All living organisms, except viruses, consist of cells. They provide all the processes necessary for the life of a plant or animal. The cell itself can be a separate organism. And how can such a complex structure live without energy? Of course not. So how does the supply of energy to cells take place? It is based on the processes that we will discuss below.

Providing cells with energy: how does it happen?

Few cells receive energy from the outside, they generate it themselves. possess a kind of "stations". And the source of energy in the cell is the mitochondria - the organoid that produces it. The process of cellular respiration takes place in it. Due to it, the cells are supplied with energy. However, they are present only in plants, animals and fungi. In bacterial cells, mitochondria are absent. Therefore, their supply of cells with energy occurs mainly due to fermentation processes, and not respiration.

Mitochondrion structure

This is a two-membrane organoid that appeared in a eukaryotic cell during evolution as a result of absorption of a smaller one.This can explain the fact that mitochondria have their own DNA and RNA, as well as mitochondrial ribosomes that produce proteins necessary for organelles.

The inner membrane has outgrowths called cristae, or ridges. The process of cellular respiration takes place on the cristae.

What is inside the two membranes is called the matrix. It contains proteins, enzymes necessary to accelerate chemical reactions, as well as RNA, DNA and ribosomes.

Cellular respiration is the basis of life

It takes place in three stages. Let's take a closer look at each of them.

The first stage is preparatory

During this stage, complex organic compounds are split into simpler ones. Thus, proteins break down to amino acids, fats to carboxylic acids and glycerol, nucleic acids to nucleotides, and carbohydrates to glucose.

Glycolysis

This is an oxygen-free stage. It consists in the fact that the substances obtained during the first stage are further degraded. The main sources of energy that the cell uses at this stage are glucose molecules. Each of them in the process of glycolysis breaks down to two molecules of pyruvate. This happens during ten successive chemical reactions. Due to the first five, glucose is phosphorylated and then split into two phosphotrioses. In the next five reactions, two molecules and two molecules of PVC (pyruvic acid) are formed. The energy of the cell is stored in the form of ATP.

The whole process of glycolysis can be simplified as follows:

2NAD + 2ADP + 2H 3 PO 4 + C 6 H 12 O 6 → 2H 2 O + 2NAD. H 2 + 2C 3 H 4 O 3 + 2ATF

Thus, using one glucose molecule, two ADP molecules and two phosphoric acid, the cell receives two ATP molecules (energy) and two pyruvic acid molecules, which it will use in the next step.

The third stage is oxidation

This stage occurs only in the presence of oxygen. The chemical reactions of this stage take place in the mitochondria. This is the main part during which the most energy is released. At this stage, reacting with oxygen, it decomposes to water and carbon dioxide. In addition, 36 ATP molecules are formed. So, we can conclude that the main sources of energy in the cell are glucose and pyruvic acid.

Summing up all the chemical reactions and omitting the details, we can express the entire process of cellular respiration in one simplified equation:

6O 2 + C 6 H 12 O 6 + 38ADP + 38H 3 PO 4 → 6CO 2 + 6H2O + 38ATF.

Thus, during respiration, from one glucose molecule, six oxygen molecules, thirty-eight ADP molecules and the same amount of phosphoric acid, the cell receives 38 ATP molecules, in the form of which energy is stored.

Variety of mitochondrial enzymes

The cell receives energy for vital activity due to respiration - oxidation of glucose, and then pyruvic acid. All these chemical reactions could not take place without enzymes - biological catalysts. Let's look at those of them that are found in mitochondria - organelles responsible for cellular respiration. All of them are called oxidoreductases, because they are needed to ensure the occurrence of redox reactions.

All oxidoreductases can be divided into two groups:

• oxidase;
• dehydrogenase;

Dehydrogenases, in turn, are divided into aerobic and anaerobic. Aerobic ones contain the coenzyme riboflavin, which the body receives from vitamin B2. Aerobic dehydrogenases contain NAD and NADP molecules as coenzymes.

Oxidases are more diverse. First of all, they are divided into two groups:

• those that contain copper;
• those that contain iron.

The former include polyphenol oxidases, ascorbate oxidase, the latter - catalase, peroxidase, cytochromes. The latter, in turn, are divided into four groups:

• cytochromes a;
• cytochromes b;
• cytochromes c;
• cytochromes d.

Cytochromes a contain iron-formylporphyrin, cytochromes b - iron protoporphyrin, c - substituted iron mesoporphyrin, d - iron dihydroporphyrin.

Are there other ways to get energy?

Despite the fact that most cells receive it as a result of cellular respiration, there are also anaerobic bacteria that do not need oxygen to exist. They generate the necessary energy through fermentation. This is a process during which, with the help of enzymes, carbohydrates are broken down without the participation of oxygen, as a result of which the cell receives energy. There are several types of fermentation, depending on the end product of chemical reactions. It can be lactic acid, alcoholic, butyric acid, acetone-butane, citric acid.

For example, consider It can be expressed with the following equation:

S 6 N 12 O 6 → C 2 H 5 OH + 2CO 2

That is, the bacterium splits one molecule of glucose into one molecule of ethyl alcohol and two molecules of carbon (IV) oxide.

Metabolism (metabolism) is a collection of all chemical reactions that take place in the body. All these reactions are divided into 2 groups.

1. Plastic exchange(assimilation, anabolism, biosynthesis) - this is when from simple substances with the expenditure of energy formed (synthesized) more complex. Example:

• During photosynthesis, glucose is synthesized from carbon dioxide and water.

2. Energy exchange(dissimilation, catabolism, respiration) - this is when complex substances decay (oxidize) to simpler ones, and at the same time energy is released necessary for life. Example:

• In the mitochondria, glucose, amino acids and fatty acids are oxidized by oxygen to carbon dioxide and water, thus forming energy (cellular respiration)

The relationship of plastic and energy metabolism

• Plastic metabolism provides the cell with complex organic substances (proteins, fats, carbohydrates, nucleic acids), including enzyme proteins for energy metabolism.
• Energy metabolism provides the cell with energy. When performing work (mental, muscular, etc.), energy metabolism increases.

ATF- a universal energetic substance of a cell (a universal accumulator of energy). Formed in the process of energy metabolism (oxidation of organic substances).

• During energy metabolism, all substances disintegrate, and ATP is synthesized. In this case, the energy of chemical bonds of disintegrated complex substances is converted into the energy of ATP, energy is stored in ATP.
• During plastic exchange, all substances are synthesized, and ATP is decomposed. Wherein ATP energy is consumed(the energy of ATP is converted into the energy of chemical bonds of complex substances, is stored in these substances).

