Plant cell organelles and their functions. Plant cell and its structure

Lesson type: combined.

Methods: verbal, visual, practical, problem-search.

Lesson Objectives

Educational: deepen students’ knowledge of the structure of eukaryotic cells, teach them to apply them in practical classes.

Developmental: improve students’ skills to work with didactic material; develop students' thinking by offering tasks for comparing prokaryotic and eukaryotic cells, plant cells and animal cells, identifying similar and distinctive features.

Equipment: poster “Structure of the cytoplasmic membrane”; task cards; Handout(structure of a prokaryotic cell, typical plant cell, structure of an animal cell).

Interdisciplinary connections: botany, zoology, human anatomy and physiology.

Lesson Plan

I. Organizational moment

Checking readiness for the lesson.
Checking the list of students.
Communicate the topic and objectives of the lesson.

II. Learning new material

Division of organisms into pro- and eukaryotes

The cells are extremely varied in shape: some are round in shape, others look like stars with many rays, others are elongated, etc. Cells also vary in size - from the smallest, difficult to distinguish in a light microscope, to perfectly visible to the naked eye (for example, the eggs of fish and frogs).

Any unfertilized egg, including the giant fossilized dinosaur eggs that are kept in paleontological museums, was also once living cells. However, if we talk about the main elements of the internal structure, all cells are similar to each other.

Prokaryotes (from lat. pro- before, earlier, instead of and Greek. karyon– nucleus) are organisms whose cells do not have a membrane-bound nucleus, i.e. all bacteria, including archaebacteria and cyanobacteria. The total number of prokaryotic species is about 6000. All the genetic information of a prokaryotic cell (genophore) is contained in a single circular DNA molecule. Mitochondria and chloroplasts are absent, and the functions of respiration or photosynthesis, which provide the cell with energy, are performed by the plasma membrane (Fig. 1). Prokaryotes reproduce without a pronounced sexual process by dividing in two. Prokaryotes are capable of carrying out a number of specific physiological processes: they fix molecular nitrogen, carry out lactic acid fermentation, decompose wood, and oxidize sulfur and iron.

After an introductory conversation, students review the structure of a prokaryotic cell, comparing the main structural features with the types of eukaryotic cells (Fig. 1).

Eukaryotes - This higher organisms having a clearly defined nucleus, which is separated from the cytoplasm by a membrane (karyomembrane). Eukaryotes include all higher animals and plants, as well as unicellular and multicellular algae, fungi and protozoa. Nuclear DNA in eukaryotes is contained in chromosomes. Eukaryotes have cellular organelles bounded by membranes.

Differences between eukaryotes and prokaryotes

– Eukaryotes have a real nucleus: the genetic apparatus of the eukaryotic cell is protected by a membrane similar to the membrane of the cell itself.
– Organelles included in the cytoplasm are surrounded by a membrane.

Structure of plant and animal cells

The cell of any organism is a system. It consists of three interconnected parts: shell, nucleus and cytoplasm.

When studying botany, zoology and human anatomy, you have already become familiar with the structure various types cells. Let's briefly review this material.

Exercise 1. Based on Figure 2, determine which organisms and tissue types the cells numbered 1–12 correspond to. What determines their shape?

Structure and functions of organelles of plant and animal cells

Using Figures 3 and 4 and using the Biological encyclopedic dictionary and textbook, students fill out a table comparing animal and plant cells.

Table. Structure and functions of organelles of plant and animal cells

Cell organelles	Structure of organelles	Function	Presence of organelles in cells
			plants	animals
Chloroplast	It is a type of plastid	Colors plants in green color, photosynthesis occurs in it
Leukoplast	The shell consists of two elementary membranes; internal, growing into the stroma, forms a few thylakoids	Synthesizes and accumulates starch, oils, proteins
Chromoplast	Plastids with yellow, orange and red colors, the color is due to pigments - carotenoids	Red, yellow color of autumn leaves, juicy fruits, etc.
	Occupies up to 90% of the volume of a mature cell, filled with cell sap	Maintaining turgor, accumulation of reserve substances and metabolic products, regulation osmotic pressure and etc.
Microtubules	Composed of the protein tubulin, located near the plasma membrane	They participate in the deposition of cellulose on cell walls and the movement of various organelles in the cytoplasm. During cell division, microtubules form the basis of the spindle structure
Plasma membrane (PMM)	Consists of a lipid bilayer penetrated by proteins immersed at varying depths	Barrier, transport of substances, communication between cells
Smooth EPR	System of flat and branching tubes	Carries out the synthesis and release of lipids
Rough EPR	It got its name because of the many ribosomes located on its surface.	Protein synthesis, accumulation and transformation for release from the cell to the outside
	Surrounded by a double nuclear membrane with pores. The outer nuclear membrane forms a continuous structure with the ER membrane. Contains one or more nucleoli	Carrier of hereditary information, center for regulating cell activity
Cell wall	Consists of long cellulose molecules arranged in bundles called microfibrils	External frame, protective shell
Plasmodesmata	Tiny cytoplasmic channels that penetrate cell walls	Unite protoplasts of neighboring cells
Mitochondria		ATP synthesis (energy storage)
Golgi apparatus	Consists of a stack of flat sacs called cisternae, or dictyosomes	Synthesis of polysaccharides, formation of CPM and lysosomes
Lysosomes		Intracellular digestion
Ribosomes	Consist of two unequal subunits - large and small, into which they can dissociate	Site of protein biosynthesis
Cytoplasm	Consists of water with a large number of dissolved substances containing glucose, proteins and ions	It houses other cell organelles and carries out all processes of cellular metabolism.
Microfilaments	Fibers made from the protein actin, usually arranged in bundles near the surface of cells	Participate in cell motility and change in shape
Centrioles	May be part of the cell's mitotic apparatus. A diploid cell contains two pairs of centrioles	Participate in the process of cell division in animals; in zoospores of algae, mosses and protozoa they form basal bodies of cilia
Microvilli	Plasma membrane protrusions	They increase the outer surface of the cell; microvilli collectively form the cell border

conclusions

1. The cell wall, plastids and central vacuole are unique to plant cells.
2. Lysosomes, centrioles, microvilli are present mainly only in the cells of animal organisms.
3. All other organelles are characteristic of both plant and animal cells.

Cell membrane structure

The cell membrane is located on the outside of the cell, separating the latter from the external or internal environment of the body. Its basis is the plasmalemma (cell membrane) and the carbohydrate-protein component.

Functions cell membrane:

– maintains the shape of the cell and gives mechanical strength to the cell and the body as a whole;
– protects the cell from mechanical damage and the entry of harmful compounds into it;
– carries out recognition of molecular signals;
– regulates the metabolism between the cell and the environment;
– carries out intercellular interaction in a multicellular organism.

Cell wall function:

– represents an external frame – a protective shell;
– ensures the transport of substances (water, salts, and molecules of many organic substances pass through the cell wall).

Outer layer Animal cells, unlike plant cell walls, are very thin and elastic. It is not visible under a light microscope and consists of a variety of polysaccharides and proteins. The surface layer of animal cells is called glycocalyx, performs the function of direct connection of animal cells with external environment, with all the substances surrounding it, does not play a supporting role.

Under the glycocalyx of the animal cell and the cell wall of the plant cell there is a plasma membrane bordering directly on the cytoplasm. The plasma membrane consists of proteins and lipids. They are arranged in an orderly manner due to various chemical interactions with each other. Lipid molecules in the plasma membrane are arranged in two rows and form a continuous lipid bilayer. Protein molecules do not form a continuous layer; they are located in the lipid layer, plunging into it to different depths. Molecules of proteins and lipids are mobile.

Functions of the plasma membrane:

– forms a barrier separating the internal contents of the cell from the external environment;
– provides transport of substances;
– provides communication between cells in the tissues of multicellular organisms.

Entry of substances into the cell

The surface of the cell is not continuous. In the cytoplasmic membrane there are numerous tiny holes - pores, through which, with or without the help of special proteins, ions and small molecules can penetrate into the cell. In addition, some ions and small molecules can enter the cell directly through the membrane. The entry of the most important ions and molecules into the cell is not passive diffusion, but active transport, requiring energy expenditure. The transport of substances is selective. Selective permeability of the cell membrane is called semi-permeability.

