What is the difference between cells? The structure of a cell, the difference between a plant cell and an animal cell. Differences in nutrition

Cell structure

Cell shapes are very diverse. In unicellular organisms, each cell is a separate organism. Its shape and structural features are associated with the environmental conditions in which this single-celled organism lives, with its way of life.

Differences in cell structure

The body of every multicellular animal and plant is composed of cells that differ in appearance, which is associated with their functions. Thus, in animals one can immediately distinguish a nerve cell from a muscle or epithelial cell (epithelium is the integumentary tissue). In plants, many cells of the leaf, stem, etc. are not the same.

Cell sizes are just as variable. The smallest of them (some bacteria) do not exceed 0.5 microns. The size of the cells of multicellular organisms ranges from several micrometers (the diameter of human leukocytes is 3-4 microns, the diameter of erythrocytes is 8 microns) to enormous sizes (the processes of one human nerve cell are more than 1 m). In most plant and animal cells, their diameter ranges from 10 to 100 microns.

Despite the diversity of structure, shapes and sizes, all living cells of any organism are similar in many features of their internal structure. A cell is a complex, integral physiological system in which all basic life processes take place: metabolism and energy, irritability, growth and self-reproduction.

Main components in the structure of a cell

The main common components of a cell are the outer membrane, cytoplasm and nucleus. A cell can live and function normally only in the presence of all these components, which closely interact with each other and with the environment.

The structure of the outer membrane. It is a thin (about 7.5 nm thick) three-layer cell membrane, visible only in an electron microscope. The two outer layers of the membrane consist of proteins, and the middle one is formed by fat-like substances. The membrane has very small pores, thanks to which it easily allows some substances to pass through and retains others. The membrane takes part in phagocytosis (the cell captures solid particles) and pinocytosis (the cell captures droplets of liquid with substances dissolved in it). Thus, the membrane maintains the integrity of the cell and regulates the flow of substances from the environment into the cell and from the cell into its environment.

On its inner surface, the membrane forms invaginations and branches that penetrate deeply into the cell. Through them, the outer membrane is connected to the shell of the nucleus. On the other hand, the membranes of neighboring cells, forming mutually adjacent invaginations and folds, very closely and reliably connect cells into multicellular tissues.

Cytoplasm is a complex colloidal system. Its structure: transparent semi-liquid solution and structural formations. The structural formations of the cytoplasm common to all cells are: mitochondria, endoplasmic reticulum, Golgi complex and ribosomes. All of them, together with the nucleus, represent the centers of certain biochemical processes, which together make up the metabolism and energy in the cell. These processes are extremely diverse and occur simultaneously in a microscopically small volume of the cell. This is related to the general feature of the internal structure of all structural elements of the cell: despite their small size, they have a large surface on which biological catalysts (enzymes) are located and various biochemical reactions are carried out.

Mitochondria are the energy centers of the cell. These are very small bodies, but clearly visible in a light microscope (length 0.2-7.0 µm). They are found in the cytoplasm and vary significantly in shape and number in different cells. The liquid contents of mitochondria are enclosed in two three-layer membranes, each of which has the same structure as the outer membrane of the cell. The inner membrane of the mitochondrion forms numerous invaginations and incomplete septa within the body of the mitochondrion. These invaginations are called cristae. Thanks to them, with a small volume, a sharp increase in the surface area is achieved on which biochemical reactions take place, and among them, first of all, the reactions of accumulation and release of energy through the enzymatic conversion of adenosine diphosphoric acid into adenosine triphosphoric acid and vice versa.

The endoplasmic reticulum is a multiply branched invagination of the outer membrane of the cell. The membranes of the endoplasmic reticulum are usually arranged in pairs, and tubules are formed between them, which can expand into larger cavities filled with biosynthesis products. Around the nucleus, the membranes that make up the endoplasmic reticulum directly pass into the outer membrane of the nucleus. Thus, the endoplasmic reticulum connects all parts of the cell together. In a light microscope, when examining the structure of a cell, the endoplasmic reticulum is not visible.

In the structure of the cell, a rough and smooth endoplasmic reticulum is distinguished. The rough endoplasmic reticulum is densely surrounded by ribosomes, where protein synthesis occurs. The smooth endoplasmic reticulum is devoid of ribosomes and synthesizes fats and carbohydrates. The tubules of the endoplasmic reticulum carry out intracellular exchange of substances synthesized in various parts of the cell, as well as exchange between cells. At the same time, the endoplasmic reticulum, as a denser structural formation, serves as the skeleton of the cell, giving its shape a certain stability.

Ribosomes are found both in the cytoplasm of the cell and in its nucleus. These are tiny grains with a diameter of about 15-20 nm, which makes them invisible in a light microscope. In the cytoplasm, the bulk of ribosomes are concentrated on the surface of the tubules of the rough endoplasmic reticulum. The function of ribosomes lies in the most important process for the life of the cell and the organism as a whole - the synthesis of proteins.

The Golgi complex was first found only in animal cells. However, recently similar structures have been discovered in plant cells. The structure of the Golgi complex is close to the structural formations of the endoplasmic reticulum: these are tubules of various shapes, cavities and vesicles formed by three-layer membranes. In addition, the Golgi complex includes rather large vacuoles. Some synthesis products accumulate in them, primarily enzymes and hormones. During certain periods of a cell’s life, these reserved substances can be removed from a given cell through the endoplasmic reticulum and are involved in the metabolic processes of the body as a whole.

The cellular center is a formation that has so far been described only in the cells of animals and lower plants. It consists of two centrioles, the structure of each of which is a cylinder up to 1 micron in size. Centrioles play an important role in mitotic cell division. In addition to the described permanent structural formations, certain inclusions periodically appear in the cytoplasm of various cells. These are droplets of fat, starch grains, protein crystals of a special shape (aleurone grains), etc. Such inclusions are found in large quantities in the cells of storage tissues. However, in the cells of other tissues such inclusions can exist as a temporary reserve of nutrients.

The nucleus, like the cytoplasm with the outer membrane, is an essential component of the vast majority of cells. Only in some bacteria, when examining the structure of their cells, it was not possible to identify a structurally formed nucleus, but in their cells all the chemical substances inherent in the nuclei of other organisms were found. There are no nuclei in some specialized cells that have lost the ability to divide (red blood cells of mammals, sieve tubes of plant phloem). On the other hand, there are multinucleated cells. The nucleus plays a very important role in the synthesis of enzyme proteins, in the transmission of hereditary information from generation to generation, and in the processes of individual development of the body.

The nucleus of a non-dividing cell has a nuclear envelope. It consists of two three-layer membranes. The outer membrane is connected through the endoplasmic reticulum to the cell membrane. Through this entire system, there is a constant exchange of substances between the cytoplasm, the nucleus and the environment surrounding the cell. In addition, there are pores in the nuclear shell, through which the nucleus is also connected to the cytoplasm. Inside, the nucleus is filled with nuclear juice, which contains clumps of chromatin, a nucleolus and ribosomes. Chromatin is made up of protein and DNA. This is the material substrate that, before cell division, is formed into chromosomes, visible in a light microscope.

Chromosomes are constant in number and shape, identical for all organisms of a given species. The functions of the nucleus listed above are primarily associated with chromosomes, or more precisely, with the DNA that is part of them.

One or more nucleoli are present in the nucleus of a nondividing cell and are clearly visible in a light microscope. At the moment of cell division it disappears. Recently, the enormous role of the nucleolus has been elucidated: ribosomes are formed in it, which then enter the cytoplasm from the nucleus and carry out protein synthesis there.

All of the above applies equally to animal cells and plant cells. Due to the specificity of metabolism, growth and development of plants and animals, in the structure of the cells of both there are additional structural features that distinguish plant cells from animal cells.

Animal cells, in addition to the listed components, have special formations in the structure of the cell - lysosomes. These are ultramicroscopic vesicles in the cytoplasm filled with liquid digestive enzymes. Lysosomes carry out the function of breaking down food substances into simpler chemical substances. There are some indications that lysosomes are also found in plant cells.

The most characteristic structural elements of plant cells (except for those common ones that are inherent in all cells) are plastids. They exist in three forms: green chloroplasts, red-orange-yellow chromoplasts, and colorless leucoplasts. Under certain conditions, leukoplasts can turn into chloroplasts (greening of potato tubers), and chloroplasts, in turn, can become chromoplasts (autumn yellowing of leaves).

Chloroplasts are a “factory” for the primary synthesis of organic substances from inorganic ones using solar energy. These are small bodies of quite varied shapes, always green in color due to the presence of chlorophyll. The structure of chloroplasts in a cell: they have an internal structure that ensures maximum development of free surfaces. These surfaces are created by numerous thin plates, clusters of which are located inside the chloroplast.