Choose the one that is most correct. In the process of plastic exchange
1) more complex carbohydrates are synthesized from less complex
2) fats are converted to glycerin and fatty acids
3) proteins are oxidized to form carbon dioxide, water, nitrogen-containing substances
4) energy is released and ATP is synthesized

Answer

Choose three options. How is plastic metabolism different from energy metabolism?
1) energy is stored in ATP molecules
2) the energy stored in ATP molecules is consumed
3) organic substances are synthesized
4) decomposition of organic substances occurs
5) end products of exchange - carbon dioxide and water
6) proteins are formed as a result of metabolic reactions

Answer

Choose the one that is most correct. In the process of plastic metabolism, molecules are synthesized in cells
1) proteins
2) water
3) ATP
4) inorganic substances

Answer

Choose the one that is most correct. What is the relationship between plastic and energy metabolism
1) plastic metabolism supplies organic substances for energy
2) energy metabolism supplies oxygen for plastic
3) plastic metabolism supplies minerals for energy
4) plastic metabolism supplies ATP molecules for energy

Answer

Choose the one that is most correct. In the process of energy metabolism, in contrast to plastic, occurs
1) expenditure of energy contained in ATP molecules
2) storage of energy in the high-energy bonds of ATP molecules
3) providing cells with proteins and lipids
4) providing cells with carbohydrates and nucleic acids

Answer

1. Establish a correspondence between the characteristics of the exchange and its type: 1) plastic, 2) energy. Write down the numbers 1 and 2 in the correct order.
A) oxidation of organic substances
B) the formation of polymers from monomers
C) cleavage of ATP
D) storage of energy in the cell
E) DNA replication
E) oxidative phosphorylation

Answer

2. Establish a correspondence between the characteristics of metabolism in the cell and its type: 1) energetic, 2) plastic. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) anoxic breakdown of glucose occurs
B) occurs on ribosomes, in chloroplasts
C) end products of exchange - carbon dioxide and water
D) organic substances are synthesized
E) the energy contained in the ATP molecules is used
E) energy is released and stored in ATP molecules

Answer

3. Establish a correspondence between the signs of human metabolism and its types: 1) plastic metabolism, 2) energy metabolism. Write down the numbers 1 and 2 in the correct order.
A) substances are oxidized
B) substances are synthesized
C) energy is stored in ATP molecules
D) energy is consumed
E) ribosomes are involved in the process
E) mitochondria are involved in the process

Answer

4. Establish a correspondence between the characteristics of metabolism and its type: 1) energy, 2) plastic. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) DNA replication
B) protein biosynthesis
C) oxidation of organic substances
D) transcription
E) synthesis of ATP
E) chemosynthesis

Answer

5. Establish a correspondence between the characteristics and types of exchange: 1) plastic, 2) energy. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) energy is stored in ATP molecules
B) biopolymers are synthesized
C) carbon dioxide and water are formed
D) oxidative phosphorylation occurs
D) DNA replication occurs

Answer

Select three processes related to energy metabolism.
1) the release of oxygen into the atmosphere
2) the formation of carbon dioxide, water, urea
3) oxidative phosphorylation
4) glucose synthesis
5) glycolysis
6) photolysis of water

Answer

Choose the one that is most correct. The energy required for muscle contraction is released when
1) the breakdown of organic substances in the digestive organs
2) muscle irritation with nerve impulses
3) oxidation of organic matter in muscles
4) ATP synthesis

Answer

Choose the one that is most correct. As a result of what process lipids are synthesized in the cell?
1) dissimilation
2) biological oxidation
3) plastic exchange
4) glycolysis

Answer

Choose the one that is most correct. The value of plastic metabolism - supplying the body
1) mineral salts
2) oxygen
3) biopolymers
4) energy

Answer

Choose the one that is most correct. Oxidation of organic substances in the human body occurs in
1) pulmonary vesicles when breathing
2) body cells in the process of plastic metabolism
3) the process of digesting food in the digestive tract
4) body cells in the process of energy metabolism

Answer

Choose the one that is most correct. What metabolic reactions in the cell are accompanied by energy expenditures?
1) the preparatory stage of energy metabolism
2) lactic acid fermentation
3) oxidation of organic substances
4) plastic exchange

Answer

1. Establish a correspondence between the processes and constituent parts of metabolism: 1) anabolism (assimilation), 2) catabolism (dissimilation). Write down the numbers 1 and 2 in the correct order.
A) fermentation
B) glycolysis
B) breathing
D) protein synthesis
E) photosynthesis
E) chemosynthesis

Answer

2. Establish a correspondence between the characteristics and metabolic processes: 1) assimilation (anabolism), 2) dissimilation (catabolism). Write down the numbers 1 and 2 in the order corresponding to the letters.
A) synthesis of organic substances of the body
B) includes a preparatory stage, glycolysis and oxidative phosphorylation
C) the released energy is stored in ATP
D) water and carbon dioxide are formed
D) requires energy costs
E) occurs in chloroplasts and ribosomes

Answer

Choose two correct answers out of five and write down the numbers under which they are indicated. Metabolism is one of the main properties of living systems, it is characterized by what happens
1) selective response to external environmental influences
2) change in the intensity of physiological processes and functions with different periods of oscillation
3) transmission from generation to generation of signs and properties
4) absorption of essential substances and excretion of waste products
5) maintaining a relatively constant physical and chemical composition of the internal environment

Answer

1. All but two of the following terms are used to describe plastic exchange. Identify two terms "falling out" from the general list, and write down the numbers under which they are indicated.
1) replication
2) duplication
3) broadcast
4) translocation
5) transcription

Answer

2. All of the concepts listed below, except for two, are used to describe the plastic metabolism in the cell. Define two concepts that "fall out" from the general list, and write down the numbers under which they are indicated.
1) assimilation
2) dissimilation
3) glycolysis
4) transcription
5) broadcast

Answer

3. The following terms, other than two, are used to characterize plastic exchange. Identify two terms that fall out of the general list, and write down the numbers under which they are indicated.
1) splitting
2) oxidation
3) replication
4) transcription
5) chemosynthesis

Answer

Choose the one that is most correct. The nitrogenous base adenine, ribose and three phosphoric acid residues are part of
1) DNA
2) RNA
3) ATP
4) squirrel

Answer

All the signs below, except two, can be used to characterize the energy metabolism in the cell. Identify two signs that "fall out" from the general list, and write in the answer the numbers under which they are indicated.
1) comes with energy absorption
2) ends in mitochondria
3) ends in ribosomes
4) is accompanied by the synthesis of ATP molecules
5) ends with the formation of carbon dioxide

Answer

Find three errors in the above text. Indicate the numbers of the proposals in which they are made.(1) Metabolism, or metabolism, is a set of reactions of synthesis and decay of substances of a cell and an organism, associated with the release or absorption of energy. (2) The set of reactions for the synthesis of high molecular weight organic compounds from low molecular weight compounds is referred to as plastic exchange. (3) ATP molecules are synthesized in reactions of plastic exchange. (4) Photosynthesis is referred to as energy metabolism. (5) As a result of chemosynthesis, organic substances are synthesized from inorganic ones due to the energy of the Sun.

Answer

© D.V. Pozdnyakov, 2009-2019

The existence of any living organism is associated with a continuous exchange of material, energy and information with the environment. The energy entering the system is spent on the synthesis of bioenergetic compounds to maintain chemical, asthmatic and electrical potentials, as well as their gradients. In the process of life, there is a continuous transformation of some types of energy into others. It is necessary to use thermodynamics as a science that studies the most general laws governing the transformation of various types of energy.

Thermodynamic system is called a part of space with material content, limited by a certain shell. The state of the system is characterized by parameters.

Extensive parameters depend on the total content of the substance (mass or volume of the system).