By phagocytosis Large molecules of organic substances, such as proteins, polysaccharides, food particles, and bacteria enter the cell. Phagocytosis occurs with the participation of the plasma membrane. At the point where the surface of the cell comes into contact with a particle of any dense substance, the membrane bends, forms a depression and surrounds the particle, which is immersed inside the cell in a “membrane capsule”. A digestive vacuole is formed, and organic substances entering the cell are digested in it.

Amoebas, ciliates, and leukocytes of animals and humans feed by phagocytosis. Leukocytes absorb bacteria, as well as a variety of solid particles that accidentally enter the body, thus protecting it from pathogenic bacteria. The cell wall of plants, bacteria and blue-green algae prevents phagocytosis, and therefore this route of entry of substances into the cell is not realized in them.

Drops of liquid containing various substances in a dissolved and suspended state also penetrate into the cell through the plasma membrane. This phenomenon was called pinocytosis. The process of fluid absorption is similar to phagocytosis. A drop of liquid is immersed in the cytoplasm in a “membrane package”. Organic substances that enter the cell along with water begin to be digested under the influence of enzymes contained in the cytoplasm. Pinocytosis is widespread in nature and is carried out by cells of all animals.

III. Reinforcing the material learned

What two large groups are all organisms divided into based on the structure of their nucleus?
Which organelles are characteristic only of plant cells?
Which organelles are unique to animal cells?
How does the structure of the cell membrane of plants and animals differ?
What are the two ways substances enter a cell?
What is the significance of phagocytosis for animals?

Cell - the basic form of organization of living matter, the elementary unit of an organism. It is a self-reproducing system that is isolated from the external environment and maintains a certain concentration chemical substances, but at the same time carries out constant exchange with the environment.

A cell is the basic structural unit of unicellular, colonial and multicellular organisms. A single cell of a unicellular organism is universal; it performs all the functions necessary to ensure life and reproduction. In multicellular organisms, cells are extremely diverse in size, shape and internal structure. This diversity is due to the division of functions performed by cells in the body.

Despite the enormous diversity, plant cells are characterized by a common structure - these are cells eukaryotic, having a formed core. They are distinguished from the cells of other eukaryotes - animals and fungi following features: 1) presence of plastids; 2) the presence of a cell wall, the main component of which is cellulose; 3) well-developed vacuole system; 4) absence of centrioles during division; 5) growth by stretching.

The shape and size of plant cells are very diverse and depend on their position in the plant body and the functions they perform. Tightly closed cells most often have the shape of polyhedra, which is determined by their mutual pressure; on sections they usually look like 4-6-gons. Cells whose diameter is approximately the same in all directions are called parenchymal. Prosenchymal These are cells that are highly elongated in length, their length exceeding their width by 5-6 or more times. Unlike animal cells, adult plant cells always have a constant shape, which is explained by the presence of a rigid cell wall.

The cell sizes of most plants range from 10 to 100 microns (most often 15-60 microns), they are visible only under a microscope. Cells that store water and nutrients are usually larger. The pulp of watermelon, lemon, and orange fruits consists of cells so large (several millimeters) that they can be seen with the naked eye. Some prosenchymal cells reach very long lengths. For example, flax bast fibers are about 40 mm long, and nettle fibers are 80 mm long, while the size of their cross-section remains within microscopic limits.

The number of cells in a plant reaches astronomical values. Thus, one leaf of a tree has more than 100 million cells.

In a plant cell, three main parts can be distinguished: 1) carbohydrate cell wall, surrounding the cell from the outside; 2) protoplast– the living contents of the cell, - pressed in the form of a rather thin wall layer to the cell wall, and 3) vacuole– space in the central part of the cell filled with watery contents – cell sap. The cell wall and vacuole are products of the vital activity of the protoplast.

2.2. Protoplast

Protoplast– active living contents of the cell. The protoplast is an extremely complex formation differentiated into various components called organelles (organelles), which are constantly found in it, have a characteristic structure and perform specific functions ( rice. 2.1). Cell organelles include core, plastids, mitochondria, ribosomes, endoplasmic net, apparatus Golgi, lysosomes, microbodies. Organelles are immersed in hyaloplasm, which ensures their interaction. Hyaloplasm with organelles, minus the nucleus, amounts to cytoplasm cells. The protoplast is separated from the cell wall by an outer membrane - plasmalemma, from the vacuole - by the inner membrane – tonoplast. All basic metabolic processes take place in the protoplast.

Rice. 2.1. The structure of a plant cell according to electron microscopy: 1 – core; 2 – nuclear membrane; 3 – nuclear pore; 4 – nucleolus; 5 – chromatin; 6 – karyoplasm; 7 – cell wall; 8 – plasmalemma; 9 – plasmodesmata; 10 – agranular endoplasmic reticulum; 11 – granular endoplasmic reticulum; 12 – mitochondria; 13 – ribosomes; 14 – lysosome; 15 – chloroplast; 16 – dictyosome; 17 – hyaloplasm; 18 – tonoplast; 19 – vacuole.

Chemical composition The protoplast is very complex and diverse. Each cell is characterized by its chemical composition depending on its physiological functions. Main classes constitutional, i.e., the compounds included in the protoplast are: water (60-90%), proteins (40-50% of the dry mass of the protoplast), nucleic acids (1-2%), lipids (2-3%), carbohydrates and other organic compounds. The composition of the protoplast also includes inorganic substances in the form of ions mineral salts(2-6%). Squirrels, nucleic acids, lipids and carbohydrates are synthesized by the protoplast itself.

In addition to constitutional substances, the cell contains spare substances (temporarily switched off from metabolism) and garbage(its final products). Spare substances and waste received a general name ergastic substances. Ergastic substances, as a rule, accumulate in the cell sap of vacuoles in dissolved form or form inclusion– shaped particles visible under a light microscope. Ergastic substances usually include substances of secondary synthesis, studied in the course of pharmacognosy - terpenoids, alkaloids, polyphenolic compounds.

In terms of physical properties, protoplast is a multiphase colloidal solution (density 1.03-1.1). This is usually a hydrosol, i.e. colloidal system with a predominant dispersion medium – water. In a living cell, the contents of the protoplast are in constant motion; it can be seen under a microscope by the movement of organelles and inclusions. Movement may be rotational(in one direction) or flowy(the direction of currents in different strands of the cytoplasm is different). Cytoplasmic flow is also called cyclosis. It provides better transport of substances and promotes cell aeration.

Cytoplasm-an essential part of a living cell where all processes occur cellular metabolism, except for the synthesis of nucleic acids that occurs in the nucleus. The basis of the cytoplasm is its matrix, or hyaloplasm, in which the organelles are embedded.

Hyaloplasma- a complex colorless, optically transparent colloidal system, it connects all the organelles immersed in it, ensuring their interaction. Hyaloplasm contains enzymes and is actively involved in cellular metabolism; biochemical processes such as glycolysis, amino acid synthesis, synthesis fatty acids and oils, etc. It is capable of active movement and participates in the intracellular transport of substances.

Some of the structural protein components of hyaloplasm form supramolecular aggregates with a strictly ordered arrangement of molecules - microtubules And microfilaments. Microtubules- These are thin cylindrical structures with a diameter of about 24 nm and a length of up to several micrometers. Their wall consists of spirally arranged spherical subunits of the protein tubulin. Microtubules are involved in the orientation of cellulose microfibrils of the cell wall formed by the plasma membrane, in intracellular transport, and maintaining the shape of the protoplast. They form spindle filaments during mitosis, flagella and cilia. Microfilaments are long filaments 5-7 nm thick, consisting of the contractile protein actin. In the hyaloplasm they form bundles - cytoplasmic fibers, or take the form of a three-dimensional network, attaching to the plasmalemma, plastids, elements of the endoplasmic reticulum, ribosomes, microtubules. It is believed that, by contracting, microfilaments generate the movement of hyaloplasm and the directed movement of organelles attached to them. The combination of microtubules and microfilaments makes up cytoskeleton.

The structure of the cytoplasm is based on biological membranes– the thinnest (4-10 nm) films, built mainly from phospholipids and proteins - lipoproteins. Lipid molecules form the structural basis of membranes. Phospholipids are arranged in two parallel layers in such a way that their hydrophilic parts are directed outward, into the aquatic environment, and the hydrophobic fatty acid residues are directed inward. Some protein molecules are located in a non-continuous layer on the surface of the lipid framework on one or both sides, some of them are immersed in this framework, and some pass through it, forming hydrophilic “pores” in the membrane ( rice. 2.2). Most membrane proteins are represented by various enzymes.

