What is the cellular structure made of. The structure of the human cell

The chemical composition of living organisms

The chemical composition of living organisms can be expressed in two forms: atomic and molecular. The atomic (elemental) composition shows the ratio of the atoms of the elements that make up living organisms. Molecular (material) composition reflects the ratio of molecules of substances.

Chemical elements are part of cells in the form of ions and molecules of inorganic and organic substances. The most important inorganic substances in the cell are water and mineral salts, the most important organic substances are carbohydrates, lipids, proteins and nucleic acids.

Water is the predominant component of all living organisms. The average water content in the cells of most living organisms is about 70%.

Mineral salts in an aqueous solution of the cell dissociate into cations and anions. The most important cations are K+, Ca2+, Mg2+, Na+, NHJ, anions - Cl-, SO2-, HPO2-, H2PO-, HCO-, NO-.

Carbohydrates - organic compounds consisting of one or more molecules of simple sugars. The content of carbohydrates in animal cells is 1-5%, and in some plant cells it reaches 70%.

Lipids - fats and fat-like organic compounds, practically insoluble in water. Their content in different cells varies greatly: from 2-3 to 50-90% in the cells of plant seeds and adipose tissue of animals.

Squirrels are biological heteropolymers whose monomers are amino acids. Only 20 amino acids are involved in the formation of proteins. They are called fundamental, or basic. Some of the amino acids are not synthesized in the organisms of animals and humans and must be supplied with plant foods (they are called essential).

Nucleic acids. There are two types of nucleic acids: DNA and RNA. Nucleic acids are polymers whose monomers are nucleotides.

Cell structure

The formation of cell theory

• Robert Hooke in 1665 discovered cells in a section of cork and was the first to use the term "cell".
• Anthony van Leeuwenhoek discovered unicellular organisms.
• Matthias Schleiden in 1838 and Thomas Schwann in 1839 formulated the main provisions of the cell theory. However, they erroneously believed that cells arise from the primary non-cellular substance.
• Rudolf Virchow proved in 1858 that all cells are formed from other cells by cell division.

Basic provisions of cell theory

1. The cell is the structural unit of all living things. All living organisms are made up of cells (viruses are an exception).
2. The cell is the functional unit of all living things. The cell shows the whole range of vital functions.
3. The cell is the unit of development of all living things. New cells are formed only as a result of the division of the original (mother) cell.
4. The cell is the genetic unit of all living things. The chromosomes of a cell contain information about the development of the whole organism.
5. The cells of all organisms are similar in chemical composition, structure and function.

Types of cell organization

Among living organisms, only viruses do not have a cellular structure. All other organisms are represented by cellular life forms. There are two types of cellular organization: prokaryotic and eukaryotic. Bacteria are prokaryotes, and plants, fungi, and animals are eukaryotes.

Prokaryotic cells are relatively simple. They do not have a nucleus, the location of DNA in the cytoplasm is called a nucleoid, the only DNA molecule is circular and not associated with proteins, cells are smaller than eukaryotic cells, the cell wall contains a glycopeptide - murein, there are no membrane organelles, their functions are performed by invaginations of the plasma membrane, ribosomes are small, microtubules are absent, so the cytoplasm is immobile, and the cilia and flagella have a special structure.

Eukaryotic cells have a nucleus in which chromosomes are located - linear DNA molecules associated with proteins; various membrane organelles are located in the cytoplasm.

Plant cells are distinguished by the presence of a thick cellulose cell wall, plastids, and a large central vacuole that shifts the nucleus to the periphery. The cell center of higher plants does not contain centrioles. The storage carbohydrate is starch.

Fungal cells have a cell membrane containing chitin, there is a central vacuole in the cytoplasm, and there are no plastids. Only some fungi have a centriole in the cell center. The main reserve carbohydrate is glycogen.