Intensive parameters do not depend on the amount of substance in the system and tends to equalize (temperature, pressure).

There are 3 types of thermodynamic systems: isolated, closed and open.

Isolated cannot exchange energy or matter with the environment. Over time, such a system comes to an equilibrium state in which all parameters are of the same value. This state corresponds to the smallest value of thermodynamic potentials and the maximum value of entropy.

Closed system can exchange substance and information with the environment.

In an open system there is an exchange, there is an exchange of matter, energy and information with the environment. She may be stationary. Stationary is called the state in which the system parameters

can take different values ​​at different points in the system, which do not change over time. Changes to any parameter lead to a change in the state of the system. The transition from one state to another is a process. The process is called reversible if the system returns to its original state through the same states as in the forward direction. The process is called necessary. flowing in only one direction. Thermodynamic potentials are a characteristic of the state of the system. The internal energy is equal to the sum of all types of energy of the particles, of which the system consists, with the exception of the kinetic and potential energy of the system as a whole. Internal energy is a function of state and is determined by the parameters of the system.

Consider the interaction of the system with the environment. Energy exchange can occur due to the amount of heat and the improvement of systemic work. Quantity of heat - heat exchange.

The process of changing energy depends on the type of processes, on the way of doing work or transferring heat. There are the following ways to get work done:

1. Mechanical work when moving bodies.

2. Mechanical work during gas expansion.

3. Work on the transfer of electric charge.

4. Work with chemical reactions.

In summary:

If several forces act on the system, then according to the 1st law of thermodynamics:

Work is associated with the transformation of various types of energy. Several types of energy are subdivided according to their ability to transform them into other types:

1. A - maximum effective energy. It includes: gravitational, light, nuclear.

2. B- chemical energy can be converted into heat and electrical energy.

3. C - thermal energy. Degradation of higher forms of energy into lower ones, the main evolutionary property of isolated systems.

Thermal energy - This is a special type of energy of lower quality, which cannot be transferred without loss to other types of energy, because thermal energy is associated with the chaotic movement of molecules. Living organisms are not a source of new energy. Oxidation of substances entering a living organism leads to the release in it of an equivalent circulation of energy associated with a chemical form or some other type of energy. An important characteristic of the system is its thermodynamic potential. There are 4 potentials:

The state functions, the change of which makes it possible to determine the performance of useful work and the amount of heat entering the system during heat exchange, according to the sign and magnitude of the potential, can be monitored in the direction of the process, when equilibrium is reached, the thermodynamic potential tends to the smallest value.

1)
2)

3)

The enthalpy change takes into account the thermal effect of a chemical reaction.

4) Gibbs thermodynamic potential.

That. change in potentials characterizes the work of all types of forces of the derived system and the amount of heat which the system exchanges with the environment. There are 4 ways of heat transfer:

1. Thermal conductivity associated with the transfer of heat through body tissues associated with Fourier's law:

2. Convection, the amount of heat that is carried by streams of different density and temperature. ...

3. Radiation, arises at the boundary of the system in the form of electromagnetic waves, the Stefan-Boltzmann law:

Ti - own temperature

Tc - medium temperature

4. Evaporation is associated with the transformation of a substance from a liquid to a gaseous state.

Taking into account all types of heat transfer, the heat balance equation can be written:

Heat transfer processes can both increase and decrease the heat of energy, with the exception of the evaporation energy, which always reduces the amount of heat inside the system. Since the body is a thermostatic system, it does not depend on external conditions to maintain a constant temperature inside the body; the body has numerous regulatory systems.

Chemical regulation occurs due to changes in oxidative processes inside the body. However, a change in the intensity of metabolism leads to serious disruption of the body's vital functions.

Physical thermoregulation allows you to change the intensity of thermal conductivity, convection and evaporation. Thermoregulation of internal organs, in which heat is mainly released, is improved with the help of blood flow, which has a high thermal conductivity. The intensity of the heat exchange process is regulated by strengthening or weakening the outflow of blood and is associated with the expansion or narrowing of blood vessels and is a response to changes in external conditions. If the temperature of the environment is higher than the body temperature, then additional heat regulation is achieved due to increased evaporation from the body surface. In addition to natural thermoregulation, artificial thermoregulation associated with isolating the body from adverse environmental conditions is of great importance. The heat balance can be checked experimentally, to determine the energy excreted by the body and the energy of nutrients entering the body. The energy of release from the body is the equivalent of one entering. That. all life processes correspond to the 1st law of thermodynamics.

The second law of thermodynamics as applied to biosystems:

The second law of thermodynamics indicates a qualitative difference in the forms of energy. Heat energy is generated in the body, it is a certain form of bound energy, i.e. in the process of life, it cannot be completely transformed into other species. The concept of entropy is used to describe bound energy.

Entropy is a function of state and is determined up to an arbitrary constant. For isolated systems, entropy does not decrease, i.e. when irreversible processes occur inside the system, the entropy increases, and when it is reversible, it does not change. They talk about the store of energy in the system, the most important thing is to know what kind of work it can do on external bodies, or inside the system itself. For this, free energy or Gibbs energy is used. For biosystems, the processes take place at a constant temperature and little changing density and volume. That. for normal conditions, a part of the internal energy of the system is freely converted, which is the same in the system of both free energy and Gibbs energy. That. to assess the capabilities of a living organism, it is necessary to take into account changes in free energy or the Gibbs potential. There are methods for calculating the change in the Gibbs potential for chemical reactions.

However, for biological systems, the law of entropy increase is not observed, which caused doubts about the possibility of applying the 2nd law of thermodynamics to animal systems. According to the formulation of this law, entropy revival determines the direction of most natural processes in nature. However, the law of entropy rebirth is valid only in an isolated system and cannot be applied to a living organism on the grounds that it is an open system. For an isolated system in a state of equilibrium, the entropy is maximal, and all thermodynamic potentials, including the self-energy and Gibbs energy, are minimal. In an open system, in a stationary state, the change in entropy may be negative, and the value of F or G may not change at all.

For isolated systems :

For open systems:

The second law of thermodynamics for open systems was first formulated by Prigogine.

The change in the entropy of open systems can be represented as two parts.

The first term determines the change in entropy due to external processes. The second term determines the change in entropy due to the processes occurring within the system.

This is due to the irreversibility of the processes of the breakdown of nutrients, the alignment of gradients, which is always accompanied by an increase in entropy. The Gibbs potential can be divided similarly to entropy.

Internal processes are accompanied by the consumption and decrease of the Gibbs potential, which, due to exchange with the environment, can both increase and decrease. In the general case, the sign and magnitude of the change in entropy change at different time intervals; therefore, it is convenient to consider the rate of change in entropy in an open system.