Rice. 2.2. Diagram of the structure of a biological membrane : B– protein molecule; Fl– phospholipid molecule.

Membranes are living components of the cytoplasm. They delimit the protoplast from the extracellular environment, create the external border of organelles and participate in the creation of their internal structure, in many ways being the bearer of their functions. A characteristic feature of membranes is their closedness and continuity - their ends are never open. In some particularly active cells, membranes can account for up to 90% of the dry matter of the cytoplasm.

One of the main properties of biological membranes is their electoral permeability(semi-permeability): some substances pass through them with difficulty or not at all (barrier property), others penetrate easily. Selective permeability of membranes creates the possibility of dividing the cytoplasm into isolated compartments - compartments– different chemical compositions, in which various biochemical processes, often opposite in direction, can occur simultaneously and independently of each other.

The boundary membranes of the protoplast are plasmalemma– plasma membrane and tonoplast– vacuolar membrane. Plasmalemma is the outer, surface membrane of the cytoplasm, usually tightly adjacent to the cell wall. It regulates the metabolism of the cell with the environment, perceives irritations and hormonal stimuli, coordinates the synthesis and assembly of cellulose microfibrils of the cell wall. The tonoplast regulates the metabolism between the protoplast and cell sap.

Ribosomes- small (about 20 nm), almost spherical granules, consisting of ribonucleoproteins - RNA complexes and various structural proteins. These are the only organelles of a eukaryotic cell that do not have membranes. Ribosomes are located freely in the cytoplasm of the cell, or are attached to the membranes of the endoplasmic reticulum. Each cell contains tens and hundreds of thousands of ribosomes. Ribosomes are located singly or in groups of 4-40 ( polyribosomes, or polysomes), where individual ribosomes are interconnected by a thread-like messenger RNA molecule that carries information about the structure of the protein. Ribosomes (more precisely, polysomes) are centers of protein synthesis in the cell.

The ribosome consists of two subunits (large and small), connected by magnesium ions. Subunits are formed in the nucleus, namely in the nucleolus, ribosomes are assembled in the cytoplasm. Ribosomes are also found in mitochondria and plastids, but their size is smaller and corresponds to the size of ribosomes in prokaryotic organisms.

Endoplasmic reticulum (endoplasmic reticulum) is an extensive three-dimensional network of channels, vesicles and cisterns, bounded by membranes, permeating the hyaloplasm. The endoplasmic reticulum in cells that synthesize proteins consists of membranes that carry outer surface ribosomes. This form is called granular, or rough (rice. 2.1). Endoplasmic reticulum that does not have ribosomes is called agranular, or smooth. The agranular endoplasmic reticulum takes part in the synthesis of fats and other lipophilic compounds (essential oils, resins, rubber).

The endoplasmic reticulum functions as the cell's communication system and is used to transport substances. The endoplasmic reticulum of neighboring cells is connected through cytoplasmic cords - plasmodesmata that pass through cell walls. The endoplasmic reticulum is the center of formation and growth of cell membranes. It gives rise to such cell components as vacuoles, lysosomes, dictyosomes, and microbodies. Through the endoplasmic reticulum, interaction between organelles occurs.

Golgi apparatus named after the Italian scientist C. Golgi, who first described it in animal cells. In plant cells, the Golgi apparatus consists of individual dictyosome, or Golgi body And Golgi vesicles. Each dictyosome is a stack of 5-7 or more flattened round cisternae with a diameter of about 1 μm, bounded by a membrane ( rice. 2.3). Along the edges, dictyosomes often turn into a system of thin branching tubes. The number of dictyosomes in a cell varies greatly (from 10-50 to several hundred) depending on the type of cell and the phase of its development. Golgi vesicles of various diameters are separated from the edges of the dictyosome cisterns or the edges of the tubes and are usually directed towards the plasmalemma or vacuole.

Rice. 2.3. Scheme of the structure of a dictyosome.

Dictyosomes are centers for the synthesis, accumulation and secretion of polysaccharides, primarily pectin substances and hemicelluloses of the cell wall matrix and mucus. Golgi vesicles transport polysaccharides to the plasmalemma. The Golgi apparatus is especially developed in cells that intensively secrete polysaccharides.

Lysosomes–organelles delimited from the hyaloplasm by a membrane and containing hydrolytic enzymes capable of destroying organic compounds. Lysosomes of plant cells are small (0.5-2 μm) cytoplasmic vacuoles and vesicles - derivatives of the endoplasmic reticulum or Golgi apparatus. The main function of lysosomes is local autolysis– destruction of individual sections of the cytoplasm of one’s own cell, ending with the formation of a cytoplasmic vacuole in its place. Local autolysis in plants has primarily a protective significance: during a temporary lack of nutrients, the cell can remain viable due to the digestion of part of the cytoplasm. Another function of lysosomes is the removal of worn-out or excess cellular organelles, as well as the cleansing of the cell cavity after the death of its protoplast, for example, during the formation of water-conducting elements.

Microbodies– small (0.5-1.5 microns) spherical organelles surrounded by a single membrane. Inside there is a fine-grained dense matrix consisting of redox enzymes. The most famous of microbodies glyoxysomes And peroxisomes. Glyoxysomes are involved in the conversion of fatty oils into sugars, which occurs during seed germination. Light respiration reactions (photorespiration) occur in peroxisomes, and the products of photosynthesis are oxidized in them to form amino acids.

Mitochondria - round or elliptical, less often thread-like organelles with a diameter of 0.3-1 μm, surrounded by two membranes. The inner membrane forms protrusions into the mitochondrial cavity - cristas, which significantly increase its internal surface. The space between the cristae is filled matrix. The matrix contains ribosomes, smaller than the ribosomes of the hyaloplasm, and strands of its own DNA ( rice. 2.4).

Rice. 2.4. Schemes of the structure of mitochondria in a three-dimensional image (1) and in a section (2): VM– inner membrane of the mitochondrion; DNA– strand of mitochondrial DNA; TO– crista; Ma– matrix; NM– outer membrane of the mitochondrion; R– mitochondrial ribosomes.

Mitochondria are called the powerhouses of the cell. They carry out intracellular breath, as a result of which organic compounds are broken down to release energy. This energy is used for the synthesis of ATP - oxidative phosphorylation. As needed, the energy stored in ATP is used for the synthesis of various substances and in various physiological processes. The number of mitochondria in a cell ranges from a few to several hundred, and there are especially many of them in secretory cells.

Mitochondria are permanent organelles that do not arise anew, but are distributed during division between daughter cells. The increase in the number of mitochondria occurs due to their division. This is possible due to the presence of its own nucleic acids in mitochondria. Mitochondria are capable of nuclear-independent synthesis of some of their proteins on their own ribosomes under the control of mitochondrial DNA. However, their independence is incomplete, since the development of mitochondria occurs under the control of the nucleus, and mitochondria are thus semi-autonomous organelles.

Plastids-organelles characteristic only of plants. There are three types of plastids: 1) chloroplasts(green plastids); 2) chromoplasts(yellow, orange or red plastids) and leucoplasts(colorless plastids). Typically, only one type of plastid is found in a cell.

Chloroplasts are of greatest importance; photosynthesis occurs in them. They contain green pigment chlorophyll, which gives plants a green color, and pigments belonging to the group carotenoids. Carotenoids range in color from yellow and orange to red and brown, but this is usually masked by chlorophyll. Carotenoids are divided into carotenes, having an orange color, and xanthophylls having a yellow color. These are lipophilic (fat-soluble) pigments; according to their chemical structure, they belong to terpenoids.

Plant chloroplasts have the shape of a biconvex lens and are 4-7 microns in size; they are clearly visible in a light microscope. The number of chloroplasts in photosynthetic cells can reach 40-50. In algae, the role of photosynthetic apparatus is performed by chromatophores. Their shape is varied: cup-shaped (Chlamydomonas), ribbon-shaped (Spirogyra), lamellar (Pinnularia), etc. Chromatophores are much larger, their number in a cell is from 1 to 5.

Chloroplasts have a complex structure. They are separated from the hyaloplasm by two membranes - external and internal. The internal contents are called stroma. The inner membrane forms inside the chloroplast a complex, strictly ordered system of membranes in the form of flat bubbles called thylakoids. Thylakoids are collected in stacks - grains, resembling columns of coins. The grana are interconnected by stromal thylakoids (intergranular thylakoids), passing through them through the length of the plastid ( rice. 2.5). Chlorophylls and carotenoids are embedded in the grana thylakoid membranes. The stroma of chloroplasts contains plastoglobules– spherical inclusions of fatty oils in which carotenoids are dissolved, as well as ribosomes similar in size to the ribosomes of prokaryotes and mitochondria, and DNA strands. Starch grains are often found in chloroplasts, this is the so-called primary, or assimilation starch– temporary storage of photosynthesis products.