Animal cells have, as a rule, a thin cell wall, do not contain plastids and a central vacuole; a centriole is characteristic of the cell center. The storage carbohydrate is glycogen.

The structure of a eukaryotic cell

A typical eukaryotic cell consists of three components: a membrane, a cytoplasm, and a nucleus.

Cell wall

Outside, the cell is surrounded by a shell, the basis of which is the plasma membrane, or plasmalemma, which has a typical structure and a thickness of 7.5 nm.

The cell membrane performs important and very diverse functions: it determines and maintains the shape of the cell; protects the cell from the mechanical effects of the penetration of damaging biological agents; carries out the reception of many molecular signals (for example, hormones); limits the internal contents of the cell; regulates the metabolism between the cell and the environment, ensuring the constancy of the intracellular composition; participates in the formation of intercellular contacts and various kinds of specific protrusions of the cytoplasm (microvilli, cilia, flagella).

The carbon component in the membrane of animal cells is called the glycocalyx.

The exchange of substances between the cell and its environment occurs constantly. The mechanisms of transport of substances into and out of the cell depend on the size of the transported particles. Small molecules and ions are transported by the cell directly across the membrane in the form of active and passive transport.

Depending on the type and direction, endocytosis and exocytosis are distinguished.

The absorption and excretion of solid and large particles are respectively called phagocytosis and reverse phagocytosis, liquid or dissolved particles - pinocytosis and reverse pinocytosis.

Cytoplasm

The cytoplasm is the internal contents of the cell and consists of hyaloplasm and various intracellular structures located in it.

Hyaloplasm (matrix) is an aqueous solution of inorganic and organic substances that can change its viscosity and are in constant motion. The ability to move or flow of the cytoplasm is called cyclosis.

The matrix is ​​an active medium in which many physical and chemical processes take place and which unites all elements of the cell into a single system.

The cytoplasmic structures of the cell are represented by inclusions and organelles. Inclusions are relatively inconstant, occurring in some types of cells at certain moments of life, for example, as a supply of nutrients (grains of starch, proteins, glycogen drops) or products to be excreted from the cell. Organelles are permanent and indispensable components of most cells that have a specific structure and perform a vital function.

The membrane organelles of a eukaryotic cell include the endoplasmic reticulum, the Golgi apparatus, mitochondria, lysosomes, and plastids.

Endoplasmic reticulum. The entire inner zone of the cytoplasm is filled with numerous small channels and cavities, the walls of which are membranes similar in structure to the plasma membrane. These channels branch, connect with each other and form a network called the endoplasmic reticulum.

The endoplasmic reticulum is heterogeneous in its structure. Two types of it are known - granular and smooth. On the membranes of the channels and cavities of the granular network there are many small round bodies - ribosomes, which give the membranes a rough appearance. The membranes of the smooth endoplasmic reticulum do not carry ribosomes on their surface.

The endoplasmic reticulum performs many different functions. The main function of the granular endoplasmic reticulum is participation in protein synthesis, which is carried out in ribosomes.

On the membranes of the smooth endoplasmic reticulum, lipids and carbohydrates are synthesized. All these synthesis products accumulate in channels and cavities, and then are transported to various cell organelles, where they are consumed or accumulated in the cytoplasm as cell inclusions. The endoplasmic reticulum connects the main organelles of the cell.

golgi apparatus

In many animal cells, such as nerve cells, it takes the form of a complex network located around the nucleus. In the cells of plants and protozoa, the Golgi apparatus is represented by individual sickle-shaped or rod-shaped bodies. The structure of this organoid is similar in the cells of plant and animal organisms, despite the variety of its shape.

The composition of the Golgi apparatus includes: cavities limited by membranes and located in groups (5-10 each); large and small bubbles located at the ends of the cavities. All these elements form a single complex.