To maintain vital activity, a continuous supply of free energy from the environment to the body is necessary to compensate for the loss of free energy due to internal processes. The decrease in entropy in the animal system during the consumption of food and solar energy simultaneously leads to an increase in the free energy of the system. Those. the influx of negative energy is not associated with the ordering of living structures. Degradation of nutrients leads to the release of free energy needed by the body. The flow of negative entropy is necessary to compensate for the increase in entropy and the loss of free energy that occurs inside the cell as a result of spontaneous life processes. That. an open system is a process of circulation and transformation of free energy. If an equilibrium with respect to temperature is achieved within an open system, then the processes of exchange with the environment proceed in equilibrium. The steady state of an open system is a steady state. The thermodynamic conditions for the emergence of a stationary state is the equality between the change in entropy inside the body and the flow of entropy into the environment. Those. for an open system, the stationary state condition is:

The constancy of entropy does not mean thermodynamic equilibrium with the environment. The equilibrium of the organism with the environment means biological death. For an open system, the constancy of entropy establishes a stationary state of the system and characterizes not the absence of reversible processes, as in the case of equilibrium in an isolated environment, but interaction with the environment in the most optimal form. That. The 2nd law of thermodynamics for open systems helps to indicate the advisability of a stationary state of the system. This principle was first formulated by Prigogine in the form of a theorem:

In a stationary state, the production of entropy within the system is constant and the lowest of all possible rates.

The theorem indicates that the steady state provides the least free energy loss. In this state, the body functions most efficiently.

Source: Olympic Sports Nutrition Center

Energy cannot arise from anywhere or disappear into nowhere, it can only transform from one type to another.

All energy on Earth comes from the Sun. Plants are able to convert solar energy into chemical energy (photosynthesis).

People cannot directly use the energy of the sun, but we can get energy from plants. We eat either the plants themselves or the flesh of animals that ate the plants. A person gets all his energy from food and drink.

Food sources of energy

A person receives all the energy necessary for life along with food. The unit of measure for energy is calorie. One calorie is the amount of heat required to heat 1 kg of water by 1 ° C. Most of our energy comes from the following nutrients:

Carbohydrates - 4kcal (17kJ) per 1g

Proteins (protein) - 4 kcal (17 kJ) per 1 g

Fat - 9kcal (37kJ) per 1g

Carbohydrates (sugars and starch) are the most important source of energy, most of them are found in bread, rice and pasta. Meat, fish, and eggs are good sources of protein. Butter, vegetable oil, and margarine are almost entirely composed of fatty acids. Fiber foods, as well as alcohol, also provide the body with energy, but the level of their consumption varies greatly from person to person.

Vitamins and minerals by themselves do not give the body energy, however, they take part in the most important processes of energy exchange in the body.

The energy value of different foods is very different. Healthy people achieve a balanced diet by consuming a wide variety of foods. Obviously, the more active a person is, the more he needs food, or the more energy-intensive it should be.

The most important source of energy for humans is carbohydrates. A balanced diet provides the body different kinds carbohydrates, but most of the energy should come from starch. V last years Much attention has been paid to the study of the relationship between the components of human nutrition and various diseases. Researchers agree that people need to reduce their intake of fatty foods in favor of carbohydrates.

How do we get energy from food?

After food is swallowed, it stays in the stomach for a while. There, under the influence of digestive juices, its digestion begins. This process continues in the small intestine, as a result of which food components break down into smaller units, and their absorption through the intestinal walls into the blood becomes possible. The body can then use the nutrients to produce energy, which is produced and stored as adenosine triphosphate (ATP).

ATP molecule made of adenosine and three phosphate groups connected in a row. Energy reserves are "concentrated" in chemical bonds between phosphate groups. To release this potential energy, one phosphate group must detach, i.e. ATP breaks down to ADP (adenosine diphosphate) with the release of energy.

Adenosine triphosphate (abbreviated ATP, English ATP) is a nucleotide that plays an extremely important role in the metabolism of energy and substances in organisms; First of all, the compound is known as a universal source of energy for all biochemical processes occurring in living systems. ATP is the main carrier of energy in the cell.

Each cell contains a very limited amount of ATP, which is usually consumed in a matter of seconds. The reduction of ADP to ATP requires energy, which is obtained during the oxidation of carbohydrates, protein and fatty acids in cells.

Energy reserves in the body.

After the nutrients are absorbed in the body, some of them are stored as reserve fuel in the form of glycogen or fat.

Glycogen also belongs to the class of carbohydrates. Its reserves in the body are limited and are stored in the liver and muscle tissue. During exercise, glycogen breaks down to glucose, and together with the fat and glucose circulating in the blood, it provides energy to working muscles. The proportion of nutrient consumed depends on the type and duration of exercise.

Glycogen is made up of glucose molecules linked in long chains. If the reserves of glycogen in the body are normal, then the excess carbohydrates entering the body will be converted to fat.

Usually protein and amino acids are not used in the body as energy sources. However, with a deficiency of nutrients against the background of increased energy consumption, amino acids contained in muscle tissue can also be used for energy. Protein from food can serve as a source of energy and turn into fat if the needs for it, as a building material, are fully satisfied.

How is energy spent during exercise?

Start training

At the very beginning of a workout, or when energy costs rise sharply (sprint), the energy requirement is greater than the level at which ATP is synthesized through the oxidation of carbohydrates. Initially, carbohydrates are "burned" anaerobically (without oxygen), this process is accompanied by the release of lactic acid (lactate). As a result, a certain amount of ATP is released - less than during an aerobic reaction (with the participation of oxygen), but faster.

Another "fast" source of energy for the synthesis of ATP is creatine phosphate. Small amounts of this substance are found in muscle tissue. The breakdown of creatine phosphate releases the energy needed to restore ADP to ATP. This process proceeds very quickly, and the reserves of creatine phosphate in the body are only enough for 10-15 seconds of "explosive" work, i.e. Creatine phosphate is a kind of buffer that covers short-term ATP deficiency.

Initial training period

At this time, aerobic metabolism of carbohydrates begins to work in the body, the use of creatine phosphate and the formation of lactate (lactic acid) cease. Fatty acid stores are mobilized and made available as a source of energy for working muscles, while the level of recovery of ADP to ATP is increased due to fat oxidation.

Main training period

Between the fifth and fifteenth minutes after the start of training in the body, the increased need for ATP stabilizes. During a long, relatively even intensity training, ATP synthesis is maintained by the oxidation of carbohydrates (glycogen and glucose) and fatty acids. The reserves of creatine phosphate are gradually restored at this time.

Creatine is an amino acid that is synthesized in the liver from arginine and glycine. It is creatine that allows athletes to withstand the highest loads with greater ease. Thanks to its action, the release of lactic acid in human muscles is delayed, which causes numerous muscle pains. On the other hand, creatine allows for strong physical activity due to the release of a large amount of energy in the body.

With an increase in load (for example, when running uphill), ATP consumption increases, and if this increase is significant, the body again switches to anaerobic oxidation of carbohydrates with the formation of lactate and the use of creatine phosphate. If the body does not have time to restore the ATP level, a state of fatigue can quickly set in.

What energy sources are used during training?

Carbohydrates are the most important and most scarce source of energy for working muscles. They are essential for any kind of physical activity. In the human body, carbohydrates are stored in small amounts as glycogen in the liver and muscles. During exercise, glycogen is consumed and, together with fatty acids and glucose circulating in the blood, is used as a source of muscle energy. The ratio of the different energy sources used depends on the type and duration of exercise.

Although fat contains more energy, its utilization is slower and ATP synthesis through fatty acid oxidation is supported by the use of carbohydrates and creatine phosphate. When carbohydrate stores are depleted, the body becomes unable to withstand high loads. Thus, carbohydrates are a source of energy, limiting the level of exercise during training.

