The set of all values of thermodynamic parameters necessary to describe the system is called thermodynamic state .
The physical characteristic of the system, the change of which during the transition of the system from one state to another is determined by the values of the parameters of the initial and final states and does not depend on the transition, is called state function (thermodynamic potential).
The state functions are:
· internal energy;
· enthalpy;
· entropy;
· free energy;
chemical and electrochemical potentials.
The amount of some quantity carried over a certain surface per unit time is called flow this value.
The phenomenon in which one process energetically provides the flow of the second process is called conjugation .
The process that is the source of energy is called...
conjugating. The process that uses energy is called conjugate
.
First and second laws of thermodynamics. According to the first law of thermodynamics, which reads as follows: the heat communicated to the system is spent on increasing the internal energy of the system and performing work on external forces by the system, different types of energy can pass into each other, but during these transformations Ī energy does not disappear and does not appear from nothing . This means that for a closed system
∆U = ∆Q –W, where ∆U is the change in the internal energy of the system; ∆Q is the heat absorbed by the system; W is the work done by the system. [Internal energy differs from heat and work in that it always changes in the same way during the transition from one state to another, regardless of the transition path!].
The change in thermal energy ∆Q of an isolated system is proportional to the absolute temperature T, that is, ∆Q = T ∙ ∆S, where ∆S is the proportionality factor, which is called the change in entropy.
The second law of thermodynamics exists in two formulations. The first formulation (Clausius's formulation) is as follows: spontaneous transfer of heat from bodies with a lower temperature to bodies with a higher temperature is impossible. The second formulation (Thomson's formulation) says that it is impossible to create a perpetual motion machine of the ĪĪ kind, that is, such a cyclic process, as a result of which all the heat absorbed by the system would be spent on doing work. According to the second law of thermodynamics, the entropy of an isolated system increases in an irreversible process, and remains unchanged in a reversible process. Entropy is a function of the state of the system, the differential of which in an infinitely small reversible process is equal to the ratio of the infinitely small amount of heat communicated to the system to the absolute temperature of the latter (ΔS=ΔQ:T). The entropy unit is J/K. Entropy is a measure of the disorder of a system: if entropy increases, this means that the system tends to move into a state with a higher thermodynamic probability, that is, into a state of less order. The conclusion follows from the second law of thermodynamics: at a constant temperature, thermal energy cannot be converted into mechanical work. Since thermal energy is due to the chaotic motion of particles, the sum of the velocity vectors of these particles in any direction is equal to zero. In mechanical work, only the energy that represents the unidirectional movement of bodies (the kinetic energy of a flying body, the energy of moving ions or electrons in an electric field) can be converted.
Conclusion according to two laws:
The first law establishes a quantitative relationship between heat, work and change in internal energy, but does not determine the direction of the thermodynamic process. It is executed always and for any systems. Basic relation of thermodynamics: TΔS ≥ ΔU+W.
The second law is statistical and is valid for systems with a large, finite number of particles. It indicates the most likely direction of the process. If it is stated that this process is impossible, then it should be understood that the probability of its completion exists, but is negligible.
Table 1. Thermodynamic potentials
Transformation of energy in a living cell. In a living cell, the chemical energy stored in organic compounds is converted into osmotic, electrical and mechanical energy. So, for example, the chemical energy of glucose is converted during cellular oxidation partly into heat, partly into the energy of macroergic bonds of ATP. Due to the hydrolysis of ATP, substances can be transferred from an area of lower to an area of \u200b\u200bhigher concentration (osmotic work), the transfer of ions to an area of \u200b\u200bhigher electrical potential (electrical work), in the animal body - muscle contraction (mechanical work). In this case, a part of the chemical energy of ATP is transferred into osmotic, electrical and mechanical energy.
Free energy and electrochemical potential. The electrical, osmotic and chemical energy of the cell is used to perform work, that is, to move particles against the forces acting on them. A quantitative measure of the conversion of these types of energy is the change in free energy (∆F). ΔF is the Helmholtz free energy (ΔF = ΔU - TΔS). Since it depends on the conditions of the process, in particular on the concentration of the reacting substances, they began to use the so-called Gibbs thermodynamic potential of 1 mole of the substance ΔG. In chemistry, for uncharged particles it is called the chemical potential - μ, for charged particles - the electrochemical potential - μ.
The flow of chemical reactions in the liquid phase does not change the pressure, but can change the volume. Therefore, for such systems, instead of changing the internal energy, the change in enthalpy (∆H) is used, which is equal to ∆U + p∆V, where p is the pressure, ∆V is the change in volume. [Note: enthalpy is a function of the state of a thermodynamic system with independent entropy parameters and pressure]. According to the laws of thermodynamics, there is a relation between the change in internal energy and the change in enthalpy: ∆G = ∆H -T∆S (at t and p = const), where ∆G is the Gibbs thermodynamic potential, ∆H is the internal energy, T * ∆S is the thermal energy.
In physicochemical systems, the change in free energy is usually described through the change in the electrochemical potential (∆μ): ∆G=m∙∆μ, where m is the amount of substance (mole) in the system. The change in the electrochemical potential during the transition of the system from state 1 to state 2 is determined by the change in chemical, osmotic and electrical energies: ∆μ \u003d μ 02 -μ 01 + RT ln (c 2 / c 1) + zF (φ 2 -φ 1). Then ∆G = m μ 02 -μ 01 +RT ln (c 2 /c 1) + zF (φ 2 -φ 1).
The physical meaning of the electrochemical potential is that its change is equal to the work that must be expended in order to:
1. synthesize 1 mol of a substance (state 2) from the starting materials (state 1) and place it in a solvent (term μ 02 -μ 01) - chemical work;
2. concentrate the solution from concentration from 1 to s 2 [term RT ln (c 2 /c 1)] - osmotic work;
3. overcome the electrical repulsion forces that arise in the presence of a potential difference (φ 2 -φ 1) between solutions [term zF (φ 2 -φ 1] - electrical work.
It should be noted that terms can be both positive and negative.
The second law of thermodynamics and the equilibrium condition. The second law of thermodynamics states that free energy cannot increase in an isolated system. In other words, in a system where ∆H = 0, ∆G = -T∆S ≤0. As long as energy transformations in this system are accompanied by transitions of different types of energy into each other without their conversion into heat, that is, ∆G=0, all these processes are reversible. But, as soon as part of the energy turns into heat, the process becomes irreversible. The concept of process reversibility is connected with the concept of dynamic equilibrium. Equilibrium is such a state of the system in which each particle can move from some state 1 to some state 2 and vice versa, but in general the proportion of states 1 and states 2 in the system does not change. In physicochemical systems, processes are in equilibrium at which ∆μ = ∆G / m = 0, that is, μ 02 -μ 01 + RT ln (c 2 / c 1) + zF (φ 2 -φ 1) = 0.
Substrates and products of a biochemical reaction or ions on both sides of the membrane can be in equilibrium. Therefore, there are applications to the equation describing the equilibrium state of the system:
1. chemical equilibrium constant equation: ∆μ 0 = -RT lnK, where K is the equilibrium constant;
2. equation of equilibrium membrane potential (Nernst equation): if the cell membrane is permeable to any one ion, then an equilibrium membrane potential is established on the membrane: φ Μ = φ 1 –φ 2 = RT / zF lnc 1 / c 2, at temperature 37C 0 φ Μ \u003d 60 ln (s 1 / s 2) mV. For a shorter writing, the concept of a dimensionless potential ψ Μ was introduced, which is equal to ln(с 1 /с 2), then the Nernst equation will look like this ψ Μ = ψ 1 - ψ 2 = ln(с 1 /с 2).
3. Boltzmann distribution: if there are two energy electronic levels in the molecule with energies E 1 and E 2, then you can find the population of these levels by electrons in the equilibrium state: ∆E = E 2 - E 1.
Experimental determination of thermodynamic parameters of biological systems. To determine the thermodynamic parameters of biological systems, two methods are used: determination of heat production (calorimetry) and measurement of equilibrium constants. Since the object in the calorimeter does not produce work, the change in energy (enthalpy) can be considered equal to the amount of heat released ∆Q. This is how the change in enthalpy ∆H is found during the studied biophysical process or biochemical reaction. Another method for studying thermodynamic parameters is based on measuring the equilibrium constants at different temperatures. But this method is only suitable when the change in enthalpy and the change in entropy do not depend on temperature. In this case, the van't Hoff equation is used: lnK = -∆H/RT + ∆S/R (for one mole of a substance).
Organisms as thermodynamic systems. When applying thermodynamics to biological systems, it is necessary to take into account the peculiarities of the organization of living systems:
1) biological systems are open to flows of matter and energy;
2) processes in living systems are irreversible;
3) living systems are far from equilibrium;
4) biological systems are heterophasic, structured, and individual phases can have a small number of molecules.
All this distinguishes biological systems from systems that are isolated and close to a state of equilibrium. Therefore, for a more adequate description of the properties of living systems, it is necessary to apply the thermodynamics of irreversible processes. In contrast to classical thermodynamics, in the thermodynamics of irreversible processes, the course of processes in time is considered. The fundamental concept in classical thermodynamics is the concept of an equilibrium state. In the thermodynamics of irreversible processes, an important concept is the concept of a stationary state of a system.
Note: It must be taken into account that a living organism is constantly developing and changing and therefore, as a whole, is not a stationary system. In this case, there is a tolerance: for a short time interval, the state of some of its sections is taken as stationary.
In contrast to thermodynamic equilibrium, the stationary state is characterized by
a constant influx of substances into the system and the removal of metabolic products;
a constant cost of free energy, which maintains the constancy of the concentrations of substances in the system;
· constancy of thermodynamic parameters (including internal energy and entropy).
The system in a stationary state can be either closed or open. An open system can exist only due to the influx of energy from outside and the outflow of energy into the environment. In biological systems, the most important flows are the flows of substances and electric charges.
Flows of substances as a result of diffusion and electrodiffusion. one. The main driving force in particle transport by simple diffusion is the concentration gradient. The flow of a substance as a result of diffusion through the cell membrane is calculated according to Fick's law for the passive transfer of substances through the membrane: D is the diffusion coefficient; K is the distribution coefficient of the substance between the membrane and the surrounding aqueous phase; l is the membrane thickness; cv is the concentration of particles inside the cell; с ext is the concentration of particles outside the cell; P is the permeability coefficient. If we consider diffusion from the standpoint of energy conversion, then the calculation must be carried out according to the following equation: Φ = – uc (dG/dx), where u = D/RT is the proportionality coefficient, which depends on the diffusion rate of molecules and is called mobility. Thus, the flow is proportional to the concentration of the substance and the gradient of the thermodynamic potential in the direction of the current.
2. The main driving force in the transfer of charged particles in the absence of a concentration gradient is the electric field. In this case, the Theorell equation is used: Φ = – cu (dμ/dx), where μ is the electrochemical potential. Thus, the flux is equal to the product of the carrier concentration, its mobility, and the gradient of its electrochemical potential. The “–” sign indicates that the flow is directed in the direction of decreasing μ. In addition, the Nernst-Planck electrodiffusion equation is used: Φ = –uRT (dc/dx) –cuz Fdφ/dx.
Flows and thermodynamic forces that determine the flow of vital processes are shown in Table 3.
Table 3. Conjugate flows and forces in nonequilibrium thermodynamics
Steady state thermodynamics. Open systems have specific features: conjugation of flows and the emergence of stationary states. These features of open systems are explained by the thermodynamics of linear irreversible processes. It describes the simultaneous flow of various interrelated stationary processes. The theory of thermodynamics of linear irreversible processes was formulated by Onsager. The experimental basis of this theory is the phenomenological laws that establish a linear relationship between the flows and the forces that cause them (see Table 2). Let us assume that there are two flows in the system - heat flow (Φ 1) and diffusion mass flow (Φ 2) and two generalizing forces - temperature difference X 1 and concentration difference X 2 . According to Onsager, in an open system, every flow depends on all the forces present, and vice versa, i.e.
Φ 1 \u003d L 11 X 1 + L 12 X 2
Φ 2 \u003d L 21 X 1 + L 22 X 2,
where L 12 and others are the coefficients of proportionality between flow 1 and force 2, etc.
These equations are called the phenomenological Onsager equations. They indicate the dependence of input and output flows, both on conjugated and non-conjugate forces. As Onsager showed, near equilibrium, the coefficients of proportionality between flows are equal to each other (L 12 = L 21). In other words, an equal action causes an equal response. For example, the retarding effect that a moving solvent has on a solute is equal to the resistance that the solute has on the solvent.
In nature, there is a situation when flows that go with an increase in energy cannot go on their own, but can flow under the action of any forces. This phenomenon is called conjugation of flows. The criterion for the possibility of conjugation of flows in the system is the positive value of the dissipative function ψ = Τ/V dS/dt ≥ 0, where Τ is the absolute temperature; dS/dt is the entropy production rate; V is the volume of the system.
