Plants, unlike animals, do not have specialized excretory organs. Therefore, each cell of a plant organism has to store within itself (in hyaloplasm, organelles, vacuoles and even the cell wall) all metabolic products: both those temporarily removed from metabolism (reserve substances) and its final products (unnecessary “waste”). Excess accumulation Such substances are accompanied by their deposition in an amorphous form or in the form of crystals - cellular inclusions. Spares nutrients- products of primary metabolism, all others - secondary.
Spare nutrients deposited in the cell in the form of starch and protein (aleurone) grains and drops of fat. As a rule, they accumulate in the cells of storage tissues of fruits, seeds, rhizomes, shoot and root tubers, bulbs, and corms.
The main reserve substance of plants is starch. It is stored in all plant organs. Easily broken down into water-soluble sugars, which in the form of a solution can move throughout the plant, starch is widely used by the plant for the synthesis of other organic substances and as a source of energy. Distinguish assimilation (primary) And spare (secondary) starch. Primary starch is synthesized in chloroplasts from glucose molecules, reserve starch is deposited in leucoplasts (amyloplasts). Starch that is hydrolyzed to sugars and in their form moves throughout the plant is called transient.
Leucoplasts filled with secondary starch are called amyloplasts, or starch grains(Fig. 59). There are three types of starch grains: simple, semi-compound And complex. In simple grains - one starch formation center, around which layers of starch are deposited. Semi-complex grains have several centers, around each of which individual layers of starch are formed first, and later common ones. In complex grains, each center has only its own layers of starch - there are no common ones. Simple starch grains are typical of corn, wheat, and rye; complex - for buckwheat, oats, rice. All three types of starch grains can be found in the storage tissue cells of the potato tuber. The size, shape and type of starch grains are specific to each plant species. By analyzing flour consisting mainly of starch, it is possible to determine by the type of starch grains what plant it was obtained from and whether it contains impurities of flour of a different origin. Observed through a microscope layering starch grains is explained by the different water content in the layers: in dark ones there is less of it, in light ones there is more. This is due to the uneven supply of starch during the day, which in turn is determined by the intensity of photosynthesis occurring in the leaves.
Rice. 59.
Especially great value In human life, starch is contained in grains of cereals (corn, wheat, rice, rye), storage tissues of potato and sweet potato tubers, and banana fruits.
Fats (lipids)- the second most important type of storage substances for plants. Being twice as caloric as proteins and carbohydrates, they represent the most energetically efficient (beneficial) group of organic substances and predominate in the cells of storage tissues of relatively small plant organs - seeds, less often - fruits. Fats, as the main reserve substance, are contained in the seeds of plants of the vast majority of species (about 90%) of angiosperms. For example, peanut seeds may contain more than 40% oils by weight of dry matter, sunflower seeds - more than 50%, castor beans - more than 60%. In olive fruits, the proportion of oil can reach 50%.
Fats are deposited in the cytoplasm, usually in the form lipid drops, which are sometimes considered as single-membrane organelles and in this case called spherosomes. They can also be deposited in leucoplasts (oleoplasts). During seed germination, fats are hydrolyzed to form soluble carbohydrates necessary for seedling development.
The bulk is obtained from seeds vegetable oils, many of which are used as food: sunflower, corn, flaxseed, mustard, hemp. The oil extracted from the olive fruit is especially highly valued - olive oil.
Storage proteins (proteins) are usually found in the form aleurone grains (protein bodies). Aleurone grains have different shapes and sizes (from 0.2 to 20 μm) and are numerous small dried vacuoles filled with proteins in amorphous and crystalline forms. Aleurone grains are simple And complex. Simple aleurone grains contain only amorphous protein and are typical of legumes, buckwheat, corn, and rice. Complex aleurone grains contain amorphous protein albumen, in which protein crystalloids are immersed globulin And Phytin globoids- a substance containing phosphorus, potassium, magnesium and calcium ions important for the plant. Such aleurone grains are formed in the cells of the storage tissues of flax, pumpkin, and sunflower seeds.