Factors limiting the body's energy reserves during exercise

1. Sources of energy used in various types of physical activity

Low intensity (jogging)

The required level of ATP reduction from ADP is relatively low and is achieved by the oxidation of fats, glucose and glycogen. When glycogen stores are depleted, the role of fats as a source of energy increases. Since fatty acids are oxidized rather slowly in order to replenish the expended energy, the ability to continue such a workout for a long time depends on the amount of glycogen in the body.

Medium intensity (fast running)

When physical activity reaches its maximum level for the continuation of aerobic oxidation processes, there is a need for a rapid replenishment of ATP stores. Carbohydrates become the main fuel for the body. However, the required level of ATP cannot be maintained only by the oxidation of carbohydrates, therefore, fat oxidation and the formation of lactate occur in parallel.

Maximum intensity (sprint)

ATP synthesis is supported mainly by the use of creatine phosphate and the formation of lactate, since the metabolism of carbohydrate and fat oxidation cannot be maintained at such a high rate.

2. Duration of training

The type of energy source depends on the duration of the workout. First, energy is released through the use of creatine phosphate. Then the body switches to the predominant use of glycogen, which provides energy for about 50-60% of ATP synthesis. The rest of the energy for the synthesis of ATP is obtained by the body through the oxidation of free fatty acids and glucose. When glycogen stores are depleted, fats become the main source of energy, while glucose is used more from carbohydrates.

3. Type of training

In those sports where periods of relatively low loads are replaced by sharp increases in activity (football, hockey, basketball), there is an alternation of the use of creatine phosphate (during peak loads) and glycogen as the main sources of energy for the synthesis of ATP. During the "quiet" phase, the body replenishes the reserves of creatine phosphate.

4. Fitness of the body

The more trained a person, the higher the body's ability to oxidative metabolism (less glycogen is converted into lactose) and the more economically energy reserves are spent. That is, a trained person performs an exercise with less energy expenditure than an untrained person.

5. Diet

The higher the level of glycogen in the body before starting a workout, the later the fatigue will come. To increase glycogen stores, you need to increase your intake of carbohydrate-rich foods. Sports nutritionists recommend diets that contain up to 70% of your calories from carbohydrates.

Pasta (pasta)

Cereals

Roots

Can of beans 45

Large portion of rice 60

Large serving of jacket potatoes 45

Two pieces of white bread 30

Large spaghetti 90

Introduce more carbohydrates into your meal plan to maintain the body's energy reserves;

Eat 75-100 g of carbohydrates 1-4 hours before training;

During the first half hour of workout, when the muscle's ability to recover is at its maximum, eat 50-100 carbohydrates;

Carbohydrate intake should be continued after exercise to replenish glycogen stores as soon as possible.

Biology(from the Greek words bios - life, logos - teaching) is a science that studies living organisms and the phenomena of living nature.

The subject of the study of biology is the variety of living organisms that inhabit the Earth.

Properties of living nature. All living organisms have a number of common features and properties that distinguish them from the bodies of inanimate nature. These are structural features, metabolism, movement, growth, reproduction, irritability, self-regulation. Let us dwell on each of the listed properties of living matter.

Highly ordered structure. Living organisms are composed of chemicals that have more high level organization than substances of inanimate nature. All organisms have a certain structural plan - cellular or non-cellular (viruses).

Metabolism and energy- this is a set of processes of respiration, nutrition, excretion, through which the body receives from the external environment the substances and energy it needs, transforms and accumulates them in its body and releases waste products into the environment.

Irritability- This is the body's response to changes in the environment, helping it to adapt and survive in changing conditions. When a needle is pricked, a person withdraws his hand, and the hydra shrinks into a lump. Plants turn towards the light, and the amoeba moves away from the crystal of table salt.

Growth and development. Living organisms grow, increase in size, develop, change due to the supply of nutrients.

Reproduction- the ability of a living to reproduce itself. Reproduction is associated with the transmission of hereditary information and is the most characteristic feature of living things. The life of any organism is limited, but as a result of reproduction, living matter is "immortal".

Traffic. Organisms are capable of more or less active movement. This is one of the clearest signs of the living. Movement takes place both inside the body and at the level of the cell.

Self-regulation. One of the most characteristic properties of a living thing is the constancy of the internal environment of the organism under changing external conditions. Body temperature, pressure, gas saturation, concentration of substances, etc. are regulated. The phenomenon of self-regulation is carried out not only at the level of the whole organism, but also at the level of the cell. In addition, due to the activity of living organisms, self-regulation is inherent in the biosphere as a whole. Self-regulation is associated with such properties of living things as heredity and variability.

Heredity- This is the ability to transmit the characteristics and properties of an organism from generation to generation in the process of reproduction.

Variability Is the ability of an organism to change its characteristics when interacting with the environment.

As a result of heredity and variability, living organisms adapt, adapt to external conditions, which allows them to survive and leave offspring.

§ 44. The structure of the cell

Most living organisms have a cellular structure. A cell is a structural and functional unit of living things. It is characterized by all the signs and functions of living organisms: metabolism and energy, growth, reproduction, self-regulation. Cells are different in shape, size, function, type of metabolism (Fig. 47).

Rice. 47. Variety of cells: 1 - green euglena; 2 - bacteria; 3 - plant cell of leaf pulp; 4 - epithelial cell; 5 - nerve cell

Cell sizes vary from 3-10 to 100 microns (1 micron = 0.001 m). Cells less than 1–3 µm in size are less common. There are also giant cells, the size of which reaches several centimeters. Cells are also very diverse in shape: spherical, cylindrical, oval, fusiform, stellate, etc. However, all cells have a lot in common. They have the same chemical composition and general structural plan.

The chemical composition of the cell. Of all the known chemical elements, about 20 are found in living organisms, and 4 of them: oxygen, carbon, hydrogen and nitrogen - account for up to 95%. These elements are called nutrient elements. Of the inorganic substances that make up living organisms, water is of the greatest importance. Its content in the cell ranges from 60 to 98%. In addition to water, the cell also contains minerals, mainly in the form of ions. These are compounds of iron, iodine, chlorine, phosphorus, calcium, sodium, potassium, etc.

In addition to inorganic substances, organic substances are also present in the cell: proteins, lipids (fats), carbohydrates (sugars), nucleic acids (DNA, RNA). They make up the bulk of the cell. The most important organic substances are nucleic acids and proteins. Nucleic acids (DNA and RNA) are involved in the transmission of hereditary information, protein synthesis, regulation of all processes of cell life.

Squirrels perform a number of functions: construction, regulatory, transport, contractile, protective, energy. But the most important is the enzymatic function of proteins.

Enzymes Are biological catalysts that accelerate and regulate all the variety of chemical reactions that take place in living organisms. Not a single reaction in a living cell proceeds without the participation of enzymes.

Lipids and carbohydrates perform mainly construction and energy functions, are reserve nutrients for the body.

So, phospholipids together with proteins, they build all membrane structures of the cell. High-molecular carbohydrate - cellulose forms the cell wall of plants and fungi.

