(slide 7) Cell is main form of the organization of live matter, elementary unit of an organism. It represents self-replicating system which is isolated from the external environment and keeps a certain concentration of chemicals, but at the same time carries out constant exchange with environment. The only cell of a unicell is universal, it performs all functions necessary for providing life and reproduction. At multicellular organism a cells are extremely various by the size, a form, an internal structure and the carried-out functions
Despite a huge variety, cells of plants are characterized by community of a structure: it is the eukaryotes having the issued kernel. From cells of others eukaryotes (animals, mushrooms) they are distinguished by the following features:
1) existence of plastids;
2) existence of a cellular wall from cellulose;
3) well developed system a vacuole;
4) absence centriole at division;
5) growth by stretching;
6) adult cells have the constant form.
Form and size of vegetative cells are very different. Size of cell can be from 10-100 mkm till several mm.
(slide 8) In a plant cell it is possible to distinguish three main parts:
1) the carbohydrate cellular wall surrounding a cell outside;
2) a protoplast live contents of a cell;
3) vacuoles - the space in the central part of a cell filled with watery contents - cellular juice. A cellular wall and vacuoles are protoplast waste products.
Protoplast is active live contents of a cell. The protoplast represents extremely difficult education differentiated on various components called by organelles which constantly in him meet have a characteristic structure and perform specific functions.
(slide 9) The kernel, plastids, mitochondrion, ribosome, endoplasmic network, Golgi's device, lysosomes, microlittle bodies belong to organellas of a cell. Organelles are shipped in a gialoplazma which provides their interaction. In cytoplasm the main biochemical processes (or metabolism) is carry out.
The chemical composition of a protoplast is very difficult and various. Each cell is characterized by the chemical composition depending on physiological functions. The main (constitutional) classes of compositions are: water (60-90%), proteins (40-50% of dry mass of a protoplast), nucleonic acids (1-2%), lipids (2-3%), carbohydrates and other organic compounds. Inorganic substances in the form of ions of mineral salts (2-6%) also are a part of a protoplast. Proteins, nucleonic acids, lipids and carbohydrates are synthesized by a protoplast.
Besides the constitutional substances, at a cell there are spare substances (which are temporarily switched off from exchange) and a garbage (his final products).
Cytoplasm - an obligatory part of living cell where there are all processes of cellular exchange, except the synthesis of nucleonic acids which is made in a kernel. A basis of cytoplasm makes its matrix with organelles are shipped.
Ribosome is small (about 20 nanometers), almost spherical granules consisting of RNA complexes and various structural proteins, have non-membrane structure. Ribosome settle down in cell cytoplasm freely, or are attached to membranes of endoplasmic network. Ribosome one by one or groups from settle down 4-40 (polysomes), they are the centers of synthesis of protein in a cell.
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The ribosome consists of two sub-units (big and small) connected among themselves by magnesium ions. Sub-units create inside of kernel, assembly of ribosome is carried out in cytoplasm. Ribosomes are found also in mitochondrion and plastids, but their size is less.
The endoplasmic network (endoplasmic reticulum) represents extensive three-dimensional network of the channels, bubbles and tanks limited to membranes. If on its surface ribosome are placed, then it carries the name granular, or rough; without ribosome is called a-granular, or smooth. The a-granular endoplasmic network takes part in synthesis of fats and other lipophilic connections (essential oils, pitches, rubber).
The endoplasmic network is used for transportation of substances. Endoplasmic network is the center of forming and growth of cellular membranes. It gives rise to such components of a cell as vacuoles, lysosomes, dictiosomes, micro bodies. At means of endoplasmic network interaction between organelles is carried out.
Golgi's device is called by name the Italian scientist C. Golgi who for the first time has described it in animal cells. In plant cells Golgi's apparatus consists from separate dictiosomes, or Golgi's little bodies and Golgi's bubbles. Each dictiosome represents a pile from 5-7 and more flattened roundish tanks with a diameter about 1 micron limited to a membrane.
The lysosomes are containing hydrolytic enzymes capable to destroy organic compounds. Lysosomes of vegetable cells represent small (0,5-2 microns) cytoplasmatic vacuoles and bubbles derivatives of endoplasmic network or Golgi's device. The main function of lysosomes - local autolysis, that is the destruction of certain sites of cytoplasm of own cell which is coming to an end with education on her place of a cytoplasmatic vacuole. Other function of lysosomes is removal of worn-out or excess cellular organelles and also clarification of a cavity of a cell after dying off of her protoplast.
(slide 9) Mitochondrion is roundish or elliptic, are more rare the threadlike organelle with a diameter of 0,3-1 microns surrounded with two membranes. The internal membrane forms outgrowths in a mitochondrion cavity Christa which considerably increase her internal surface. The space between crosses is filled matrix. In a matrix there are ribosome and threads of own DNA.
Mitochondrion is called power stations of a cell. Increase in number of mitochondrion happens due to its own division.