On the surface, the chloroplast, like other structural elements of the cytoplasm, is covered with a double membrane. Each of them, in turn, is three-layered, like the outer membrane of the cell.

Chromoplasts are close in nature to chloroplasts, but contain yellow, orange and other pigments close to chlorophyll, which determine the color of fruits and flowers in plants.

Unlike animals, plants grow throughout their lives. This occurs both by increasing the number of cells through division and by increasing the size of the cells themselves. In this case, most of the cell body structure is occupied by vacuoles. Vacuoles are dilated lumens of tubules in the endoplasmic reticulum, filled with cell sap.

The structure of the shell of plant cells, in addition to the outer membrane, additionally consists of fiber (cellulose), which forms a thick cellulose wall at the periphery of the outer membrane. In specialized cells, these walls often acquire specific structural complications.

According to their structure, the cells of all living organisms can be divided into two large sections: non-nuclear and nuclear organisms.

In order to compare the structure of plant and animal cells, it should be said that both of these structures belong to the superkingdom of eukaryotes, which means they contain a membrane membrane, a morphologically shaped nucleus and organelles for various purposes.

In contact with

Features of the structure of a plant cell:

Features of the structure of an animal cell:

Brief comparison of plant and animal cells

What follows from this

1. The fundamental similarity in the structural features and molecular composition of plant and animal cells indicates the relationship and unity of their origin, most likely from unicellular aquatic organisms.
2. Both species contain many elements of the Periodic Table, which mainly exist in the form of complex compounds of inorganic and organic nature.
3. However, what is different is that in the process of evolution these two types of cells have moved far away from each other, because They have completely different methods of protection from various adverse influences of the external environment and also have different methods of nutrition from each other.
4. A plant cell is mainly distinguished from an animal cell by its strong shell, consisting of cellulose; special organelles - chloroplasts with chlorophyll molecules in their composition, with the help of which we carry out photosynthesis; and well-developed vacuoles with a supply of nutrients.

Analysis of the effectiveness of financial investments.

Financial investments can be in the form of securities, contributions to the authorized capital, granted loans and borrowings.

A retrospective assessment of the effectiveness of financial investments is made by comparing the amount of income received and the amount of expenses of a specific type of asset.

Average annual profitability changes under the influence of the structure of each type of investment and the level of profitability of each deposit.

SrUD = ∑ Sd.v. i × Ud.D i

Assessment and forecasting of the economic efficiency of financial investments is carried out using relative and absolute indicators. The main factors influencing efficiency are:

2. current intrinsic value.

Current intrinsic value depends on 3 factors:

1) Expected receipt of funds;

2) Rate of return;

3) Duration of the period of income generation.

TVnSt = ∑ (Exp.DS / (1 + N d) n)

Table 4.

Analysis of the effectiveness of using long-term
financial investments

D total = ∑ Ud.v. i × D r i

Factor analysis of total profitability is carried out using the absolute difference method:

1) ∆ D total. (sp.v.) = (2 × 46 + (-2) × 42.6) / 100 = + 0.068

2) ∆ D total. (D r.) = (-1.6 × 64 + 17.4 × 36) / 100 = 5.24

Balance of factors: 0.068 + 5.24 = 5.31

2. The main chemical components of protoplast. Organic substances of the cell. Proteins - biopolymers formed by amino acids, make up 40-50% of the dry mass of the protoplast. They participate in building the structure and functions of all organelles. Chemically, proteins are divided into simple (proteins) and complex (proteids). Complex proteins can form complexes with lipids - lipoproteins, with carbohydrates - glycoproteins, with nucleic acids - nucleoproteins, etc.

Proteins are part of enzymes that regulate all vital processes.

Nucleic acids - DNA and RNA - are the most important biopolymers of the protoplast, the content of which is 1-2% of its mass. These are substances for storing and transmitting hereditary information. DNA is mainly found in the nucleus, RNA - in the cytoplasm and nucleus. DNA contains the carbohydrate component deoxyribose, and RNA contains ribonucleic acid. Nucleic acids are polymers whose monomers are nucleotides. A nucleotide consists of a nitrogenous base, a ribose or deoxyribose sugar, and a phosphoric acid residue. Nucleotides are of five types depending on the nitrogenous base. The DNA molecule is represented by two polynucleotide helical chains, the RNA molecule - by one.

Lipids are fat-like substances contained in an amount of 2-3%. These are reserve energy substances that are also part of the cell wall. Fat-like compounds cover plant leaves with a thin layer, preventing them from getting wet during heavy rains. The protoplast of a plant cell contains simple (fatty oils) and complex lipids (lipoids, or fat-like substances).

Carbohydrates. Carbohydrates are part of the protoplast of each cell in the form of simple compounds (water-soluble sugars) and complex carbohydrates (insoluble or slightly soluble) - polysaccharides. Glucose (C 6 H 12 O 6) is a monosaccharide. It is especially abundant in sweet fruits; it plays a role in the formation of polysaccharides and easily dissolves in water. Fructose, or fruit sugar, is a monosaccharide that has the same formula, but tastes much sweeter. Sucrose (C 12 H 22 O 11) – disaccharide, or cane sugar; found in large quantities in sugar cane and sugar beet roots. Starch and cellulose are polysaccharides. Starch is a reserve energy polysaccharide, cellulose is the main component of the cell wall. In the cell sap of dahlia root tubers, chicory, dandelion, elecampane and other Asteraceae roots, another polysaccharide is found - inulin.

Organic substances in cells also contain vitamins - physiologically active organic compounds that control the course of metabolism, hormones that regulate the processes of growth and development of the body, phytoncides - liquid or volatile substances secreted by higher plants.

Inorganic substances in the cell. Cells contain from 2 to 6% inorganic substances. More than 80 chemical elements were found in the composition of the cell. Based on their content, the elements that make up a cell can be divided into three groups.

Macroelements. They account for about 99% of the total cell mass. The concentrations of oxygen, carbon, nitrogen and hydrogen are especially high. Their share makes up 98% of all macroelements. The remaining 2% include potassium, magnesium, sodium, calcium, iron, sulfur, phosphorus, chlorine.

Microelements. These include mainly heavy metal ions that are part of enzymes, hormones and other vital substances. Their content in the cell ranges from 0.001 to 0.000001%. Microelements include boron, cobalt, copper, molybdenum, zinc, vanadium, iodine, bromine, etc.

Ultramicroelements. Their share does not exceed 0.000001%. These include uranium, radium, gold, mercury, beryllium, cesium, selenium and other rare metals.

Water is an integral part of any cell; it is the main environment of the body, directly involved in many reactions. Water is a source of oxygen released during photosynthesis and hydrogen, which is used to restore the products of carbon dioxide assimilation. Water is a solvent. There are hydrophilic substances (from the Greek "hydros" - water and "phileo" - love), highly soluble in water, and hydrophobic (Greek "phobos" - fear) - substances that are difficult or not at all soluble in water (fats, fat-like substances, etc.). Water is the main means of transport of substances in the body (ascending and descending currents of solutions through the vessels of plants) and in the cell.

3. Cytoplasm. In the protoplast, the majority is occupied by the cytoplasm with organelles, the smaller part is occupied by the nucleus with the nucleolus. Cytoplasm has plasma membranes: 1) plasmalemma - outer membrane (shell); 2) tonoplast - the inner membrane in contact with the vacuole. Between them is mesoplasm - the bulk of the cytoplasm. The mesoplasm includes: 1) hyaloplasm (matrix) – the structureless part of the mesoplasm; 2) endoplasmic reticulum (reticulum); 3) Golgi apparatus; 4) ribosomes; 5) mitochondria (chondriosomes); 6) spherosomes; 7) lysosomes; 8) plastids.

2. The main chemical components of protoplast. Organic substances of the cell. Proteins - biopolymers formed by amino acids, make up 40-50% of the dry mass of the protoplast. They participate in building the structure and functions of all organelles. Chemically, proteins are divided into simple (proteins) and complex (proteids). Complex proteins can form complexes with lipids - lipoproteins, with carbohydrates - glycoproteins, with nucleic acids - nucleoproteins, etc.

Proteins are part of enzymes that regulate all vital processes.