The dissipative function is a measure of the dissipation of the system's energy into heat. It determines the rate of increase in entropy in a system in which irreversible processes take place. The higher the value of the dissipative function, the faster the energy of all types is converted into heat. In addition, the dissipative function determines the possibility of a spontaneous flow of the process: for ψ>0, the process is possible, for ψ<0 – нет.
Thermodynamics shows that if the system is non-equilibrium, but close to equilibrium, then ψ can be represented by the sum of the products of generalized forces - Xi and generalized flows - Φi, that is, the sum of the powers of the processes ψ = ∑ΦiXi ≥0. The positive value of the dissipative function ψ means that in any energy converter, the input power must exceed the output. In most biological processes, chemical energy is converted into osmotic, electrical, and mechanical energy. In all these processes, part of the chemical energy is dissipated into heat. For biological processes, the coupling efficiency is 80-90%, that is, only 10-20% of the energy is converted into heat.
The stationary state of an open system is characterized by Prigogine's theorem: in a stationary state with fixed external parameters, the rate of entropy production in the system is constant in time and minimal in magnitude.
If the criterion for the evolution of a system in classical thermodynamics is that the entropy for irreversible processes in an isolated system tends to a maximum value ( Clausius criterion), then in an open system the production of entropy tends to a minimum ( Prigogine's criterion). Prigogine's criterion (Δψ>0) - stability criterion - in case of deviation from the steady state Δψ<0. Это является доказательством того, что второй закон термодинамики выполняется в живой природе.
It follows from Prigogine's theorem that if the system is taken out of the stationary state, then it will change until the specific rate of entropy production takes the smallest value. That is, until the dissipative function reaches a minimum.
Ways of energy conversion in a living cell. The molecular mechanism of coupling reactions of oxidation and phosphorylation was deciphered by Mitchell in 1976. The author developed the chemiosmotic theory of oxidative phosphorylation. The second part of Mitchell's theory is that there is an asymmetric ATPase in the membrane that works reversibly, that is, it can also be an ATP synthetase:
ATP + HOH (atp-ase) ADP + F + 2H +
The asymmetry in the action of ATPase is that
a) during ATP hydrolysis, the proton H+ and hydroxyl OH- are captured on opposite sides of the membrane;
b) during the synthesis of ATP, water dissociates into OH-, which enters the side more acidic from the membrane, and H+, which diffuses in the opposite direction.
In general, the process of ADP phosphorylation is carried out due to a change in free energy during the neutralization of the OH- ion in an acidic environment, and the H+ ion in an alkaline environment.
From the point of view of energy conversion, the process of oxidative phosphorylation consists of two stages:
1. The conversion of the chemical energy of electron transfer into energy associated with the difference in electrochemical potentials of protons as a result of conjugation of electron transfer along the respiratory chain and proton transfer through the membrane. In this case: Δμ H+ = FΔφ M + RT ln ( 1 / 2), where Δμ H+ is the difference of electrochemical potentials; Δφ M is the electrical potential difference between the outer and inner sides of the mitochondrial membrane; ( 1 and 2 are proton concentrations in the environment and inside mitochondria.
2. The conversion of energy, determined by the difference in electrical potentials, into the chemical energy of the macroergic bond of ATP (conjugation of the transfer of 2H + and the synthesis of one ATP molecule from ADP and phosphate). This can be conditionally represented as Δμ H+ → QUOTE ~ ~.
It has now been shown that in the presence of a difference in the electrochemical potentials of H+ on the coupling membrane, not only chemical work (synthesis of ATP), but also osmotic work (during the transport of various compounds through membranes), mechanical work (movement of flagella in bacteria), and heat is also released (thermoregulatory uncoupling of oxidative phosphorylation).
Symbolically, the chemiosmotic theory of conjugation of the processes of oxidation (i.e., electron transfer - e) and phosphorylation (synthesis of macroergs - QUOTE ~ ~) can be represented as a diagram e QUOTE ∆μ H+ QUOTE QUOTE~~. The following main consequences of the chemiosmotic theory follow from this scheme:
1. If Δμ H+ = 0, then ATP synthesis does not occur during electron transfer.
2. During the operation of the respiratory chain, the membrane potential is generated (е→Δφ M).
3. The creation of a sufficient electrical potential on the energy-coupling membrane with the “+” sign outside will lead to the synthesis of ATP from ADP and orthophosphate (Δφ M → QUOTE ~) ~).
4. Due to the membrane potential, it is possible to stop and even "reverse" the flow of electrons in the respiratory chain (Δφ M →e).
5. During the hydrolysis of ATP on the conjugating membrane, the membrane potential is generated (QUOTE ~ ~ → Δφ M).
So, the main types of work in a living cell - electrical and osmotic - are performed with the direct participation of biological membranes. The processes of synthesis and breakdown of ATP play a central role in the energy of the cell. In the cell, ATP is an accumulator of chemical energy.
Energy is used for various chemical reactions that take place in the cell. Some organisms use the energy of sunlight for biochemical processes - these are plants, while others use the energy of chemical bonds in substances obtained in the process of nutrition - these are animal organisms. Substances from food are extracted by splitting or biological oxidation in the process of cellular respiration.
Cellular respiration is a biochemical process in a cell that occurs in the presence of enzymes, as a result of which water and carbon dioxide are released, energy is stored in the form of macroenergetic bonds of ATP molecules. If this process takes place in the presence of oxygen, then it is called "aerobic". If it occurs without oxygen, then it is called "anaerobic".
Biological oxidation includes three main stages:
1. Preparatory,
2. Anoxic (glycolysis),
3. Complete decomposition of organic substances (in the presence of oxygen).
Preparatory stage. Substances taken with food are broken down into monomers. This stage begins in the gastrointestinal tract or in the lysosomes of the cell. Polysaccharides are broken down into monosaccharides, proteins into amino acids, fats into glycerols and fatty acids. The energy released at this stage is dissipated in the form of heat. It should be noted that cells use carbohydrates for energy processes, and preferably monosaccharides. And the brain can use for its work only the monosaccharide - glucose.
Glucose is broken down by glycolysis into two three-carbon molecules of pyruvic acid. Their further fate depends on the presence of oxygen in the cell. If oxygen is present in the cell, then pyruvic acid enters the mitochondria for complete oxidation to carbon dioxide and water (aerobic respiration). If there is no oxygen, then in animal tissues pyruvic acid turns into lactic acid. This stage takes place in the cytoplasm of the cell. Glycolysis produces only two ATP molecules.
Oxygen is essential for the complete oxidation of glucose. At the third stage in the mitochondria, pyruvic acid is completely oxidized to carbon dioxide and water. As a result, another 36 ATP molecules are formed.
In total, 38 ATP molecules are formed from one glucose molecule in three stages, taking into account the two ATP obtained in the process of glycolysis.
Thus, we have considered the energy processes occurring in cells. The stages of biological oxidation were characterized. This concludes our lesson, all the best to you, goodbye!
The difference between breathing and burning. The respiration that occurs in the cell is often compared to the combustion process. Both processes occur in the presence of oxygen, release of energy and oxidation products. But, unlike combustion, respiration is an ordered process of biochemical reactions occurring in the presence of enzymes. During respiration, carbon dioxide arises as the end product of biological oxidation, and during combustion, the formation of carbon dioxide occurs by direct combination of hydrogen with carbon. Also during respiration, a certain amount of ATP molecules is formed. That is, respiration and combustion are fundamentally different processes.
biomedical significance. For medicine, not only the metabolism of glucose is important, but also fructose and galactose. Especially important in medicine is the ability to form ATP in the absence of oxygen. This makes it possible to maintain intensive work of the skeletal muscle in conditions of insufficient efficiency of aerobic oxidation. Tissues with increased glycolytic activity are able to remain active during periods of oxygen starvation. In the heart muscle, the possibilities for glycolysis are limited. It is difficult to tolerate impaired blood supply, which can lead to ischemia. Several diseases are known due to the lack of enzymes that regulate glycolysis:
- hemolytic anemia (in fast-growing cancer cells, glycolysis occurs at a rate exceeding the capacity of the citric acid cycle), which contributes to an increased synthesis of lactic acid in organs and tissues. Elevated levels of lactic acid in the body can be a symptom of cancer.
Fermentation. Microbes are able to obtain energy in the process of fermentation. Fermentation has been known to people since time immemorial, for example, in the manufacture of wine. Even earlier it was known about lactic acid fermentation. People consumed dairy products without suspecting that these processes are associated with the activity of microorganisms. This was first proved by Louis Pasteur. Moreover, different microorganisms secrete different fermentation products. Now we will talk about alcoholic and lactic acid fermentation. As a result, ethyl alcohol, carbon dioxide are formed and energy is released. Brewers and winemakers have used certain types of yeast to stimulate fermentation, which turns sugars into alcohol. Fermentation is carried out mainly by yeast, but also by some bacteria and fungi. Saccharomyces yeast is traditionally used in our country. In America - bacteria of the genus Pseudomonas. And in Mexico, bacteria "moving rods" are used. Our yeasts tend to ferment hexoses (six-carbon monosaccharides) such as glucose or fructose. The process of alcohol formation can be represented as follows: from one glucose molecule, two alcohol molecules, two carbon dioxide molecules and two ATP molecules are formed. This method is less profitable than aerobic processes, but allows you to maintain life in the absence of oxygen. Now let's talk about lactic acid fermentation. One molecule of glucose forms two molecules of lactic acid and two molecules of ATP are released. Lactic acid fermentation is widely used for the production of dairy products: cheese, curdled milk, yogurt. Lactic acid is also used in the manufacture of soft drinks.
Tasks of the C1-C4 part
1. What environmental factors contribute to the regulation of the number of wolves in the ecosystem?
Answer:
1) anthropogenic: deforestation, overshooting;
2) biotic: lack of food, competition, spread of diseases.
2. Determine the type and phase of cell division shown in the figure. What processes take place in this phase?
Answer:
1) the figure shows the metaphase of mitosis;
2) spindle fibers are attached to the centromeres of chromosomes;
3) in this phase, two-chromatid chromosomes line up in the plane of the equator.
3. Why does plowing the soil improve the living conditions of cultivated plants?
Answer:
1) contributes to the destruction of weeds and weakens competition with cultivated plants;
2) contributes to the supply of plants with water and minerals;
3) increases the supply of oxygen to the roots.
4. How is a natural ecosystem different from an agroecosystem?
Answer:
1) great biodiversity and diversity of food relationships and food chains;
2) a balanced circulation of substances;
3) long periods of existence.
5. Expand the mechanisms that ensure the constancy of the number and shape of chromosomes in all cells of organisms from generation to generation?
Answer:
1) due to meiosis, gametes with a haploid set of chromosomes are formed;
2) during fertilization in the zygote, the diploid set of chromosomes is restored, which ensures the constancy of the chromosome set;
3) the growth of the organism occurs due to mitosis, which ensures the constancy of the number of chromosomes in somatic cells.
6. What is the role of bacteria in the cycle of matter?
Answer:
1) heterotrophic bacteria - decomposers decompose organic substances into minerals that are absorbed by plants;
2) autotrophic bacteria (photo, chemotrophs) - producers synthesize organic substances from inorganic ones, ensuring the circulation of oxygen, carbon, nitrogen, etc.
7. What are the characteristics of mossy plants?
Answer:
2) mosses reproduce both sexually and asexually with alternating generations: sexual (gametophyte) and asexual (sporophyte);
3) an adult moss plant is a sexual generation (gametophyte) and a box with spores is asexual (sporophyte);
4) fertilization occurs in the presence of water.
8. Squirrels, as a rule, live in a coniferous forest and feed mainly on spruce seeds. What biotic factors can lead to a reduction in the squirrel population?
9. It is known that the Golgi apparatus is especially well developed in the glandular cells of the pancreas. Explain why.
Answer:
1) in the cells of the pancreas, enzymes are synthesized that accumulate in the cavities of the Golgi apparatus;
2) in the Golgi apparatus, enzymes are packed in the form of bubbles;
3) from the Golgi apparatus, enzymes are carried into the pancreatic duct.
10. Ribosomes from different cells, the entire set of amino acids and the same molecules of mRNA and tRNA were placed in a test tube, and all the conditions for protein synthesis were created. Why will one type of protein be synthesized on different ribosomes in a test tube?
Answer:
1) the primary structure of a protein is determined by the sequence of amino acids;
2) templates for protein synthesis are the same mRNA molecules, in which the same primary protein structure is encoded.
11. What features of the structure are characteristic of representatives of the Chordata type?
Answer:
1) internal axial skeleton;
2) the nervous system in the form of a tube on the dorsal side of the body;
3) gaps in the digestive tube.