Rice. 2.5. Scheme of the structure of a chloroplast in a three-dimensional image (1) and in a section (2): Vm– internal membrane; Gr– grana; DNA– strand of plastid DNA; NM– outer membrane; Pg– plastoglobule; R– chloroplast ribosomes; WITH– stroma; TIG– grana thylakoid; Tim– intergranular thylakoid.

Chlorophyll and chloroplasts are formed only in light. Plants grown in the dark are not green and are called etiolated. Instead of typical chloroplasts, modified plastids are formed in them, which do not have a developed internal membrane system - etioplasts.

The main function of chloroplasts is photosynthesis, the formation of organic substances from inorganic ones due to light energy. Chlorophyll plays a central role in this process. It absorbs light energy and directs it to carry out photosynthesis reactions. These reactions are divided into light-dependent and dark (not requiring the presence of light). Light-dependent reactions consist of the conversion of light energy into chemical energy and the decomposition (photolysis) of water. They are confined to thylakoid membranes. Dark reactions - the reduction of carbon dioxide in air with hydrogen in water to carbohydrates (fixation of CO 2) - occur in the stroma of chloroplasts.

In chloroplasts, as in mitochondria, ATP synthesis occurs. In this case, the source of energy is sunlight, which is why it is called photophosphorylation. Chloroplasts are also involved in the synthesis of amino acids and fatty acids and serve as a storage facility for temporary starch reserves.

The presence of DNA and ribosomes indicates, as in the case of mitochondria, the existence in chloroplasts of their own protein synthesizing system. Indeed, most thylakoid membrane proteins are synthesized on chloroplast ribosomes, while the majority of stromal proteins and membrane lipids are of extraplastid origin.

Leukoplasts - small colorless plastids. They are found mainly in the cells of organs hidden from sunlight, such as roots, rhizomes, tubers, and seeds. Their structure is generally similar to the structure of chloroplasts: a shell of two membranes, stroma, ribosomes, DNA strands, plastoglobules are similar to those of chloroplasts. However, unlike chloroplasts, leucoplasts have a poorly developed internal membrane system.

Leukoplasts are organelles associated with the synthesis and accumulation of reserve nutrients, primarily starch, rarely proteins and lipids. Leukoplasts that accumulate starch , are called amyloplasts. This starch has the form of grains, in contrast to the assimilative starch of chloroplasts, it is called spare, or secondary. The storage protein can be deposited in the form of crystals or amorphous inclusions in the so-called proteinoplasts, fatty oils - in the form of plastoglobules in elaioplasts.

Leukoplasts that do not accumulate reserve nutrients are often found in cells; their role is not yet fully understood. In the light, leucoplasts can turn into chloroplasts.

Chromoplasts - plastids are orange, red and yellow in color, which is caused by pigments belonging to the group of carotenoids. Chromoplasts are found in the cells of the petals of many plants (marigold, buttercup, dandelion), mature fruits (tomato, rose hip, rowan, pumpkin, watermelon), rarely in root vegetables (carrots), as well as in autumn leaves.

The internal membrane system in chromoplasts is usually absent. Carotenoids are most often dissolved in plastoglobule fatty oils ( rice. 2.6), and chromoplasts are more or less spherical in shape. In some cases (carrot roots, watermelon fruits), carotenoids are deposited in the form of crystals various shapes. The crystal stretches the membranes of the chromoplast, and it takes on its shape: jagged, needle-shaped, crescent-shaped, lamellar, triangular, diamond-shaped, etc.

Rice. 2.6. Chromoplast of mesophyll cell of buttercup petal: VM– internal membrane; NM– outer membrane; Pg– plastoglobule; WITH– stroma.

The significance of chromoplasts has not yet been fully elucidated. Most of them are aging plastids. They, as a rule, develop from chloroplasts, while chlorophyll and the internal membrane structure are destroyed in plastids, and carotenoids accumulate. This occurs when the fruits ripen and the leaves turn yellow in the fall. The indirect biological significance of chromoplasts is that they determine the bright color of flowers and fruits, which attracts insects for cross-pollination and other animals for distribution of fruits. Leucoplasts can also transform into chromoplasts.

All three types of plastids are formed from proplastid– small colorless bodies that are found in the meristematic (dividing) cells of roots and shoots. Proplastids are capable of dividing and, as they differentiate, they turn into different types of plastids.

In an evolutionary sense, the primary, original type of plastid is the chloroplast, from which the plastids of the other two types originated. During the process of individual development (ontogenesis), almost all types of plastids can transform into each other.

Plastids share many features with mitochondria that distinguish them from other components of the cytoplasm. This is, first of all, a shell of two membranes and relative genetic autonomy due to the presence of its own ribosomes and DNA. This uniqueness of organelles formed the basis of the idea that the predecessors of plastids and mitochondria were bacteria, which in the process of evolution were built into a eukaryotic cell and gradually turned into chloroplasts and mitochondria.

Core- the main and essential part of a eukaryotic cell. The nucleus is the control center for the cell's metabolism, its growth and development, and controls the activities of all other organelles. The nucleus stores genetic information and passes it on to daughter cells during cell division. The nucleus is present in all living plant cells, with the exception of mature segments of phloem sieve tubes. Cells with their nucleus removed usually die quickly.

The nucleus is the largest organelle, its size is 10-25 microns. Very large nuclei in germ cells (up to 500 microns). The shape of the nucleus is often spherical or ellipsoidal, but in highly elongated cells it can be lenticular or spindle-shaped.

The cell usually contains one nucleus. In young (meristematic) cells it usually occupies a central position. As the central vacuole grows, the nucleus moves toward the cell wall and is located in the wall layer of the cytoplasm.

In terms of chemical composition, the nucleus differs sharply from other organelles in its high (15-30%) content of DNA - the substance of the cell’s heredity. 99% of the cell's DNA is concentrated in the nucleus; it forms complexes with nuclear proteins - deoxyribonucleoproteins. The nucleus also contains significant amounts of RNA (mainly mRNA and rRNA) and proteins.

The structure of the nucleus is the same in all eukaryotic cells. In the nucleus there are chromatin And nucleolus, which are immersed in karyoplasm; The nucleus is separated from the cytoplasm nuclear shell with pores ( rice. 2.1).

Nuclear envelope consists of two membranes. The outer membrane bordering the hyaloplasm carries attached ribosomes. The shell is permeated with fairly large pores, thanks to which the exchange between the cytoplasm and the nucleus is greatly facilitated; protein macromolecules, ribonucleoproteins, ribosomal subunits, etc. pass through the pores. The outer nuclear membrane in some places is combined with the endoplasmic reticulum.

Karyoplasm (nucleoplasm, or nuclear juice)- the main substance of the nucleus, serves as a medium for the distribution of structural components - chromatin and the nucleolus. It contains enzymes, free nucleotides, amino acids, mRNA, tRNA, waste products of chromosomes and the nucleolus.

Nucleolus- dense, spherical body with a diameter of 1-3 microns. Usually the nucleus contains 1-2, sometimes several, nucleoli. The nucleoli are the main carrier of RNA in the nucleus and consist of ribonucleoproteins. The function of the nucleoli is the synthesis of rRNA and the formation of ribosomal subunits.

Chromatin- the most important part of the core. Chromatin consists of DNA molecules associated with proteins - deoxyribonucleoproteins. During cell division, chromatin differentiates into chromosomes. Chromosomes are compacted spiral strands of chromatin; they are clearly visible in the metaphase of mitosis, when the number of chromosomes can be counted and their shape can be examined. Chromatin and chromosomes ensure the storage of hereditary information, its duplication and transmission from cell to cell.

Number and shape of chromosomes ( karyotype) are the same in all cells of the body of organisms of the same species. The nuclei of somatic (non-reproductive) cells contain diploid(double) set of chromosomes – 2n. It is formed as a result of the fusion of two germ cells with haploid(single) set of chromosomes – n. In a diploid set, each pair of chromosomes is represented by homologous chromosomes, one derived from the maternal and the other from the paternal organism. Sex cells contain one chromosome from each pair of homologous chromosomes.

