faster than in the skin.
Folk wisdom says: "mow the scythe until dew." Tell me, what does diffusion and morning mowing have to do with it? The explanation is very simple. During morning dew, grasses have increased turgor pressure, stomata are open, stems are elastic, which facilitates their mowing (grass mowed with closed stomata dries worse).
In horticulture, when budding and grafting plants on sections, due to diffusion, callus is formed (from the Latin Callus - corn) - wound tissue in the form of an influx at the sites of damage and promotes their healing, ensures the fusion of the scion with the rootstock.
Callus is used to obtain a culture of isolated tissues (explantation). This is a method of long-term preservation and cultivation in special nutrient media of cells, tissues, small organs or their parts isolated from the body of humans, animals and plants. It is based on methods of growing a culture of microorganisms that provide asepsis, nutrition, gas exchange and removal of metabolic products of cultivated objects. One of the advantages of the tissue culture method is the ability to observe the vital activity of cells using a microscope. For this, plant tissue is grown on nutrient media containing auxins and cytokinins. Callus usually consists of poorly differentiated homogeneous cells of the educational tissue, but with a change in growing conditions, primarily the content of phytohormones in the nutrient medium, the formation of phloem, xylem and other tissues is possible in it, as well as the development of various organs and the whole plant.
II.7. Design of individual experiments.
Using the scientific literature, I tried to repeat the experiments that were most interesting to me. I depicted the diffusion mechanism and the results of these experiments in the presentation in the form of animation models.
EXPERIENCE 1. Take two test tubes: one half filled with water, the other half filled with sand. Pour water into a test tube with sand. The volume of the mixture of water and sand in the test tube is less than the sum of the volumes of water and sand.
EXPERIENCE 2. Half fill a long glass tube with water, and then pour colored alcohol on top. General level mark liquids in the tube with a rubber ring. After mixing water and alcohol, the volume of the mixture decreases.
(Experiments 1 and 2. prove that there are gaps between the particles of matter; during diffusion, they are filled with particles of matter - an alien.)
EXPERIENCE 3. We bring a cotton wool moistened with ammonia into contact with a cotton wool moistened with an indicator of phenolphthalein. We observe the staining of fleece in raspberry color.
Now a cotton swab moistened with ammonia is placed on the bottom of a glass vessel, and moistened with phenolphthalein. We attach to the lid and cover the glass vessel with this lid. After some time, the cotton wool moistened with phenolphthalein begins to stain.
As a result of interaction with ammonia, phenolphthalein turns crimson, which we observed when cotton wool came into contact. But why, then, in the second case, a cotton wool moistened with phenolphthalein. It also stains, because now the fleece was not brought into contact? Answer: continuous chaotic motion of particles of matter.
EXPERIENCE 4. Along the wall inside a tall cylindrical vessel, lower a narrow strip of filter paper impregnated with a mixture of starch paste with a solution of the phenolphthalein indicator. Place iodine crystals at the bottom of the vessel. Close the vessel tightly with a lid, to which cotton wool soaked in ammonia solution is suspended.
Due to the interaction of iodine with starch, a blue-violet color rises up a strip of paper. At the same time, a crimson color spreads downward - proof of the movement of ammonia molecules. After a few minutes, the boundaries of the colored areas of the paper will meet, and then the blue and crimson colors will mix, that is, diffusion occurs.[ 10]
EXPERIENCE 5.(they spend it together) Take a clock with a second hand, a tape measure, a bottle of toilet water and stand in different corners of the room. One notes the time and opens the vial. Another notes the time when he smells the toilet water. By measuring the distance between the experimenters, we find the diffusion rate. For accuracy, the experiment is repeated 3-4 times, and the average value of the speed is found. If the distance between the experimenters is 5 meters, then the smell is felt after 12 minutes. That is, the diffusion rate in this case is 2.4 m/min.
EXPERIENCE 6. DETERMINATION OF PLASMA VISCOSITY BY THE PLASMOLYSIS METHOD (according to P.A. Genkel).
advance speed convex plasmolysis in plant cells, when treated with a hypertanic solution, depends on the viscosity of the cytoplasm; the lower the viscosity of the cytoplasm, the sooner the concave plasmolysis turns into a convex one. The viscosity of the cytoplasm depends on the degree of dispersion of colloidal particles and their hydration, on the water content in the cell, on the age of the cells, and other factors.