Cytoplasm is a thick transparent colloidal solution. Depending on the physiological functions performed, each cell has its own chemical composition. The basis of the cytoplasm is its hyaloplasm, or matrix, the role of which is to unite all cellular structures into a single system and ensure interaction between them. The cytoplasm has an alkaline reaction of the environment and consists of 60-90% water in which various substances are dissolved: up to 10-20% proteins, 2-3% fat-like substances, 1.5% organic and 2-3% inorganic compounds. The most important physiological process occurs in the cytoplasm - respiration, or glycolysis, as a result of which glucose is broken down without oxygen in the presence of enzymes, releasing energy and producing water and carbon dioxide.

The cytoplasm is permeated with membranes - thin films of phospholipid structure. The membranes form the endoplasmic reticulum - a system of small tubules and cavities that form a network. The endoplasmic reticulum is called rough (granular) if the membranes of the tubules and cavities contain ribosomes or groups of ribosomes that perform protein synthesis. If the endoplasmic reticulum is devoid of ribosomes, it is called smooth (agranular). Lipids and carbohydrates are synthesized on the membranes of the smooth endoplasmic reticulum.

The Golgi apparatus is a system of flattened cisterns lying parallel and bounded by double membranes. From the ends of the tanks, vesicles are detached, through which the final or toxic products of the cell's vital activity are removed, and the substances necessary for the synthesis of complex carbohydrates (polysaccharides) for the construction of the cell wall are supplied back to the dictyosomes. The Golgi complex is also involved in the formation of vacuoles. One of the most important biological properties of the cytoplasm is cyclosis (the ability to move), the intensity of which depends on temperature, degree of illumination, oxygen supply and other factors.

Ribosomes are tiny particles (from 17 to 23 nm) formed by ribonucleoproteins and protein molecules. They are present in the cytoplasm, nucleus, mitochondria, plastids; There are single and group (polysomes). Ribosomes are centers of protein synthesis.

Mitochondria are the “energy stations” of all eukaryotic cells. Their shape is varied: from round to cylindrical and even rod-shaped bodies. Their number ranges from several tens to several thousand in each cell. Dimensions no more than 1 micron. On the outside, mitochondria are surrounded by a double-membrane membrane. The inner membrane is presented in the form of lamellar outgrowths - cristae. They reproduce by division.

The main function of mitochondria is to participate in cell respiration with the help of enzymes. In mitochondria, energy-rich molecules of adenosine triphosphoric acid (ATP) are synthesized as a result of oxidative phosphorylation. The mechanism of oxidative phosphorylation was discovered by the English biochemist P. Mitchell in 1960.

Plastids. These organelles, unique to plants, are found in all living plant cells. Plastids are relatively large (4-10 microns) living plant bodies of different shapes and colors. There are three types of plastids: 1) chloroplasts, colored green; 2) chromoplasts, colored yellow-red; 3) leucoplasts that do not have color.

Chloroplasts are found in all green plant organs. In higher plants there are several dozen plastids in the cells, in lower plants (algae) - 1-5. They are large and varied in shape. Chloroplasts contain up to 75% water, proteins, lipids, nucleic acids, enzymes and dyes - pigments. For the formation of chlorophyll, certain conditions are necessary - light, iron and magnesium salts in the soil. The chloroplast is separated from the cytoplasm by a double membrane membrane; its body consists of colorless fine-grained stroma. The stroma is penetrated by parallel plates - lamellae, discs. The discs are collected in stacks - grana. The main function of chloroplasts is photosynthesis.

Chromoplasts are found in carrot roots, fruits of many plants (sea buckthorn, rose hips, rowan, etc.), in green leaves of spinach, nettles, in flowers (roses, gladioli, calendula), the color of which depends on the presence of carotenoid pigments in them: carotene - orange - red and xanthophyll - yellow.

Leucoplasts are colorless plastids with no pigments. They are protein substances in the form of spherical, spindle-shaped grains concentrated around the core. They carry out the synthesis and accumulation of reserve nutrients, mainly starch, proteins and fats. Leukoplasts are found in the cytoplasm, epidermis, young hairs, underground organs of plants and in the tissues of the seed embryo.

Plastids can change from one type to another.

Core.

The nucleus is one of the main organelles of a eukaryotic cell. A plant cell has one nucleus. Hereditary information is stored and reproduced in the nucleus. The size of the kernel varies from plant to plant, from 2-3 to 500 microns. The shape is often round or lenticular. In young cells, the nucleus is larger than in old cells and occupies a central position. The core is surrounded by a double membrane with pores that regulate metabolism. The outer membrane is integrated with the endoplasmic reticulum. Inside the nucleus is nuclear juice - karyoplasm with chromatin, nucleoli and ribosomes. Chromatin is a structureless medium of special nucleoprotein threads rich in enzymes.

The bulk of DNA is concentrated in chromatin. During cell division, chromatin turns into chromosomes - gene carriers. Chromosomes are formed by two identical strands of DNA - chromatids. Each chromosome has a constriction in the middle - a centromere. The number of chromosomes varies from plant to plant: from two to several hundred. Each plant species has a constant set of chromosomes. Chromosomes synthesize nucleic acids necessary for the formation of proteins. The set of quantitative and qualitative characteristics of the chromosome set of a cell is called a karyotype. Changes in the number of chromosomes occur as a result of mutations. The hereditary multiple increase in the number of chromosomes in plants is called polyploidy.

The nucleoli are spherical, rather dense bodies with a diameter of 1-3 microns. The nucleus contains 1-2, sometimes several nucleoli. The nucleolus is the main carrier of RNA in the nucleus. The main function of the nucleolus is rRNA synthesis.

Division of nucleus and cell. Cell reproduction occurs through cell division. The period between two successive divisions constitutes the cell cycle. When cells divide, the plant grows and its total mass increases. There are three ways of cell division: mitosis, or karyokinesis (indirect division), meiosis (reduction division) and amitosis (direct division).

Mitosis is characteristic of all cells of plant organs, except sex cells. As a result of mitosis, the total mass of the plant grows and increases. The biological significance of mitosis lies in the strictly identical distribution of reduplicated chromosomes between daughter cells, which ensures the formation of genetically equivalent cells. Mitosis was first described by the Russian botanist I.D. Chistyakov in 1874. In the process of mitosis, several phases are distinguished: prophase, metaphase, anaphase and telophase. The interval between two cell divisions is called interphase. In interphase, general cell growth, reduplication of organelles, DNA synthesis, formation and preparation of structures for the beginning of mitotic division take place.

Prophase is the longest phase of mitosis. During prophase, chromosomes become visible under a light microscope. In prophase, the nucleus undergoes two changes: 1. the dense coil stage; 2. loose ball stage. At the dense coil stage, the chromosomes become visible under a light microscope, unwind from the coil or spiral, and stretch out. Each chromosome consists of two chromatids located parallel to each other. Gradually they shorten, thicken and separate, the nuclear membrane and nucleolus disappear. The nucleus increases in volume. At the opposite poles of the cell, an achromatin spindle is formed - a fission spindle, consisting of non-staining threads extending from the poles of the cell (loose ball stage).

In metaphase, the formation of the division spindle ends, the chromosomes acquire a certain shape of a particular plant species and are assembled in one plane - the equatorial one, in the place of the former nucleus. The achromatin spindle gradually contracts, and the chromatids begin to separate from each other, remaining connected at the centromere.

In anaphase, the centromere divides. The resulting sister centromeres and chromatids are directed to opposite poles of the cell. Independent chromatids become daughter chromosomes, and, therefore, there will be exactly as many of them as in the mother cell.

Telophase is the last phase of cell division, when the daughter chromosomes reach the cell poles, the division spindle gradually disappears, the chromosomes elongate and become difficult to see in a light microscope, and a median plate is formed in the equatorial plane. Gradually, a cell wall is formed and, at the same time, nucleoli and a nuclear envelope around two new nuclei (1. stage of a loose ball; 2. stage of a dense ball). The resulting cells enter the next interphase.

The duration of mitosis is approximately 1-2 hours. The process from the formation of the median plate to the formation of a new cell is called cytokinesis. Daughter cells are twice as small as the mother cells, but then they grow and reach the size of the mother cell.

Meiosis. It was first discovered by the Russian botanist V.I. Belyaev in 1885. This type of cell division is associated with the formation of spores and gametes, or germ cells with a haploid number of chromosomes (n). Its essence lies in reducing (reducing) the number of chromosomes by 2 times in each cell formed after division. Meiosis consists of two successive divisions. Meiosis, unlike mitosis, consists of two types of division: reduction (increase); equatorial (mitotic division). Reduction division occurs during the first division, which consists of several phases: prophase I, metaphase I, anaphase I, telophase I. In equatorial division there are: prophase II, metaphase II, anaphase II, telophase II. In reduction division there is an interphase.