The Golgi apparatus performs many important functions. Through the channels of the endoplasmic reticulum, the products of the synthetic activity of the cell - proteins, carbohydrates and fats - are transported to it. All these substances first accumulate, and then enter the cytoplasm in the form of large and small bubbles and are either used in the cell itself during its life activity, or removed from it and used in the body. For example, in the cells of the pancreas of mammals, digestive enzymes are synthesized, which accumulate in the cavities of the organoid. Then vesicles filled with enzymes form. They are excreted from the cells into the pancreatic duct, from where they flow into the intestinal cavity. Another important function of this organoid is that fats and carbohydrates (polysaccharides) are synthesized on its membranes, which are used in the cell and which are part of the membranes. Thanks to the activity of the Golgi apparatus, the renewal and growth of the plasma membrane occurs.

Mitochondria

The cytoplasm of most animal and plant cells contains small bodies (0.2-7 microns) - mitochondria (Greek "mitos" - thread, "chondrion" - grain, granule).

Mitochondria are clearly visible in a light microscope, with which you can see their shape, location, count the number. The internal structure of mitochondria was studied using an electron microscope. The shell of the mitochondrion consists of two membranes - outer and inner. The outer membrane is smooth, it does not form any folds and outgrowths. The inner membrane, on the contrary, forms numerous folds that are directed into the cavity of the mitochondria. The folds of the inner membrane are called cristae (lat. "crista" - comb, outgrowth). The number of cristae is not the same in the mitochondria of different cells. There can be from several tens to several hundreds, and there are especially many cristae in the mitochondria of actively functioning cells, for example, muscle cells.

Mitochondria are called the "power stations" of cells" since their main function is the synthesis of adenosine triphosphate (ATP). This acid is synthesized in the mitochondria of the cells of all organisms and is a universal source of energy necessary for the implementation of the vital processes of the cell and the whole organism.

New mitochondria are formed by the division of already existing mitochondria in the cell.

Lysosomes

They are small round bodies. Each lysosome is separated from the cytoplasm by a membrane. Inside the lysosome are enzymes that break down proteins, fats, carbohydrates, nucleic acids.

Lysosomes approach the food particle that has entered the cytoplasm, merge with it, and one digestive vacuole is formed, inside which there is a food particle surrounded by lysosome enzymes. Substances formed as a result of the digestion of a food particle enter the cytoplasm and are used by the cell.

Possessing the ability to actively digest nutrients, lysosomes are involved in the removal of parts of cells, whole cells and organs that die in the process of vital activity. The formation of new lysosomes occurs in the cell constantly. Enzymes contained in lysosomes, like any other proteins, are synthesized on the ribosomes of the cytoplasm. Then these enzymes enter through the channels of the endoplasmic reticulum to the Golgi apparatus, in the cavities of which lysosomes are formed. In this form, lysosomes enter the cytoplasm.

plastids

Plastids are found in the cytoplasm of all plant cells. There are no plastids in animal cells. There are three main types of plastids: green - chloroplasts; red, orange and yellow - chromoplasts; colorless - leukoplasts.

Mandatory for most cells are also organelles that do not have a membrane structure. These include ribosomes, microfilaments, microtubules, and the cell center.

Ribosomes. Ribosomes are found in the cells of all organisms. These are microscopic bodies of rounded shape with a diameter of 15-20 nm. Each ribosome consists of two particles of different sizes, small and large.

One cell contains many thousands of ribosomes, they are located either on the membranes of the granular endoplasmic reticulum, or lie freely in the cytoplasm. Ribosomes are made up of proteins and RNA. The function of ribosomes is protein synthesis. Protein synthesis is a complex process that is carried out not by one ribosome, but by a whole group, including up to several dozen combined ribosomes. This group of ribosomes is called a polysome. The synthesized proteins are first accumulated in the channels and cavities of the endoplasmic reticulum and then transported to the organelles and cell sites where they are consumed. The endoplasmic reticulum and the ribosomes located on its membranes are a single apparatus for the biosynthesis and transport of proteins.