12. Clover grows in a meadow, pollinated by bumblebees. What biotic factors can lead to a decline in the clover population?
Answer:
1) a decrease in the number of bumblebees;
2) an increase in the number of herbivorous animals;
3) reproduction of plants of competitors (cereals, etc.).
13. The total mass of mitochondria in relation to the mass of cells of various organs of the rat is: in the pancreas - 7.9%, in the liver - 18.4%, in the heart - 35.8%. Why do the cells of these organs have a different content of mitochondria?
Answer:
1) mitochondria are the energy stations of the cell, ATP molecules are synthesized and accumulated in them;
2) for the intensive work of the heart muscle, a lot of energy is needed, therefore the content of mitochondria in its cells is the highest;
3) in the liver, the number of mitochondria is higher compared to the pancreas, since it has a more intensive metabolism.
14. Explain why beef that has not passed sanitary control is dangerous to eat undercooked or lightly fried.
Answer:
1) in beef meat there may be finns of bovine tapeworm;
2) in the digestive canal, an adult worm develops from the Finn, and the person becomes the final owner.
15. Name the plant cell organoid shown in the figure, its structures, indicated by numbers 1-3, and their functions.
Answer:
1) the depicted organoid is a chloroplast;
2) 1 - grana thylakoids, participate in photosynthesis;
3) 2 - DNA, 3 - ribosomes, are involved in the synthesis of their own chloroplast proteins.
16. Why bacteria cannot be classified as eukaryotes?
Answer:
1) in their cells, the nuclear substance is represented by one circular DNA molecule and is not separated from the cytoplasm;
2) do not have mitochondria, Golgi complex, EPS;
3) do not have specialized germ cells, there are no meiosis and fertilization.
17. What changes in biotic factors can lead to an increase in the population of the naked slug that lives in the forest and feeds mainly on plants?
18. In the leaves of plants, the process of photosynthesis proceeds intensively. Does it occur in mature and unripe fruits? Explain the answer.
Answer:
1) photosynthesis occurs in immature fruits (while they are green), since they contain chloroplasts;
2) as they mature, chloroplasts turn into chromoplasts, in which photosynthesis does not occur.
19. What stages of gametogenesis are indicated in the figure by the letters A, B and C? What set of chromosomes do cells have at each of these stages? To the development of what specialized cells does this process lead?
Answer:
1) A - stage (zone) of reproduction (division), diploid cells;
2) B - growth stage (zone), diploid cell;
3) B - stage (zone) of maturation, haploid cells, spermatozoa develop.
20. How do bacterial cells differ in structure from the cells of organisms of other kingdoms of wildlife? List at least three differences.
Answer:
1) there is no formed core, nuclear membrane;
2) a number of organelles are absent: mitochondria, ER, Golgi complex, etc.;
3) have one ring chromosome.
21. Why are plants (producers) considered the initial link in the circulation of substances and the transformation of energy in an ecosystem?
Answer:
1) create organic substances from inorganic;
2) accumulate solar energy;
3) provide organic matter and energy to the organisms of other parts of the ecosystem.
22. What processes ensure the movement of water and minerals through the plant?
Answer:
1) from the root to the leaves, water and minerals move through the vessels due to transpiration, which results in a sucking force;
2) the upward current in the plant is promoted by root pressure, which occurs as a result of the constant supply of water to the root due to the difference in the concentration of substances in the cells and the environment.
23. Consider the cells shown in the figure. Determine what letters denote prokaryotic and eukaryotic cells. Provide evidence for your point of view.
Answer:
1) A - prokaryotic cell, B - eukaryotic cell;
2) the cell in figure A does not have a formed nucleus, its hereditary material is represented by a ring chromosome;
3) the cell in figure B has a well-formed nucleus and organelles.
24. What is the complication of the circulatory system of amphibians compared to fish?
Answer:
1) the heart becomes three-chambered;
2) the second circle of blood circulation appears;
3) the heart contains venous and mixed blood.
25. Why is a mixed forest ecosystem considered more sustainable than a spruce forest ecosystem?
Answer:
1) there are more species in a mixed forest than in a spruce forest;
2) in a mixed forest, food chains are longer and more branched than in a spruce forest;
3) there are more tiers in a mixed forest than in a spruce forest.
26. A section of a DNA molecule has the following composition: GATGAATAGTGCTTC. List at least three consequences that an accidental replacement of the seventh nucleotide of thymine with cytosine (C) can lead to.
Answer:
1) a gene mutation will occur - the codon of the third amino acid will change;
2) in a protein, one amino acid can be replaced by another, as a result, the primary structure of the protein will change;
3) all other protein structures can change, which will lead to the appearance of a new trait in the body.
27. Red algae (crimson) live at great depths. Despite this, photosynthesis occurs in their cells. Explain how photosynthesis occurs if the water column absorbs the rays of the red-orange part of the spectrum.
Answer:
1) for photosynthesis, rays are needed not only in the red, but also in the blue part of the spectrum;
2) purple cells contain a red pigment that absorbs the rays of the blue part of the spectrum, their energy is used in the process of photosynthesis.
28. Find errors in the given text. Indicate the numbers of sentences in which errors were made, correct them.
1. Coelenterates are three-layer multicellular animals. 2. They have a gastric or intestinal cavity. 3. The intestinal cavity includes stinging cells. 4. Coelenterates have a mesh (diffuse) nervous system. 5. All intestinal - free-floating organisms.
1) 1 - coelenterates - two-layer animals;
2)3 - stinging cells are contained in the ectoderm, and not in the intestinal cavity;
3)5 - among the coelenterates there are attached forms.
29. How does gas exchange occur in the lungs and tissues in mammals? What is the reason for this process?
Answer:
1) gas exchange is based on diffusion, which is due to the difference in the concentration of gases (partial pressure) in the air of the alveoli and in the blood;
2) oxygen from the area of high pressure in the alveolar air enters the blood, and carbon dioxide from the area of high pressure in the blood enters the alveoli;
3) in the tissues, oxygen from the high pressure area in the capillaries enters the intercellular substance and then into the cells of the organs. Carbon dioxide from the area of high pressure in the intercellular substance enters the blood.
30. What is the participation of functional groups of organisms in the circulation of substances in the biosphere? Consider the role of each of them in the cycle of substances in the biosphere.
Answer:
1) producers synthesize organic substances from inorganic substances (carbon dioxide, water, nitrogen, phosphorus and other minerals), release oxygen (except for chemotrophs);
2) consumers (and other functional groups) of organisms use and convert organic substances, oxidize them during respiration, absorbing oxygen and releasing carbon dioxide and water;
3) decomposers decompose organic substances to inorganic compounds of nitrogen, phosphorus, etc., returning them to the environment.
31. A section of a DNA molecule encoding a sequence of amino acids in a protein has the following composition: G-A-T-G-A-A-T-A-G-TT-C-T-T-C. Explain the consequences of accidentally adding a guanine (G) nucleotide between the seventh and eighth nucleotides.
Answer:
1) a gene mutation will occur - the codes of the third and subsequent amino acids may change;
2) the primary structure of the protein may change;
3) a mutation can lead to the appearance of a new trait in an organism.
32. What plant organs are damaged by May beetles at different stages of individual development?
Answer:
1) plant roots damage larvae;
2) tree leaves damage adult beetles.
33. Find errors in the given text. Indicate the numbers of sentences in which errors were made, correct them.
1. Flatworms are three-layered animals. 2. Type Flatworms include white planaria, human roundworm and liver fluke. 3. Flatworms have an elongated flattened body. 4. They have a well-developed nervous system. 5. Flatworms are dioecious animals that lay eggs.
Mistakes made in sentences:
1) 2 - the type of Flatworms does not include the human roundworm, it is a Roundworm;
2) 4 - in flatworms, the nervous system is poorly developed;
3) 5 - Flatworms - hermaphrodites.
34. What is a fetus? What is its significance in the life of plants and animals?
Answer:
1) fruit - generative organ of angiosperms;
2) contains seeds, with the help of which the reproduction and resettlement of plants occurs;
3) the fruits of plants are food for animals.
35. Most of the bird species fly away for the winter from the northern regions, despite their warm-bloodedness. Name at least three factors that cause these animals to migrate.
Answer:
1) food objects of insectivorous birds become unavailable for getting;
2) ice cover on water bodies and snow cover on the ground deprive herbivorous birds of food;
3) change in the length of daylight hours.
36. Which milk, sterilized or freshly milked, will go sour faster under the same conditions? Explain the answer.
Answer:
1) freshly milked milk will sour faster, as it contains bacteria that cause fermentation of the product;
2) when milk is sterilized, cells and spores of lactic acid bacteria die, and milk is stored longer.
37. Find errors in the given text. Indicate the numbers of sentences in which errors were made, explain them.
1. The main classes of the type of arthropods are Crustaceans, Arachnids and Insects. 2. The body of crustaceans and arachnids is divided into head, thorax and abdomen. 3. The body of insects consists of a cephalothorax and an abdomen. 4. Spider antennae don't. 5. Insects have two pairs of antennae, while crustaceans have one pair.
Mistakes made in sentences:
1) 2 - the body of crustaceans and arachnids consists of a cephalothorax and abdomen;
2)3 - the body of insects consists of a head, chest and abdomen;
3-5 - insects have one pair of antennae, and crustaceans have two pairs.
38. Prove that the rhizome of a plant is a modified shoot.
Answer:
1) the rhizome has nodes in which there are rudimentary leaves and buds;
2) at the top of the rhizome is the apical bud, which determines the growth of the shoot;
3) adventitious roots depart from the rhizome;
4) the internal anatomical structure of the rhizome is similar to the stem.
39. Man uses chemicals to control pests. Indicate at least three changes in the life of an oak forest if all herbivorous insects are destroyed in it by a chemical method. Explain why they will happen.
Answer:
1) the number of insect pollinated plants will decrease sharply, since herbivorous insects are pollinators of plants;
2) the number of insectivorous organisms (consumers of the second order) will sharply decrease or they will disappear due to disruption of food chains;
3) part of the chemicals used to kill insects will enter the soil, which will lead to disruption of plant life, death of soil flora and fauna, all violations can lead to the death of oak forests.
40. Why can antibiotic treatment lead to bowel dysfunction? Name at least two reasons.
Answer:
1) antibiotics kill beneficial bacteria that live in the human intestine;
2) fiber breakdown, water absorption and other processes are disturbed.
41. What part of the sheet is indicated in the figure by the letter A and what structures does it consist of? What are the functions of these structures?
1) the letter A denotes a vascular fibrous bundle (vein), the bundle includes vessels, sieve tubes, mechanical tissue;
2) vessels provide water transport to the leaves;
3) sieve tubes provide transport of organic substances from leaves to other organs;
4) mechanical tissue cells give strength and are the framework of the sheet.
42. What are the characteristic features of the fungi kingdom?
Answer:
1) the body of fungi consists of filaments - hyphae, forming a mycelium;
2) reproduce sexually and asexually (spores, mycelium, budding);
3) grow throughout life;
4) in the cell: the shell contains a chitin-like substance, a reserve nutrient - glycogen.
43. In a small reservoir formed after the flood of the river, the following organisms were found: ciliates-shoes, daphnia, white planarians, a large pond snail, cyclops, hydras. Explain whether this body of water can be considered an ecosystem. Give at least three pieces of evidence.
Answer:
The named temporary reservoir cannot be called an ecosystem, since in it:
1) there are no producers;
2) there are no decomposers;
3) there is no closed circulation of substances and food chains are broken.
44. Why is a note placed under the tourniquet, which is applied to stop bleeding from large blood vessels, indicating the time of its application?
Answer:
1) after reading the note, you can determine how much time has passed since the tourniquet was applied;
2) if after 1-2 hours it was not possible to deliver the patient to the doctor, then the tourniquet should be loosened for a while. This will prevent tissue necrosis.
45. Name the structures of the spinal cord, indicated in the figure by numbers 1 and 2, and describe the features of their structure and function.
Answer:
1) 1 - gray matter, formed by the bodies of neurons;
2) 2 - white matter, formed by long processes of neurons;
3) gray matter performs a reflex function, white matter - a conductive function.
46. What role do salivary glands play in digestion in mammals? List at least three functions.
Answer:
1) the secretion of the salivary glands moistens and disinfects food;
2) saliva is involved in the formation of the food bolus;
3) saliva enzymes contribute to the breakdown of starch.
47. As a result of volcanic activity, an island was formed in the ocean. Describe the sequence of ecosystem formation on a newly formed piece of land. List at least three items.
Answer:
1) the first to settle are microorganisms and lichens that provide soil formation;
2) plants settle on the soil, the spores or seeds of which are carried by wind or water;
3) as vegetation develops, animals appear in the ecosystem, primarily arthropods and birds.