The number of chromosomes in different organisms varies from two to several hundred. As a rule, each species has a characteristic and constant set of chromosomes, fixed in the process of evolution of this species. Changes in the chromosome set occur only as a result of chromosomal and genomic mutations. The hereditary multiple increase in the number of sets of chromosomes is called polyploidy, multiple changes in the chromosome set – aneuploidy. Plants - polyploids characterized by larger sizes, greater productivity, resistance to unfavorable factors external environment. They are of great interest as a source material for breeding and creating highly productive varieties of cultivated plants. Polyploidy also plays a major role in speciation in plants.

Cell division

The emergence of new nuclei occurs due to the division of existing ones. In this case, the nucleus is normally never divided by a simple constriction in half, since this method cannot ensure an absolutely identical distribution of the hereditary material between the two daughter cells. This is achieved through a complex nuclear fission process called mitosis.

Mitosis is a universal form of nuclear division, similar in plants and animals. It distinguishes four phases: prophase, metaphase, anaphase And telophase(rice. 2.7). The period between two mitotic divisions is called interphase.

IN prophase chromosomes begin to appear in the nucleus. At first they look like a ball of tangled threads. Then the chromosomes shorten, thicken and are arranged in an orderly manner. At the end of prophase, the nucleolus disappears, and the nuclear membrane is fragmented into separate short cisterns, indistinguishable from the elements of the endoplasmic reticulum; the karyoplasm is mixed with the hyaloplasm. At the two poles of the nucleus, clusters of microtubules appear, from which filaments are subsequently formed mitotic spindles.

IN metaphase chromosomes finally separate and gather in one plane in the middle between the poles of the nucleus, forming metaphase record. Chromosomes are formed by two identical lengths folded chromatids, each of which contains one DNA molecule. Chromosomes are constricted - centromere, which divides them into two equal or unequal arms. In metaphase, the chromatids of each chromosome begin to separate from each other, the connection between them is maintained only in the centromere region. The mitotic spindle threads are attached to the centromeres. They consist of parallel groups of microtubules. The mitotic spindle is an apparatus for the specific orientation of chromosomes in the metaphase plate and the distribution of chromosomes at the poles of the cell.

IN anaphase each chromosome finally splits into two chromatids, which become sister chromosomes. Then, with the help of spindle threads, one of the pair of sister chromosomes begins to move to one pole of the nucleus, the second - to the other.

Telophase occurs when sister chromosomes reach the cell poles. The spindle disappears, the chromosomes grouped at the poles decondense and lengthen - they pass into interphase chromatin. Nucleoli appear, and a shell gathers around each of the daughter nuclei. Each daughter chromosome consists of only one chromatid. The completion of the second half, carried out by DNA reduplication, occurs already in the interphase nucleus.

Rice. 2.7. Scheme of mitosis and cytokinesis of a cell with the number of chromosomes 2 n=4 : 1 – interphase; 2.3 – prophase; 4 – metaphase; 5 – anaphase; 6 – telophase and formation of the cell plate; 7 – completion of cytokinesis (transition to interphase); IN– mitotic spindle; KP– developing cell plate; F– phragmoplast fibers; Hm– chromosome; I– nucleolus; nuclear weapons– nuclear membrane.

The duration of mitosis ranges from 1 to 24 hours. As a result of mitosis and subsequent interphase, cells receive the same hereditary information and contain chromosomes identical in number, size and shape to the mother cells.

In telophase, cell division begins - cytokinesis. First, numerous fibers appear between the two daughter nuclei; the collection of these fibers has the shape of a cylinder and is called phragmoplast(rice. 2.7). Like spindle filaments, phragmoplast fibers are formed by groups of microtubules. In the center of the phragmoplast, in the equatorial plane between the daughter nuclei, Golgi vesicles containing pectin substances accumulate. They merge with each other and give rise to cellular record, and the membrane limiting them becomes part of the plasmalemma.

The cell plate is disc-shaped and grows centrifugally towards the walls of the mother cell. Phragmoplast fibers control the direction of movement of the Golgi vesicles and the growth of the cell plate. When the cell plate reaches the walls of the mother cell, the formation of the septum and the separation of the two daughter cells are completed, and the phragmoplast disappears. After cytokinesis is complete, both cells begin to grow, reach the size of the mother cell, and then can divide again or proceed to differentiation.

Meiosis(reduction nuclear division) is a special method of division in which, unlike mitosis, there is a reduction (decrease) in the number of chromosomes and a transition of cells from a diploid to a haploid state. In animals, meiosis is the main link gametogenesis(the process of gamete formation), and in plants - sporogenesis(the process of spore formation). If there were no meiosis, the number of chromosomes during the fusion of cells during the sexual process would have to double indefinitely.

Meiosis consists of two successive divisions, in each of which the same four stages can be distinguished as in ordinary mitosis ( Fig.2.8).

In the prophase of the first division, as in the prophase of mitosis, the chromatin of the nucleus passes into a condensed state - chromosomes typical for a given plant species are formed, the nuclear membrane and nucleolus disappear. However, during meiosis, homologous chromosomes are not arranged in disorder, but in pairs, in contact with each other along their entire length. In this case, paired chromosomes can exchange individual sections of chromatids with each other. In the metaphase of the first division, homologous chromosomes form not a single-layer, but a two-layer metaphase plate. In anaphase of the first division, the homologous chromosomes of each pair diverge along the poles of the spindle without longitudinally separating them into isolated chromatids. As a result, in telophase, at each of the division poles, the haploid number of chromosomes is reduced by half, consisting of not one, but two chromatids. The distribution of homologous chromosomes among daughter nuclei is random.

Immediately after the telophase of the first division, the second stage of meiosis begins - ordinary mitosis with the division of chromosomes into chromatids. As a result of these two divisions and subsequent cytokinesis, four haploid daughter cells are formed - tetrad. Moreover, between the first and second nuclear divisions there is no interphase, and, therefore, no DNA reduplication. Upon fertilization diploid set chromosomes are restored.

Rice. 2.8. Scheme of meiosis with the number of chromosomes 2 n=4 : 1 – metaphase I (homologous chromosomes are assembled in pairs in the metaphase plate); 2 – anaphase I (homologous chromosomes move away from each other towards the spindle poles without splitting into chromatids); 3 – metaphase II (chromosomes are located in the metaphase plate in one row, their number is halved); 4 – anaphase II (after splitting, the daughter chromosomes move away from each other); 5 – telophase II (a tetrad of cells is formed); IN– mitotic spindle; Hm 1 – chromosome from one chromatid; Hm 2 - a chromosome of two chromatids.

The significance of meiosis lies not only in ensuring the constancy of the number of chromosomes in organisms from generation to generation. Due to the random distribution of homologous chromosomes and the exchange of their individual sections, the sex cells formed in meiosis contain a wide variety of chromosome combinations. This provides diversity of chromosome sets, increases the variability of traits in subsequent generations and, thus, provides material for the evolution of organisms.

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04.03.2018

Plant cells, like the cells of most living organisms, consist of a cell membrane that separates the contents of the cell (protoplast) from its environment. The cell membrane includes a fairly rigid and durable cell wall(outside) and thin, elastic cytoplasmic membrane(inside). The outer layer of the cell wall, which is a porous cellulose shell with lignin present in it, consists of pectins. Such components determine the strength and rigidity of the plant cell, provide its shape, and contribute to better protection of the intracellular contents (protoplast) from unfavorable conditions. The components of the cytoplasmic membrane are proteins and lipids. Both the cell wall and the membrane have semi-permeable abilities and perform a transport function, allowing water and nutrients necessary for life to pass into the cell, as well as regulating the exchange of substances between cells and with the environment.

The protoplast of a plant cell includes an internal semi-liquid medium with a fine-grained structure (cytoplasm), consisting of water, organic compounds and mineral salts, which contains the nucleus - the main part of the cell - and otherorganoids. The liquid contents of a cell were first described and named (1825–1827) by the Czech physiologist and microscopist Jan Purkinė. Organelles are permanent cellular structures that perform specific functions intended only for them. In addition, they differ from each other in structure and chemical composition. Distinguish non-membrane organelles (ribosomes, cell center, microtubules, microfilaments), single membrane(vacuoles, lysosomes, Golgi complex, endoplasmic reticulum) and double membrane(plastids, mitochondria).