Microtubules and microfilaments

Filamentous structures, consisting of various contractile proteins and causing the motor functions of the cell. Microtubules have the form of hollow cylinders, the walls of which are composed of proteins - tubulins. Microfilaments are very thin, long, filamentous structures composed of actin and myosin.

Microtubules and microfilaments penetrate the entire cytoplasm of the cell, forming its cytoskeleton, causing cyclosis, intracellular movements of organelles, segregation of chromosomes during the division of nuclear material, etc.

Cell center (centrosome). In animal cells, an organoid is located near the nucleus, which is called the cell center. The main part of the cell center is made up of two small bodies - centrioles located in a small area of ​​​​densified cytoplasm. Each centriole has the shape of a cylinder up to 1 µm long. Centrioles play an important role in cell division; they are involved in the formation of the fission spindle.

In the process of evolution, different cells adapted to living in different conditions and performing specific functions. This required the presence in them of special organoids, which are called specialized, in contrast to the general-purpose organelles discussed above. These include contractile vacuoles of protozoa, myofibrils of muscle fibers, neurofibrils and synaptic vesicles of nerve cells, microvilli of epithelial cells, cilia and flagella of some protozoa.

Nucleus

The nucleus is the most important component of eukaryotic cells. Most cells have a single nucleus, but there are also multinucleated cells (in a number of protozoa, in the skeletal muscles of vertebrates). Some highly specialized cells lose nuclei (mammalian erythrocytes, for example).

The nucleus, as a rule, has a spherical or oval shape, less often it can be segmented or fusiform. The nucleus consists of the nuclear membrane and karyoplasm containing chromatin (chromosomes) and nucleoli.

The nuclear envelope is formed by two membranes (outer and inner) and contains numerous pores through which various substances are exchanged between the nucleus and the cytoplasm.

Karyoplasm (nucleoplasm) is a jelly-like solution that contains a variety of proteins, nucleotides, ions, as well as chromosomes and the nucleolus.

The nucleolus is a small rounded body, intensely stained and found in the nuclei of non-dividing cells. The function of the nucleolus is the synthesis of rRNA and their connection with proteins, i.e. assembly of ribosome subunits.

Chromatin - lumps, granules and filamentous structures that are specifically stained by some dyes, formed by DNA molecules in combination with proteins. Different parts of DNA molecules in the composition of chromatin have different degrees of helicity, and therefore differ in color intensity and the nature of genetic activity. Chromatin is a form of existence of genetic material in non-dividing cells and provides the possibility of doubling and realizing the information contained in it. In the process of cell division, DNA spiralization occurs and chromatin structures form chromosomes.

Chromosomes are dense, intensely staining structures that are units of the morphological organization of the genetic material and ensure its precise distribution during cell division.

The number of chromosomes in the cells of each biological species is constant. Usually in the nuclei of body cells (somatic) chromosomes are presented in pairs, in germ cells they are not paired. A single set of chromosomes in germ cells is called haploid (n), a set of chromosomes in somatic cells is called diploid (2n). The chromosomes of different organisms differ in size and shape.

A diploid set of chromosomes in cells of a particular type of living organisms, characterized by the number, size and shape of chromosomes, is called a karyotype. In the chromosome set of somatic cells, paired chromosomes are called homologous, chromosomes from different pairs are called non-homologous. Homologous chromosomes are the same in size, shape, composition (one inherited from the mother, the other from the father). The chromosomes in the karyotype are also divided into autosomes, or non-sex chromosomes, which are the same in male and female individuals, and heterochromosomes, or sex chromosomes involved in sex determination and differing in males and females. The human karyotype is represented by 46 chromosomes (23 pairs): 44 autosomes and 2 sex chromosomes (the female has two identical X chromosomes, the male has X and Y chromosomes).

