The importance of water for the cell. role of water in the cell. What is thermal conductivity and heat capacity of water

Due to its structure, water plays a vital role in the life of any cell. It is responsible for metabolic processes, thermoregulation, ensures the transport of substances and maintains cellular structure. Our body lives thanks to the life of our cells. And life in them is supported due to the unique structure and properties of the water molecule. In terms of quantitative composition, water ranks first in the composition of any cell.

Presence of water in tissues

Water is distributed unevenly in our tissues.

Muscle tissue – 65%

Bone tissue - 22%

Adipose tissue – 99%

Blood – 83%

Vitreous body of the eye – 99%

Brain tissue – 85%

Tooth enamel -0.2%

Participation of water in chemical reactions

From a chemical point of view, water in cells is the catalyst necessary for the flow of various processes. As a reagent, water is involved in many chemical reactions occurring inside the body's cells. Water participates in the process of hydrolysis (destruction with the addition of a water molecule). When food is digested, hydrolysis of fats, proteins and carbohydrates occurs, releasing energy that ensures the vital activity of cells. During the hydrolysis of salts, water is a source of electrons and protons.

For intracellular processes to occur, two properties of water are necessary - the ability to form hydrogen bonds and reversible ionization.

Transport of substances

In the cells of the body, it is water that performs the transport function. Water molecules are involved in the processes of removing waste products from the cell. Due to their properties, water molecules are able to penetrate into the intercellular space, bringing nutrients to the cells.

Water is the main component of blood and lymph. If there is a lack of it, the vessel becomes brittle and the blood becomes thick. This leads to local hemorrhage and thrombosis.

Maintaining Cell Structure

Liquid water is practically incompressible. This property allows water molecules to maintain the structure of the cell, and also creates optimal intracellular pressure. This ensures a constant structure of organs and tissues.

Participation of water in thermoregulation

The water molecule has a high heat capacity, which will allow it to maintain a constant temperature inside the cells of the body. In addition, when fats are broken down, a large amount of energy is released, which is also used to maintain temperature.

Water inside the cell

In the cells of the body, water exists in two states:

1 Associated with protein molecules - 4-5%. Such bonds are called solvate; they form a shell around protein molecules, preventing their interaction. According to his physical and chemical composition solvate water differs sharply from free water. It does not dissolve salts, and the freezing point is -40C.

2 Free water. It makes up 95% and participates in all of the listed processes.

Since school we know that our life is impossible without water. A person experiences thirst if he loses 3% of water; if he loses 20%, cell death will occur. This will lead to the death of the body. Monitor the amount of water you consume and its quality.

Properties of water and its role in the cell:

In the first place among the substances of the cell is water. It makes up about 80% of the cell's mass. Water is doubly important for living organisms, because it is necessary not only as a component of cells, but for many also as a habitat.

1. Water determines physical properties cells - its volume, elasticity.

2. Many chemical processes flow only in aqueous solution.

3. Water is a good solvent: many substances enter the cell from the external environment in an aqueous solution, and in an aqueous solution, waste products are removed from the cell.

4. Water has high heat capacity and thermal conductivity.

5. Water has a unique property: when it is cooled from +4 to 0 degrees, it expands. Therefore, ice turns out to be lighter than liquid water and remains on its surface. This is very important for organisms living in the aquatic environment.

6. Water can be good lubricant.

The biological role of water is determined by the small size of its molecules, their polarity and ability to connect with each other through hydrogen bonds.

Biological functions of water:

transport. Water ensures the movement of substances in the cell and body, the absorption of substances and the removal of metabolic products. In nature, water carries waste products into soils and water bodies.

metabolic. Water is the medium for all bio chemical reactions, electron donor during photosynthesis; it is necessary for the hydrolysis of macromolecules to their monomers.

Water is involved in the formation of lubricating fluids and mucus, secretions and juices in the body.

With very few exceptions (bone and tooth enamel), water is the predominant component of the cell. Water is necessary for cell metabolism (exchange), since physiological processes occur exclusively in an aqueous environment. Water molecules are involved in many enzymatic reactions cells. For example, the breakdown of proteins, carbohydrates and other substances occurs as a result of their interaction with water catalyzed by enzymes. Such reactions are called hydrolysis reactions.