48. Experienced gardeners apply fertilizer to the grooves located along the edges of the near-stem circles of fruit trees, and do not distribute them evenly. Explain why.
Answer:
1) the root system grows, the suction zone moves behind the root tip;
2) roots with a developed suction zone - root hairs - are located along the edges of the near-stem circles.
49. What modified shoot is shown in the picture? Name the elements of the structure, indicated in the figure by the numbers 1, 2, 3, and the functions that they perform.
Answer:
1) bulb;
2) 1 - juicy scaly leaf, in which nutrients and water are stored;
3) 2 - adventitious roots that ensure the absorption of water and minerals;
4) 3 - kidney, ensures the growth of the shoot.
50. What are the features of the structure and life of mosses? List at least three items.
Answer:
1) most mosses are leafy plants, some of them have rhizoids;
2) mosses have a poorly developed conducting system;
3) mosses reproduce both sexually and asexually, with alternation of generations: sexual (gametophyte) and asexual (sporophyte); an adult moss plant is a sexual generation, and a spore box is asexual.
51. As a result of a forest fire, part of the spruce forest burned out. Explain how it will self-heal. List at least three steps.
Answer:
1) herbaceous light-loving plants develop first;
2) then shoots of birch, aspen, pine appear, the seeds of which fell with the help of the wind, a small-leaved or pine forest is formed.
3) under the canopy of light-loving species, shade-tolerant spruces develop, which subsequently completely crowd out other trees.
52. To establish the cause of a hereditary disease, the patient's cells were examined and a change in the length of one of the chromosomes was found. What research method allowed to establish the cause of this disease? What kind of mutation is it associated with?
Answer:
1) the cause of the disease is established using the cytogenetic method;
2) the disease is caused by a chromosomal mutation - the loss or addition of a chromosome fragment.
53. What letter in the figure indicates the blastula in the development cycle of the lancelet. What are the features of blastula formation?
Answer:
1) the blastula is designated by the letter G;
2) the blastula is formed during the crushing of the zygote;
3) the size of the blastula does not exceed the size of the zygote.
54. Why are fungi isolated in a special kingdom of the organic world?
Answer:
1) the body of mushrooms consists of thin branching threads - hyphae, forming a mycelium, or mycelium;
2) mycelium cells store carbohydrates in the form of glycogen;
3) fungi cannot be attributed to plants, since their cells do not have chlorophyll and chloroplasts; the wall contains chitin;
4) mushrooms cannot be attributed to animals, since they absorb nutrients from the entire surface of the body, and do not swallow them in the form of food lumps.
55. In some forest biocenoses, mass shooting of diurnal birds of prey was carried out to protect chicken birds. Explain how this event affected the number of chickens.
Answer:
1) at first, the number of chickens increased, since their enemies (naturally regulating the number) were destroyed;
2) then the number of chickens decreased due to lack of food;
3) the number of sick and weakened individuals increased due to the spread of diseases and the absence of predators, which also affected the decrease in the number of chickens.
56. The color of the fur of a white hare changes throughout the year: in winter the hare is white, and in summer it is gray. Explain what type of variability is observed in an animal and what determines the manifestation of this trait.
Answer:
1) a manifestation of modification (phenotypic, non-hereditary) variability is observed in a hare;
2) the manifestation of this trait is determined by changes in environmental conditions (temperature, day length).
57. Name the stages of embryonic development of the lancelet, indicated in the figure by the letters A and B. Expand the features of the formation of each of these stages.
A B
Answer:
1) A - gastrula - the stage of a two-layer embryo;
2) B - neurula, has the beginnings of a future larva or adult organism;
3) the gastrula is formed by invagination of the blastula wall, and in the neurula, the neural plate is first laid, which serves as a regulator for laying the rest of the organ systems.
58. What are the main features of the structure and vital activity of bacteria. List at least four features.
Answer:
1) bacteria - pre-nuclear organisms that do not have a formalized nucleus and many organelles;
2) according to the method of nutrition, bacteria are heterotrophs and autotrophs;
3) high rate of reproduction by division;
4) anaerobes and aerobes;
5) unfavorable conditions are experienced in a state of dispute.
59. What is the difference between the ground-air environment and the water?
Answer:
1) oxygen content;
2) differences in temperature fluctuations (wide amplitude of fluctuations in the ground-air environment);
3) the degree of illumination;
4) density.
Answer:
1) seaweed has the ability to accumulate the chemical element iodine;
2) Iodine is essential for normal thyroid function.
61. Why is a shoe ciliate cell considered an integral organism? What organelles of ciliates-shoes are indicated in the figure by the numbers 1 and 2 and what functions do they perform?
Answer:
1) the ciliate cell performs all the functions of an independent organism: metabolism, reproduction, irritability, adaptation;
2) 1 - a small nucleus, participates in the sexual process;
3) 2 - a large core, regulates vital processes.
61. What are the features of the structure and life of fungi? List at least three features.
62. Explain the harm to plants caused by acid rain. Give at least three reasons.
Answer:
1) directly damage the organs and tissues of plants;
2) pollute the soil, reduce fertility;
3) reduce the productivity of plants.
63. Why are passengers advised to suck on lollipops when taking off or landing an airplane?
Answer:
1) a rapid change in pressure during takeoff or landing of an aircraft causes discomfort in the middle ear, where the initial pressure on the eardrum lasts longer;
2) swallowing movements improve air access to the auditory (Eustachian) tube, through which the pressure in the middle ear cavity equalizes with the pressure in the environment.
64. How does the circulatory system of arthropods differ from the circulatory system of annelids? Indicate at least three signs that prove these differences.
Answer:
1) in arthropods, the circulatory system is open, and in annelids it is closed;
2) arthropods have a heart on the dorsal side;
3) annelids do not have a heart, its function is performed by an annular vessel.
65. What type is the animal shown in the picture? What is indicated by numbers 1 and 2? Name other representatives of this type.
Answer:
1) to the type of intestinal;
2) 1 - ectoderm, 2 - intestinal cavity;
3) coral polyps, jellyfish.
66. What are the morphological, physiological and behavioral adaptations to environmental temperature in warm-blooded animals?
Answer:
1) morphological: heat-insulating covers, subcutaneous fat layer, changes in the surface of the body;
2) physiological: increased intensity of evaporation of sweat and moisture during breathing; narrowing or dilation of blood vessels, changes in the level of metabolism;
3) behavioral: construction of nests, burrows, changes in daily and seasonal activity depending on the temperature of the environment.
67. How is the receipt of genetic information from the nucleus to the ribosome?
Answer:
1) mRNA synthesis occurs in the nucleus in accordance with the principle of complementarity;
2) mRNA - a copy of the DNA section containing information about the primary structure of the protein moves from the nucleus to the ribosome.
68. What is the complication of ferns in comparison with mosses? Give at least three signs.
Answer:
1) ferns have roots;
2) in ferns, unlike mosses, a developed conductive tissue has formed;
3) in the development cycle of ferns, the asexual generation (sporophyte) prevails over the sexual (gametophyte), which is represented by the outgrowth.
69. Name the embryonic layer of a vertebrate animal, indicated in the figure by the number 3. What type of tissue and what organs are formed from it.
Answer:
1) germinal layer - endoderm;
2epithelial tissue (intestinal and respiratory epithelium);
3) organs: intestines, digestive glands, respiratory organs, some endocrine glands.
70. What role do birds play in the biocenosis of the forest? Give at least three examples.
Answer:
1) regulate the number of plants (distribute fruits and seeds);
2) regulate the number of insects, small rodents;
3) serve as food for predators;
4) fertilize the soil.
71. What is the protective role of leukocytes in the human body?
Answer:
1) leukocytes are capable of phagocytosis - devouring and digesting proteins, microorganisms, dead cells;
2) leukocytes are involved in the production of antibodies that neutralize certain antigens.
72. Find errors in the given text. Indicate the numbers of the proposals in which they are made, correct them.
According to the chromosome theory of heredity:
1. Genes are located on chromosomes in a linear order. 2. Everyone occupies a certain place - an allele. 3. Genes on one chromosome form a linkage group. 4. The number of linkage groups is determined by the diploid boron of chromosomes. 5. Violation of gene linkage occurs in the process of conjugation of chromosomes in the prophase of meiosis.
Mistakes made in sentences:
1)2 - location of the gene - locus;
2)4 - the number of linkage groups is equal to the haploid set of chromosomes;
3)5 - disruption of gene linkage occurs during crossing over.
73. Why do some scientists refer to green euglena as a plant, and others as an animal? List at least three reasons.
Answer:
1) capable of heterotrophic nutrition, like all animals;
2) capable of active movement in search of food, like all animals;
3) contains chlorophyll in the cell and is capable of autotrophic nutrition, like plants.
74. What processes take place at the stages of energy metabolism?
Answer:
1) at the preparatory stage, complex organic substances are split into less complex ones (biopolymers - to monomers), energy is dissipated in the form of heat;
2) in the process of glycolysis, glucose is broken down to pyruvic acid (or lactic acid, or alcohol) and 2 ATP molecules are synthesized;
3) at the oxygen stage, pyruvic acid (pyruvate) is broken down to carbon dioxide and water and 36 ATP molecules are synthesized.
75. In a wound formed on the human body, bleeding eventually stops, but suppuration may occur. Explain what properties of blood this is due to.
Answer:
1) bleeding stops due to blood clotting and the formation of a blood clot;
2) suppuration is due to the accumulation of dead leukocytes that have carried out phagocytosis.
76. Find errors in the given text, correct them. Indicate the numbers of sentences in which errors were made, explain them.
1. Proteins are of great importance in the structure and life of organisms. 2. These are biopolymers whose monomers are nitrogenous bases. 3. Proteins are part of the plasma membrane. 4. Many proteins perform an enzymatic function in the cell. 5. In protein molecules, hereditary information about the characteristics of an organism is encrypted. 6. Protein and tRNA molecules are part of ribosomes.
Mistakes made in sentences:
1) 2 - protein monomers are amino acids;
2)5 - hereditary information about the characteristics of the organism is encrypted in DNA molecules;
3)6- ribosomes contain rRNA molecules, not tRNA.
77. What is myopia? In what part of the eye is the image focused in a nearsighted person? What is the difference between congenital and acquired forms of myopia?
Answer:
1) myopia is a disease of the organs of vision, in which a person does not distinguish distant objects;
2) in a nearsighted person, the image of objects appears in front of the retina;
3) with congenital myopia, the shape of the eyeball changes (lengthens);
4) acquired myopia is associated with a change (increase) in the curvature of the lens.
78. What is the difference between the skeleton of the human head and the skeleton of the head of great apes? List at least four differences.
Answer:
1) the predominance of the brain of the skull over the facial;
2) reduction of the jaw apparatus;
3) the presence of a chin protrusion on the lower jaw;
4) reduction of superciliary arches.
79. Why is the volume of urine excreted by the human body per day not equal to the volume of liquid drunk during the same time?
Answer:
1) part of the water is used by the body or is formed in metabolic processes;
2) part of the water evaporates through the respiratory organs and sweat glands.
80. Find errors in the given text, correct them, indicate the numbers of the sentences in which they are made, write down these sentences without errors.
1. Animals are heterotrophic organisms; they feed on ready-made organic substances. 2. There are unicellular and multicellular animals. 3. All multicellular animals have bilateral body symmetry. 4. Most of them have developed various organs of locomotion. 5. Only arthropods and chordates have a circulatory system. 6. Postembryonic development in all multicellular animals is direct.
Mistakes made in sentences:
1) 3 - not all multicellular animals have bilateral symmetry of the body; for example, in coelenterates it is radial (radial);
2) 5 - the circulatory system is also present in annelids and mollusks;
3) 6 - direct postembryonic development is not inherent in all multicellular animals.
81. What is the importance of blood in human life?
Answer:
1) performs a transport function: delivery of oxygen and nutrients to tissues and cells, removal of carbon dioxide and metabolic products;
2) performs a protective function due to the activity of leukocytes and antibodies;
3) participates in the humoral regulation of the vital activity of the organism.
82. Use information about the early stages of embryogenesis (zygote, blastula, gastrula) to confirm the sequence of development of the animal world.
Answer:
1) the zygote stage corresponds to a unicellular organism;
2) the blastula stage, where cells are not differentiated, is similar to colonial forms;
3) the embryo at the gastrula stage corresponds to the structure of the intestinal cavity (hydra).
83. The introduction of large doses of drugs into a vein is accompanied by their dilution with saline (0.9% NaCl solution). Explain why.
Answer:
1) the introduction of large doses of drugs without dilution can cause a sharp change in the composition of the blood and irreversible phenomena;
2) the concentration of physiological saline (0.9% NaCl solution) corresponds to the concentration of salts in the blood plasma and does not cause the death of blood cells.
84. Find errors in the given text, correct them, indicate the numbers of the sentences in which they are made, write down these sentences without errors.