Prophase I. Chromosomes are shaped like long double strands. A chromosome consists of two chromatids. This is the leptonema stage. Then homologous chromosomes are attracted to each other, forming pairs - bivalents. This stage is called zygonema. Paired homologous chromosomes consist of four chromatids, or tetrads. Chromatids can be located parallel to each other or intersect with each other, exchanging sections of chromosomes. This stage is called crossing over. In the next stage of prophase I - pachynema, the chromosomal strands thicken. In the next stage, diplonema, the chromatid tetrads are shortened. The conjugating chromosomes move closer to each other so that they become indistinguishable. The nucleolus and nuclear envelope disappear, and the achromatin spindle is formed. In the last stage - diakinesis - the bivalents are directed towards the equatorial plane.

Metaphase I. Bivalents are located along the equator of the cell. Each chromosome is attached by an achromatin spindle to the centromere.

Anaphase I. The filaments of the achromatin spindle contract, and homologous chromosomes in each bivalent diverge to opposite poles, and at each pole there will be half the number of chromosomes of the mother cell, i.e. the number of chromosomes decreases (reduction) and two haploid nuclei are formed.

Telophase I. This phase is weakly expressed. Chromosomes decondense; the nucleus takes on an interphase appearance, but chromosome doubling does not occur in it. This stage is called interkinesis. It is short-lived, absent in some species, and then the cells immediately after telophase I enter prophase II.

The second meiotic division occurs as mitosis.

Prophase II. It occurs quickly, following telophase I. There are no visible changes in the nucleus and the essence of this stage is that the nuclear membranes are reabsorbed and four division poles appear. Two poles appear near each nucleus.

Metaphase II. The duplicated chromosomes line up at their equators and the stage is called the mother star or equatorial plate stage. Spindle threads extend from each division pole and attach to the chromatids.

Anaphase II. The division poles stretch the filaments of the spindle, which begin to dissolve and stretch the doubled chromosomes. There comes a moment of chromosome breakage and their divergence to the four poles.

Telophase II. Around each pole of the chromosomes there is a loose coil stage and a dense coil stage. After which the centrioles dissolve and nuclear membranes and nucleoli are restored around the chromosomes. After which the cytoplasm divides.

The result of meiosis is the formation of four daughter cells from one mother cell with a haploid set of chromosomes.

Each plant species is characterized by a constant number of chromosomes and a constant shape. Among higher plants, the phenomenon of polyploidy is often encountered, i.e. multiple repetitions of one set of chromosomes in the nucleus (triploids, tetraploids, etc.).

In old and diseased plant cells, direct (amitosis) division of the nucleus can be observed by simply constricting it into two parts with an arbitrary amount of nuclear matter. This division was first described by N. Zheleznov in 1840.

Protoplast derivatives.

Protoplast derivatives include:

1) vacuoles;

2) inclusions;

3) cell wall;

4) physiologically active substances: enzymes, vitamins, phytohormones, etc.;

5) metabolic products.

Vacuoles - cavities in the protoplast - derivatives of the endoplasmic reticulum. They are bounded by a membrane - the tonoplast and filled with cell sap. Cell sap accumulates in the channels of the endoplasmic reticulum in the form of droplets, which then merge to form vacuoles. Young cells contain many small vacuoles; old cells usually contain one large vacuole. Sugars (glucose, fructose, sucrose, inulin), soluble proteins, organic acids (oxalic, malic, citric, tartaric, formic, acetic, etc.), various glycosides, tannins, alkaloids (atropine, papaverine, morphine) are dissolved in the cell sap etc.), enzymes, vitamins, phytoncides, etc. The cell sap of many plants contains pigments - anthocyanin (red, blue, purple in different shades), anthochlores (yellow), antopheines (dark brown). Seed vacuoles contain protein proteins. Many inorganic compounds are also dissolved in cell sap.

Vacuoles are places where metabolic end products are deposited.

Vacuoles form the internal aqueous environment of the cell, with their help the regulation of water-salt metabolism is carried out. Vacuoles maintain turgor hydrostatic pressure inside cells, which helps maintain the shape of non-lignified parts of plants - leaves, flowers. Turgor pressure is associated with the selective permeability of the tonoplast for water and the phenomenon of osmosis - one-sided diffusion of water through a semi-permeable partition towards an aqueous solution of salts of higher concentration. The water entering the cell sap exerts pressure on the cytoplasm, and through it on the cell wall, causing its elastic state, i.e. providing turgor. Lack of water in the cell leads to plasmolysis, i.e. to a reduction in the volume of vacuoles and separation of protoplasts from the shell. Plasmolysis can be reversible.

Inclusions are substances formed as a result of the life of a cell, either in reserve or as waste. Inclusions are localized either in the hyaloplasm and organelles, or in the vacuole in a solid or liquid state. Inclusions are reserve nutrients, for example, starch grains in potato tubers, bulbs, rhizomes and other plant organs, deposited in a special type of leucoplasts - amyloplasts.

The cell wall is a solid structure that gives each cell its shape and strength. It plays a protective role, protecting the cell from deformation, resists the high osmotic pressure of the large central vacuole and prevents cell rupture. The cell wall is a product of the vital activity of the protoplast. The primary cell wall is formed immediately after cell division and consists mainly of pectin substances and cellulose. As it grows, it becomes rounded, forming intercellular spaces filled with water, air or pectin substances. When the protoplast dies, the dead cell is able to conduct water and perform its mechanical role.

The cell wall can only grow in thickness. A secondary cell wall begins to be deposited on the inner surface of the primary cell wall. Thickening can be internal or external. External thickenings are possible only on the free surface, for example, in the form of spines, tubercles and other formations (spores, pollen grains). The internal thickening is represented by sculptural thickenings in the form of rings, spirals, vessels, etc. Only the pores - places in the secondary cell wall - remain unthickened. Through the pores along plasmodesmata - strands of cytoplasm - the exchange of substances between cells occurs, irritation is transmitted from one cell to another, etc. Pores can be simple or bordered. Simple pores are found in parenchymal and prosenchymal cells, bordered by vessels and tracheids that conduct water and minerals.

The secondary cell wall is built mainly from cellulose, or fiber (C 6 H 10 O 5) n - a very stable substance, insoluble in water, acids and alkalis.

With age, cell walls undergo modifications and are impregnated with various substances. Types of modifications: suberization, lignification, cutinization, mineralization and mucilage. Thus, during suberization, the cell walls are impregnated with a special substance suberin, during lignification - with lignin, during cutinization - with the fat-like substance cutin, during mineralization - with mineral salts, most often calcium carbonate and silica; during mucusification, the cell walls absorb a large amount of water and swell greatly.

Enzymes, vitamins, phytohormones. Enzymes are organic catalysts of a protein nature and are present in all organelles and cell components.

Vitamins are organic substances of different chemical compositions that are present as components in enzymes and act as catalysts. Vitamins are designated by capital letters of the Latin alphabet: A, B, C, D, etc. There are water-soluble vitamins (B, C, PP, H, etc.) and fat-soluble (A, D, E).

Water-soluble vitamins are found in cell sap, and fat-soluble vitamins are found in the cytoplasm. More than 40 vitamins are known.

Phytohormones are physiologically active substances. The most studied growth hormones are auxin and gibberellin.

Flagella and cilia. Flagella are motor devices in prokaryotes and in most lower plants.

Many algae and male reproductive cells of higher plants have cilia, with the exception of angiosperms and some gymnosperms.

Plant tissue

1. General characteristics and classification of fabrics.

2. Educational tissues.

3. Integumentary tissues.

4. Basic fabrics.

5. Mechanical fabrics.

6. Conductive fabrics.

7. Excretory tissues.

The concept of tissues as groups of similar cells appeared already in the works of the first botanist-anatomists in the 17th century. Malpighi and Grew described the most important tissues, in particular, they introduced the concepts of parenchyma and prosenchyma.

The classification of tissues based on physiological functions was developed in the late 19th and early 20th centuries. Schwendener and Haberlandt.

Tissues are groups of cells that have a homogeneous structure, the same origin and perform the same function.

Depending on the function performed, the following types of tissues are distinguished: educational (meristems), basic, conductive, integumentary, mechanical, excretory. Cells that make up a tissue and have more or less the same structure and functions are called simple; if the cells are not the same, then the tissue is called complex or complex.

Tissues are divided into educational, or meristem, and permanent (integumentary, conductive, basic, etc.).

Classification of fabrics.

1. Educational tissues (meristems):

1) apical;

2) lateral: a) primary (procambium, pericycle);

b) secondary (cambium, phellogen)

3) insertion;

4) wounded.

2. Basic:

1) assimilation parenchyma;

2) storage parenchyma.