Water serves as a source of hydrogen ions during photosynthesis. Water in a cell is in two forms: free and bound. Free water makes up 95% of all water in the cell and is used mainly as a solvent and as a dispersion medium for the colloidal system of protoplasm. Bound water, which accounts for only 4% of the total water in the cell, is loosely bonded to proteins by hydrogen bonds.

Due to the asymmetric distribution of charges, the water molecule acts as a dipole and can therefore be bound by both positively and negatively charged protein groups. The dipole property of a water molecule explains its ability to orient itself in an electric field and attach to various molecules and sections of molecules that carry a charge. As a result, hydrates are formed

Due to its high heat capacity, water absorbs heat and thereby prevents sudden temperature fluctuations in the cell. The water content of the body depends on its age and metabolic activity. It is highest in the embryo (90%) and gradually decreases with age. The water content of different tissues varies depending on their metabolic activity. For example, in gray matter brain water up to 80%, and in bones up to 20%. Water is the main means of moving substances in the body (blood flow, lymph, ascending and descending currents of solutions through the vessels of plants) and in the cell. Water serves as a “lubricant”, necessary wherever there are rubbing surfaces (for example, in joints). Water has its maximum density at 4°C. Therefore, ice, which has a lower density, is lighter than water and floats on its surface, which protects the reservoir from freezing. This property of water saves the lives of many aquatic organisms.

A high water content in a cell is the most important condition for its activity. With the loss of most of the water, many organisms die, and a number of unicellular and even multicellular organisms temporarily lose all signs of life. This state is called suspended animation. After hydration, the cells awaken and become active again.

The water molecule is electrically neutral. But the electric charge inside the molecule is distributed unevenly: in the region of hydrogen atoms (more precisely, protons), positive charge predominates, in the region where oxygen is located, the density of negative charge is higher. Therefore, a water particle is a dipole. The dipole property of a water molecule explains its ability to orient itself in an electric field and attach to various molecules and sections of molecules that carry a charge. As a result, hydrates are formed. The ability of water to form hydrates is due to its universal solvent properties. If the energy of attraction of water molecules to molecules of a substance is greater than the energy of attraction between water molecules, then the substance dissolves. Depending on this, a distinction is made between hydrophilic (Greek hydros - water and phileo - love) substances that are highly soluble in water (for example, salts, alkalis, acids, etc.), and hydrophobic (Greek hydros - water and phobos - fear) substances, difficult or not at all soluble in water (fats, fat-like substances, rubber, etc.). The composition of cell membranes includes fat-like substances that limit the transition from the external environment to cells and back, as well as from one part of the cell to another.

Most reactions occurring in a cell can only occur in an aqueous solution. Water is a direct participant in many reactions. For example, the breakdown of proteins, carbohydrates and other substances occurs as a result of their interaction with water catalyzed by enzymes. Such reactions are called hydrolysis reactions (Greek hydros - water and lysis - splitting).

Water has a high heat capacity and at the same time relatively high thermal conductivity for liquids. These properties make water an ideal liquid for maintaining thermal equilibrium of cells and organisms.

Water is the main medium for the biochemical reactions of the cell. It is a source of oxygen released during photosynthesis and hydrogen, which is used to restore the products of carbon dioxide assimilation. And finally, water is the main means of transport of substances in the body (blood and lymph flow, ascending and descending currents of solutions through the vessels of plants) and in the cell.

Not all compounds contained in a cell are specific to living nature. Substances such as water or salts are widely distributed outside living things. But in organisms and the products of their vital activity, a large number of carbon-containing substances have long been discovered, characteristic only of living cells and organisms and therefore called “organic substances”.

Detailed solution to paragraph 7 in biology for 10th grade students, authors Kamensky A.A., Kriksunov E.A., Pasechnik V.V. 2014

Gdz workbook in Biology for grade 10 you can find

1. What structure does water have?

Answer. The water molecule has an angular structure: the nuclei included in its composition form an isosceles triangle, at the base of which there are two hydrogens, and at the apex - an oxygen atom. Internuclear O-H distances close to 0.1 nm, the distance between the nuclei of hydrogen atoms is 0.15 nm. Of the six electrons that make up the outer electron layer of the oxygen atom in the water molecule, two electron pairs form covalent O-N connections, and the remaining four electrons represent two lone pairs of electrons.

A water molecule is a small dipole containing positive and negative charges at its poles. There is a lack of electron density near hydrogen nuclei, and on opposite side molecules, near the oxygen nucleus, there is an excess of electron density. It is this structure that determines the polarity of the water molecule.