1. Animals of the arthropod type have an outer chitinous cover and jointed limbs. 2. The body of most of them consists of three sections: the head, chest and abdomen. 3. All arthropods have one pair of antennae. 4. Their eyes are complex (faceted). 5. The circulatory system of insects is closed.
Mistakes made in sentences:
1)3 - not all arthropods have one pair of antennae (arachnoids do not have them, and crustaceans have two pairs each);
2) 4 - not all arthropods have compound (compound) eyes: in arachnids they are simple or absent, in insects, along with compound eyes, they can be simple;
3-5 - the circulatory system in arthropods is not closed.
85. What are the functions of the human digestive system?
Answer:
1) mechanical processing of food;
2) chemical processing of food;
3) movement of food and removal of undigested residues;
4) absorption of nutrients, mineral salts and water into the blood and lymph.
86. What characterizes biological progress in flowering plants? List at least three features.
Answer:
1) a wide variety of populations and species;
2) wide settlement on the globe;
3) adaptability to life in different environmental conditions.
87. Why should food be chewed thoroughly?
Answer:
1) well-chewed food is quickly saturated with saliva in the oral cavity and begins to be digested;
2) well-chewed food is quickly saturated with digestive juices in the stomach and intestines and therefore easier to digest.
88. Find errors in the given text. Indicate the numbers of the proposals in which they are made, correct them.
1. A population is a collection of freely interbreeding individuals of the same species that inhabit a common territory for a long time. 2. Different populations of the same species are relatively isolated from each other, and their individuals do not interbreed. 3. The gene pool of all populations of the same species is the same. 4. The population is the elementary unit of evolution. 5. A group of frogs of the same species living in a deep puddle for one summer is a population.
Mistakes made in sentences:
1)2 - populations of the same species are partially isolated, but individuals of different populations can interbreed;
2)3 — gene pools of different populations of the same species are different;
3)5 - a group of frogs is not a population, since a group of individuals of the same species is considered a population if it occupies the same space for a large number of generations.
89. Why is it recommended to drink salted water in summer with prolonged thirst?
Answer:
1) in summer, sweating increases in a person;
2) mineral salts are excreted from the body with sweat;
3) salted water restores the normal water-salt balance between the tissues and the internal environment of the body.
90. What proves that a person belongs to the class of mammals?
Answer:
1) the similarity of the structure of organ systems;
2) the presence of hairline;
3) the development of the embryo in the uterus;
4) feeding offspring with milk, caring for offspring.
91. What processes maintain the constancy of the chemical composition of human blood plasma?
Answer:
1) processes in buffer systems maintain the reaction of the medium (pH) at a constant level;
2) neurohumoral regulation of the chemical composition of plasma is carried out.
92. Find errors in the given text. Indicate the numbers of the proposals in which they are made, explain them.
1. A population is a collection of freely interbreeding individuals of different species that inhabit a common territory for a long time. 2. The main group characteristics of a population are the number, density, age, sex and spatial structures. 3. The totality of all the genes of a population is called the gene pool. 4. Population is a structural unit of living nature. 5. The number of populations is always stable.
Mistakes made in sentences:
1)1 - a population is a collection of freely interbreeding individuals of the same species, inhabiting the common territory of the population for a long time;
2)4 - the population is a structural unit of the species;
3-5 - the number of populations can change in different seasons and years.
93. What structures of the integument of the body provide protection for the human body from the effects of environmental temperature factors? Explain their role.
Answer:
1) subcutaneous fatty tissue protects the body from cooling;
2) sweat glands form sweat, which, when evaporated, protects against overheating;
3) the hair on the head protects the body from cooling and overheating;
4) changing the lumen of skin capillaries regulates heat transfer.
94. Give at least three progressive biological features of a person, which he acquired in the process of long evolution.
Answer:
1) an increase in the brain and cerebral part of the skull;
2) upright posture and corresponding changes in the skeleton;
3) liberation and development of the hand, opposition of the thumb.
95. What division of meiosis is similar to mitosis? Explain how it is expressed and what set of chromosomes in the cell leads to.
Answer:
1) similarity with mitosis is observed in the second division of meiosis;
2) all phases are similar, sister chromosomes (chromatids) diverge to the poles of the cell;
3) the resulting cells have a haploid set of chromosomes.
96. What is the difference between arterial bleeding and venous bleeding?
Answer:
1) with arterial bleeding, scarlet blood;
2) it shoots out of the wound with a strong jet, a fountain.
97. The scheme of what process occurring in the human body is shown in the figure? What underlies this process and how does the composition of the blood change as a result? Explain the answer.
capillary
Answer:
1) the figure shows a diagram of gas exchange in the lungs (between the pulmonary vesicle and the blood capillary);
2) gas exchange is based on diffusion - the penetration of gases from a place with high pressure to a place with less pressure;
3) as a result of gas exchange, the blood is saturated with oxygen and turns from venous (A) to arterial (B).
98. What effect does hypodynamia (low motor activity) have on the human body?
Answer:
hypodynamia leads to:
1) to a decrease in the level of metabolism, an increase in adipose tissue, overweight;
2) weakening of the skeletal and cardiac muscles, increasing the load on the heart and reducing the endurance of the body;
3) venous blood stagnation in the lower extremities, vasodilation, circulatory disorders.
(Other formulations of the answer are allowed that do not distort its meaning.)
99. What are the characteristics of plants that live in arid conditions?
Answer:
1) the root system of plants penetrates deep into the soil, reaches the groundwater or is located in the surface layer of the soil;
2) in some plants, water is stored in leaves, stems and other organs during drought;
3) the leaves are covered with a wax coating, pubescent or modified into spines or needles.
100. What is the reason for the need for iron ions to enter the human blood? Explain the answer.
Answer:
2) erythrocytes provide transport of oxygen and carbon dioxide.
101. Through what vessels and what kind of blood enters the chambers of the heart, indicated in the figure by numbers 3 and 5? With what circle of blood circulation is each of these structures of the heart connected?
Answer:
1) venous blood enters the chamber marked with the number 3 from the superior and inferior vena cava;
2) the chamber marked with the number 5 receives arterial blood from the pulmonary veins;
3) the chamber of the heart, indicated by the number 3, is associated with a large circle of blood circulation;
4) the chamber of the heart, indicated by the number 5, is associated with the pulmonary circulation.
102. What are vitamins, what is their role in the life of the human body?
Answer:
1) vitamins - biologically active organic substances needed in small quantities;
2) they are part of enzymes, participating in metabolism;
3) increase the body's resistance to adverse environmental influences, stimulate growth, development of the body, restoration of tissues and cells.
103. The body shape of the Kalima butterfly resembles a leaf. How did a similar body shape form in a butterfly?
Answer:
1) the appearance in individuals of various hereditary changes;
2) preservation by natural selection of individuals with a modified body shape;
3) reproduction and distribution of individuals with a body shape resembling a leaf.
104. What is the nature of most enzymes and why do they lose their activity when the level of radiation increases?
Answer:
1) most enzymes are proteins;
2) under the action of radiation, denaturation occurs, the structure of the protein-enzyme changes.
105. Find errors in the given text. Indicate the numbers of proposals in which they are made, correct them.
1. Plants, like all living organisms, feed, breathe, grow, reproduce. 2. According to the method of nutrition, plants are classified as autotrophic organisms. 3. When breathing, plants absorb carbon dioxide and release oxygen. 4. All plants reproduce by seeds. 5. Plants, like animals, grow only in the first years of life.
Mistakes made in sentences:
1) 3 - when breathing, plants absorb oxygen and release carbon dioxide;
2-4 - only flowering and gymnosperms reproduce by seeds, and algae, mosses, ferns - by spores;
3-5 - plants grow throughout their lives, have unlimited growth.
106. What is the reason for the need for iron ions to enter the human blood? Explain the answer.
Answer:
1) iron ions are part of the hemoglobin of erythrocytes;
2) erythrocyte hemoglobin provides transport of oxygen and carbon dioxide, as it is able to bind to these gases;
3) the supply of oxygen is necessary for the energy metabolism of the cell, and carbon dioxide is its final product to be removed.
107. Explain why people of different races are classified as the same species. Give at least three pieces of evidence.
Answer:
1) the similarity of the structure, life processes, behavior;
2) genetic unity - the same set of chromosomes, their structure;
3) interracial marriages produce offspring capable of reproduction.
108. In ancient India, a person suspected of a crime was offered to swallow a handful of dry rice. If he did not succeed, the guilt was considered proven. Give a physiological justification for this process.
Answer:
1) swallowing is a complex reflex act, which is accompanied by salivation and irritation of the root of the tongue;
2) with strong excitement, salivation is sharply inhibited, the mouth becomes dry, and the swallowing reflex does not occur.
109. Find errors in the given text. Indicate the numbers of the proposals in which they are made, explain them.
1. The composition of the food chain of biogeocenosis includes producers, consumers and decomposers. 2. The first link in the food chain are consumers. 3. Consumers in the world accumulate energy absorbed in the process of photosynthesis. 4. In the dark phase of photosynthesis, oxygen is released. 5. Reducers contribute to the release of energy accumulated by consumers and producers.
Mistakes made in sentences:
1) 2 - the first link is the producers;
2) 3 - consumers are not capable of photosynthesis;
3)4 - oxygen is released in the light phase of photosynthesis.
110. What are the causes of anemia in humans? List at least three possible reasons.
Answer:
1) large blood loss;
2) malnutrition (lack of iron and vitamins, etc.);
3) violation of the formation of erythrocytes in the hematopoietic organs.
111. The wasp fly is similar in color and body shape to a wasp. Name the type of its protective device, explain its significance and the relative nature of fitness.
Answer:
1) type of adaptation - mimicry, imitation of the color and shape of the body of an unprotected animal to a protected one;
2) resemblance to a wasp warns a possible predator about the danger of being stung;
3) the fly becomes the prey of young birds that have not yet developed a reflex to the wasp.
112. Make up a food chain using all of the following objects: humus, cross-spider, hawk, great tit, housefly. Determine the consumers of the third order in the compiled chain.
Answer:
1) humus -> housefly -> spider-cross -> great tit -> hawk;
2) consumer of the third order - great tit.
113. Find errors in the given text. Indicate the numbers of sentences in which errors were made, correct them.
1. Annelids are the most highly organized animals of the cut of other types of worms. 2. Annelids have an open circulatory system. 3. The body of the annelids consists of identical segments. 4. There is no body cavity in annelids. 5. The nervous system of annelids is represented by the peripharyngeal ring and the dorsal nerve chain.
Mistakes made in sentences:
1) 2 - Annelids have a closed circulatory system;
2) 4 - Annelids have a body cavity;
3-5 - the nerve chain is located on the ventral side of the body.
114. Name at least three aromorphoses in terrestrial plants that allowed them to be the first to master the land. Justify the answer.
Answer:
1) the emergence of integumentary tissue - the epidermis with stomata - contributing to protection against evaporation;
2) the appearance of a conducting system that ensures the transport of substances;
3) the development of a mechanical tissue that performs a supporting function.
115. Explain the reason for the great diversity of marsupials in Australia and their absence on other continents.
Answer:
1) Australia separated from other continents during the heyday of marsupials before the appearance of placental animals (geographical isolation);
2) the natural conditions of Australia contributed to the divergence of signs of marsupials and active speciation;
3) on other continents, marsupials were replaced by placental mammals.
116. In what cases does a change in the sequence of DNA nucleotides not affect the structure and functions of the corresponding protein?
Answer:
1) if, as a result of a nucleotide substitution, another codon appears that codes for the same amino acid;
2) if the codon formed as a result of a nucleotide substitution encodes another amino acid, but with similar chemical properties that does not change the structure of the protein;
3) if nucleotide changes occur in intergenic or non-functioning DNA regions.
117. Why is the relationship between pike and perch in the river ecosystem considered competitive?
Answer:
1) are predators, eat similar food;
2) live in the same reservoir, need similar conditions for life, mutually oppress each other.
118. Find errors in the given text. Indicate the numbers of sentences in which errors were made, correct them.
1. The main classes of the type of arthropods are Crustaceans, Arachnids and Insects. 2. Insects have four pairs of legs, and arachnids have three pairs. 3. The crayfish has simple eyes, and the cross-spider has complex eyes. 4. In arachnids, spider warts are located on the abdomen. 5. Spider-cross and Maybug breathe with the help of lung sacs and trachea.
Mistakes made in sentences:
1) 2 - insects have three pairs of legs, and arachnids - four pairs;
2) 3 - crayfish has compound eyes, and the cross-spider has simple eyes;
3-5 - the May beetle does not have lung sacs, but only tracheae.
119. What are the features of the structure and life of cap mushrooms? List at least four features.
Answer:
1) have a mycelium and a fruiting body;
2) reproduce by spores and mycelium;
3) according to the method of nutrition - heterotrophs;
4) most form mycorrhiza.