When seeds germinate, aleurone grains located in the cells of their storage tissues swell, and proteins with phytin are split into more simple substances, necessary for the formation of a seedling.
Products of secondary metabolism. Some of the final products of metabolism can accumulate in specialized cells or in special containers. Among them the most common essential oils, resins, calcium oxalate, etc.
Essential oils They are a mixture of organic nitrogen-free volatile compounds (terpenes and their derivatives - aldehydes, ketones, alcohols, etc.). They are contained in the tissues of flowers, leaves, seeds, fruits, without participating in metabolism. There are about 3 thousand species of plants that produce essential oils. Many of them are used in medicine, cosmetology, and the perfume industry. Essential oils of lavender, rose, mint, citrus plants, etc. are especially highly valued.
Resins - complex compounds that accumulate in the form of droplets in the cytoplasm or cell sap. They can also be released outside the cells. Being impenetrable to water and having antiseptic properties, resins serve as plant protection, sometimes covering the surfaces of its organs. Plant resins are used in industry and medicine. The fossilized resin of extinct coniferous plants - amber - is especially valued.
Rice. 60.
Calcium oxalate crystallizes in cell sap (Fig. 60). Unlike crystals of organic substances, it is no longer included in the metabolism, but is its final product. By forming calcium oxalate, the plant removes metabolic processes excess calcium. Calcium oxalate crystals are represented by: single polyhedra(dry scales of onion bulb), Rafidami - bunches of small needle-shaped crystals (grape leaves), Druze - spherical structures formed by fused crystals (rhubarb rhizome, sweet potato tuber), crystal sand(nightshade leaves).
Can be found in plant cells cystoliths - grape-shaped formations that arise on the projections of the cell wall and are crystals of calcium carbonate (typical of nettles and mulberries).
Organelles for special purposes - (available only in cells of highly specialized tissues and ensure the performance of strictly specific functions of these tissues): in epithelial cells - cilia, microvilli, tonofibrils; in neural tissues - neurofibrils and basophilic substance; V muscle tissue- myofibrils.
Cilia- organelles similar in structure and function to centrioles, i.e. have a similar structure and provide motor function. A cilium is an outgrowth of cytoplasm on the surface of a cell, covered with a cytolemma. Along this outgrowth, there are 9 pairs of microtubules located inside, parallel to each other, forming a cylinder; in the center of this cylinder along, and therefore in the center of the cilium, there is another pair of central microtubules. At the base of this outgrowth-cilium, perpendicular to it, there is another similar structure.
Microvilli- these are outgrowths of the cytoplasm on the surface of cells, covered on the outside with cytolemma, increasing the surface area of the cell. Found in epithelial cells that provide absorption functions (intestines, renal tubules).
Myofibrils- consist of contractile proteins actin and myosin, are found in muscle cells and provide the contraction process.
Neurofibrils- found in neurocytes and are a collection of neurofibrils and neurotubules. In the body, the cells are arranged randomly, and in the processes - parallel to each other. They perform the function of the skeleton of neurocytes (i.e., the function of the cytoskeleton), and in the processes they participate in the transport of substances from the body of neurocytes along the processes to the periphery.
Basophilic substance- present in neurocytes, under an electron microscope it corresponds to granular type EPS, i.e. organelle responsible for protein synthesis. Provides intracellular regeneration in neurocytes (renewal of worn-out organelles, in the absence of the ability of neurocytes to mitosis).
Tonofibrils- filamentous formations in animal epithelial cells. Previously it was believed that they stretch from one cell to another. However, electron microscopic studies have refuted the idea of the continuity of T. It has been shown that T. converge in the region of desmosomes, where they bend and return deep into the cell. Probably, T. provide the mechanical strength of cells.