2. What amount of water (in%) is contained in various cells?

The amount of water varies in different tissues and organs. Thus, in humans, its content in the gray matter of the brain is 85%, and in bone tissue- 22%. The highest water content in the body is observed in the embryonic period (95%) and gradually decreases with age.

The water content in various plant organs varies within fairly wide limits. It varies depending on environmental conditions, age and type of plants. Thus, the water content in lettuce leaves is 93-95%, corn - 75-77%. The amount of water varies in different plant organs: sunflower leaves contain 80-83% water, stems - 87-89%, roots - 73-75%. The water content of 6-11% is typical mainly for air-dried seeds, in which vital processes are inhibited. Water is contained in living cells, dead xylem elements and intercellular spaces. In the intercellular spaces, water is in a vapor state. The main evaporative organs of the plant are the leaves. In this regard, it is natural that greatest number water fills the intercellular spaces of leaves. In the liquid state, water is found in various parts of the cell: cell membrane, vacuole, cytoplasm. Vacuoles are the most water-rich part of the cell, where its content reaches 98%. At the highest water content, the water content in the cytoplasm is 95%. The lowest water content is characteristic of cell membranes. quantitation water content in cell membranes difficult; it apparently ranges from 30 to 50%. Forms of water in different parts plant cells are also different.

3. What is the role of water in living organisms?

Answer. Water is the predominant component of all living organisms. It has unique properties due to its structural features: water molecules have the shape of a dipole and hydrogen bonds are formed between them. The average water content in the cells of most living organisms is about 70%. Water in the cell is present in two forms: free (95% of all cell water) and bound (4-5% bound to proteins).

Functions of water:

1.Water as a solvent. Many chemical reactions in the cell are ionic and therefore occur only in an aqueous environment. Substances that dissolve in water are called hydrophilic (alcohols, sugars, aldehydes, amino acids), those that do not dissolve are called hydrophobic (fatty acids, cellulose).

2.Water as a reagent. Water is involved in many chemical reactions: polymerization reactions, hydrolysis, and in the process of photosynthesis.

3.Transport function. Movement throughout the body along with water of substances dissolved in it to its various parts and removal of unnecessary products from the body.

4.Water as a thermostabilizer and thermostat. This function is due to such properties of water as high heat capacity - it softens the effect on the body of significant temperature changes in environment; high thermal conductivity - allows the body to maintain the same temperature throughout its entire volume; high heat of evaporation - used to cool the body during sweating in mammals and transpiration in plants.

5.Structural function. The cytoplasm of cells contains from 60 to 95% water, and it is this that gives the cells their normal shape. In plants, water maintains turgor (the elasticity of the endoplasmic membrane), in some animals it serves as a hydrostatic skeleton (jellyfish)

Questions after § 7

1. What is the peculiarity of the structure of the water molecule?

Answer. Unique properties water is determined by the structure of its molecule. A water molecule consists of an O atom linked to two H atoms by polar covalent bonds. The characteristic arrangement of electrons in a water molecule gives it electrical asymmetry. The more electronegative oxygen atom attracts the electrons of the hydrogen atoms more strongly, as a result of which the common pairs of electrons in the water molecule are shifted towards it. Therefore, although the water molecule as a whole is uncharged, each of the two hydrogen atoms carries a partially positive charge (denoted 8+), and the oxygen atom carries a partially negative charge (8-). The water molecule is polarized and is a dipole (has two poles).

The partially negative charge of the oxygen atom of one water molecule is attracted by the partially positive hydrogen atoms of other molecules. Thus, each water molecule tends to hydrogen bond with four neighboring water molecules.

2. What is the importance of water as a solvent?

Answer. Due to the polarity of molecules and the ability to form hydrogen bonds, water easily dissolves ionic compounds (salts, acids, bases). Some non-ionic but polar compounds are also soluble in water, i.e., the molecule of which contains charged (polar) groups, for example sugars, simple alcohols, amino acids. Substances that are highly soluble in water are called hydrophilic (from the Greek hygros - wet and philia - friendship, inclination). When a substance goes into solution, its molecules or ions can move more freely and, therefore, the reactivity of the substance increases. This explains why water is the main medium in which most chemical reactions occur, and all hydrolysis reactions and numerous redox reactions occur with the direct participation of water.