Fats, starch and glycogen are reserve nutrients for cells and the body as a whole. Glucose, fructose, sucrose and others Sahara are part of the roots and leaves, plant fruits. Glucose is an indispensable component of the blood plasma of humans and many animals. When carbohydrates and fats are broken down in the body, a large amount of energy is released, which is necessary for vital processes.

Cellular structures. The cell consists of an outer cell membrane, cytoplasm with organelles and a nucleus (Fig. 48).

Rice. 48. Combined scheme of the structure of animal (A) and plant (B) cells: 1 - shell; 2 - outer cell membrane; 3 - core; 4 - chromatin; 5 - the nucleolus; 6 - endoplasmic reticulum (smooth and granular); 7 - mitochondria; 8 - chloroplasts; 9 - Golgi apparatus; 10 - lysosome; 11 - cell center; 12 - ribosomes; 13 - vacuole; 14 - cytoplasm

Outer cell membrane Is a single-membrane cellular structure that limits the living contents of the cells of all organisms. Possessing selective permeability, it protects the cell, regulates the intake of substances and exchange with the external environment, and maintains a certain shape of the cell. The cells of plant organisms, fungi, in addition to the membrane on the outside, also have a shell. This non-living cellular structure consists of cellulose in plants and chitin in fungi, gives strength to the cell, protects it, is the "skeleton" of plants and fungi.

V cytoplasm, the semi-liquid contents of the cell are all organelles.

Endoplasmic reticulum permeates the cytoplasm, providing communication between individual parts of the cell and the transport of substances. Distinguish between smooth and granular EPS. Ribosomes are located on the granular EPS.

Ribosomes- these are small mushroom-shaped bodies on which protein synthesis takes place in the cell.

Golgi apparatus provides packing and removal of synthesized substances from the cell. In addition, from its structures are formed lysosomes. These ball-shaped bodies contain enzymes that break down nutrients entering the cell, allowing for intracellular digestion.

Mitochondria Are semi-autonomous membrane structures of an oblong shape. Their number in cells is different and increases as a result of division. Mitochondria are the power plants of the cell. In the process of breathing in them, the final oxidation of substances by atmospheric oxygen takes place. In this case, the released energy is stored in ATP molecules, the synthesis of which occurs in these structures.

Chloroplasts, semi-autonomous membrane organelles, characteristic only of plant cells. Chloroplasts are green in color due to the chlorophyll pigment, they provide the process of photosynthesis.

In addition to chloroplasts, plant cells have and vacuoles, filled with cell sap.

Cell center participates in the process of cell division. It consists of two centrioles and a centrosphere. During division, they form spindle threads and ensure an even distribution of chromosomes in the cell.

Core- it is the center of regulation of cell activity. The nucleus is separated from the cytoplasm by a nuclear membrane, in which there are pores. Inside, it is filled with karyoplasm, which contains DNA molecules that ensure the transmission of hereditary information. Here is the synthesis of DNA, RNA, ribosomes. Often one or more dark rounded formations can be seen in the nucleus - these are the nucleoli. Here ribosomes are formed and accumulated. In the nucleus, DNA molecules are not visible, since they are in the form of thin strands of chromatin. Before dividing DNA, they spiralize, thicken, form complexes with a protein and turn into clearly visible structures - chromosomes (Fig. 49). Usually, the chromosomes in the cell are paired, the same in shape, size and hereditary information. Paired chromosomes are called homologous. A double paired set of chromosomes is called diploid. Some cells and organisms contain a single, unpaired set called haploid.

Rice. 49. A - chromosome structure: 1 - centromere; 2 - the shoulders of the chromosome; 3 - DNA molecules; 4 - sister chromatids; B - types of chromosomes: 1 - equal shoulder; 2 - versatile; 3 - one-shoulder

The number of chromosomes for each type of organism is constant. So, in human cells there are 46 chromosomes (23 pairs), in wheat cells 28 (14 pairs), pigeon 80 (40 pairs). These organisms contain a diploid set of chromosomes. Some organisms, such as algae, mosses, fungi, have a haploid set of chromosomes. Sex cells in all organisms are haploid.

In addition to those listed, some cells have specific organelles - cilia and flagella, providing movement mainly in unicellular organisms, but they are also present in some cells of multicellular organisms. For example, flagella are found in green euglena, chlamydomonas, some bacteria, and cilia - in ciliates, cells of the ciliary epithelium of animals.

§ 45. Features of cell life

Metabolism and energy in the cell. The basis of cell life is metabolism and energy conversion. The set of chemical transformations occurring in a cell or organism, interconnected and accompanied by the transformation of energy, is called metabolism and energy.

The synthesis of organic substances, accompanied by the absorption of energy, is called assimilation or plastic exchange. Decay, splitting of organic substances, accompanied by the release of energy, is called dissimilation or energy exchange.

The main source of energy on Earth is the Sun. Plant cells with special structures in chloroplasts capture the energy of the Sun, converting it into the energy of chemical bonds between molecules of organic substances and ATP.

ATF(adenosine triphosphate) is an organic substance, a universal accumulator of energy in biological systems. Solar energy is converted into the energy of chemical bonds of this substance and is spent on the synthesis of glucose, starch and other organic substances.

Atmospheric oxygen, strange as it may seem, is a byproduct of the life process of plants - photosynthesis.

The process of synthesis of organic substances from inorganic substances under the influence of the energy of the Sun is called photosynthesis.

The generalized equation of photosynthesis can be represented as follows:

6CO 2 + 6H 2 O - light> C 6 H 12 O 6 + 6O 2.

In plants, organic matter is created in the process of primary synthesis from carbon dioxide, water and mineral salts. Animals, fungi, many bacteria use ready-made organic matter (from plants). In addition, during photosynthesis, oxygen is formed, which is necessary for living organisms to breathe.

In the process of feeding and breathing, organic matter is broken down and oxidized by oxygen. The released energy is partly released in the form of heat, and partly again stored in the synthesized ATP molecules. This process takes place in the mitochondria. The end products of the decay of organic substances are water, carbon dioxide, ammonia compounds, which are again used in the process of photosynthesis. The energy stored in ATP is spent on the secondary synthesis of organic substances characteristic of each organism, on growth, reproduction.

So, plants provide all organisms not only with nutrients, but also with oxygen. In addition, they transform the energy of the Sun and transfer it through organic matter to all other groups of organisms.

§ 46. Types of metabolism in organisms

Metabolism as the main property of organisms. The body is in a complex relationship with the environment. From it he receives food, water, oxygen, light, heat. By creating a mass of living matter through these substances and energy, he builds his body. However, using this environment, the organism, due to its vital activity, simultaneously affects it, changes it. Consequently, the main process of the relationship between the body and the environment is metabolism and energy.

Metabolic types. Environmental factors have different meaning for different organisms. Plants need light, water and carbon dioxide, minerals for growth and development. Such conditions are insufficient for animals and fungi. They need organic nutrients. All organisms are divided into autotrophic and heterotrophic according to the method of nutrition, the source of obtaining organic substances and energy.

Autotrophic organisms synthesize organic substances in the process of photosynthesis from inorganic (carbon dioxide, water, mineral salts), using the energy of sunlight. These include all plant organisms that photosynthesize cyanobacteria. Chemosynthetic bacteria are also capable of autotrophic nutrition, using the energy that is released during the oxidation of inorganic substances: sulfur, iron, nitrogen.