3. Conductive:

1) xylem (wood);

2) phloem (bast).

4. Integumentary (borderline):

1) external: a) primary (epidermis);

b) secondary (periderm);

c) tertiary (crust, or rhytide)

2) external: a) rhizoderm;

b) velamen

3) internal: a) endoderm;

b) exodermis;

c) parietal cells of vascular bundles in leaves

5. Mechanical (supporting, skeletal) tissues:

1) collenchyma;

2) sclerenchyma:

a) fibers;

b) sclereids

6. Excretory tissues (secretory).

2. Educational tissues. Educational tissues, or meristems, are constantly young, actively dividing groups of cells. They are located in places where various organs grow: the tips of roots, the tops of stems, etc. Thanks to meristems, plant growth and the formation of new permanent tissues and organs occur.

Depending on the location in the plant body, the educational tissue can be apical or apical, lateral or lateral, intercalary or intercalary, and wound. Educational tissues are divided into primary and secondary. Thus, apical meristems are always primary; they determine the length of the plant. In low-organized higher plants (horsetails, some ferns), the apical meristems are weakly expressed and are represented by only one initial, or initial dividing cell. In gymnosperms and angiosperms, the apical meristems are well defined and are represented by many initial cells forming growth cones.

Lateral meristems, as a rule, are secondary and due to them the axial organs (stems, roots) grow in thickness. The lateral meristems include the cambium and cork cambium (phellogen), the activity of which contributes to the formation of cork in the roots and stems of the plant, as well as a special aeration tissue - lentils. The lateral meristem, like the cambium, forms wood and bast cells. During unfavorable periods of a plant’s life, the activity of the cambium slows down or stops altogether. Intercalary, or intercalary, meristems are most often primary and are preserved in the form of separate sections in zones of active growth, for example, at the base of internodes and at the base of petioles of cereal leaves.

3. Integumentary tissues. Cover tissues protect the plant from the adverse effects of the external environment: solar overheating, excessive evaporation, sudden changes in air temperature, drying wind, mechanical stress, from the penetration of pathogenic fungi and bacteria into the plant, etc. There are primary and secondary integumentary tissues. Primary integumentary tissues include the skin, or epidermis, and epiblema, and secondary tissues include the periderm (cork, cork cambium and phelloderm).

The skin, or epidermis, covers all organs of annual plants, young green shoots of perennial woody plants of the current growing season, and above-ground herbaceous parts of plants (leaves, stems and flowers). The epidermis most often consists of a single layer of tightly packed cells without intercellular space. It is easily removable and is a thin transparent film. The epidermis is a living tissue, consisting of a gradual layer of protoplast with leukoplasts and a nucleus, a large vacuole occupying almost the entire cell. The cell wall is mainly cellulose. The outer wall of the epidermal cells is thicker, the lateral and internal ones are thin. The side and inner walls of the cells have pores. The main function of the epidermis is the regulation of gas exchange and transpiration, carried out mainly through the stomata. Water and inorganic substances penetrate through the pores.

Epidermal cells of different plants are not the same in shape and size. In many monocotyledonous plants, the cells are elongated; in most dicotyledonous plants, they have sinuous side walls, which increases the density of their adhesion to each other. The epidermis of the upper and lower parts of the leaf also differs in its structure: on the lower side of the leaf there are a larger number of stomata in the epidermis, and on the upper side there are much fewer of them; on the leaves of aquatic plants with leaves floating on the surface (water lily, water lily), stomata are present only on the upper side of the leaf, and in plants completely submerged in water there are no stomata.

Stomata are highly specialized formations of the epidermis, consisting of two guard cells and a slit-like formation between them - the stomatal fissure. Crescent-shaped guard cells regulate the size of the stomatal fissure; the gap can open and close depending on the turgor pressure in the guard cells, the carbon dioxide content in the atmosphere and other factors. Thus, during the day, when stomatal cells participate in photosynthesis, the turgor pressure in the stomatal cells is high, the stomatal fissure is open, and at night, on the contrary, it is closed. A similar phenomenon is observed in dry times and when leaves wither, and is associated with the adaptation of stomata to store moisture inside the plant. Many species that grow in wet areas, especially tropical rainforests, have stomata through which water is released. The stomata are called hydathodes. Water in the form of droplets is released out and drips from the leaves. The “crying” of a plant is a kind of weather predictor and is scientifically called guttation. Hydathodes are located along the edge of the leaf; they do not have an opening or closing mechanism.

The epidermis of many plants has protective devices against unfavorable conditions: hairs, cuticle, waxy coating, etc.

Hairs (trichomes) are peculiar outgrowths of the epidermis; they can cover the entire plant or some of its parts. Hairs can be living or dead. The hairs help reduce moisture evaporation, protect the plant from overheating, being eaten by animals, and from sudden temperature fluctuations. Therefore, plants in arid - arid regions, high mountains, and subpolar regions of the globe, as well as plants in weedy habitats, are most often covered with hairs.

Hairs are unicellular and multicellular. Single-celled hairs are presented in the form of papillae. Papillae are found on the petals of many flowers, giving them a velvety feel (tagetis, pansy). Single-celled hairs may be simple (on the underside of many fruit crops) and are usually dead. Single-celled hairs can be branched (shepherd's purse). More often, the hairs are multicellular, differing in structure: linear (potato leaves), bushy-branched (mullein), scaly and stellate-squamous (representatives of the Sucker family), massive (tufts of hairs from plants of the Lamiaceae family). There are glandular hairs in which essential substances (labiaceae and umbelliferous plants), stinging substances (nettle), etc. can accumulate. Stinging hairs of nettle, thorns of roses, blackberries, thorns on the fruits of umbellifers, datura, chestnut, etc. are peculiar outgrowths called emergents, in the formation of which, in addition to epidermal cells, deeper layers of cells take part.

Epiblema (rhizoderm) is the primary single-layer integumentary tissue of the root. It is formed from the outer cells of the apical meristem of the root near the root cap. The epiblema covers the young root endings. Through it, water and mineral nutrition of the plant from the soil is carried out. There are many mitochondria in the epiblema. Epiblema cells are thin-walled, with more viscous cytoplasm, and lack stomata and cuticle. The epiblema is short-lived and is constantly renewed through mitotic divisions.

Periderm is a complex multilayer complex of secondary integumentary tissue (cork, cork cambium, or phellogen, and phelloderm) of the stems and roots of perennial dicotyledonous plants and gymnosperms, which are capable of continuously thickening. By the autumn of the first year of life, the shoots become lignified, which is noticeable by a change in their color from green to brown-gray, i.e. There was a change from the epidermis to the periderm, which could withstand the unfavorable conditions of the winter period. The periderm is based on a secondary meristem - phellogen (cork cambium), formed in the cells of the main parenchyma lying under the epidermis.

Phellogen forms cells in two directions: outward - cork cells, inward - living phelloderm cells. The cork consists of dead cells filled with air, they are elongated, tightly adjacent to each other, there are no pores, the cells are air- and water-tight. Cork cells have a brown or yellowish color, which depends on the presence of resinous or tannin substances in the cells (cork oak, Sakhalin velvet). Cork is a good insulating material, does not conduct heat, electricity or sound, and is used to seal bottles, etc. A thick layer of cork has cork oak, types of velvet, and cork elm.

Lentils are “ventilation” holes in the plug to ensure gas and water exchange of living, deeper plant tissues with the external environment. Externally, lentils are similar to lentil seeds, which is why they got their name. As a rule, lenticels are laid to replace stomata. The shapes and sizes of lentils are different. Quantitatively, there are much fewer lenticels than stomata. Lentils are round, thin-walled, chlorophyll-free cells with intercellular spaces that lift the skin and break it. This layer of loose, slightly suberized parenchyma cells that make up the lentil is called fulfilling tissue.

The crust is a powerful integumentary complex of dead outer cells of the periderm. It forms on perennial shoots and roots of woody plants. The crust has a cracked and uneven shape. It protects tree trunks from mechanical damage, ground fires, low temperatures, sunburn, and the penetration of pathogenic bacteria and fungi. The crust grows due to the growth of new layers of periderm underneath it. In tree and shrub plants, the crust appears (for example, in pine) in the 8-10th year, and in oak - in the 25-30th year of life. The bark is part of the bark of trees. On the outside, it constantly peels off, throwing off all kinds of spores of fungi and lichens.