Working process. Make a thin cut of the epidermis from an aloe leaf, or peel off the epidermis from soft onion scales. The prepared sections are stained in a watch glass for 10 minutes in a solution of neutral red at a concentration of 1:5000. Then the sections of the object are placed on a glass slide in a drop of sucrose at a low concentration and covered with one cover slip. Under the microscope, the state of plasmolysis is noted. First, concave plasmolysis is noted in the cells. In the future, this form is either preserved, or, with one speed or another, passes into a convex form. It is important to note the time of transition from concave to convex plasmolysis. The time interval during which concave plasmolysis turns into convex is an indicator of the degree of viscosity of the protoplasm. The longer the transition time to convex plasmolysis, the greater the viscosity of the plasma. Plasmolysis in onion cells begins faster than in aloe skin. This means that the cytoplasm of aloe cells is more viscous.
EXPERIENCE 7. PLASMOLYSIS. DEPLASMOLYSIS. PENETRATION OF SUBSTANCES INTO THE VACUOL [2]
Some organic substances quickly penetrate into the vacuole. In cells, when they are kept in solutions of such substances, plasmolysis is relatively quickly lost and deplasmolysis occurs.
Deplasmolysis is the restoration of turgor in cells(i.e., the reverse of plasmolysis).
Working process. Sections of the upper epidermis of the painted onion scales (concave side) are placed in a drop of 1 M solution of urea or glycerin fertilizer for plants directly on a glass slide, covered with a coverslip. After 15-30 minutes, the objects are examined under a microscope. Plasmolyzed cells are clearly visible. Leave sections in a drop of solution for another 30-40 minutes. Then again they are examined under a microscope and deplasmolysis is observed - the restoration of turgor.
Output : Plants cannot precisely control the amount of chemicals entering and exiting cells.
III. Conclusion.
The laws of diffusion are subject to the processes of physical and chemical movements of elements in the earth's interior and in the Universe, as well as the processes of vital activity of cells and tissues of living organisms. Diffusion plays an important role in various fields of science and technology, in processes occurring in animate and inanimate nature. Diffusion affects the course of many chemical reactions, as well as many physical and chemical processes and phenomena: membrane, evaporation, condensation, crystallization, dissolution, swelling, combustion, catalytic, chromatographic, luminescent, electrical and optical in semiconductors, neutron moderation in nuclear reactors etc. Diffusion is of great importance in the formation of a double electric layer at the phase boundaries, diffusiophoresis and electrophoresis, in photographic processes for fast image acquisition, etc. Diffusion serves as the basis for many common technical operations: powder sintering, chemical-thermal treatment of metals, metallization and welding of materials, tanning leather and fur, dyeing fibers, moving gases with diffusion pumps. The role of diffusion has increased significantly due to the need to create materials with predetermined properties for developing areas of technology (nuclear power engineering, astronautics, radiation and plasma-chemical processes, etc.). Knowing the laws that govern diffusion makes it possible to prevent undesirable changes in products that occur under the influence of high loads and temperatures, irradiation, and much more ...
What would the world be like without diffusion? Stop the thermal movement of particles - and everything around will become dead!
In my work, I summarized the material collected on the topic of the abstract and prepared a presentation made in the Power Point editor for its defense. This presentation, in my opinion, will be able to diversify the material of the lesson on this topic. Some of the experiments described in the literature were repeated and slightly modified by me. The most interesting examples of diffusion are presented on the presentation slides in animation models.
IV. Used Books:
1. V. F. Antonov, A. M. Chernysh, V. I. Pasechnik, et al., Biophysics.
M., Arktos-Vika-press, 1996
2. Afanasiev Yu.I., Yurina N.A., Kotovsky E.F. etc. Histology.
M. Medicine, 1999.
3. Alberts B., Bray D., Lewis J. et al. Molecular biology of the cell.
In 3 volumes. Volume 1. M., Mir, 1994.