The process of autotrophic assimilation is carried out due to the energy of sunlight or the oxidation of inorganic substances, while organic substances are synthesized from inorganic ones. Depending on the absorption of inorganic matter, a distinction is made between the assimilation of carbon, assimilation of nitrogen, assimilation of sulfur and other mineral substances. Autotrophic assimilation is associated with the processes of photosynthesis and chemosynthesis and is called primary synthesis of organic matter.

Heterotrophic organisms get ready-made organic substances from autotrophs. The source of energy for them is the energy stored in organic substances and released during the chemical reactions of decomposition and oxidation of these substances. These include animals, fungi, many bacteria.

During heterotrophic assimilation, the body absorbs ready-made organic substances and converts them into its own organic substances due to the energy contained in the absorbed substances. Heterotrophic assimilation includes the processes of food consumption, digestion, assimilation and synthesis of new organic substances. This process is called secondary synthesis of organic substances.

Dissimilation processes in organisms also differ. One of them requires oxygen for life - this aerobic organisms. Others do not need oxygen, and their life processes can proceed in an oxygen-free environment - this is anaerobic organisms.

Distinguish between external and internal breathing. Gas exchange between the body and the external environment, which includes the absorption of oxygen and the release of carbon dioxide, as well as the transport of these substances through the body to individual organs, tissues and cells, is called external respiration. In this process, oxygen is not used, but only transported.

Internal, or cellular, respiration includes biochemical processes that lead to the absorption of oxygen, the release of energy and the formation of water and carbon dioxide. These processes take place in the cytoplasm and mitochondria of eukaryotic cells or on special membranes of prokaryotic cells.

Generalized equation of the breathing process:

C 6 H 12 O 6 + 6O 2> 6CO 2 + 6H 2 O.

2. Another form of dissimilation is anaerobic, or oxygen-free, oxidation. The processes of energy metabolism in this case proceed according to the type of fermentation. Fermentation- This is a form of dissimilation, in which energy-rich organic substances are decomposed with the release of energy to less energy-rich, but also organic substances.

Depending on the end products, the types of fermentation are distinguished: alcoholic, lactic acid, acetic acid, etc. Alcoholic fermentation occurs in yeast fungi, some bacteria, and also occurs in some plant tissues. Lactic acid fermentation occurs in lactic acid bacteria, and also occurs in the muscle tissue of humans and animals with a lack of oxygen.

The relationship of metabolic reactions in autotrophic and heterotrophic organisms. Through metabolic processes, autotrophic and heterotrophic organisms in nature are interconnected (Fig. 50).

Rice. 50. The flow of matter and energy in the biosphere

The most important groups of organisms are autotrophs, which are able to synthesize organic substances from inorganic ones. Most autotrophs are green plants that, during photosynthesis, convert inorganic carbon, carbon dioxide, into complex organic compounds. During photosynthesis, green plants also release oxygen, which is necessary for the respiration of living creatures.

Heterotrophs assimilate only ready-made organic substances, receiving energy from their breakdown. Autotrophic and heterotrophic organisms are interconnected by processes of metabolism and energy. Photosynthesis is practically the only process that provides organisms with nutrients and oxygen.

Despite the large scale of photosynthesis, the green plants of the Earth use only 1% of the solar energy falling on the leaves. One of the most important tasks of biology is to increase the utilization of solar energy by cultivated plants, and to create productive varieties.

In recent years Special attention attracts the unicellular alga chlorella, which contains up to 6% chlorophyll in its body and has a remarkable ability to absorb up to 20% of solar energy. With artificial breeding, chlorella multiplies rapidly, and the protein content in its cell rises. This protein is used as a dietary supplement for many foods. It has been established that from 1 hectare of water surface it is possible to receive daily up to 700 kg of dry matter of chlorella. In addition, a large amount of vitamins is synthesized in chlorella.

Another interest in chlorella is associated with space travel. Chlorella in artificial conditions can provide oxygen released during photosynthesis, spaceship.

Section 47. Irritability and movement of organisms

The concept of irritability. Microorganisms, plants and animals react to a wide variety of environmental influences: to mechanical influences (prick, pressure, shock, etc.), to changes in temperature, intensity and direction of light rays, to sound, electrical stimuli, changes in the chemical composition of the air , water or soil, etc. This leads to certain fluctuations in the body between a stable and an unstable state. Living organisms are capable of analyzing these states to the extent of their development and reacting to them accordingly. Similar properties of all organisms are called irritability and excitability.

Irritability- This is the body's ability to respond to external or internal influences.

Irritability arose in living organisms as an adaptation that provides a better metabolism and protection from the effects of environmental conditions.

Excitability Is the ability of living organisms to perceive the effects of stimuli and respond to them with an excitation reaction.

The impact of the environment affects the state of the cell and its organelles, tissues, organs and the body as a whole. The body responds with appropriate responses.

The simplest manifestation of irritability is traffic. It is typical even for the simplest organisms. This can be observed in the experiment on an amoeba under a microscope. If you place small lumps of food or sugar crystals next to the amoeba, then it begins to actively move towards the nutrient. With the help of pseudopods, the amoeba envelops the lump, drawing it into the cell. There, a digestive vacuole is immediately formed, in which food is digested.

With the increasing complexity of the structure of the body, both metabolism and manifestations of irritability become more complicated. Unicellular organisms and plants do not have special organs for the perception and transmission of stimuli coming from the environment. Multicellular animals have sense organs and a nervous system, thanks to which they perceive stimuli, and the answers to them achieve great accuracy and expediency.

Irritability in unicellular organisms. Taxis.

The simplest forms of irritability are observed in microorganisms (bacteria, unicellular fungi, algae, protozoa).

In the example with the amoeba, we observed the movement of the amoeba towards the stimulus (food). Such a motor reaction of unicellular organisms in response to stimulation from the external environment is called taxis. Taxis is caused by chemical irritation, which is why it is also called chemotaxis(fig. 51).

Rice. 51. Chemotaxis in ciliates

Taxis can be positive or negative. Place the tube with the culture of ciliates-shoes in a closed cardboard box with a single hole located opposite the middle part of the tube and expose it to the light.

After a few hours, all ciliates will concentrate in the lighted part of the tube. This is positive phototaxis.

Taxis are characteristic of multicellular animals. For example, blood leukocytes show positive chemotaxis in relation to substances secreted by bacteria, concentrate in places where these bacteria accumulate, capture and digest them.

Irritability in multicellular plants. Tropisms. Although multicellular plants lack sensory organs and nervous systems, they nevertheless clearly exhibit various forms of irritability. They consist in changing the direction of growth of a plant or its organs (root, stem, leaves). Such manifestations of irritability in multicellular plants are called tropisms.

Stem with leaves exhibit positive phototropism and grow towards the light, and the root - negative phototropism(fig. 52). Plants respond to the Earth's gravitational field. Pay attention to the trees growing along the side of the mountain. Although the soil surface is sloping, the trees grow vertically. The reaction of plants to gravity is called geotropism(fig. 53). The root that emerges from a germinating seed is always directed downward towards the ground - positive geotropism. A leafy shoot that develops from a seed is always directed upward from the ground - negative geotropism.