120. What aromorphoses allowed the ancient amphibians to master the land.
Answer:
1) the appearance of pulmonary respiration;
2) the formation of dissected limbs;
3) the appearance of a three-chambered heart and two circles of blood circulation.
The life cycle of a cell clearly demonstrates that the life of a cell breaks down into a period of interkinesis and mitosis. During interkinesis, all vital processes are actively carried out, except for division. Let's focus on them first. The main life process of a cell is metabolism.
On the basis of it, the formation of specific substances, growth, cell differentiation, as well as irritability, movement and self-reproduction of cells occur. In a multicellular organism, the cell is part of the whole. Therefore, the morphological features and nature of all vital processes of the cell are formed under the influence of the organism and the external environment. The body exerts its influence on cells mainly through the nervous system, as well as through the action of hormones of the endocrine glands.
Metabolism is a certain order of the transformation of substances, leading to the preservation and self-renewal of the cell. In the process of metabolism, on the one hand, substances enter the cell that are processed and are part of the cell body, and on the other hand, substances that are decay products are removed from the cell, that is, the cell and the environment exchange substances. Chemically, metabolism is expressed in chemical reactions following one after another in a certain order. Strict order in the course of the transformation of substances is provided by protein substances - enzymes that play the role of catalysts. Enzymes are specific, that is, they act in a certain way only on certain substances. Under the influence of enzymes, a given substance of all possible transformations changes many times faster in only one direction. The new substances formed as a result of this process change further under the influence of other, equally specific enzymes, etc.
The driving principle of metabolism is the law of unity and struggle of opposites. Indeed, the metabolism is determined by two contradictory and at the same time common processes - assimilation and dissimilation. The substances received from the external environment are processed by the cell and turn into substances characteristic of this cell (assimilation). Thus, the composition of its cytoplasm, nucleus organelles is updated, trophic inclusions are formed, secrets, hormones are produced. The processes of assimilation are synthetic, they go on with the absorption of energy. The source of this energy is the processes of dissimilation. As a result, their previously formed organic substances are destroyed, and energy is released and products are formed, some of which are synthesized into new cell substances, while others are excreted from the cell (excretions). The energy released as a result of dissimilation is used in assimilation. Thus, assimilation and dissimilation are two, although different, but closely related aspects of metabolism.
The nature of metabolism is different not only in different animals, but even within the same organism in different organs and tissues. This specificity is manifested in the fact that the cells of each organ are able to assimilate only certain substances, build specific substances of their body from them, and release quite certain substances into the external environment. Along with the metabolism, energy is also exchanged, that is, the cell absorbs energy from the external environment in the form of heat, light and, in turn, releases radiant and other types of energy.
Metabolism is composed of a number of private processes. The main ones are:
1) penetration of substances into the cell;
2) their "processing" with the help of nutrition and respiration processes (aerobic and anaerobic);
3) the use of products of "processing" for various synthetic processes, an example of which may be the synthesis of proteins and the formation of a secret;
4) removal of waste products from the cell.
The plasmalemma plays an important role in the penetration of substances, as well as in the removal of substances from the cell. Both of these processes can be considered from the physicochemical and morphological point of view. Permeability is due to passive and active transfer. The first occurs due to the phenomena of diffusion and osmosis. However, substances can enter the cell contrary to these laws, which indicates the activity of the cell itself and its selectivity. It is known, for example, that sodium ions are pumped out of the cell, even if their concentration in the external environment is higher than in the cell, while potassium ions, on the contrary, are pumped into the cell. This phenomenon is described under the name "sodium-potassium pump" and is accompanied by the expenditure of energy. The ability to penetrate into the cell decreases as the number of hydroxyl groups (OH) in the molecule increases when an amino group (NH2) is introduced into the molecule. Organic acids penetrate more easily than inorganic acids. Ammonia penetrates especially quickly from alkalis. For permeability, the size of the molecule is also important. The permeability of a cell changes depending on the reaction, temperature, lighting, age and physiological state of the cell itself, and these reasons can increase the permeability of some substances and at the same time weaken the permeability of others.
The morphological picture of the permeability of substances from the environment is well traced and is carried out by phagocytosis (phagein - to eat) and pinocytosis (pynein - to drink). The mechanisms of both seem to be similar and differ only quantitatively. With the help of phagocytosis, larger particles are captured, and with the help of pinocytosis, smaller and less dense ones. First, substances are adsorbed by the surface of the plasmalemma covered with mucopolysaccharides, then together with it they sink deep into, and a bubble is formed, which then separates from the plasmalemma (Fig. 19). The processing of infiltrated substances is carried out in the course of processes resembling digestion and culminating in the formation of relatively simple substances. Intracellular digestion begins with the fact that phagocytic or pinocytic vesicles fuse with primary lysosomes, which contain digestive enzymes, and a secondary lysosome, or digestive vacuole, is formed. In them, with the help of enzymes, the decomposition of substances into simpler ones occurs. This process involves not only lysosomes, but also other components of the cell. Thus, mitochondria provide the energy side of the process; channels of the cytoplasmic reticulum can be used to transport processed substances.
Intracellular digestion ends with the formation, on the one hand, of relatively simple products, from which complex substances (proteins, fats, carbohydrates) are synthesized again, which are used to renew cellular structures or form secrets, and on the other hand, products to be removed from the cell as excretions. Examples of the use of processed products are protein synthesis and the formation of secrets.
Rice. 19. Scheme of pinocytosis:
L - formation of a pinocytic canal (1) and pinocytic vesicles (2). Arrows show the direction of plasmalemma invagination. B-Zh - successive stages of pinocytosis; 3 - adsorbed particles; 4 - particles captured by cell outgrowths; 5 - cell plasma membrane; D, E, B - successive stages of pinocytotic vacuole formation; G - food particles are released from the vacuole shell.
Protein synthesis is carried out on ribosomes and conditionally occurs in four stages.
The first step involves the activation of amino acids. Their activation occurs in the cytoplasmic matrix with the participation of enzymes (aminoacyl - RNA synthetases). About 20 enzymes are known, each of which is specific for only one amino acid. Activation of an amino acid is carried out when it is combined with an enzyme and ATP.
As a result of the interaction, pyrophosphate is cleaved from ATP, and the energy that is in the connection between the first and second phosphate groups is completely transferred to the amino acid. The amino acid activated in this way (aminoacyladenylate) becomes reactive and acquires the ability to combine with other amino acids.
The second stage is the binding of the activated amino acid to transfer RNA (t-RNA). In this case, one t-RNA molecule attaches only one molecule of the activated amino acid. The same enzyme is involved in these reactions as in the first stage, and the reaction ends with the formation of a complex of t-RNA and an activated amino acid. The tRNA molecule consists of a double helix closed at one end. The closed (head) end of this helix is represented by three nucleotides (anticodon), which determine the attachment of this t-RNA to a specific site (codon) of a long messenger RNA (i-RNA) molecule. An activated amino acid is attached to the other end of the tRNA (Fig. 20). For example, if a tRNA molecule has a UAA triplet at the head end, then only the amino acid lysine can be attached to its opposite end. Thus, each amino acid has its own specific t-RNA. If the three terminal nucleotides in different tRNAs are the same, then its specificity is determined by the sequence of nucleotides in another part of the tRNA. The energy of the activated amino acid attached to the tRNA is used to form peptide bonds in the polypeptide molecule. The activated amino acid is transported by tRNA through the hyaloplasm to the ribosomes.
The third stage is the synthesis of polypeptide chains. The messenger RNA, leaving the nucleus, stretches through the small subunits of several ribosomes of a certain polyribosome, and the same synthesis processes are repeated in each of them. During the broach, the laying of that mole
Rice. 20. Scheme of polypeptide synthesis on ribosomes by means of i-RNA and t-RNA: /, 2 - ribosome; 3 - t-RNA carrying anticodons at one end: ACC, AUA. Ayv AGC, and at the other end, respectively, amino acids: tryptophan, roller, lysine, serine (5); 4-n-RNA, in which the codes are located: UGG (tryptophan)» URU (valine). UAA (lysine), UCG (serine); 5 - synthesized polypeptide.
A t-RNA coule, the triplet of which corresponds to the code word of the m-RNA. Then the code word shifts to the left, and with it the t-RNA attached to it. The amino acid brought by it is connected by a peptide bond with the previously brought amino acid of the synthesizing polypeptide; t-RNA is separated from i-RNA, translation (writing off) of i-RNA information occurs, that is, protein synthesis. Obviously, two t-RNA molecules are attached to ribosomes at the same time: one at the site carrying the synthesized polypeptide chain, and the other at the site to which the next amino acid is attached before it falls into its place in the chain.
The fourth stage is the removal of the polypeptide chain from the ribosome and the formation of a spatial configuration characteristic of the synthesized protein. Finally, the protein molecule that has completed its formation becomes independent. tRNA can be used for repeated synthesis, while mRNA is destroyed. The duration of the formation of a protein molecule depends on the number of amino acids in it. It is believed that the addition of one amino acid lasts 0.5 seconds.
The synthesis process requires the expenditure of energy, the source of which is ATP, which is formed mainly in the mitochondria and in a small amount in the nucleus, and with increased cell activity also in the hyaloplasm. In the nucleus in the hyaloplasm, ATP is formed not on the basis of an oxidative process, as in mitochondria, but on the basis of glycolysis, that is, an anaerobic process. Thus, the synthesis is carried out due to the coordinated work of the nucleus, hyaloplasm, ribosomes, mitochondria and the granular cytoplasmic reticulum of the cell.
The secretory activity of the cell is also an example of the coordinated work of a number of cellular structures. Secretion is the production by a cell of special products that in a multicellular organism are most often used in the interests of the whole organism. So, saliva, bile, gastric juice and other secrets serve to process food into
Rice. 21. Scheme of one of the possible ways of secretion synthesis in the cell and its excretion:
1 - secret in the kernel; 2 - exit of the pro-secret from the kernel; 3 - accumulation of prosecret in the cistern of the cytoplasmic reticulum; 4 - separation of the tank with a secret from the cytoplasmic reticulum; 5 - lamellar complex; 6 - a drop of secret in the area of the lamellar complex; 7- mature secretion granule; 8-9 - successive stages of secretion; 10 - secret outside the cell; 11 - cell plasmalemma.
Digestive organs. Secrets can be formed either only by proteins (a number of hormones, enzymes), or consist of glycoproteins (mucus), ligu-proteins, glycolipoproteins, less often they are represented by lipids (fat of milk and sebaceous glands) t or inorganic substances (hydrochloric acid of the fundic glands).
In secretory cells, two ends can usually be distinguished: basal (facing the pericapillary space) and apical (facing the space where the secretion is secreted). In the arrangement of the components of the secretory cell, zoning is observed, and from the basal to the apical ends (poles), they form the following row: granular cytoplasmic reticulum, nucleus, lamellar complex, secretion granules (Fig. 21). The plasmalemma of the basal and apical poles often carries microvilli, as a result of which the surface for the entry of substances from the blood and lymph through the basal pole and the removal of the finished secret through the apical pole increases.
With the formation of a secret of a protein nature (pancreas), the process begins with the synthesis of proteins specific for the secret. Therefore, the nucleus of secretory cells is rich in chromatin, has a well-defined nucleolus, due to which all three types of RNA are formed that enter the cytoplasm and participate in protein synthesis. Sometimes, apparently, secretion synthesis begins in the nucleus and ends in the cytoplasm, but most often in the hyaloplasm and continues in the granular cytoplasmic reticulum. The tubules of the cytoplasmic reticulum play an important role in the accumulation of primary products and their transport. In this regard, there are many ribosomes in the secretory cells and the cytoplasmic reticulum is well developed. Sections of the cytoplasmic reticulum with the primary secret are torn off and directed to the lamellar complex, passing into its vacuoles. Here the formation of secretory granules occurs.
In this case, a lipoprotein membrane is formed around the secret, and the secret itself matures (loses water), becoming more concentrated. The finished secret in the form of granules or vacuoles leaves the lamellar complex and is released through the apical pole of the cells. Mitochondria provide energy for this entire process. Secrets of a non-protein nature are apparently synthesized in the cytoplasmic reticulum and in some cases even in mitochondria (lipid secrets). The secretion process is regulated by the nervous system. In addition to constructive proteins and secrets, as a result of metabolism in the cell, substances of a trophic nature (glycogen, fat, pigments, etc.) can be formed, energy is produced (radiant, thermal and electrical biocurrents).
The metabolism is completed with the release into the external environment of a number of substances that, as a rule, are not used by the cell and are often
Even harmful to her. The removal of substances from the cell is carried out, as well as the intake, on the basis of passive physical and chemical processes (diffusion, osmosis), and by active transfer. The morphological picture of excretion often has a character opposite to that of phagocytosis. The excreted substances are surrounded by a membrane.