Inclusions are unstable structures of the cytoplasm that can appear or disappear, depending on the functional state of the cell. Classification of inclusions:
I. Trophic inclusions - granules of nutrients (proteins, fats, carbohydrates) deposited in reserve. Examples include: glycogen in neutrophil granulocytes, hepatocytes, muscle fibers; fat droplets in hepatocytes and lipocytes; protein granules in the yolk of eggs, etc.
II. Pigment inclusions are granules of endogenous or exogenous pigments. Examples: melanin in skin melanocytes (for protection against UV rays), hemaglobin in red blood cells (for transporting oxygen and carbon dioxide), rhodopsin and iodopsin in rods and cones of the retina (provide black-and-white and color vision), etc.
III. Secretory inclusions are droplets (granules) of secreted substances prepared for release from any secretory cells (in the cells of all exocrine and endocrine glands). Example: milk droplets in lactocytes, zymogenic granules in pancreatocytes, etc.
IV. Excretory inclusions are the final (harmful) products of metabolism that must be removed from the body. Example: inclusions of urea, uric acid, creatinine in the epithelial cells of the renal tubules.
Cytoplasmic inclusions- these are optional components of the cell that appear and disappear depending on the intensity and nature of metabolism in the cell and on the conditions of existence of the organism. Inclusions have the form of grains, lumps, drops, vacuoles, granules of various sizes and shapes. Their chemical nature is very diverse. Depending on the functional purpose, inclusions are grouped into groups:
trophic;
pigments;
excreta, etc.
special inclusions (hemoglobin)
Among trophic inclusions(reserve nutrients) fats and carbohydrates play an important role. Proteins as trophic inclusions are used only in rare cases (in eggs in the form of yolk grains).
Pigment inclusions give cells and tissues a certain color.
Secrets and hormones accumulate in glandular cells, as they are specific products of their functional activity.
Excreta- the final products of cell activity that must be removed from it.
Most popular currently symbiotic hypothesis origin of eukaryotic cells, according to which the basis, or host cell, in the evolution of a cell of the eukaryotic type was anaerobic prokaryote, capable only of amoeboid movement. The transition to aerobic respiration is associated with the presence of mitochondria in the cell, which occurred through changes in symbionts - aerobic bacteria that penetrated the host cell and coexisted with it.
According to intussusception hypothesis , the ancestral form of the eukaryotic cell was aerobic prokaryote(Fig. 1.4). Inside such a host cell, several genomes were located simultaneously, initially attached to the cell membrane. Organelles with DNA, as well as a nucleus, arose by invagination and unlacing of sections of the shell, followed by functional specialization into the nucleus, mitochondria, and chloroplasts. In the process of further evolution, the nuclear genome became more complex and a system of cytoplasmic membranes appeared.
Chromosomes- these are the main structural elements of the cell nucleus, which are carriers of genes in which hereditary information is encoded. Having the ability to reproduce themselves, chromosomes provide a genetic connection between generations. The average lengths of human metaphase chromosomes lie in the range of 1.5-10 microns. The chemical basis of the structure of chromosomes are nucleoproteins - complexes of nucleic acids (see) with the main proteins - histones and protamines.
Chromosomes perform function the basic genetic apparatus of the cell. They contain genes in a linear order, each of which occupies a strictly defined location, called a locus. Alternative forms of a gene (i.e., its different states) occupying the same locus are called alleles (from the Greek allelon - mutually different, different). Any chromosome contains only a single allele at a given locus, despite the fact that two, three or more alleles of one gene may exist in a population.
Both in composition and in their physical role, all microscopically visible and histochemically detectable non-permanent inclusions can be divided into several well-characterized groups.
The simplest classification of them is as follows:
I. Trophic inclusions (from the Greek trophe - food)
1. Undefined inclusions chemical composition;
2. Inclusions, well characterized chemically, representing mostly reserve substances in the cell:
a) proteins
b) fatty substances,
c) glycogen (carbohydrates).
II. Pigment inclusions.
III. Vitamins.
IY. Products isolated in the cytoplasm and subject to removal from cells: 1. excretory inclusions. 2. secretory products.