4. Great Encyclopedia of Cyril and Methodius 2006
5. Varikash V.M. and others. Physics in wildlife. Minsk, 1984.
6. Demyankov E.N. Tasks in biology. M. Vlados, 2004.
7. Nikolaev N.I. Diffusion in membranes. M. Chemistry, 1980, p.76
8. Peryshkin A.V. Physics. 7. M. Bustard, 2004.
9. Physical Encyclopedic Dictionary, M., 1983, p. 174-175, 652, 754
10. Shablovsky V. Entertaining physics. St. Petersburg, "trigon" 1997, p.416
11.xttp//bio. fizten/ru./
12. xttp//markiv. narod.ru/
13. "http://en.wikipedia.org/wiki/%D0%94%D0%B8%D1%84%D1%84%D1%83%D0%B7%D0%B8%D1%8F" Categories: Phenomena at the atomic level | Thermodynamic phenomena | Transfer phenomena | Diffusion
Lesson on general biology
Lesson topic: Diffusion is the basis of life
Type training session: integrated lesson(according to the classification of T.I. Shamova)
Tasks of the lesson:
1. Educational aspect - the formation of knowledge about the structure, properties and functions of the inner layer of the cell membrane - the plasma membrane (and, in its example, other cell membranes), the development of the concept of the correspondence of the structure to the functions performed.
2. Developing aspect - to activate the thinking of students, the ability to compare, analyze, the ability to independently formulate conclusions, to promote development logical thinking, cognitive activity of students.
3. Educational aspect - increasing motivation for studying biology, increasing interest in subjects of the natural science cycle, using a variety of methods of activity, to show that knowledge of the properties of a living organism is possible only with the integration of knowledge obtained by various sciences.
During the classes
Preparing students for work in the classroom: greeting, positive psychological attitude to work, organization of attention for all students.
Teacher. Good afternoon, dear students! I am glad to meet you and look forward to your help and cooperation in the lesson. Handing you a basket of tangerines, I invite you to work together. If you accept my offer, then open your palms towards me, and if not, turn them away from me. It is a pleasure to look at these fruits, bright "orange balls" give us a feeling of joy, delight and elation!
2. Student motivation
As an epigraph to our lesson, I chose the words of the Hungarian radiochemist D. Hevesy: (1st presentation slide)
Question: How do you understand these words?
Students reasoning
Organization of students' work on new theme
2. Reception "Basket of Ideas"
Invites students to clean the tangerine.
Question: What has changed in the audience?
Question: Why did this happen?
The teacher puts the answers of the students (figuratively) into the "basket of ideas"
Question: “What do you think, what phenomenon underlies these processes?”
Summarizes.
The main condition is not to repeat what has already been said by others.
Teacher: Why does this happen, which is proof of the continuous movement of molecules in animate and inanimate nature? What processes underlie these movements? We will talk about this with you today.
3. Goal setting
Teacher: Invites students to formulate the topic of the lesson.
Corrects the topic of the lesson: "Diffusion is the basis of life."
Helps students with the formulation of the purpose of the lesson. The purpose of our lesson:prove that diffusion is the basis of life.
Teacher: lesson objectives: to expand knowledge about the structure, properties and functions of the cytoplasmic membrane, to show the relationship of such disciplines as "Physics" and "Biology" in this lesson, and to prove that diffusion is the basis of life.
3. Actualization of knowledge.
Teacher: The material of the topic of today's lesson is based on the knowledge you received earlier in the study of biology. We will remember some moments with you now.
Crossword "Basic cell structures"
(2nd presentation slide)
Teacher: The last word in the crossword is "shell".
Question: "And what cellular structure is located under the shell?"
4. And learning new material
Teacher: Under the cell wall is a plasma membrane (membrane - skin, film), bordering directly on the cytoplasm. The thickness of the plasma membrane is about 10 nm.
Teacher:
1. Sets question:"Remember what substances are part of the plasma membrane?"
2. A story about the structure of the plasma membrane (a diagram of the structure of the membrane is shown on the slide)
(3rd presentation slide)
Students: Proteins and lipids. They are in two layers.
Teacher: Lipid molecules in the plasma membrane are arranged in two rows and form a continuous layer. Most of all in the membranes of phospholipids, they contain a residue of phosphoric acid. Phospholipid molecules are arranged in such a way that the hydrophilic "tails" are facing inward, and the hydrophobic "heads" are facing outward, towards the water.In addition to lipids, the membrane contains proteins (up to 60%). They define specific functions membranes. Molecules of proteins and lipids are mobile, able to move, mainly in the plane of the membrane. Protein molecules do not form a continuous layer.
Distinguish:
peripheral proteins- located on the outer or inner surface of the membrane, they can convert signals from the external and internal environment,
semi-integral proteins– immersed in the bilayer to different depths, support the structure of the membrane,
transmembrane proteins- penetrate the membrane through, contacting with the external and internal environment of the cell, catalyze metabolic reactions, ensure the transport of cations and anions, form pores.