The resulting vesicle approaches the cell membrane, comes into contact with it, then breaks through, and the contents of the vesicle are outside the cell.
Metabolism, as we have already said, also determines other vital manifestations of the cell, such as cell growth and differentiation, irritability, and the ability of cells to reproduce themselves.
Cell growth is an external manifestation of metabolism, expressed in an increase in cell size. Growth is possible only if, in the process of metabolism, assimilation prevails over dissimilation, and each cell grows only up to a certain limit.
Cell differentiation is a series of qualitative changes that proceed differently in different cells and are determined by the environment and the activity of DNA sections called genes. As a result, different-quality cells of various tissues arise, and in the future, the cells undergo age-related changes that are little studied. However, it is known that cells become depleted of water, protein particles become larger, which entails a decrease in the total surface of the dispersed phase of the colloid and, as a consequence, a decrease in the intensity of metabolism. Therefore, the vital potential of the cell decreases, oxidative, reduction and other reactions slow down, the direction of some processes changes, due to which various substances accumulate in the cell.
The irritability of a cell is its reaction to changes in the external environment, due to which temporary contradictions that arise between the cell and the environment are eliminated, and the living structure is adapted to the already changed external environment.
In the phenomenon of irritability, the following points can be distinguished:
1) the impact of an environmental agent (for example, mechanical, chemical, radiation, etc.)
2) the transition of the cell to an active, that is, excitable, state, which manifests itself in a change in biochemical and biophysical processes inside the cell, and the permeability of the cell and oxygen uptake can increase, the colloidal state of its cytoplasm changes, electric currents of action appear, etc.;
3) the response of the cell to the influence of the environment, and in different cells the response manifests itself in different ways. Thus, a local change in metabolism occurs in the connective tissue, a contraction occurs in the muscular tissue, a secret is secreted in the glandular tissues (saliva, bile, etc.), a nerve impulse occurs in the nerve cells. area, spreads throughout the tissue. In a nerve cell, excitation can spread not only to other elements of the same tissue (resulting in the formation of complex excitable systems - reflex arcs), but also to transfer to other tissues. Thanks to this, the regulatory role of the nervous system is carried out. The degree of complexity of these reactions depends on the height of the organization of the animal. Depending on the strength and nature of the irritating agent, the following three types of irritability are distinguished: normal, paranecrosis, and necrotic. If the strength of the stimulus does not go beyond the limits of the usual, inherent in the environment in which the cell or the organism as a whole lives, then the processes that arise in the cell eventually eliminate the contradiction with the external environment, and the cell returns to its normal state. In this case, no violation of the cell structure visible under a microscope occurs. If the strength of the stimulus is great or it affects the cell for a long time, then a change in intracellular processes leads to a significant disruption of the function, structure and chemistry of the cell. Inclusions appear in it, structures are formed in the form of threads, lumps, nets, etc. The reaction of the cytoplasm shifts towards acidity, a change in the structure and physico-chemical properties of the cell disrupts the normal functioning of the cell, puts it on the verge of life and death. This condition Nasonov and Aleksandrov called paranecrotic* It is reversible and can result in cell restoration, but it can also lead to cell death. Finally, if the agent acts with a very strong force, the processes inside the cell are so severely disturbed that recovery is impossible and the cell dies. After this, a number of structural changes occur, that is, the cell enters a state of necrosis or necrosis.
Motion. The nature of the movement inherent in the cell is very diverse. First of all, there is a continuous movement of the cytoplasm in the cell, which is obviously associated with the implementation of metabolic processes. Further, various cytoplasmic formations can move very actively in the cell, for example, cilia in the ciliated epithelium, mitochondria; makes motion and the nucleus. In other cases, the movement is expressed in a change in the length or volume of the cell, followed by its return to its original position. Such movement is observed in muscle cells, in muscle fibers and in pigment cells. Movement in space is also widespread. It can be carried out with the help of pseudopods, like an amoeba. This is how leukocytes and some cells of connective and other tissues move. Sperm have a special form of movement in space. Their translational movement occurs due to a combination of serpentine bends of the tail and rotation of the spermatozoa around the longitudinal axis. In relatively simply organized beings and in some cells of highly organized multicellular animals, movement in space is caused and directed by various agents of the external environment and is called taxis.
There are: chemotaxis, thigmotaxis and rheotaxis. Chemotaxis - movement towards or away from chemicals. Such taxis is detected by blood leukocytes, which move like amoeboids towards the bacteria that have entered the body, releasing certain substances, Tigmotaxis - movement towards or away from the touched solid body. For example, a light touch of food particles on an amoeba causes it to envelop them and then swallow them. Strong mechanical irritation can cause movement in the direction opposite to the irritating beginning. Rheotaxis - movement against the flow of a fluid. The ability for rheotaxis is possessed by sperm moving in the uterus against the current of mucus towards the egg cell.
The ability to self-reproduce is the most important property of living matter, without which life is impossible. Every living system is characterized by a chain of irreversible changes that end in death. If these systems did not give rise to new systems capable of starting the cycle over again, life would cease.
The function of self-reproduction of the cell is carried out by division, which is a consequence of the development of the cell. In the process of its life, due to the predominance of assimilation over dissimilation, the mass of cells increases, but the volume of the cell increases faster than its surface. Under these conditions, the intensity of metabolism decreases, deep physicochemical and morphological rearrangements of the cell occur, assimilation processes are gradually inhibited, which has been convincingly proven with the help of labeled atoms. As a result, the growth of the cell first stops, and then its further existence becomes impossible, and division occurs.
The transition to division is a qualitative leap, or a consequence of quantitative changes in assimilation and dissimilation, a mechanism for resolving contradictions between these processes. After cell division, as it were, they become rejuvenated, their life potential increases, since already due to a decrease in size, the proportion of the active surface increases, the metabolism in general and its assimilation phase in particular are intensified.
Thus, the individual life of a cell is made up of a period of interphase, characterized by an increased metabolism, and a period of division.
Interphase is divided with some degree of conventionality:
1) for the presynthetic period (Gj), when the intensity of assimilation processes gradually increases, but DNA reduplication has not yet begun;
2) synthetic (S), characterized by the height of synthesis, during which DNA doubling occurs, and
3) postsynthetic (G2), when DNA synthesis processes stop.
There are the following main types of division:
1) indirect division (mitosis, or karyokinesis);
2) meiosis, or reduction division, and
3) amitosis, or direct division.
Energy is necessary for all living cells - it is used for various biological and chemical reactions occurring in the cell. Some organisms use the energy of sunlight for biochemical processes - these are plants (Fig. 1), while others use the energy of chemical bonds in substances obtained in the process of nutrition - these are animal organisms. The extraction of energy is carried out by splitting and oxidizing these substances, in the process of breathing, this breathing is called biological oxidation, or cellular respiration.
Rice. 1. The energy of sunlight
Cellular respiration- this is a biochemical process in the cell, proceeding with the participation of enzymes, as a result of which water and carbon dioxide are released, energy is stored in the form of high-energy bonds of ATP molecules. If this process takes place in the presence of oxygen, then it is called aerobic, but if it occurs without oxygen, then it is called anaerobic.
Biological oxidation includes three main stages:
1. Preparatory.
2. Anoxic (glycolysis).
3. Complete decomposition of organic substances (in the presence of oxygen).
Substances taken with food are broken down into monomers. This stage begins in the gastrointestinal tract or in the lysosomes of the cell. Polysaccharides break down into monosaccharides, proteins into amino acids, fats into glycerol and fatty acids. The energy released at this stage is dissipated in the form of heat. It should be noted that cells use carbohydrates for energy processes, and monosaccharides are better, and the brain can use only a monosaccharide - glucose for its work (Fig. 2).
Rice. 2. Preparatory stage
Glucose is broken down by glycolysis into two three-carbon molecules of pyruvic acid. The further fate of pyruvic acid depends on the presence of oxygen in the cell. If oxygen is present in the cell, then pyruvic acid passes into the mitochondria for complete oxidation to carbon dioxide and water (aerobic respiration). If there is no oxygen, then in animal tissues pyruvic acid turns into lactic acid. This stage takes place in the cytoplasm of the cell.
glycolysis- this is a sequence of reactions, as a result of which one molecule of glucose is split into two molecules of pyruvic acid, while energy is released, which is enough to convert two ADP molecules into two ATP molecules (Fig. 3). 
Rice. 3. Anoxic stage
Oxygen is essential for the complete oxidation of glucose. At the third stage, pyruvic acid is completely oxidized in mitochondria to carbon dioxide and water, resulting in the formation of another 36 ATP molecules, since this stage occurs with the participation of oxygen, it is called oxygen, or aerobic (Fig. 4). 
Rice. 4. Complete breakdown of organic matter
In total, 38 ATP molecules are formed from one glucose molecule in three stages, taking into account the two ATP obtained in the process of glycolysis.
Thus, we have considered the energy processes occurring in cells, characterized the stages of biological oxidation.
The respiration that occurs in the cell with the release of energy is often compared with the combustion process. Both processes occur in the presence of oxygen, release of energy and oxidation products - carbon dioxide and water. But, unlike combustion, respiration is an ordered process of biochemical reactions occurring in the presence of enzymes. During respiration, carbon dioxide arises as the end product of biological oxidation, and during combustion, the formation of carbon dioxide occurs by direct combination of hydrogen with carbon. Also, during respiration, in addition to water and carbon dioxide, a certain amount of ATP molecules is formed, that is, respiration and combustion are fundamentally different processes (Fig. 5).
Rice. 5. Differences between breathing and combustion
Glycolysis is not only the main pathway for the metabolism of glucose, but also the main pathway for the metabolism of dietary fructose and galactose. Especially important in medicine is the ability of glycolysis to form ATP in the absence of oxygen. This makes it possible to maintain intensive work of the skeletal muscle in conditions of insufficient efficiency of aerobic oxidation. Tissues with increased glycolytic activity are able to remain active during periods of oxygen starvation. In the heart muscle, the possibilities for glycolysis are limited. It is difficult to tolerate impaired blood supply, which can lead to ischemia. Several diseases are known to be caused by insufficient activity of glycolysis enzymes, one of which is hemolytic anemia (in fast-growing cancer cells, glycolysis occurs at a rate exceeding the capacity of the citric acid cycle), which contributes to an increased synthesis of lactic acid in organs and tissues (Fig. 6). 
Rice. 6. Hemolytic anemia
Elevated levels of lactic acid in the body can be a symptom of cancer. This metabolic feature is sometimes used to treat some forms of tumors.
Microbes are able to obtain energy in the process of fermentation. Fermentation has been known to people since time immemorial, for example, in the manufacture of wine, lactic acid fermentation was known even earlier (Fig. 7). 
Rice. 7. Making wine and cheese
People consumed dairy products without suspecting that these processes are associated with the activity of microorganisms. The term "fermentation" was introduced by the Dutchman Van Helmont for processes that go with the release of gas. This was first proved by Louis Pasteur. Moreover, different microorganisms secrete different fermentation products. We will talk about alcoholic and lactic acid fermentation. Alcoholic fermentation- This is the process of oxidation of carbohydrates, as a result of which ethyl alcohol, carbon dioxide are formed and energy is released. Brewers and winemakers have used the ability of certain types of yeast to stimulate fermentation, which turns sugars into alcohol. Fermentation is carried out mainly by yeasts, but also by some bacteria and fungi (Fig. 8).
Rice. 8. Yeast, flour mushrooms, fermentation products - kvass and vinegar
In our country, Saccharomyces yeast is traditionally used, in America - bacteria from the genus Pseudomonas, in Mexico, bacteria "mobile sticks" are used, in Asia, mucor fungi are used. Our yeasts tend to ferment hexoses (six-carbon monosaccharides) such as glucose or fructose. The process of alcohol formation can be represented as follows: from one glucose molecule, two alcohol molecules, two carbon dioxide molecules are formed, and two ATP molecules are released.
C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2 + 2ATP
Compared to respiration, such a process is less energetically beneficial than aerobic processes, but allows you to maintain life in the absence of oxygen. At lactic acid fermentation one molecule of glucose forms two molecules of lactic acid, and two molecules of ATP are released, this can be described by the equation:
C 6 H 12 O 6 → 2C 3 H 6 O 3 + 2ATP
The process of formation of lactic acid is very close to the process of alcoholic fermentation, glucose, as in alcoholic fermentation, is broken down to pyruvic acid, then it passes not into alcohol, but into lactic acid. Lactic acid fermentation is widely used for the production of dairy products: cheese, cottage cheese, curdled milk, yoghurts (Fig. 9).