4. Basic fabrics. Ground tissue, or parenchyma, occupies most of the space between other permanent tissues of stems, roots and other plant organs. Basic tissues consist mainly of living cells, varying in shape. The cells are thin-walled, but sometimes thickened and lignified, with walled cytoplasm and simple pores. Parenchyma consists of the bark of stems and roots, the core of stems, rhizomes, the pulp of juicy fruits and leaves; it serves as a storage facility for nutrients in the seeds. There are several subgroups of basic tissues: assimilation, storage, aquifer and pneumatic.

Assimilation tissue, or chlorophyll-bearing parenchyma, or chlorenchyma, is the tissue in which photosynthesis occurs. The cells are thin-walled, contain chloroplasts and a nucleus. Chloroplasts, like the cytoplasm, are arranged wall-to-wall. Chlorenchyma is located directly under the skin. Chlorenchyma is mainly concentrated in the leaves and young green shoots of plants. The leaves are distinguished between palisade, or columnar, and spongy chlorenchyma. The cells of palisade chlorenchyma are elongated, cylindrical in shape, with very narrow intercellular spaces. Spongy chlorenchyma has more or less rounded, loosely arranged cells with a large number of intercellular spaces filled with air.

Aerenchyma, or air-bearing tissue, is parenchyma with significantly developed intercellular spaces in various organs, characteristic of aquatic, coastal-aquatic and marsh plants (reeds, rushes, egg capsules, pondweeds, water plants, etc.), the roots and rhizomes of which are located in silt, poor in oxygen . Atmospheric air reaches the underwater organs through the photosynthetic system through transfer cells. In addition, air-bearing intercellular spaces communicate with the atmosphere through peculiar pneumatodes - stomata of leaves and stems, pneumatodes of aerial roots of some plants (Monstera, philodendron, ficus banyan, etc.), cracks, holes, channels surrounded by communication regulator cells. Aerenchyma reduces the specific gravity of the plant, which probably helps maintain the vertical position of aquatic plants, and for aquatic plants with leaves floating on the surface of the water, it helps keep the leaves on the surface of the water.

Aquiferous tissue stores water in the leaves and stems of succulent plants (cacti, aloe, agaves, crassula, etc.), as well as plants of saline habitats (soleros, biyurgun, sarsazan, saltwort, comb grass, black saxaul, etc.), usually in arid areas. The leaves of cereals also have large water-bearing cells with mucous substances that retain moisture. Sphagnum moss has well-developed aquifer cells.

Storage fabrics - tissues in which, at a certain period of plant development, they deposit metabolic products - proteins, carbohydrates, fats, etc. The cells of the storage tissue are usually thin-walled, the parenchyma is living. Storage tissues are widely represented in tubers, bulbs, thickened roots, the core of stems, endosperm and seed embryos, parenchyma of conducting tissues (beans, aroids), reservoirs of resins and essential oils in the leaves of laurel, camphor tree, etc. Storage tissue can turn into chlorenchyma, for example, during the germination of potato tubers and bulbs of bulbous plants.

5. Mechanical fabrics. Mechanical or supporting tissues - This is a kind of armature, or stereo. The term stereom comes from the Greek “stereos” - solid, durable. The main function is to provide resistance to static and dynamic loads. In accordance with their functions, they have an appropriate structure. In terrestrial plants they are most developed in the axial part of the shoot - the stem. Cells of mechanical tissue can be located in the stem either along the periphery, or in a continuous cylinder, or in separate areas in the edges of the stem. In the root, which bears mostly tensile strength, the mechanical tissue is concentrated in the center. The structural feature of these cells is the strong thickening of the cell walls, which give the tissues strength. Mechanical tissues are the most well developed in woody plants. Based on the structure of cells and the nature of thickening of cell walls, mechanical tissues are divided into two types: collenchyma and sclerenchyma.

Collenchyma is a simple primary supporting tissue with living cell contents: nucleus, cytoplasm, sometimes with chloroplasts, with unevenly thickened cell walls. Based on the nature of the thickenings and the connection of cells with each other, three types of collenchyma are distinguished: angular, lamellar and loose. If the cells are thickened only at the corners, then this is angular collenchyma, and if the walls are thickened parallel to the surface of the stem and the thickening is uniform, then this is lamellar collenchyma . The cells of angular and lamellar collenchyma are located tightly to each other, without forming intercellular spaces. Loose collenchyma has intercellular spaces, and thickened cell walls are directed towards the intercellular spaces.

Evolutionarily, collenchyma arose from parenchyma. Collenchyma is formed from the main meristem and is located under the epidermis at a distance of one or several layers from it. In young shoot stems it is located in the form of a cylinder along the periphery, in the veins of large leaves - on both sides. Living collenchyma cells are able to grow in length without interfering with the growth of young growing parts of the plant.

Sclerenchyma is the most common mechanical tissue, consisting of cells with lignified (with the exception of flax bast fibers) and uniformly thickened cell walls with a few slit-like pores. Sclerenchyma cells are elongated and have a prosenchymal shape with pointed ends. The shells of sclerenchyma cells are close to steel in strength. The lignin content in these cells increases the strength of sclerenchyma. Sclerenchyma is found in almost all vegetative organs of higher land plants. In aquatic species it is either absent entirely or is poorly represented in the submerged organs of aquatic plants.

There are primary and secondary sclerenchyma. Primary sclerenchyma comes from the cells of the main meristem - procambium or pericycle, secondary - from cambium cells. There are two types of sclerenchyma: sclerenchyma fibers, consisting of dead thick-walled cells with pointed ends, with a lignified shell and a few pores, like bast and wood fibers , or libroform fibers, and sclereids - structural elements of mechanical tissue, located alone or in groups between living cells of different parts of the plant: seed coats, fruits, leaves, stems. The main function of sclereids is to resist compression. The shape and size of sclereids are varied.

6. Conductive fabrics. Conductive tissues transport nutrients in two directions. The ascending (transpiration) flow of liquids (aqueous solutions and salts) goes through the vessels and tracheids of the xylem from the roots up the stem to the leaves and other organs of the plant. The downward flow (assimilation) of organic substances is carried out from the leaves along the stem to the underground organs of the plant through special sieve-like phloem tubes. The conducting tissue of the plant is somewhat reminiscent of the human circulatory system, since it has an axial and radial highly branched network; nutrients enter every cell of a living plant. In each plant organ, xylem and phloem are located side by side and are presented in the form of strands - conducting bundles.

There are primary and secondary conducting tissues. Primary ones differentiate from procambium and are formed in young plant organs; secondary conducting tissues are more powerful and are formed from cambium.

Xylem (wood) is represented by tracheids and trachea , or vessels .

Tracheids are elongated closed cells with obliquely cut jagged ends; in the mature state they are represented by dead prosenchymal cells. The length of the cells is on average 1-4 mm. Communication with neighboring tracheids occurs through simple or bordered pores. The walls are unevenly thickened; according to the nature of the thickening of the walls, tracheids are distinguished as annular, spiral, scalariform, reticulated and porous. Porous tracheids always have bordered pores. Sporophytes of all higher plants have tracheids, and in most horsetails, lycophytes, pteridophytes and gymnosperms they serve as the only conducting elements of the xylem. Tracheids perform two main functions: conducting water and mechanically strengthening the organ.

Trachea or vessels - the most important water-conducting elements of the xylem of angiosperms. Tracheas are hollow tubes consisting of individual segments; in the partitions between the segments there are holes - perforations, thanks to which the fluid flows. Tracheas, like tracheids, are a closed system: the ends of each trachea have beveled transverse walls with bordered pores. Tracheal segments are larger than tracheids: in different plant species they range from 0.1-0.15 to 0.3-0.7 mm in diameter. The length of the trachea ranges from several meters to several tens of meters (for lianas). The trachea consists of dead cells, although in the initial stages of formation they are alive. It is believed that tracheae arose from tracheids in the process of evolution.

In addition to the primary shell, most vessels and tracheids have secondary thickenings in the form of rings, spirals, ladders, etc. Secondary thickenings form on the inner wall of blood vessels. Thus, in an annular vessel, the internal thickenings of the walls are in the form of rings located at a distance from each other. The rings are located across the vessel and slightly oblique. In a spiral vessel, the secondary membrane is layered from the inside of the cell in the form of a spiral; in a mesh vessel, the non-thickened areas of the shell look like slits, reminiscent of mesh cells; in the scalene vessel, thickened places alternate with non-thickened ones, forming a semblance of a ladder.

Tracheids and vessels - tracheal elements - are distributed in the xylem in different ways: in a cross section in continuous rings, forming ring-vascular wood , or dispersed more or less evenly throughout the xylem, forming scattered-vascular wood . The secondary shell is usually impregnated with lignin, giving the plant additional strength, but at the same time limiting its growth in length.