(one or more) is the most important component of the protoplast, characteristic only of plant cells. In young cells, as a rule, several small vacuoles are present, but as the cell grows and ages, the small vacuoles merge into one large (central) vacuole. It is a reservoir limited by a membrane (tonoplast) with cell sap inside it. The main component of cell sap is water (70–95%), in which organic and inorganic compounds are dissolved: salts, sugars (fructose, glucose, sucrose), organic acids (oxalic, malic, citric, acetic, etc.), proteins, amino acids. All these products are intermediate results of metabolism and temporarily accumulate in vacuoles as reserve nutrients in order to subsequently participate in the metabolic processes of the cell. The cell sap also contains tannins (tannins), phenols, alkaloids, anthocyanins and various pigments, which are excreted into the vacuole, while being isolated from the cytoplasm. Unnecessary products of the cell's vital activity (waste), for example, potassium oxalate, also enter the vacuoles.

Thanks to vacuoles, the cell is provided with water reserves and nutrients(proteins, fats, vitamins, mineral salts), and also maintains osmotic intracellular pressure (turgor). In the vacuoles, old proteins and organelles are broken down.

Second distinctive feature plant cell - the presence of double-membrane organelles in it - plastid. The discovery of these organelles, their description and classification (1880 - 1883) belongs to German scientists - naturalist A. Schimper and botanist W. Meyer. Plastids are viscous protein bodies and are divided into three main types: leucoplasts, chromoplasts and chloroplasts. All of them, under the influence of certain environmental factors, are capable of changing from one type to another.

Among all types of plastids, the most important role is played by chloroplasts: They carry out the process of photosynthesis. These organelles are distinguished by their green color, which is due to the presence in their composition of a significant amount of chlorophyll - a green pigment that absorbs the energy of sunlight and synthesizes organic substances from water and carbon dioxide. Chloroplasts are separated from the cell cytoplasm by two membranes (external and internal) and have a lens-shaped oval shape(length is about 5 – 10 µm, and width ranges from 2 to 4 µm). In addition to chlorophyll, chloroplasts contain carotenoids (auxiliary orange pigments). The number of chloroplasts in a plant cell can vary from 1 - 2 (protozoan algae) to 15 - 20 pieces (leaf cell of higher plants).

Small colorless plastids leucoplasts found in the cells of those plant organs that are hidden from sunlight (roots or rhizomes, tubers, bulbs, seeds). Their shape is very diverse (spherical, ellipsoidal, cupped, dumbbell-shaped). They synthesize nutrients (mainly starch, less often fats and proteins) from mono- and disaccharides. When exposed to sunlight, leucoplasts tend to transform into chloroplasts.

Chromoplasts are formed as a result of the accumulation of carotenoids and contain a significant amount of yellow, orange, red, and brown pigments. They are present in the cells of fruits and petals, determining their bright color. Chromoplasts are disc-shaped, crescent-shaped, jagged, spherical, diamond-shaped, triangular, etc. They cannot participate in the process of photosynthesis due to the lack of chlorophyll in them.

Double membrane organelles mitochondria are represented by small (several microns in length) formations, often cylindrical, but also granule-like, thread-like or round in shape. They were first discovered using special staining and described by the German biologist R. Altmann as bioplastics (1890). The name mitochondria was given to them by the German pathologist K. Benda (1897). The outer membrane of the mitochondrion consists of lipids and half the amount of protein compounds; it has smooth surface. The composition of the inner membrane is dominated by protein complexes, and the amount of lipids does not exceed a third of them. The inner membrane has a folded surface; it forms comb-like folds ( cristas), due to which its surface is significantly increased. The space inside the mitochondrion is filled with a denser than the cytoplasm viscous substance of protein origin - the matrix. Mitochondria are very sensitive to environmental conditions, and under its influence they can be destroyed or change shape.

They perform very difficult physiological role in cell metabolic processes. It is in mitochondria that the enzymatic breakdown of organic compounds (fatty acids, carbohydrates, amino acids) occurs, and, again, under the influence of enzymes, adenosine triphosphoric acid (ATP) molecules are synthesized, which is a universal source of energy for all living organisms. Mitochondria synthesize energy and are, in essence, the “energy station” of the cell. The number of these organelles in one cell is not constant and ranges from several tens to several thousand. The more active the cell’s vital activity, the more large quantity it contains mitochondria. During cell division, mitochondria are also capable of dividing by forming a constriction. In addition, they can merge with each other to form one mitochondrion.

Golgi apparatus named after its discoverer, the Italian scientist C. Golgi (1897). The organoid is located near the nucleus and is a membrane structure in the form of multi-tiered flat disc-shaped cavities located one above the other, from which numerous tubular formations branch off, ending in vesicles. The main function of the Golgi apparatus is to remove waste products from the cell. The device tends to accumulate secretory substances inside the cavities, including pectin, xylose, glucose, ribose, and galactose. System of small bubbles ( vesicle), located on the periphery of this organelle, performs an intracellular transport role, moving polysaccharides synthesized inside the cavities to the periphery. Having reached the cell wall or vacuole, the vesicles, breaking down, give them their internal contents. The formation of primary lysosomes also occurs in the Golgi apparatus.

were discovered by the Belgian biochemist Christian de Duve (1955). They are small bodies bounded by one protective membrane and are one of the forms of vesicles. They contain more than 40 different hydrolytic enzymes (glycosidases, proteinases, phosphatases, nucleases, lipases, etc.) that break down proteins, fats, nucleic acids, carbohydrates, and therefore participate in the destruction of individual organelles or areas of the cytoplasm. Lysosomes play an important role in defense reactions and intracellular nutrition.

Ribosomes- These are very small non-membrane organelles close to spherical or ellipsoidal in shape. Formed in the cell nucleus. Due to their small size, they are perceived as “granularity” of the cytoplasm. Some of them are in a free state in the internal environment of the cell (cytoplasm, nucleus, mitochondria, plastids), while the rest are attached to the outer surfaces of the membranes of the endoplasmic reticulum. The number of ribosomes in a plant cell is relatively small and averages about 30,000. Ribosomes are located singly, but sometimes they can form groups - polyribosomes (polysomes). This organoid consists of two parts of different sizes, which can exist separately, but at the time the organoid functions, they are combined into one structure. The main function of ribosomes is the synthesis of protein molecules from amino acids.

The cytoplasm of a plant cell is penetrated by a huge number of ultramicroscopic strands, branched tubes, vesicles, channels and cavities, bounded by three-layer membranes and forming a system known as endoplasmic reticulum (EPS). The discovery of this system belongs to the English scientist K. Porter (1945). The EPS is in contact with all organelles of the cell and together with them constitutes a single intracellular system that carries out the metabolism and energy, as well as providing intracellular transport. The ER membranes are connected on one side to the outer cytoplasmic membrane, and on the other to outer shell nuclear membrane.

The structure of EPS is heterogeneous; there are two types: granular, on the membranes of which ribosomes are located and agranular(smooth) – without ribosomes. In the ribosomes of the granular network, protein synthesis occurs, which then enters the EPS channels, and carbohydrates and lipids are synthesized on the membranes of the agranular network, which also then enter the EPS channels. Thus, biosynthesis products accumulate in the channels and cavities of the ER, which are then transported to the cell organelles. In addition, the endoplasmic reticulum divides the cell's cytoplasm into isolated compartments, thereby providing a separate environment for different reactions.

Core It is the largest cellular organelle, bounded from the cytoplasm by an extremely thin and elastic double-membrane nuclear envelope and is the most important part of a living cell. The discovery of the plant cell nucleus belongs to the Scottish botanist R. Brown (1831). In young cells, the nucleus is located closer to the center, in old cells it is shifted to the periphery, which is associated with the formation of one large vacuole, occupying a significant part of the protoplast. As a rule, plant cells have only one nucleus, although binucleate and multinucleate cells occur. The chemical composition of the nucleus is represented by proteins and nucleic acids.

The nucleus contains a significant amount of DNA (deoxyribonucleic acid), which acts as a carrier of hereditary properties. It is in the nucleus (in the chromosomes) that all hereditary information is stored and reproduced, which determines the individuality, characteristics, functions, characteristics of the cell and the entire organism as a whole. In addition, one of the most important purposes of the nucleus is to control metabolism and most processes occurring in the cell. Information coming from the nucleus determines the physiological and biochemical development of the plant cell.

Inside the nucleus there are from one to three non-membrane small bodies of round shape - nucleoli immersed in a colorless, homogeneous, gel-like mass - nuclear juice (karyoplasm). The nucleoli consist mainly of protein; 5% of their content is RNA (ribonucleic acid). The main function of nucleoli is RNA synthesis and the formation of ribosomes.