Teacher: Membrane Properties
But before moving on to the properties of membranes, let's recall what you know from the physics course.
Question: “What explains, from the point of view of physics, one of the properties of a liquid - fluidity?”
Question: "In what case is this phenomenon observed?"
Answers: It is explained by the mutual attraction of the molecules of the liquid. This phenomenon is observed if the distance between the molecules of the liquid is comparable to the size of the molecule.
Invites students to fill in the diagram as they explain the material
(4th presentation slide)
Teacher: We will explain the properties of the membrane in experiments with a soap bubble.
Problem question: "Why did we take a soap bubble?"
Demonstration of the structure of a soap bubble.
(5th presentation slide)
Teacher: Answer: But the fact is that the molecules of soap and phospholipids that make up the membranes have a similar structure.
An experience: A student demonstrates the flow of liquid in the wall of a soap bubble hanging on a plastic tube.
The first property of membranes is mobility.
The lipid bilayer is essentially a liquid formation, within the plane of which the molecules can move freely - “flow” without loss of contacts due to mutual attraction. Hydrophobic tails can slide freely relative to each other.
An experience: The student demonstrates how when a soap bubble is pierced and then the needle is removed, the integrity of its wall is immediately restored.
Teacher: The second property is the ability to self-close.
Due to this ability, cells can fuse by fusion of their plasma membranes (for example, during the development of muscle tissue). The same effect is observed when the cell is cut into two parts with a microknife, after which each part is surrounded by a closed plasma membrane.
Question: “In what case, from the point of view of physics, is there a mutual attraction between molecules?”
Answer: mutual attraction is observed if the distance between the molecules is comparable to the size of the molecule, but if the distance becomes much larger, then mutual attraction does not appear.
Video clip "Facilitated diffusion"
Teacher: The third most important property of a membrane is its selective permeability. This means that molecules and ions pass through it at different speeds, and the larger the size of the molecules, the slower their passage through the membrane. This property defines the plasma membrane as osmotic barrier. Water and the gases dissolved in it have the maximum penetrating power; ions pass through the membrane much more slowly.
Teacher: Name the properties of the membrane:
Students answer: 1. Mobility. 2. Self-closing. 3. Selective permeability. (6th presentation slide)
Teacher: Now let's rest a little.
Physical education minute
Teacher:
Demonstration of experience “Observation of plasmolysis and deplasmolysis of a plant cell”(video clip)
Questions:
What is plasmolysis?
What phenomenon is called deplasmolysis?
What is osmosis?
Draws conclusions with students.
Teacher: Output:
PLASMOLYSIS - separation of the parietal layer of the cytoplasm from the hard shell of the plant cell.
DEPLASMOLYSIS
OSMOSIS
We made sure that the plasma membrane has selective permeability
Teacher: Oparin Alexander Ivanovich said that after the membranes appeared ... the first living organisms could form from the soup boiled in the seas. On what basis did the scientist come to such a statement?
Students: The membrane separates the cellular contents from the external environment.
Teacher: Let's remember what are the main functions of the cell membrane?
Students: 1. Barrier
2. Transport
3. Receptor
Video clip "Functions of the membrane"
Teacher: Let us dwell on the transport function of the membrane in more detail.
Teacher: Exercise 1. Imagine that you have come to a wall, to a fence, to an obstacle that you need to overcome. How will you try to get inside?
Students are divided into two groups, each group is given a sheet of paper, which is divided by a vertical line into two columns. The group is given 2 minutes to reflect. Students should suggest as many ways of penetration as possible and write them down in the left column of the sheet.
Advertising group work, as a result of which the list of each group is supplemented by the most successful proposals.
Task 2. Imagine that it is necessary to overcome the barrier not to a person who has approached a fence or a wall, but to a substance located next to a living cell. He needs to get inside the cell. Try to find analogies to each of the ways you suggested to overcome obstacles. Write them down on the right side of a piece of paper.
Socialization in groups. Students read aloud the methods of penetration into the cell and record the most successful analogies of other groups.
Teacher: (summarizes the work of the groups and explains the modes of transport through the membrane).
Diffusion
Video fragment "Diffusion in the membrane"
Osmosis is the movement of a solvent from an area of high concentration to an area of lower concentration.