In addition to vessels and tracheids, xylem includes ray elements , consisting of cells forming the medullary rays. The medullary rays consist of thin-walled living parenchyma cells through which nutrients flow horizontally. The xylem also contains living wood parenchyma cells, which function as short-range transport and serve as a storage site for reserve substances. All xylem elements come from the cambium.

Phloem is a conductive tissue through which glucose and other organic substances are transported - products of photosynthesis from leaves to places of their use and deposition (to growth cones, tubers, bulbs, rhizomes, roots, fruits, seeds, etc.). Phloem is also primary and secondary. Primary phloem is formed from procambium, secondary (phloem) - from cambium. Primary phloem lacks medullary rays and a less powerful system of sieve elements than tracheids.

During the formation of a sieve tube, mucus bodies appear in the protoplast of cells - segments of the sieve tube, which take part in the formation of a mucus cord near the sieve plates. This completes the formation of the sieve tube segment. Sieve tubes function in most herbaceous plants for one growing season and up to 3-4 years in tree and shrub plants. Sieve tubes consist of a number of elongated cells communicating with each other through perforated partitions - strainers . The shells of functioning sieve tubes do not become lignified and remain alive. Old cells are clogged with the so-called corpus callosum, and then they die and are flattened under the pressure of younger functioning cells on them.

Phloem includes phloem parenchyma , consisting of thin-walled cells in which reserve nutrients are deposited. The medullary rays of the secondary phloem also carry out short-range transportation of organic nutrients - products of photosynthesis.

Vascular bundles are strands formed, as a rule, by xylem and phloem. If strands of mechanical tissue (usually sclerenchyma) are adjacent to the conductive bundles, then such bundles are called vascular-fibrous . Other tissues can be included in the vascular bundles - living parenchyma, laticifers, etc. The vascular bundles can be complete, when both xylem and phloem are present, and incomplete, consisting only of xylem (xylem, or woody, vascular bundle) or phloem (phloem, or bast, conducting bundle).

The vascular bundles were originally formed from procambium. There are several types of conductive bundles. Part of the procambium can be preserved and then turn into cambium, then the bundle is capable of secondary thickening. These are open bunches. Such vascular bundles predominate in most dicotyledonous and gymnosperm plants. Plants with open tufts are able to grow in thickness due to the activity of the cambium, with woody areas being approximately three times larger than phloem areas . If, during the differentiation of the vascular bundle from the procambial cord, all the educational tissue is completely spent on the formation of permanent tissues, then the bundle is called closed.

Closed vascular bundles are found in the stems of monocots. Wood and bast in bundles can have different relative positions. In this regard, several types of vascular bundles are distinguished: collateral, bicollateral, concentric and radial. Collateral, or lateral, are bundles in which xylem and phloem are adjacent to each other. Bicollateral, or two-sided, are bundles in which two strands of phloem adjoin the xylem side by side. In concentric bundles, xylem tissue completely surrounds phloem tissue or vice versa. In the first case, such a bundle is called centrifloem. Centrophloem bundles are present in the stems and rhizomes of some dicotyledonous and monocotyledonous plants (begonia, sorrel, iris, many sedges and lilies).

Ferns have them. There are also intermediate vascular bundles between closed collateral and centrifloem ones. In the roots there are radial bundles, in which the central part and rays along the radii are left by wood, and each ray of wood consists of central larger vessels, gradually decreasing along the radii. The number of rays varies from plant to plant. Between the wood rays there are bast areas. The vascular bundles stretch along the entire plant in the form of cords, which begin in the roots and run along the entire plant along the stem to the leaves and other organs. In leaves they are called veins. Their main function is to conduct descending and ascending currents of water and nutrients.

7. Excretory tissues. Excretory, or secretory, tissues are special structural formations capable of releasing metabolic products and droplet-liquid media from a plant or isolating metabolic products in its tissues. Metabolic products are called secretions. If they are released outward, then these are exocrine tissues , if they remain inside the plant, then - internal secretion . As a rule, these are living parenchymal thin-walled cells, but as secretion accumulates in them, they lose their protoplast and their cells become suberized.

The formation of liquid secretions is associated with the activity of intracellular membranes and the Golgi complex, and their origin is with assimilation, storage and integumentary tissues. The main function of liquid secretions is to protect the plant from being eaten by animals, damaged by insects or pathogens. Endocrine tissues are presented in the form of idioblast cells, resin ducts, lacticifers, essential oil canals, secretion receptacles, glandular capitate hairs, glands. Idioblast cells often contain crystals of calcium oxalate (representatives of the Liliaceae, Nettles, etc. families), mucus (representatives families Malvaceae, etc.), terpenoids (representatives of the families Magnoliaceae, Pepper, etc.), etc.

Vegetative organs of higher plants

1. Root and its functions. Root metamorphosis.

2. Escape and escape system.

3. Stem.

The vegetative organs of plants include the root, stem and leaf, which make up the body of higher plants. The body of lower plants (algae, lichens) - the thallus, or thallus - is not divided into vegetative organs. The body of higher plants has a complex morphological or anatomical structure. It consistently becomes more complex from bryophytes to flowering plants due to the increasing dismemberment of the body through the formation of a system of branched axes, which leads to an increase in the total area of ​​​​contact with the environment. In lower plants it is a system of thalli, or thallus. , in higher plants - systems of shoots and roots.

The type of branching varies among different groups of plants. Dichotomous, or forked, branching is distinguished, when the old growth cone is divided into two new ones . This type of branching is found in many algae, some liver mosses, mosses, and angiosperms - in some palm trees. There are isotomic and anisotomic axis systems. In an isotomic system, after the top of the main axis stops growing, two identical lateral branches grow underneath it, and in an anisotomic system, one branch sharply outgrows the other . The most common type of branching is the lateral one, in which lateral axes appear on the main axis. This type of branching is inherent in a number of algae, roots and shoots of higher plants. . For higher plants, two types of lateral branching are distinguished: monopodial and sympodial.

With monopodial branching, the main axis does not stop growing in length and forms lateral shoots below the growth cone, which are weaker than the main axis. Sometimes a false dichotomy occurs in monopodially branching plants , when the growth of the top of the main axis stops, and under it two more or less identical lateral branches, called dichasias (mistletoe, lilac, horse chestnut, etc.), are formed, outgrowing it. Monopodial branching is characteristic of many gymnosperms and herbaceous angiosperms. Sympodial branching is very common, in which the apical bud of the shoot dies over time and one or more lateral buds begin to develop intensively, becoming “leaders” . They form side shoots that protect the shoot that has stopped growing.

The complication of branching, starting from algae thalli, probably occurred in connection with the emergence of plants on land and the struggle for survival in a new air environment. At first, these “amphibious” plants were attached to the substrate with the help of thin root-like threads - rhizoids, which subsequently, due to the improvement of the above-ground part of the plant and the need to extract large volumes of water and nutrients from the soil, evolved into a more advanced organ - the root . There is still no consensus on the order of origin of leaves or stems.

Sympodial branching is more evolutionarily advanced and has great biological significance. Thus, in case of damage to the apical bud, the role of “leader” is assumed by the lateral shoot. Trees and shrubs with sympodial branching tolerate pruning and crown formation (lilac, boxwood, sea buckthorn, etc.).

Root and root system. Root morphology. The root is the main organ of a higher plant.

The main functions of the root are to anchor the plant in the soil, actively absorb water and minerals from it, synthesize important organic substances, such as hormones and other physiologically active substances, and store substances.

The anatomical structure of the root corresponds to the function of anchoring the plant in the soil. In woody plants, the root has, on the one hand, maximum strength, and on the other, great flexibility. The anchoring function is facilitated by the appropriate location of histological structures (for example, wood is concentrated in the center of the root).

The root is an axial organ, usually cylindrical in shape. It grows as long as the apical meristem, covered with a root cap, is preserved. Leaves never form at the end of the root. The root branches to form a root system.

The collection of roots of one plant forms the root system. The root systems include the main root, lateral and adventitious roots. The main root originates from the embryonic root. Lateral roots extend from it, which can branch. Roots originating from the above-ground parts of the plant - leaves and stems - are called adventitious. Propagation by cuttings is based on the ability of individual parts of a stem, shoot, and sometimes leaf to form adventitious roots.

There are two types of root systems - taproot and fibrous. The tap root system has a clearly visible main root. This system is characteristic of most dicotyledonous plants. The fibrous root system consists of adventitious roots and is observed in most monocots.