Substances that are poorly or completely insoluble in water are called hydrophobic (from the Greek phobos - fear). These include fats, nucleic acids, some proteins and polysaccharides. Such substances can form interfaces with water at which many chemical reactions take place. Therefore, the fact that water does not dissolve non-polar substances is also very important for living organisms. Among the physiologically important properties of water is its ability to dissolve gases (O2, CO2, etc.).

3. What is thermal conductivity and heat capacity of water?

Answer. Water has a high heat capacity, i.e. the ability to absorb thermal energy with a minimal increase in own temperature. The large heat capacity of water protects body tissues from rapid and strong temperature increases. Many organisms cool themselves by evaporating water (transpiration in plants, sweating in animals).

4. Why is it believed that water is an ideal liquid for a cell?

Answer. A high water content in a cell is the most important condition for its activity. With the loss of most of the water, many organisms die, and a number of unicellular and even multicellular organisms temporarily lose all signs of life. This state is called suspended animation. After hydration, the cells awaken and become active again.

5. What is the role of water in the cell

Ensuring cell elasticity. The consequences of cell loss of water are wilting of leaves, drying out of fruits;

Acceleration of chemical reactions by dissolving substances in water;

Ensuring the movement of substances: the entry of most substances into the cell and their removal from the cell in the form of solutions;

Ensuring the dissolution of many chemical substances(a number of salts, sugars);

Participation in a number of chemical reactions;

Participation in the process of thermoregulation due to the ability to slowly heat up and slowly cool down.

6. What structural and physicochemical characteristics water determine its biological role in the cell?

Answer. The structural physicochemical properties of water determine its biological functions.

Water is a good solvent. Due to the polarity of molecules and the ability to form hydrogen bonds, water easily dissolves ionic compounds (salts, acids, bases).

Water has a high heat capacity, i.e. the ability to absorb thermal energy with a minimal increase in its own temperature. The large heat capacity of water protects body tissues from rapid and strong temperature increases. Many organisms cool themselves by evaporating water (transpiration in plants, sweating in animals).

Water also has high thermal conductivity, ensuring uniform distribution of heat throughout the body. Consequently, high specific heat capacity and high thermal conductivity make water an ideal liquid for maintaining the thermal equilibrium of cells and organisms.

Water practically does not compress, creating turgor pressure, determining the volume and elasticity of cells and tissues. Thus, it is the hydrostatic skeleton that maintains the shape of roundworms, jellyfish and other organisms.

Water is characterized by an optimal surface tension force for biological systems, which arises due to the formation of hydrogen bonds between water molecules and molecules of other substances. Due to the force of surface tension, capillary blood flow, ascending and descending currents of solutions in plants occur.

In certain biochemical processes, water acts as a substrate.

Literally from childhood, every person knows that water plays a very important role for us. Hygiene, cleaning, drinking - each of these integral elements of life is associated with water. Gradually exploring the world, the child learns about the role of water in the cell. Perhaps, only from this moment it becomes clear how great its significance is: life itself is unthinkable without water. Thanks to its properties, it makes possible the functioning of complex organisms.

Molecule structure

The role of water in the life of a cell is directly related to the characteristics of its structure. Everyone knows the formula of the main fluid of our body. Each consists of one oxygen atom and two hydrogen atoms. They are combined into a single whole due to polarity, based on the formation of a common electron pair between two atoms. A characteristic feature of water molecules is its electrical asymmetry. The oxygen atom is more electronegative and attracts electrons from hydrogen atoms more strongly. The consequence of this is a displacement of common pairs of electrons towards the oxygen atom.

Dipole

The role of water in a cell depends on the characteristics inherent in this substance. As a result of the displacement of a common pair of electrons, it becomes polarized. A water molecule is characterized by the presence of two poles: each hydrogen atom has a partially positive charge, and each oxygen atom has a partially negative charge. Together they create a neutral molecule.

Thus, each structural unit water is a dipole. The structural features of the molecule also determine the nature of the connection between neighboring structures. The partially negative oxygen atom is attracted to the hydrogen atoms of other molecules. So-called hydrogen bonds are formed between them. Each water molecule strives to communicate in a similar way with its four neighbors. All these structural nuances determine the biological role of water in the cell.

Peculiarities

Hydrogen bonds, characteristic of water molecules, determine many of its properties. The connections between oxygen and hydrogen atoms are particularly strong, meaning that breaking them requires an impressive amount of energy. As a result, water has high temperature boiling, as well as melting and vaporization. Among similar substances, water is the only substance present on Earth simultaneously in three states of aggregation. The role of water in a cell is also based on this feature.