Teacher: We are talking about diffusion in experiments. I again return you to inanimate nature and ask you to remember, what is diffusion from the point of view of physics?
Diffusion This is the phenomenon of mutual penetration of molecules of one substance between the molecules of another.
Teacher: What are the characteristics of diffusion in animate and inanimate nature? What determines the rate of diffusion?
Discussion of students, hypotheses
Teacher: So, do you think that the rate of diffusion depends on temperature and on the state of aggregation of the substance? Why?
Estimated student responses
Teacher: Now let's test your hypothesis experimentally.
An experience
Equipment: 2 glasses with water of different temperatures, glasses, pipette, coffee
Working process:
Pour the same amount of water, but at different temperatures, into two identical glass vessels.
Drop 2-3 drops of hot and cold water on the glasses (on different glasses)
From the top, place a few grains of instant coffee.
Watch what is happening. (1 - 2 min)
Measure the time it takes for all the water in the glass to color.
Does the phenomenon of diffusion take place in this experiment? Why?
Record the results in a table.
experience number
Glass of water
Coloring time
Cold
hot
What can you say about the rate of diffusion in the first and second vessels?
Now, in both vessels, diffusion involves the same substances that are in the same aggregate states. So the diffusion rate must be the same? But the results of the experiment show the opposite. Why?
The diffusion rate increases with increasing temperature, since the molecules of interacting bodies begin to move faster. This statement is true for substances in any state of aggregation.
Output: Diffusion occurs in liquids and accelerates with increasing temperature.
5. Primary check of understanding of the studied material.
Teacher: Returns to question, given at the beginning of the lesson: “Tell me, why did the smell of tangerine, after we began to peel it, spread throughout the audience?”
Question:"What physical phenomenon underlies the mechanism of transport of substances into the cell through the cytoplasmic membrane?"
Consolidation.
Invites students to complete a test task (using a multimedia presentation) to consolidate the studied material.
1. Select the main functions of the plasma membrane
a) transport, barrier, receptor
b) transport, energy, barrier
c) transport, energy, catalytic
2. What substances are included in the plasma membrane?
a) carbohydrates and proteins
b) proteins and lipids
c) proteins and nucleic acids
3. What process is shown in this picture?
a) osmosis
b) diffusion
c) plasmolysis
4. What process is shown in this picture?
a) plasmolysis
b) deplasmolysis
c) mitosis
5. Let's turn to beans that are on your tables. We pre-soaked one bean in hot water, the other remained dry. I think that the difference in the size of the beans is visible. What process are you seeing here?
a) plasmolysis
b) osmosis
c) growth
Mutual check test task
7. Analysis
Teacher: Let's turn to the epigraph of our lesson
"The thinking mind does not feel happy until it succeeds in tying together the disparate facts it observes"
Question: Do you think I chose the right epigraph for our lesson? Explain why?
Students discuss and answer the question.
Teacher: So Why is diffusion the basis of life?
Students: Diffusion is of great importance in the life processes of living objects. Diffusion plays an important role in plant nutrition, the transfer of nutrients, oxygen in the human and animal body.
Teacher: "Where do you think (in life, in the profession) you will need knowledge about diffusion?"
Teacher: What phenomenon connects the disciplines "Physics" and "Biology" in the study of the properties and functions of the plasma membrane?
8. Homework
Informs students homework, explains the implementation.
1. Solve the word "Letter confusion".
The penetration of molecules of one substance into the intermolecular spaces of another
The state of matter in which diffusion occurs at the highest rate
Diffusion in one direction through semi-permeable membranes
The result of emissions into the atmosphere and rivers of hazardous production waste
Messy……. molecules leads to the diffusion of substances.
Physical quantity that accelerates the diffusion process
The introduction of drugs through the skin, using an electric current.
2. Create a booklet "Diffusion in my profession."
3. Pick up a few proverbs in which the phenomenon of diffusion is observed.
4. Conduct an experiment.
The first and second tasks are performed by all students.
Third and fourth - optional.
9. Reflection
It is proposed that students “dress up” the tree with tangerines:
If you liked the lesson, learned a lot of new and interesting things, then an orange tangerine is attached to the tree;
If the lesson was not pleasant, it was boring and uninteresting, then a white tangerine is attached to the tree.
Invites students to name the most active student of the lesson, this student is awarded a basket of tangerines for active work in the integrated lesson "Diffusion is the basis of life"