I. Trophic inclusions.
1. Inclusions of uncertain chemical composition.
In most cases this is very small formations, standing at the limit of visibility of modern light microscopes. During life cycle cells they either appear in the cytoplasm or disappear. These inclusions consist of different salt solutions, or inclusions of varying degrees of density with protein, carbohydrate, fat, lipoid or mixed content. Under certain conditions, such inclusions can accumulate in cells in significant quantities, which in most cases indicates changes in the metabolism itself.
2. Inclusions that are well characterized chemically.
Protein substances.
IN in good condition In animals and humans, protein substances as reserve material are usually not deposited in the cytoplasm of cells. But in the cytoplasm of eggs, as well as in cells after fragmentation, protein inclusions are always present. They most often have the shape of round, sometimes very small, sometimes quite large granules.
Fatty substances.
Drops of visible microscopic fat in the large quantities can be found in all cells of the body. By. As a rule, in the cytoplasm of cells that are not specifically adapted to the accumulation of fatty substances, very little reserve fat is deposited during normal cellular metabolism. With a decrease in oxidative processes or with an increase in the function of fat formation, a significant amount of fat may appear in the cytoplasm of cells. This phenomenon is called simple cell obesity. Fat inclusions usually have the form of rounded drops of various sizes. This indicates that the fatty substances are in a liquid state.
Carbohydrate substances (glycogens).
Constant integral part The cytoplasm contains carbohydrates (sugars). However, only the polysaccharide glycogen can be found in animal and human cells. Formed from glucose, as mentioned earlier, it is deposited as a reserve energy material. By breaking down into glucose, glycogen thereby supplies the body with glucose as it is consumed by the tissues, which is the main energy source of our body. It should be noted that normally glycogen can be deposited only in the cytoplasm of cells.
II. Pigment inclusions.
Pigments are colored substances formed in the cells of plants and animals. By their presence in cells, pigments determine the color of organisms. All pigments can be divided into two large groups:
blood pigments and products of their transformations,
pigments that do not take part in respiration processes.
Blood pigments.
This group includes primarily hemoglobin, which is the main constituent of the erythrocyte (red blood cell), and its breakdown products.
Hemoglobin is a complex compound formed by the protein globin with a colored complex protein compound containing iron. Since it contains iron, hemoglobin attaches oxygen to itself, being the main carrier of oxygen throughout the body to all tissues. The breakdown products of hemoglobin include hematoidin, hematosiderin, and malarial pigment, which are formed as a result of the breakdown of hemoglobin in blood cells when the malarial plasmodium penetrates them.
Pigments that do not take part in respiration processes.
This group includes substances of quite heterogeneous physiological significance. In the cytoplasm of cells, they are in most cases isolated in the form of granules. The following pigments are distinguished:
carotenoids;
chromolipoids;
melanins.
Carotenoids.
In terms of their chemical composition, carotenoids are unsaturated carbohydrates that do not contain nitrogen. The yellow or red color of carotenoids makes them easy to see under a microscope. Carotenoids are not produced in the cytoplasm of cells themselves, but enter the human body from plant food. Deposited in the cytoplasm of cells, carotenoids are rarely isolated in it in the form of pure substances, usually due to their good solubility in fats; they are always part of fat droplets, thus forming mixtures.
Chromolipoids.
Chromolipoids in the cytoplasm of cells are found in the form of droplets of yellow or brown, belonging to fatty substances and formed in cells as a result of the oxidation of cytoplasmic fats. In the cytoplasm they form mixtures with fats.
Melanins.
Important group pigments that produce a wide range of colors, from yellow to black. Melanins determine the color of the skin of humans and animals. Therefore, they can be called color pigments. Melanins are formed in the cytoplasm of cells from protein breakdown products. At various diseases the amount of melanin can increase significantly.
III. Vitamins
To date, only two vitamins can be found in the cytoplasm of cells: vitamin A and vitamin C.