The nucleus stores and implements genetic information, controls the process of protein biosynthesis, and through proteins - all other life processes. The nucleus is involved in the replication and distribution of hereditary information between daughter cells, and, consequently, in the regulation of cell division and the development of the body.

A cell is a single living system consisting of two inextricably linked parts - the cytoplasm and the nucleus (color table XII).

Cytoplasm- this is an internal semi-liquid environment in which the nucleus and all organelles of the cell are located. It has a fine-grained structure, penetrated by numerous thin threads. It contains water, dissolved salts and organic matter. The main function of the cytoplasm is to unite and ensure the interaction of the nucleus and all organelles of the cell.

outer membrane surrounds the cell with a thin film consisting of two layers of protein, between which there is a fatty layer. It is permeated with numerous small pores through which ions and molecules are exchanged between the cell and the environment. The membrane thickness is 7.5-10 nm, the pore diameter is 0.8-1 nm. In plants, a fiber sheath forms on top of it. The main functions of the outer membrane are to limit the internal environment of the cell, protect it from damage, regulate the flow of ions and molecules, remove metabolic products and synthesized substances (secrets), connect cells and tissues (due to outgrowths and folds). The outer membrane ensures the penetration of large particles into the cell by phagocytosis (see sections in "Zoology" - "Protozoa", in "Anatomy" - "Blood"). In a similar way, the cell absorbs liquid drops - pinocytosis (from the Greek "pino" - I drink).

Endoplasmic reticulum(EPS) is a complex system of channels and cavities consisting of membranes, penetrating the entire cytoplasm. EPS is of two types - granular (rough) and smooth. On the membranes of the granular network there are many tiny bodies - ribosomes; they do not exist in a smooth network. The main function of EPS is participation in the synthesis, accumulation and transportation of the main organic substances produced by the cell. Protein is synthesized in granular ER, while carbohydrates and fats are synthesized in smooth ER.

Ribosomes- small bodies, 15-20 nm in diameter, consisting of two particles. There are hundreds of thousands of them in every cell. Most ribosomes are located on the membranes of the granular ER, and some are located in the cytoplasm. They are composed of proteins and rRNA. The main function of ribosomes is protein synthesis.

Mitochondria- these are small bodies, 0.2-0.7 microns in size. Their number in a cell reaches several thousand. They often change shape, size and location in the cytoplasm, moving to their most active part. The outer cover of the mitochondria consists of two three-layer membranes. The outer membrane is smooth, the inner one forms numerous outgrowths on which respiratory enzymes are located. The internal cavity of mitochondria is filled with fluid, which houses ribosomes, DNA and RNA. New mitochondria are formed when old ones divide. The main function of mitochondria is the synthesis of ATP. They synthesize a small amount of proteins, DNA and RNA.

plastids unique to plant cells. There are three types of plastids - chloroplasts, chromoplasts and leukoplasts. They are capable of mutual transition into each other. Plastids reproduce by division.

Chloroplasts(60) are green, oval in shape. Their size is 4-6 microns. From the surface, each chloroplast is bounded by two three-layer membranes - outer and inner. Inside it is filled with a liquid, in which there are several dozens of special, interconnected cylindrical structures - gran, as well as ribosomes, DNA and RNA. Each grana consists of several tens of flat membrane sacs superimposed on each other. On the transverse section, it has a rounded shape, its diameter is 1 µm. All the chlorophyll is concentrated in the grains, and the process of photosynthesis takes place in them. The resulting carbohydrates first accumulate in the chloroplast, then enter the cytoplasm, and from it to other parts of the plant.

Chromoplasts determine the red, orange and yellow color of flowers, fruits and autumn leaves. They have the form of polyhedral crystals located in the cytoplasm of the cell.

Leucoplasts colorless. They are found in unpainted parts of plants (stems, tubers, roots), have a round or rod-shaped shape (5-6 microns in size). They store reserves.