Microscopic structure of the root. In a longitudinal section of a young growing root, several zones can be distinguished: the division zone, the growth zone, the absorption zone and the conduction zone. The apex of the root, where the growth cone is located, is covered by a root cap. The cover protects it from damage by soil particles. As the root passes through the soil, the cells of the root cap are constantly sloughed off and die, and new ones are continuously formed to replace them due to the division of cells of the educational tissue of the root tip. This is the division zone. The cells of this zone grow intensively and stretch along the axis of the root, forming a growth zone. At a distance of 1-3 mm from the root tip there are many root hairs (absorption zone), which have a large absorption surface and absorb water and minerals from the soil. Root hairs are short-lived. Each of them represents an outgrowth of a superficial root cell. Between the suction site and the base of the stem there is a conduction zone.

The center of the root is occupied by conductive tissue, and between it and the root skin there is developed tissue consisting of large living cells - parenchyma. Solutions of organic substances necessary for root growth move down through the sieve tubes, and water with mineral salts dissolved in it moves from bottom to top through the vessels.

Water and minerals are absorbed by plant roots largely independently, and there is no direct connection between the two processes. Water is absorbed due to the force, which is the difference between osmotic and turgor pressure, i.e. passively. Minerals are absorbed by plants as a result of active absorption.

Plants are capable of not only absorbing mineral compounds from solutions, but also actively dissolving chemical compounds insoluble in water. In addition to CO 2, plants emit a number of organic acids - citric, malic, tartaric, etc., which contribute to the dissolution of sparingly soluble soil compounds.

Root modifications . The ability of roots to modify over a wide range is an important factor in the struggle for existence. Due to the acquisition of additional functions, the roots are modified. They can accumulate reserve nutrients - starch, various sugars and other substances. The thickened main roots of carrots, beets, and turnips are called root vegetables. Sometimes adventitious roots, like dahlias, thicken, they are called root tubers. The structure of roots is greatly influenced by environmental factors. A number of tropical woody plants that live in oxygen-poor soils form respiratory roots.

They develop from underground lateral horses and grow vertically upward, rising above water or soil. Their function is to supply the underground parts with air, which is facilitated by a thin bark, numerous lenticels and a highly developed system of air-bearing cavities - intercellular spaces. Aerial roots can also absorb moisture from the air. Adventitious roots growing from the above-ground part of the stem can act as supports. Support horses are often found in tropical trees growing along the shores of the seas in the tidal zone. They provide plant stability in unstable soil. In tropical rain forest trees, the lateral roots often take on a board-like shape. Board-shaped roots usually develop in the absence of a taproot and spread in the surface layers of the soil.

Roots have a complex relationship with organisms living in the soil. Soil bacteria settle in the tissues of the roots of some plants (lateral, birch and some others). The bacteria feed on the organic substances of the root (mainly carbon) and cause the growth of parenchyma at the sites of their penetration - the so-called nodules. Nodule bacteria - nitrifiers have the ability to convert atmospheric nitrogen into compounds that can be absorbed by the plant. Lateral crops such as clover and alfalfa accumulate from 150 to 300 kg of nitrogen per hectare. In addition, legumes use organic substances from the body of bacteria to form seeds and fruits.

The vast majority of flowering plants have symbiotic relationships with fungi.

Venue area. After the root hairs die, the cells of the outer layer of the cortex appear on the surface of the root. By this time, the membranes of these cells become poorly permeable to water and air. Their living contents die. Thus, instead of living root hairs, there are now dead cells on the surface of the root. They protect the internal parts of the root from mechanical damage and pathogenic bacteria. Consequently, that part of the root on which the root hairs have already died will not be able to absorb the roots.

A cell is a structural and functional unit of a living organism that carries genetic information, provides metabolic processes, and is capable of regeneration and self-reproduction.

There are unicellular individuals and developed multicellular animals and plants. Their vital activity is ensured by the work of organs that are built from different tissues. Tissue, in turn, is represented by a collection of cells similar in structure and functions.

Cells of different organisms have their own characteristic properties and structure, but there are common components inherent in all cells: both plant and animal.

Organelles common to all cell types

Core- one of the important components of the cell, contains genetic information and ensures its transmission to descendants. It is surrounded by a double membrane, which isolates it from the cytoplasm.

Cytoplasm- a viscous transparent medium that fills the cell. All organelles are located in the cytoplasm. The cytoplasm consists of a system of microtubules, which ensures the precise movement of all organelles. It also controls the transport of synthesized substances.

Cell membrane– a membrane that separates the cell from the external environment, ensures the transport of substances into the cell and the removal of products of synthesis or vital activity.

Endoplasmic reticulum– a membrane organelle, consists of cisterns and tubules, on the surface of which ribosomes are synthesized (granular EPS). Places where there are no ribosomes form the smooth endoplasmic reticulum. The granular and agranular network are not delimited, but pass into each other and connect to the core shell.

Golgi complex- a stack of tanks, flattened in the center and expanded at the periphery. Designed to complete the synthesis of proteins and their further transport from the cell; together with EPS, it forms lysosomes.

Mitochondria– double-membrane organelles, the inner membrane forms protrusions into the cell – cristae. Responsible for ATP synthesis and energy metabolism. Performs a respiratory function (absorbing oxygen and releasing CO 2).

Ribosomes– are responsible for protein synthesis; small and large subunits are distinguished in their structure.

Lysosomes– carry out intracellular digestion due to the content of hydrolytic enzymes. Break down trapped foreign substances.

In both plant and animal cells, in addition to organelles, there are unstable structures - inclusions. They appear when metabolic processes in the cell increase. They perform a nutritional function and contain:

• Starch grains in plants, and glycogen in animals;
• proteins;
• Lipids are high-energy compounds that are more valuable than carbohydrates and proteins.

There are inclusions that do not play a role in energy metabolism; they contain waste products of the cell. In the glandular cells of animals, inclusions accumulate secretions.

Organelles unique to plant cells

Animal cells, unlike plant cells, do not contain vacuoles, plastids, or a cell wall.

Cell wall is formed from the cell plate, forming the primary and secondary cell walls.

The primary cell wall is found in undifferentiated cells. During maturation, a secondary membrane is formed between the membrane and the primary cell wall. In its structure it is similar to the primary one, only it has more cellulose and less water.

The secondary cell wall is equipped with many pores. A pore is a place where there is no secondary wall between the primary shell and the membrane. The pores are located in pairs in adjacent cells. Cells located nearby communicate with each other by plasmodesmata - this is a channel that is a strand of cytoplasm lined with plasmolemma. Through it, cells exchange synthesized products.

Functions of the cell wall:

1. Maintaining cell turgor.
2. Gives shape to cells, acting as a skeleton.
3. Accumulates nutritious foods.
4. Protects from external influences.

Vacuoles– organelles filled with cell sap are involved in the digestion of organic substances (similar to the lysosomes of an animal cell). They are formed through the joint work of the ER and the Golgi complex. First, several vacuoles form and function; during cell aging, they merge into one central vacuole.

Plastids- autonomous double-membrane organelles, the inner shell has outgrowths - lamellae. All plastids are divided into three types:

• Leukoplasts– non-pigmented formations, capable of storing starch, proteins, lipids;
• chloroplasts– green plastids, contain the pigment chlorophyll, capable of photosynthesis;
• chromoplasts– orange crystals due to the presence of carotene pigment.

Organelles unique to animal cells

The difference between a plant cell and an animal cell is the absence of a centriole, a three-layer membrane.

Centrioles– paired organelles located near the nucleus. They take part in the formation of the spindle and contribute to the uniform divergence of chromosomes to different poles of the cell.

Plasma membrane— animal cells are characterized by a three-layer, durable membrane, built from lipids and proteins.

Comparative characteristics of plant and animal cells

Thanks to chloroplasts, plant cells carry out the processes of photosynthesis - convert the energy of the sun into organic substances; animal cells are not capable of this.

Mitotic division of a plant occurs predominantly in the meristem, characterized by the presence of an additional stage - preprophase; in the animal body, mitosis is inherent in all cells.

The sizes of individual plant cells (about 50 microns) exceed the sizes of animal cells (about 20 microns).

The relationship between plant cells is carried out through plasmodesmata, and in animals - through desmosomes.

Vacuoles in a plant cell occupy most of its volume; in animals they are small formations in small quantities.

The cell wall of plants is made of cellulose and pectin; in animals, the membrane consists of phospholipids.

Plants are not able to actively move, so they have adapted to an autotrophic method of nutrition, independently synthesizing all the necessary nutrients from inorganic compounds.

Animals are heterotrophs and use exogenous organic substances.

The similarity in the structure and functionality of plant and animal cells indicates the unity of their origin and belonging to eukaryotes. Their distinctive features are due to their different ways of living and eating.