IV. Products to be excreted from the cell
Excretory inclusions.
Substances formed during the breakdown of basic components cytoplasm and subsequently removed from the cell, and subsequently from the body during external environment. Excreta can be of a wide variety of chemical compositions, for example, urea, uric acid salts, breakdown products of blood pigments, bile pigments, etc.
Secretory inclusions.
They consist of substances released by the cell into the external environment of the body. This includes: fat secreted sebaceous glands and serving to lubricate the skin, mucus secreted by the salivary and other glands, digestive enzymes, etc.
Cell nucleus.
The nucleus was first discovered in plants in 1831 by the botanist R. Brown. He described it as a vesicle-shaped body located in the center of the cell (Fig. 1, 2). Currently, it can be considered proven that the cells of all plant and animal organisms, with the exception of a few, have a nucleus. If you cut off a section of the cytoplasm from the cell body, it will eventually disintegrate. Cytoplasm alone without a nucleus is incapable of long-term existence. At the same time, the area with the nucleus can again restore the lost part of the cytoplasm. If the structure of the nucleus is disrupted by puncturing it, the cells die.
The shape of the nucleus is less varied than the shape of the cell. Most nuclei have a simple spherical or ellipsoidal shape.
The core size ranges from 3 to 25 microns. Most human cells are mononuclear. However, there are binuclear (hepatocytes, cardiomyocytes), multinuclear (muscle fibers - myosymplasts). The nucleus includes the nuclear envelope, nucleoplasm, chromatin, and nucleolus.
Nuclear envelope consists of inner and outer nuclear membranes each 8 nm thick. The nuclear envelope is penetrated by many round nuclear pores with a diameter of 50-70 nm. Through nuclear pores, substances are exchanged between the nucleus and the cytoplasm.
Nucleoplasm- the non-staining part of the nucleus, is a colloidal solution of proteins surrounding the chromatin and nucleolus.
Chromatin(from the Greek chroma - paint). It stains well when fixed in dye. Chromatin is chromosomal material. It consists of DNA, proteins, and a small amount of RNA.
Nucleolus(one or more are detected in all cells in the form of an intensely stained round body. The nucleolus contains ribonucleoproteins (RNI) and a large number of RNA strands.
The main function of the nucleus is participation in the process of reproduction and cell division.
Features of the structure and function of fat cells.
Fat cells, like all other cells of our body, have a well-defined cellular shape, consisting of a nucleus and cytoplasm and having a cytoplasmic membrane that separates these cells from other cellular structures.
Functionally, fat cells are elements that serve to accumulate reserve fat and have very significant sizes (up to 120 microns) and the appearance of spherical bubbles filled with fat. The fat droplet occupies the entire central part of the cell and is surrounded by a thin cytoplasmic rim, forming a kind of shell around this droplet. Next to the fat accumulation in the cell there is a nucleus (Fig. 5, 6). In some cases, fat cells are located individually or in small groups, in other cases they form clusters in connective tissue large masses, having a lobed structure. In such cases we talk about adipose tissue. The fatty substances that make up fat cells mainly consist of neutral fats. Studying physical condition led to the conclusion that fat droplets are an emulsion formed as a result of the dissolution of a highly watered phase in a mixture of fatty substances. Such emulsions are characterized by the fact that they are on the border between solid and liquid states, forming pasty masses.
Both the amount of fat and the number of fat cells themselves are subject to significant
2 An example of a pasty state can be a wide variety of ointments or lipsticks
Hesitation. During fasting, the fat content in them decreases. With increased nutrition, it increases. Fat cells in their full development stage are apparently incapable of dividing. Despite all the searches, no one has yet been able to find the mitotic state of their nucleus, i.e. cell division. The formation of fat cells occurs from undifferentiated elements, in particular from reticular cells of connective tissue, as well as cambial cells and histiocytes, which accompany in large numbers blood vessels, around which the main mass of fat cells is usually located. In the body adipose tissue plays not only a reserve, but also a mechanical role, forming soft mats in some organs, such as the skin.