Interaction with hydrophilic substances

The inherent ability of water particles to form hydrogen bonds allows the main body fluid to dissolve many compounds. Such substances are called hydrophilic, that is, “friendly” to water. These include ionic compounds: salts, bases and acids. Hydrophilic substances also include nonionic compounds that have polarity. Their molecules contain charged groups. These are amino acids, sugars, simple alcohols and some other compounds.
The role of water in the life of a cell is reduced to creating the environment necessary to accelerate all reactions. A solution is a state of a substance in which all its molecules can move much more freely, that is, the ability to react becomes much higher than in their usual form.

Thanks to these properties, water has become the main medium for the occurrence of the vast majority of chemical reactions. Moreover, for example, hydrolysis and the entire set of redox processes are carried out only with the direct participation of the main cell fluid.

Reagent

The huge role of water in the life of a cell is undeniable. She participates in all important processes. For example, water is necessary for photosynthesis. One of its stages, photolysis of water, involves the separation of hydrogen atoms and their inclusion in the resulting organic compounds. In this case, freed oxygen is released into the atmosphere.

Humans and animals are associated with the already mentioned hydrolysis, the destruction of substances with the addition of water. One of the most important reactions of this kind in a cell is the breakdown of the ATP molecule, which occurs with the release of energy, which is used for other vital processes.

Interaction with hydrophobic substances

Some proteins, as well as fats and nucleic acids, do not dissolve in water at all, or this process is very difficult. Such substances are called hydrophobic, that is, “fearing” water. The role of water in the cell and body is also associated with its interaction with similar compounds.

Water molecules are able to separate from the liquid itself. As a result, so-called interfaces are formed. Many chemical reactions take place on them. Thus, it is thanks to the interaction of the phospholipids that make up the cell membrane with water that a lipid bilayer is formed.

Heat capacity

In the cell lies in its participation in thermoregulation. quite high. This means that when an impressive amount is absorbed, the temperature of the water changes only slightly. This characteristic helps to maintain constant temperature inside the cell, which is necessary for the normal course of many processes and maintaining a constant internal environment.

Even heat distribution

Another one characteristic feature water - thermal conductivity. It also helps maintain a constant internal environment. Water is capable of transferring an impressive amount of heat from an area of the body where it is in excess to those cells and tissues that lack it.

In addition, thermoregulation is also carried out due to the fact that during the transition from one state of aggregation to another, hydrogen bonds must be destroyed. And this, as already mentioned, requires large amounts of energy.

Hydrostatic skeleton

The role of water in the life of a cell does not end there. The main body fluid has another property: it practically does not compress. This characteristic allows water to play the role of a hydrostatic skeleton in the cell. Water creates turgor pressure, thereby determining such properties of cells and tissues as volume and elasticity. It is easy to understand the role of water in a cell in this sense if you look at trees. The usual leaf shape is created by high blood pressure in cells. There are many similar examples in the organic world. For example, the familiar shape of jellyfish or roundworms is also supported by a hydrostatic skeleton.

Loss of water by cells, accordingly, leads to reverse processes. A change in shape begins: the leaves wither, the fruits wrinkle, the skin loses its elasticity.

Participation in the transportation of substances

Water molecules, using hydrogen bonds, are able to connect not only with each other, but also with other substances. As a result of this interaction, a substance appears that plays a significant role in the transport of substances in the body. Thus, the consequence of cohesion (the adhesion of molecules under the influence and in the case of water - with the help of hydrogen bonds) is the movement nutrients in plant capillaries. Thanks to this same property, water moves from the soil through the root hairs into the plant.

Also, the force of surface tension makes capillary blood flow possible in animals and humans. Water is involved in the movement of substances and the removal of decay products from the body.

It turns out that the answer to the question “what is the role of water in the cell?” quite unambiguous - it is huge. Thanks to the basic properties of the molecular structure of this liquid, all basic processes are possible, without which life is unthinkable. Water helps to increase the reactivity of substances, maintains the shape of cells and organs, participates in providing them with everything they need, and is part of many chemical reactions. Water is the source of life and this is definitely not a metaphor. All major metabolic processes are associated with it, and it also underlies the interaction of various compounds.

It is because of these properties that water is the substance that is sought first when exploring other planets in an attempt to understand whether they are suitable for life.