We invite you to familiarize yourself with the materials and.

: cellulose membrane, membrane, cytoplasm with organelles, nucleus, vacuoles with cell sap.

The presence of plastids is the main feature of a plant cell.

Functions of the cell membrane- determines the shape of the cell, protects against environmental factors.

Plasma membrane- a thin film, consisting of interacting molecules of lipids and proteins, delimits the internal contents from the external environment, ensures the transport of water, minerals and organic substances into the cell by osmosis and active transport, and also removes waste products.

Cytoplasm- the internal semi-liquid environment of the cell, in which the nucleus and organelles are located, provides connections between them, and participates in basic life processes.

Endoplasmic reticulum- a network of branching channels in the cytoplasm. It is involved in the synthesis of proteins, lipids and carbohydrates, and in the transport of substances. Ribosomes are bodies located on the ER or in the cytoplasm, consisting of RNA and protein, and are involved in protein synthesis. EPS and ribosomes are a single apparatus for the synthesis and transport of proteins.

Mitochondria- organelles delimited from the cytoplasm by two membranes. Organic substances are oxidized in them and ATP molecules are synthesized with the participation of enzymes. Increase in the surface of the inner membrane on which enzymes are located due to cristae. ATP is an energy-rich organic substance.

Plastids(chloroplasts, leucoplasts, chromoplasts), their content in the cell is the main feature of the plant organism. Chloroplasts are plastids containing the green pigment chlorophyll, which absorbs light energy and uses it to synthesize organic substances from carbon dioxide and water. Chloroplasts are separated from the cytoplasm by two membranes, numerous outgrowths - grana on the inner membrane, in which chlorophyll molecules and enzymes are located.

Golgi complex- a system of cavities delimited from the cytoplasm by a membrane. The accumulation of proteins, fats and carbohydrates in them. Carrying out the synthesis of fats and carbohydrates on membranes.

Lysosomes- bodies delimited from the cytoplasm by a single membrane. The enzymes they contain accelerate the breakdown of complex molecules into simple ones: proteins into amino acids, complex carbohydrates to simple ones, lipids to glycerol and fatty acids, and also destroy dead parts of the cell, whole cells.

Vacuoles- cavities in the cytoplasm filled with cell sap, a place of accumulation of reserve nutrients, harmful substances; they regulate the water content in the cell.

Core- the main part of the cell, covered on the outside with a two-membrane, pore-pierced nuclear envelope. Substances enter the core and are removed from it through the pores. Chromosomes are carriers of hereditary information about the characteristics of an organism, the main structures of the nucleus, each of which consists of one DNA molecule combined with proteins. The nucleus is the site of DNA, mRNA, and rRNA synthesis.

The presence of an outer membrane, cytoplasm with organelles, and a nucleus with chromosomes.

Outer or plasma membrane- delimits the contents of the cell from the environment (other cells, intercellular substance), consists of lipid and protein molecules, provides communication between cells, transport of substances into the cell (pinocytosis, phagocytosis) and out of the cell.

Cytoplasm- the internal semi-liquid environment of the cell, which provides communication between the nucleus and organelles located in it. The main life processes take place in the cytoplasm.

Cell organelles:

1) endoplasmic reticulum (ER)- a system of branching tubules, participates in the synthesis of proteins, lipids and carbohydrates, in the transport of substances in the cell;

2) ribosomes- bodies containing rRNA are located on the ER and in the cytoplasm and participate in protein synthesis. EPS and ribosomes are a single apparatus for protein synthesis and transport;

3) mitochondria- “power stations” of the cell, delimited from the cytoplasm by two membranes. The inner one forms cristae (folds), increasing its surface. Enzymes on the cristae accelerate the oxidation of organic substances and the synthesis of energy-rich ATP molecules;

4) Golgi complex- a group of cavities delimited by a membrane from the cytoplasm, filled with proteins, fats and carbohydrates, which are either used in vital processes or removed from the cell. The membranes of the complex carry out the synthesis of fats and carbohydrates;

5) lysosomes- bodies filled with enzymes accelerate the breakdown of proteins into amino acids, lipids into glycerol and fatty acids, polysaccharides into monosaccharides. In lysosomes, dead parts of the cell, whole cells, are destroyed.

Cellular inclusions- accumulations of reserve nutrients: proteins, fats and carbohydrates.

Core- most an important part cells. It is covered with a double-membrane shell with pores, through which some substances penetrate into the nucleus, and others enter the cytoplasm. Chromosomes are the main structures of the nucleus, carriers of hereditary information about the characteristics of the organism. It is transmitted during the division of the mother cell to daughter cells, and with germ cells to daughter organisms. The nucleus is the site of DNA, mRNA, and rRNA synthesis.

Exercise:

Explain why organelles are called specialized cell structures?

Answer: organelles are called specialized cell structures, since they perform strictly defined functions, hereditary information is stored in the nucleus, ATP is synthesized in mitochondria, photosynthesis occurs in chloroplasts, etc.

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Historical discoveries

1609 - the first microscope was made (G. Galileo)

1665 - discovered cell structure cork fabric (R. Hooke)

1674 - bacteria and protozoa discovered (A. Leeuwenhoek)

1676 - plastids and chromatophores are described (A. Leeuwenhoek)

1831 - cell nucleus discovered (R. Brown)

1839 - cell theory was formulated (T. Schwann, M. Schleiden)

1858 - the statement “Every cell is from a cell” was formulated (R. Virchow)

1873 - chromosomes discovered (F. Schneider)

1892 - viruses are discovered (D. I. Ivanovsky)

1931 - constructed electron microscope(E. Ruske, M. Knol)

1945 - endoplasmic reticulum discovered (K. Porter)

1955 - ribosomes discovered (J. Pallade)

Section: The doctrine of the cell
Topic: Cell theory. Prokaryotes and eukaryotes

Cell (Latin "tskllula" and Greek "cytos") - elementary life vy system, the basic structural unit of plant and animal organisms, capable of self-renewal, self-regulation and self-reproduction. English was discovered by the scientist R. Hooke in 1663, and he also proposed this term. The eukaryotic cell is represented by two systems - the cytoplasm and the nucleus. The cytoplasm consists of various organelles, which can be classified into: double-membrane - mitochondria and plastids; and single-membrane - endoplasmic reticulum (ER), Golgi apparatus, plasmalemma, tonoplasts, spherosomes, lysosomes; non-membrane - ribosomes, centrosomes, hyaloplasm. The nucleus consists of a nuclear membrane (double membrane) and non-membrane structures - chromosomes, nucleolus and nuclear juice. In addition, cells contain various inclusions.

CELL THEORY: The creator of this theory is the German scientist T. Schwann, who, based on the works of M. Schleiden, L. Oken , V 1838 -1839 With formulated the following provisions:

1. All plant and animal organisms are made up of cells
   
2. each cell functions independently of the others, but together with all
3. All cells arise from structureless matter of nonliving matter.

Later, R. Virchow (1858) made a significant clarification to the last position of the theory:
4. all cells arise only from cells through their division.

MODERN CELL THEORY:

1. cellular organization arose at the dawn of life and went through a long evolutionary path from prokaryotes to eukaryotes, from precellular organisms to single- and multicellular organisms.
2. new cells are formed by division from pre-existing ones
   
3. the cell is microscopicth living system consisting of cytoplasm and nucleus surrounded by a membrane (with the exception of prokaryotes)
4. in the cell are carried out:
   

• metabolism - metabolism;
• reversible physiological processes- breathing, intake and release of substances, irritability, movement;
• irreversible processes - growth and development.

5. a cell can be an independent organism. All multicellular organisms also consist of cells and their derivatives. The growth, development and reproduction of a multicellular organism is a consequence of the vital activity of one or several cells.

Prokaryotes (prenuclear e, prenuclear) constitute a superkingdom, which includes one kingdom - crushers, uniting the subkingdom of archaebacteria, bacteria and oxobacteria (division of cyanobacteria and chloroxybacteria)

Eucarotes (nuclear) also constitute a super-kingdom. It unites the kingdoms of fungi, animals, and plants.

Features of the structure of prokaryotic and eukaryotic cells.