Chapter III. “Tissue is a collection of cells of the same structure.”
Leather and its derivatives.
The skin is a very important and functionally very versatile organ. The skin performs a number of vital functions that cannot be ignored.
1. The skin forms a dense and durable cover that protects the underlying parts from mechanical damage and from loss of water, and also prevents the penetration of various pathogens into the internal environment. Skin in normal condition is impermeable not only to microorganisms, but also to dissolved toxic and harmful substances.
2. The skin protects the underlying tissues from strong light irritations (ultraviolet rays).
3. The skin is an organ that regulates heat transfer. In this function, the main role is played by the release of sweat, which in turn enhances the transfer of heat, and the hairline, which protects against excessive cooling.
4. The skin takes part in metabolism, removing some breakdown products through sweat.
5. The skin participates in gas exchange, carrying out cutaneous respiration.
6. Lastly, the skin is very important body feelings in which they are concentrated
All of the above applies to the epidermis itself. Excretory ducts sweat glands do not have this property, which is what doctors use by prescribing rubbing in various external medicines(ointments, etc.).
tactile, temperature and pain nerve endings.
Skin structure.
Epithelial outer part The skin is called the epidermis, and the connective tissue is called the skin itself (derma) (Fig. 7). The skin is connected to the underlying parts using a looser connective tissue layer called the subcutaneous fat layer or subcutaneous tissue. Main role in protective function The structure of the skin is played by the epithelial layer, or epidermis, while the strength of the skin is determined by the connective tissue of the skin itself (dermis).
Epidermis.
The human skin epidermis is represented by stratified epithelium. A pattern is found on the surface of the epidermis.
In addition to membrane and non-membrane organelles, cells may contain cellular inclusions, which are non-permanent formations that appear and disappear during the life of the cell. The main location of inclusions is the cytoplasm, but sometimes they are also found in the nucleus.
By nature, all inclusions are products of cellular metabolism. They accumulate mainly in the form of granules, droplets and crystals. The chemical composition of inclusions is very diverse.
Lipoids are usually deposited in the cell in the form of small droplets. A large number of fat droplets are found in the cytoplasm of a number of protozoa, such as ciliates. In mammals, fat droplets are found in specialized fat cells, in connective tissue. Often, a significant amount of fatty inclusions is deposited as a result of pathological processes, for example, with fatty degeneration of the liver. Drops of fat are found in the cells of almost all plant tissues; a lot of fat is contained in the seeds of some plants.
Polysaccharide inclusions most often have the formula of granules of various sizes. In multicellular animals and protozoa, glycogen deposits are found in the cytoplasm of cells. Glycogen granules are clearly visible in light microscope. Accumulations of glycogen are especially large in the cytoplasm of striated muscle fibers and in liver cells and neurons. In plant cells, starch is most often deposited from polysaccharides. It looks like granules various shapes and sizes, and the shape of starch granules is specific for each plant species and for certain tissues. The cytoplasm of potato tubers and cereal grains is rich in starch deposits; Each starch granule consists of individual layers, and each layer, in turn, includes radially arranged crystals, almost invisible under a light microscope.
Protein inclusions are less common than fat and carbohydrate inclusions. The cytoplasm of eggs is rich in protein granules, where they have the form of plates, balls, disks, and rods. Protein inclusions are found in the cytoplasm of liver cells, protozoan cells and many other animals.
Cellular inclusions include some pigments, for example, the yellow and brown pigment lipofuscin, which is common in tissues, round granules of which accumulate during the life of cells, especially as they age. This also includes yellow and red pigments - lipochromes. They accumulate in the form of small droplets in the cells of the adrenal cortex and in some cells of the ovaries. The pigment retinin is part of the visual purple of the retina. The presence of certain pigments is associated with the performance of special functions by these cells. Examples include the red respiratory pigment hemoglobin in red blood cells or the pigment melanin in melanophore cells of the integumentary tissues of animals.