Cell Center found in animal and lower plant cells. It consists of two small cylinders - centrioles (about 1 micron in diameter), located perpendicular to each other. Their walls consist of short tubes, the cavity is filled with a semi-liquid substance. Their main role is the formation of the division spindle and the uniform distribution of chromosomes among daughter cells.

Golgi complex was named after the Italian scientist who first discovered it in nerve cells. It has a diverse shape and consists of cavities limited by membranes, tubules extending from them and bubbles located at their ends. The main function is the accumulation and excretion of organic substances synthesized in the endoplasmic reticulum, the formation of lysosomes.

Lysosomes- rounded little bodies with a diameter of about 1 micron. From the surface, the lysosome is limited by a three-layer membrane, inside it there is a complex of enzymes that can break down carbohydrates, fats and proteins. There are several dozen lysosomes in a cell. New lysosomes are formed in the Golgi complex. Their main function is to digest food that has entered the cell by phagocytosis and remove dead organelles.

Organelles of movement- flagella and cilia - are cell outgrowths and have the same structure in animals and plants (their common origin). The movement of multicellular animals is provided by muscle contractions. The main structural unit of a muscle cell is myofibrils - thin threads more than 1 cm long, 1 micron in diameter, arranged in bundles along the muscle fiber.

Cell inclusions- Carbohydrates, fats and proteins - are non-permanent components of the cell. They are periodically synthesized, accumulated in the cytoplasm as reserve substances and used in the course of the life of the organism.

Carbohydrates are concentrated in grains of starch (in plants) and glycogen (in animals). There are many of them in liver cells, potato tubers and other organs. Fats accumulate in the form of droplets in plant seeds, subcutaneous tissue, connective tissue, etc. Proteins are deposited in the form of grains in animal eggs, plant seeds, and other organs.

Nucleus one of the most important organelles in the cell. It is separated from the cytoplasm by the nuclear membrane, which consists of two three-layer membranes, between which there is a narrow strip of semi-liquid substance. Through the pores of the nuclear envelope, the exchange of substances between the nucleus and the cytoplasm takes place. The cavity of the nucleus is filled with nuclear juice. It contains the nucleolus (one or more), chromosomes, DNA, RNA, proteins and carbohydrates. The nucleolus is a rounded body ranging in size from 1 to 10 microns or more; it synthesizes RNA. Chromosomes are only visible in dividing cells. In the interphase (non-dividing) nucleus, they are present in the form of thin long filaments of chromatin (DNA-to-protein connections). They contain hereditary information. The number and shape of chromosomes in each species of animals and plants are strictly defined. Somatic cells that make up all organs and tissues contain a diploid (double) set of chromosomes (2 n); germ cells (gametes) - haploid (single) set of chromosomes (n). The diploid set of chromosomes in the nucleus of a somatic cell is created from paired (identical), homologous chromosomes. Chromosomes of different pairs (non-homologous) differ from each other in shape, location centromeres and secondary stretches.

prokaryotes- These are organisms with small, primitively arranged cells, without a clearly defined nucleus. These include blue-green algae, bacteria, phages and viruses. Viruses are DNA or RNA molecules covered with a protein coat. They are so small that they can only be seen with an electron microscope. They lack cytoplasm, mitochondria and ribosomes, so they are not able to synthesize the protein and energy necessary for their life. Once in a living cell and using other people's organic matter and energy, they develop normally.

eukaryotes- organisms with larger typical cells containing all the main organelles: nucleus, endoplasmic reticulum, mitochondria, ribosomes, Golgi complex, lysosomes and others. Eukaryotes include all other plant and animal organisms. Their cells have a similar type of structure, which convincingly proves the unity of their origin.

The cells of our body are diverse in structure and function. Cells of blood, bone, nerve, muscle and other tissues externally and internally differ greatly. However, almost all of them have common features characteristic of animal cells.

Membrane organization of the cell

The membrane is at the core of the human cell. It, like a constructor, forms the membrane organelles of the cell and the nuclear membrane, and also limits the entire volume of the cell.