Sign	prokaryotes	eukaryotes
	1 structural features
Presence of a kernel	there is no separate core	morphologically distinct nucleus, separated from the cytoplasm by a double membrane
Number of chromosomes and their structure	in bacteria - one circular chromosome attached to the mesosome - double-stranded DNA not associated with histone proteins. Cyanobacteria have several chromosomes in the center of the cytoplasm	Specific for each species. Chromosomes are linear, double-stranded DNA is associated with histone proteins
Plasmids Presence of a nucleolus	available none	present in mitochondria and plastids Available
Ribosomes	smaller than eukaryotes. Distributed throughout the cytoplasm. Usually free, but may be associated with membrane structures. Make up up to 40% of the cell mass	large, found in the cytoplasm in a free state or associated with the membranes of the endoplasmic reticulum. Plastids and mitochondria also contain ribosomes.
Single-membrane closed organelles	none. their functions are performed by outgrowths of the cell membrane	Numerous: endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes, etc.
Double membrane organelles	Lack of comfort	Mitochondria - in all eukaryotes; plastids - in plants
Cell center	Absent	Found in animal cells and fungi; in plants - in the cells of algae and mosses
Mesosoma	Available in bacteria. Participates in cell division and metabolism.	Absent
Cell wall	In bacteria it contains murein, in cyanobacteria it contains cellulose, pectin substances, and a little murein.	In plants - cellulose, in fungi - chitinous, in animal cells there is no cell wall
Capsule or mucous layer	Found in some bacteria	Absent
Flagella	simple structure, do not contain microtubules. Diameter 20 nm	Complex structure, contain microtubules (similar to microtubules of centrioles) Diameter 200 nm
Cell size	Diameter 0.5 - 5 µm	The diameter is usually up to 50 microns. The volume can exceed the volume of a prokaryotic cell by more than a thousand times.
	2. Features of cell activity
Movement of the cytoplasm	Absent	Occurs frequently
Aerobic cellular respiration	In bacteria - in mesosomes; in cyanobacteria - on cytoplasmic membranes	Occurs in mitochondria
Photosynthesis	There are no chloroplasts. Occurs on membranes that do not have specific forms	In chloroplasts containing special membranes assembled into grana
Phagocytosis and pinocytosis	Absent (impossible due to the presence of a rigid cell wall)	Characteristic of animal cells, absent in plants and fungi
Sporulation	Some representatives are capable of forming spores from the cell. They are intended only to withstand unfavorable environmental conditions, since they have a thick wall	Sporulation is characteristic of plants and fungi. Spores are designed to reproduce
Methods of cell division	Equal binary transverse fission, rarely budding (budding bacteria). Mitosis and meiosis are absent	Mitosis, meiosis, amitosis

Topic: Cell structure and functions

Plant cell: Animal cell :

Cell structure. Structural system of the cytoplasm

Organelles	Structure	Functions
Outer cell membrane	ultramicroscopic film consisting of a bimolecular layer of lipids. The integrity of the lipid layer can be interrupted by protein molecules - pores. In addition, proteins lie mosaic on both sides of the membrane, forming enzyme systems.	isolates the cellfrom the environment, has selective permeability,regulates the process of substances entering the cell; ensures the exchange of substances and energy with the external environment, promotes the connection of cells in tissue, participates in pinocytosis and phagocytosis; regulates the water balance of the cell and removes it from it final products life activity.
Endoplasmic reticulum ER	Ultramicroscopic membrane system, aboutforming tubes, tubules, cisternae vesicles. The structure of the membranes is universal; the entire network is united into a single whole with the outer membrane of the nuclear envelope and the outer cell membrane. The granular ER carries ribosomes, while the smooth ER lacks them.	Provides transport of substances both within the cell and between neighboring cells.Divides the cell into separate sections in which various physiological processes occur simultaneously and chemical reactions. Granular EPS is involved in protein synthesis. In the EPS channels, protein molecules acquire secondary, tertiary and quaternary structures, fats are synthesized, and ATP is transported
Mitochondria	Microscopic organelles with a double-membrane structure. The outer membrane is smooth, the inner one isIt produces outgrowths of various shapes - cristae. The mitochondrial matrix (semi-liquid substance) contains enzymes, ribosomes, DNA, RNA. They reproduce by division.	A universal organelle that is a respiratory and energy center. During the oxygen stage of dissimilation in the matrix, with the help of enzymes, organic substances are broken down, releasing energy that goes into synthesis ATP (on cristae)
Ribosomes	Ultramicroscopic organelles are round or mushroom-shaped, consisting of two parts - subunits. They do not have a membrane structure and consist of protein and rRNA. Subunits are formed in the nucleolus. They unite along mRNA molecules into chains - polyribosomes - in the cytoplasm	Universal organelles of all animal and plant cells. They are found in the cytoplasm in a free state or on the membranes of the ER; in addition, contained in mitochondria and chloroplasts. Proteins are synthesized in ribosomes according to the principle of matrix synthesis; a polypeptide chain is formed - the primary structure of the protein molecule.
Leukoplasts	Microscopic organelles with a double-membrane structure. The inner membrane forms 2-3 outgrowths. The shape is round. Colorless. Like all plastids, they are capable of division.	Characteristic of plant cells. They serve as a site for the deposition of reserve nutrients, mainly starch grains. In the light, their structure becomes more complex and they transform into chloroplasts. Formed from proplastids.
Golgi apparatus (dictyosome)	microscopic single-membrane organelles, consisting of a stack of flat cisterns, along the edges of which tubes branch off, separating small bubbles. Has two poles: construction and secretory	the most mobile and changing organelle. Products of synthesis, decay, and substances entering the cell, as well as substances that are removed from the cell, accumulate in the tanks. Packed in vesicles, they enter the cytoplasm. in a plant cell they participate in the construction of the cell wall.
Chloroplasts	Microscopic organelles with a double-membrane structure. The outer membrane is smooth. VnThe morning membrane forms a system of two-layer plates - stroma thylakoids and granal thylakoids. In the thylakoid membranes, pigments - chlorophyll and carotenoids - are concentrated between layers of protein and lipid molecules. The protein-lipid matrix contains its own ribosomes, DNA, and RNA. The shape of chloroplasts is lenticular. The color is green.	Characteristic of plant cells. Photosynthetic organelles capable of creating inorganic substances(CO2 and H2O) in the presence of light energy and chlorophyll pigment, organic substances - carbohydrates and free oxygen. Synthesis of own proteins. They can be formed from proplastids or leucoplasts, and in the fall they transform into chromoplasts (red and orange fruits, red and yellow leaves). Capable of division.
Chromoplasts	Micro organelles with a double-membrane structure. Chromoplasts themselves have spherical shape, and those formed from chloroplasts take the form ofcarotenoid tallow, typical for this plant species. The color is red. orange, yellow	Characteristic of plant cells. They give flower petals a color that is attractive to pollinating insects. In the autumn leaves and ripe fruits, separated from the plant, contain crystalline carotenoids - the end products of metabolism
Lysosomes	Microscopic single-membrane organelles of round shape. their number depends on the vital activity of the cell and its physiologicalsky state. Lysosomes contain lysing (dissolving) enzymes synthesized on ribosomes. separated from dictysomes in the form of vesicles	Digestion of food caught in animal cell during phagocytosis. protective function. In the cells of any organisms, autolysis (self-dissolution of organelles) occurs, especially under conditions of food or oxygen starvation. in plants, organelles dissolve during the formation of cork tissue, blood vessels, wood, and fibers.
Cell center (Centrosome)	Ultramicroscopic organelle of non-membranous striplets. consists of two centrioles. each has a cylindrical shape, the walls are formed by nine triplets of tubes, and in the middle there is a homogeneous substance. The centrioles are located perpendicular to each other.	Takes part in the division of cells of animals and lower plants. At the beginning of division, the centrioles diverge to different poles of the cell. The spindle strands extend from the centrioles to the centromeres of the chromosomes. in anaphase, these strands are attracted to the poles by the chromatids. After the end of division, the centrioles remain in the daughter cells, double and form the cell center.
Organoids of movement	cilia - numerous cytoplasmic projections on the surface of the membrane flagella - eat nal cytoplasmic projections on the cell surface false legs (pseudopodia) - amoeboid protrusions of the cytoplasm myofibrils - thin filaments 1 cm or more long cytoplasm carrying out stream and circular movement	removing dust particles. movement movement are formed in unicellular animals in different places cytoplasm for food capture and movement. Characteristic of blood leukocytes, as well as endoderm cells of coelenterates. serve to contract muscle fibers movement of cell organelles in relation to a source of light, heat, or chemical stimulus.