Tropisms are very diverse and play a large role in plant life. They are pronounced in the direction of growth in various climbing and climbing plants, such as grapes, hops.

Rice. 52. Phototropism

Rice. 53. Geotropism: 1 - a flower pot with straight-growing radish seedlings; 2 - a flower pot laid on its side and kept in the dark to eliminate phototropism; 3 - seedlings in a flower pot are bent in the opposite direction to the action of gravity (stems have negative geotropism)

In addition to tropisms, other types of movements are observed in plants - nastia. They differ from tropisms in the absence of a certain orientation towards the stimulus that caused them. For example, if you touch the leaves of a bashful mimosa, they quickly fold in the longitudinal direction and go down. After a while, the leaves return to their previous position (Fig. 54).

Rice. 54. Nastia at the bashful mimosa: 1 - in a normal state; 2 - with irritation

The flowers of many plants react to light and moisture. For example, a tulip flowers open in the light and close in the dark. In a dandelion, the inflorescence closes in cloudy weather and opens in clear weather.

Irritability in multicellular animals. Reflexes. In connection with the development of the nervous system, sense organs and organs of movement in multicellular animals, the forms of irritability become more complicated and depend on the close interaction of these organs.

In its simplest form, such irritation occurs already in coelenterates. If you prick a freshwater hydra with a needle, it will shrink into a ball. External irritation is perceived by a sensitive cell. The excitement that arises in it is transmitted to the nerve cell. The nerve cell transmits the excitation to the musculocutaneous cell, which reacts to the irritation by contraction. This process is called reflex (reflection).

Reflex- This is the body's response to irritation, carried out by the nervous system.

The concept of a reflex was expressed by Descartes. Later it was developed in the works of I. M. Sechenov, I. P. Pavlov.

The path traversed by nervous excitement from the organ that perceives the irritation to the organ that performs the response is called reflex arc.

In organisms with a nervous system, there are two types of reflexes: unconditioned (innate) and conditioned (acquired). Conditioned reflexes are formed on the basis of unconditioned ones.

Any irritation causes a change in the metabolism in cells, which leads to excitation and a response.

§ 48. Life cycle of a cell

The period of a cell's vital activity, in which all metabolic processes take place, is called the life cycle of the cell.

The cell cycle consists of interphase and division.

Interphase Is the period between two cell divisions. It is characterized by active metabolic processes, protein synthesis, RNA, accumulation of nutrients by the cell, growth and increase in volume. By the end of the interphase, DNA duplication (replication) occurs. As a result, each chromosome contains two DNA molecules and consists of two sister chromatids. The cell is ready to divide.

Cell division. The ability to divide is the most important property of cellular life. The self-reproduction mechanism works already at the cellular level. The most common way of cell division is mitosis (Fig. 55).

Rice. 55. Interphase (A) and phases of mitosis (B): 1 - prophase; 2 - metaphase; 3 - anaphase; 4 - telophase

Mitosis- This is the process of the formation of two daughter cells, identical to the original mother cell.

Mitosis consists of four successive phases, ensuring an even distribution of genetic information and organelles between the two daughter cells.

1. V prophase the nuclear membrane disappears, the chromosomes spiralize as much as possible and become clearly visible. Each chromosome consists of two sister chromatids. The centrioles of the cell center diverge to the poles and form a division spindle.

2. V metaphase chromosomes are located in the equatorial zone, the spindle filaments are connected to chromosome centromeres.

3. Anaphase characterized by the divergence of sister chromatids-chromosomes to the poles of the cell. Each pole has the same number of chromosomes as there were in the original cell.

4. V telophase division of the cytoplasm and organelles occurs, a septum from the cell membrane is formed in the center of the cell, and two new daughter cells appear.

The whole process of division lasts from several minutes to 3 hours, depending on the type of cells and the organism. The stage of cell division in time is several times shorter than its interphase. The biological meaning of mitosis is to ensure the constancy of the number of chromosomes and hereditary information, complete identity of the original and newly emerging cells.

Section 49. Forms of reproduction of organisms

In nature, there are two types of reproduction of organisms: asexual and sexual.

Asexual reproduction- This is the formation of a new organism from one cell or a group of cells of the original mother's organism. In this case, only one parent participates in reproduction, which transfers its hereditary information to daughter individuals.

Asexual reproduction is based on mitosis. There are several forms of asexual reproduction.

Simple division, or division in two, characteristic of unicellular organisms. From one cell, by mitosis, two daughter cells are formed, each of which becomes a new organism.

Budding- This is a form of asexual reproduction, in which a daughter organism is separated from the parent. This form is typical for yeast, hydra and some other animals.

In spore plants (algae, mosses, ferns), reproduction occurs with the help of dispute, special cells formed in the maternal body. Each spore, germinating, gives rise to a new organism.

Vegetative propagation- This is reproduction by separate organs, parts of organs or body. It is based on the ability of organisms to repair missing body parts - regeneration. It is found in plants (reproduction by stems, leaves, shoots), in lower invertebrates (coelenterates, flat and annelid worms).

Sexual reproduction- This is the formation of a new organism with the participation of two parent individuals. The new organism carries hereditary information from both parents.

During sexual reproduction, the germ cells merge - gametes male and female body. Sex cells are formed as a result of a special type of division. In this case, unlike the cells of an adult organism, which carry a diploid (double) set of chromosomes, the resulting gametes have a haploid (single) set. As a result of fertilization, a paired, diploid set of chromosomes is restored. One chromosome from a pair is paternal and the other is maternal. Gametes are formed in the gonads or specialized cells during meiosis.

Meiosis- this is a cell division in which the chromosome set of a cell is halved (Fig. 56). This division is called reduction.

Rice. 56. Phases of meiosis: A - first division; B - second division. 1, 2 - prophase I; 3 - metaphase I; 4 - anaphase I; 5 - telophase I; 6 - prophase II; 7 - metaphase II; 8 - anaphase II; 9 - telophase II

For meiosis, the same stages are characteristic as for mitosis, but the process consists of two successive divisions (meiosis I and meiosis II). As a result, not two, but four cells are formed. The biological meaning of meiosis is to ensure the constancy of the number of chromosomes in newly formed organisms during fertilization. Female reproductive cell - egg, always large, contains many nutrients, often immobile.

Male reproductive cells - sperm, small, often mobile, have flagella, much more of them are formed than eggs. In seed plants, male gametes are immobile and are called sperm.

Fertilization- the process of fusion of male and female germ cells, as a result of which zygote.

An embryo develops from the zygote, which gives rise to a new organism.

Fertilization is external and internal. External fertilization characteristic of the inhabitants of the waters. Sex cells go out into the external environment and merge outside the body (fish, amphibians, algae). Internal fertilization characteristic of terrestrial organisms. Fertilization takes place in the female genital organs. The embryo can develop both in the body of the maternal organism (mammals) and outside it - in the egg (birds, reptiles, insects).

The biological significance of fertilization lies in the fact that when gametes merge, the diploid set of chromosomes is restored, and the new organism carries hereditary information and the characteristics of two parents. This increases the variety of characteristics of organisms, increases their vitality.