The membrane is built from a double layer of lipids. From the outside of the cell, protein molecules are mosaically placed on lipids.

Selective permeability is the main property of the membrane. It means that some substances are passed through the membrane, while others are not.

Rice. 1. Scheme of the structure of the cytoplasmic membrane.

Functions of the cytoplasmic membrane:

• protective;
• regulation of metabolism between the cell and the environment;
• maintaining the shape of the cells.

Cytoplasm

The cytoplasm is the liquid medium of the cell. Organelles and inclusions are located in the cytoplasm.

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Functions of the cytoplasm:

• water tank for chemical reactions;
• unites all parts of the cell and provides interaction between them.

Rice. 2. Scheme of the structure of a human cell.

Organelles

• Endoplasmic reticulum (ER)

The system of channels penetrating the cytoplasm. Participates in the metabolism of proteins and lipids.

• golgi apparatus

Located around the core, it looks like flat tanks. Function: transfer, sorting and accumulation of proteins, lipids and polysaccharides, as well as the formation of lysosomes.

• Lysosomes

They look like bubbles. They contain digestive enzymes and carry out protective and digestive functions.

• Mitochondria

Synthesize ATP, a substance that is a source of energy.

• Ribosomes

Perform protein synthesis.

• Nucleus

Main components:

• nuclear membrane;
• nucleolus;
• karyoplasm;
• chromosomes.

The nuclear membrane separates the nucleus from the cytoplasm. Nuclear juice (karyoplasm) is the liquid internal environment of the nucleus.

The number of chromosomes does not indicate the level of organization of the species. So, a human has 46 chromosomes, a chimpanzee has 48, a dog has 78, a turkey has 82, a rabbit has 44, and a cat has 38.

Kernel functions:

• preservation of hereditary information about the cell;
• transmission of hereditary information to daughter cells during division;
• implementation of hereditary information through the synthesis of proteins characteristic of this cell.

Special purpose organelles

These are organelles that are not characteristic of all human cells, but of cells of individual tissues or groups of cells. For example:

• flagella of male germ cells , providing their movement;
• myofibrils of muscle cells , providing their reduction;
• neurofibrils of nerve cells - threads that ensure the transmission of a nerve impulse;
• photoreceptors eyes, etc.

Inclusions

Inclusions are various substances temporarily or permanently present in the cell. It:

• pigment inclusions that give color (for example, melanin - a brown pigment that protects from ultraviolet rays);
• trophic inclusions , which are a store of energy;
• secretory inclusions located in the cells of the glands;
• excretory inclusions , for example, sweat droplets in sweat gland cells.

Rice. 3. Cells of different human tissues.

The cells of the human body reproduce by dividing.

What have we learned?

The structure and functions of human cells are similar to those of animal cells. They are built on a common principle and contain the same components. The structure of cells of different tissues is very peculiar. Some of them have special organelles.

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Historical discoveries

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

1665 - cellular structure of cork tissue discovered (R. Hooke)

1674 - bacteria and protozoa are discovered (A. Leeuwenhoek)

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

1831 - the cell nucleus was discovered (R. Brown)

1839 - the cellular theory is formulated (T. Schwann, M. Schleiden)

1858 - the position "Each cell from a cell" was formulated (R. Virchow)

1873 - chromosomes were discovered (F. Schneider)

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

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

1945 - endoplasmic reticulum discovered (K. Porter)

1955 - ribosomes are discovered (J. Pallade)

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 the structureless substance of inanimate matter.

1. cellular organization arose at the dawn of life and went through a long evolutionary path from prokaryotes to eukaryotes, from precellular organisms to unicellular and multicellular organisms.
2. new cells are formed by division from pre-existing ones
   
3. the cell is microscopicand a living system consisting of a cytoplasm and a 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.

Features of the structure of prokaryotic and eukaryotic cells.