Rice. 9. Lactic acid bacteria and products of lactic acid fermentation
In the process of cheese formation, first lactic acid bacteria are involved, which produce lactic acid, then propionic acid bacteria convert lactic acid into propionic acid, due to this, cheeses have a rather specific sharp taste. Lactic acid bacteria are used in the preservation of fruits and vegetables, lactic acid is used in the confectionery industry and the manufacture of soft drinks.
Bibliography
1. Mamontov S.G., Zakharov V.B., Agafonova I.B., Sonin N.I. Biology. General patterns. - Bustard, 2009.
2. Ponomareva I.N., Kornilova O.A., Chernova N.M. Fundamentals of General Biology. Grade 9: A textbook for students in grade 9 educational institutions / Ed. prof. I.N. Ponomareva. - 2nd ed., revised. - M.: Ventana-Graf, 2005.
3. Pasechnik V.V., Kamensky A.A., Kriksunov E.A. Biology. An Introduction to General Biology and Ecology: A 9th Grade Textbook, 3rd ed., stereotype. - M.: Bustard, 2002.
1. Website "Biology and Medicine" ()
3. Internet site "Medical Encyclopedia" ()
Homework
1. What is biological oxidation and its stages?
2. What is glycolysis?
3. What are the similarities and differences between alcoholic and lactic acid fermentation?
- Types of nutrition of living organisms
- Photosynthesis
- energy exchange
1. Vitality of all organisms is possible only if they have energy. According to the method of obtaining energy, all cells and organisms are divided into two groups: autotrophs and heterotrophs.
Heterotrophs(Greek heteros - different, different and trophe - food, nutrition) are not capable of synthesizing organic compounds from inorganic ones themselves, they need to get them from the environment. Organic substances serve for them not only as food, but also as a source of energy. Heterotrophs include all animals, fungi, most bacteria, as well as chlorophyll-free land plants and algae.
Heterotrophic organisms are classified according to the way they obtain food. holozoic(animals) that capture solid particles, and osmotrophic(fungi, bacteria) that feed on dissolved substances.
Diverse heterotrophic organisms are capable of jointly decomposing all substances that are synthesized by autotrophs, as well as mineral substances synthesized as a result of human production activities. Heterotrophic organisms, together with autotrophs, constitute a single biological system on Earth, united by trophic relationships.
Autotrophs- organisms that feed (i.e., receive energy) from inorganic compounds, these are some bacteria and all green plants. Autotrophs are divided into chemotrophs and phototrophs.
Chemotrophs- organisms that use the energy released during redox reactions. Chemotrophs include nitrifying (nitrogen-fixing) bacteria, sulfuric, hydrogen (methane-forming), manganese, iron-forming and carbon monoxide-using bacteria.
Phototrophs- only green plants. Light is their source of energy.
2. Photosynthesis(Greek phos - genus. fall. photos - light and synthesis - connection) - the formation of organic substances by the cells of green plants, as well as some bacteria, with the participation of light energy, the process of converting light energy into chemical energy. Occurs with the help of pigments (chlorophyll and some others) in the thylakoids of chloroplasts and cell chromatophores. Photosynthesis is based on redox reactions, in which electrons are transferred from a donor-reductant (water, hydrogen, etc.) to an acceptor (Latin acceptor - receiver) - carbon dioxide, acetate with the formation of reduced compounds - carbohydrates and the release of oxygen, if water is oxidized.
Photosynthetic bacteria that use donors other than water do not emit oxygen.
Light reactions of photosynthesis(caused by light) flow in the grana of thylakoids of chloroplasts. Visible light quanta (photons) interact with chlorophyll molecules, transferring them to an excited state. An electron in the composition of chlorophyll absorbs a quantum of light of a certain length and, like steps, moves along the chain of electron carriers, losing energy, which serves to phosphorylate ADP into ATP. This is a very efficient process: 30 times more ATP is produced in chloroplasts than in the mitochondria of the same plants. This accumulates the energy necessary for the following - the dark reactions of photosynthesis. Substances act as electron carriers: cytochromes, plastoquinone, ferredoxin, flavoprotein, reductase, etc. Some of the excited electrons are used to reduce NADP + to NADPH. Under the action of sunlight in chloroplasts, water is split - photolysis, in this case, electrons are formed that compensate for their loss by chlorophyll; as a by-product, oxygen is released into the atmosphere of our planet. This is the oxygen that we breathe and which is necessary for all aerobic organisms.
The chloroplasts of higher plants, algae, and cyanobacteria contain two photosystems of different structure and composition. When light quanta are absorbed by pigments (a reaction center - a complex of chlorophyll with a protein that absorbs light with a wavelength of 680 nm - P680) of photosystem II, electrons are transferred from water to an intermediate acceptor and through a chain of carriers to the reaction center of photosystem I. And this photosystem is a reaction center will reveal the foam of the chlorophyll molecule in combination with a special protein-KOM, which absorbs light with a wavelength of 700 nm - P700. In the molecules of chlorophyll F1 there are "holes" - unfilled places of electrons that have passed into PLDPH. These "holes" are filled with electrons formed during the functioning of the FI. That is, photosystem II supplies electrons for photosystem I, which are spent in it for the reduction of NADP + and NADPH. Along the path of movement of photosystem II electrons excited by light to the final acceptor - chlorophyll of photosystem I, ADP is phosphorylated into energy-rich ATP. Thus, the energy of light is stored in ATP molecules and is further consumed for the synthesis of carbohydrates, proteins, nucleic acids and other vital processes of plants, and through them the vital activity of all organisms that feed on plants.
Dark reactions, or carbon fixation reactions, not associated with light, are carried out in the stroma of chloroplasts. The key place in them is occupied by the fixation of carbon dioxide and the conversion of carbon into carbohydrates. These reactions are cyclic in nature, since part of the intermediate carbohydrates undergoes a process of condensation and rearrangement to ribulose diphosphate, the primary CO 2 acceptor, which ensures the continuous operation of the cycle. This process was first described by the American biochemist Melvin Calvin.
The transformation of the inorganic compound CO 2 into organic compounds - carbohydrates, in the chemical bonds of which solar energy is stored, occurs with the help of a complex enzyme - ribulose-1,5-diphosphate carboxylase. It provides the addition of one CO 2 molecule to five-carbon ribulose-1,5-diphosphate, resulting in the formation of a six-carbon intermediate short-lived compound. This compound, due to hydrolysis, breaks down into two three-carbon molecules of phosphoglyceric acid, which is reduced using ATP and NADPH to three-carbon sugars (triose phosphates). They form the end product of photosynthesis - glucose.
Part of the triose phosphates, having gone through the processes of condensation and rearrangement, turning first into ribulose monophosphate, and then into ribulose diphosphate, is again included in the continuous cycle of creating glucose molecules. Glucose can be enzymatically polymerized into
starch and cellulose - the basic polysaccharide of plants.
A feature of the photosynthesis of some plants (sugarcane, corn, amaranth) is the initial conversion of carbon through four-carbon compounds. Such plants received the index C 4 -plants, and photosynthesis in them carbon metabolism. C 4 -plants attract the attention of researchers due to their high photosynthetic productivity.
Ways to increase the productivity of agricultural plants:
Sufficient mineral nutrition, which can ensure the best course of metabolic processes;
More complete illumination, which can be achieved with the help of certain plant sowing rates, taking into account the light consumption of photophilous and shade-tolerant;
The normal amount of carbon dioxide in the air (with an increase in its content, the process of plant respiration, which is associated with photosynthesis, is disrupted);
Soil moisture, corresponding to the needs of plants in moisture, depending on climatic and agrotechnical conditions.
The importance of photosynthesis in nature.
As a result of photosynthesis on Earth, 150 billion tons of organic matter are formed annually and approximately 200 billion tons of free oxygen are released. Photosynthesis not only provides and maintains the modern composition of the Earth's atmosphere, necessary for the life of its inhabitants, but also prevents an increase in the concentration of CO 2 in the atmosphere, preventing overheating of our planet (due to the so-called greenhouse effect). Oxygen released during photosynthesis is essential for organisms to breathe and protect them from harmful short-wave ultraviolet radiation.
Chemosynthesis(late Greek chemeta - chemistry and Greek synthesis - connection) - an autotrophic process of creating organic matter by bacteria that do not contain chlorophyll. Chemosynthesis is carried out due to the oxidation of inorganic compounds: hydrogen, hydrogen sulfide, ammonia, iron oxide (II), etc. The assimilation of CO 2 proceeds, as in photosynthesis (Calvin cycle), with the exception of methane-forming, homo-acetate bacteria. The energy obtained from oxidation is stored in bacteria in the form of ATP.
Chemosynthetic bacteria play an exceptionally important role in the biogeochemical cycles of chemical elements in the biosphere. The vital activity of nitrifying bacteria is one of the most important factors in soil fertility. Chemosynthetic bacteria oxidize compounds of iron, manganese, sulfur, etc.
Chemosynthesis was discovered by the Russian microbiologist Sergei Nikolaevich Vinogradsky (1856-1953) in 1887.
3. Energy exchange
Three stages of energy metabolism are carried out with the participation of special enzymes in various parts of cells and organisms.
The first stage is preparatory- proceeds (in animals in the digestive organs) under the action of enzymes that break down molecules with di- and polysaccharides, fats, proteins, nucleic acids into smaller molecules: glucose, glycerol and fatty acids, amino acids, nucleotides. This releases a small amount of energy that is dissipated in the form of heat.
The second stage is anoxic, or incomplete oxidation. It is also called anaerobic respiration (fermentation), or glycolysis. Enzymes of glycolysis are localized in the liquid part of the cytoplasm - hyaloplasm. Glucose undergoes splitting, each molene in which is stepwise split and oxidized with the participation of enzymes to two three-carbon molecules of pyruvic acid CH 3 - CO - COOH, where COOH is a carboxyl group characteristic of organic acids.
Nine enzymes are sequentially involved in this conversion of glucose. In the process of glycolysis, glucose molecules are oxidized, i.e., hydrogen atoms are lost. The hydrogen acceptor (and electron) in these reactions are nicotinamide nindinucleotide (NAD +) molecules, which are similar in string to NADP + and differ only in the absence of a phosphoric acid residue in the ribose molecule. When pyruvic acid is reduced by reduced NAD, the end product of glycolysis, lactic acid, is formed. Phosphoric acid and ATP are involved in the breakdown of glucose.
In summary, this process looks like this:
C 6 H 12 O 6 + 2H 3 P0 4 + 2ADP \u003d 2C 3 H 6 0 3 + 2ATP + 2H 2 0.
In yeast fungi, the glucose molecule, without the participation of oxygen, is converted into ethyl alcohol and carbon dioxide (alcoholic fermentation):
C 6 H 12 O 6 + 2H 3 P0 4 + 2ADP - 2C 2 H b 0H + 2C0 2 + 2ATP + 2H 2 O.
In some microorganisms, the breakdown of glucose without oxygen can result in the formation of acetic acid, acetone, etc. In all cases, the breakdown of one glucose molecule is accompanied by the formation of two ATP molecules, in macroergic bonds of which 40% of energy is stored, the rest is dissipated in the form of heat.
The third stage of energy metabolism(stage of oxygen splitting , or stage of aerobic respiration) is carried out in mitochondria. This stage is associated with the mitochondrial matrix and the inner membrane; enzymes are involved in it, which are an enzymatic ring "conveyor", called the Krebs cycle, named after the scientist who discovered it. This complex and long way of work of many enzymes is also called tricarboxylic acid cycle.
Once in the mitochondria, pyruvic acid (PVA) is oxidized and converted into an energy-rich substance - acetyl coenzyme A, or acetyl-CoA for short. In the Krebs cycle, acetyl-CoA molecules come from different energy sources. In the process of PVC oxidation, electron acceptors NAD + are reduced to NADH, and another type of acceptors is reduced - FAD to FADH 2 (FAD is a flavin adenine dinucleotide). The energy stored in these molecules is used to synthesize ATP, the universal biological energy accumulator. During the stage of aerobic respiration, electrons from NADH and FADH 2 move along a multistage chain of their transfer to the final electron acceptor, molecular oxygen. Several electron carriers are involved in the transfer: coenzyme Q, cytochromes and, most importantly, oxygen. When electrons move from stage to stage of the respiratory conveyor, energy is released, which is spent on ATP synthesis. Inside the mitochondria, H + cations combine with O 2 ~ anions to form water. In the Krebs cycle, CO 2 is formed, and in the electron transport chain - water. At the same time, one molecule of glucose, being completely oxidized with the access of oxygen to CO 2 and H 2 0, contributes to the formation of 38 ATP molecules. From the foregoing, it follows that the oxygen splitting of organic substances, or aerobic respiration, plays the main role in providing the cell with energy. With oxygen deficiency or its complete absence, oxygen-free, anaerobic, splitting of organic substances occurs; the energy of such a process is only enough to create two ATP molecules. Thanks to this, living beings can do without oxygen for a short time.