(slide 10) Plastids are the organelles characteristic only for plants. Distinguish three types of plastids: 1) chloroplasts (plastid of green color); 2) chromoplasts (plastid of yellow, orange or red color) and leucoplasts (colourless plastids). Usually in a cell plastids only of one type meet.
Chloroplasts have the greatest value, in them photosynthesis proceeds. They contain a green pigment the chlorophyll giving to plants green color, and the pigments relating to group of karotinoids. Chloroplasts of plants have the form of a biconvex lens and the sizes of 4-7 microns; they are well visible in a light microscope. The number of chloroplasts in photosynthesizing cell can reach 40-50. At seaweed the role of the photosynthetic device is carried out by chromatophores, they are much larger, their number in a cage from 1 to 5.
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Chloroplasts have complex structure. They are also have two membranes external and internal. Internal contents are called Strom. The internal membrane forms in chloroplast difficult, strictly ordered system of the membranes having the form of the flat bubbles called by tilacoid which are collected in piles - grans. Often in chloroplasts starched grains meet - primary, or assimilatory starch, temporary storage of products of photosynthesis.
The main function of chloroplasts is photosynthesis, formation of organic substances from inorganic due to energy of light.
Leucoplasts are small colourless plastids. They meet generally in cells of the bodies hidden from sunlight such as roots, rhizomes, tubers, seeds. Their structure is in general similar to a structure of chloroplasts: a cover from two membranes, Strom, a ribosome, DNA threads are similar to that of chloroplsts. Leucoplasts are the organelles connected with synthesis and accumulation of spare nutrients, first of all starch, seldom proteins and lipids. Starch has an appearance of grains, unlike assimilatory starch of chloroplasts; it is called spare, or secondary. Often in cells the leucoplasts which aren't accumulating spare nutrients meet, their role still is up to the end not found out. On sun light some leucoplasts can turn into chloroplasts.
Chromoplasts are plastids of orange, red and yellow color which is caused by the pigments relating to group of carotinoids. Chromoplasts meet in cells of petals of many plants (a marigold, a buttercup, a dandelion), mature fruits (a tomato, a rose, a mountain ash, pumpkin, watermelon), is rare - root crops (carrots) and also in autumn leaves.
The internal membrane system in chromoplasts, as a rule, is absent. Chromoplasts have more or less spherical shape. In certain cases (carrots root crops, watermelon fruits) carotinoids are deposited in the form of crystals of various form.
The value of chromoplasts up to the end isn't found out yet. Most of them represent the growing old plastids. They, as a rule, develop from chloroplasts, at the same time in plastids the chlorophyll and internal membrane structure collapse, and carotinoids collect. It occurs when maturing fruits and yellowing leaves in the fall. The indirect biological value of chromoplasts consists that they cause the bright coloring of flowers and fruits attracting insects to cross-pollination and other animals for distribution of fruits.
Kernel (nuclear) is the main and obligatory part of eukaryotic cell. The kernel is control center of a cell metabolism, its growth and development, controls activity of all other organelles. The kernel stores genetic information and transfers it to daughter cells in the course of cellular division. The kernel is available in all living plant cells; the exception is made only by mature cribriform tubes of a phloem. Cells with a remote kernel, as a rule, quickly perish.
Kernel is the largest organelle, it size makes 10-25 microns. Very big kernels have gametes (untill 500 microns). The kernel form more often spherical or ellipsoidal, but in strongly extended cells can be lens-shaped or spindle-shaped.
The cell, as a rule, contains one kernel. In young people (meristem) cells it usually holds the central position. In process of growth of the central vacuole displaced kernel to a cellular wall and settles down in a wall layer of cytoplasm.
On the chemical composition the kernel differs from other organelles high markedly (15-30%) the content of DNA substances of heredity of a cell. In a kernel 99% of DNA of a cell is concentrated. The kernel contains in significant amounts of RNA (in the main mRNK and rRNK) and also proteins.
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The structure of a kernel is identical at all eukaryotic cells. In a kernel distinguish chromatin and a kernel which are shipped in a karyoplasms; from cytoplasm the kernel is separated by a nuclear cover with a time.
Nucleolus is - a dense, spherical little body with a diameter of 1-3 microns. Usually the kernel contains 1-2, sometimes several nucleoli. Nucleoli are the kernel RNA main carrier, consist of ribonucleo-proteids. Function of nucleolus is synthesis of rRNK and formation of subunits of ribosome.
Vacuoles contain almost in all plant cells. They represent the cavities in a cell filled with watery contents cellular juice. Cellular juice is isolated from cytoplasm by selectively permeable vacuole membrane tonoplast. For the majority of mature cells of plants it is characteristic large central vacuoles, occupying up to 70-90% of volume of a cell.
Except function of accumulation of spare substances and garbage, vacuoles in plant cells perform one more important function maintenance of turgor. The water coming to cellular juice puts pressure upon a protoplast, and through him and upon a cellular wall, causing intense, her elastic condition, or turgor of a cell.
(slide 11) Inclusions. Formation of inclusions is caused by excess accumulation of some products of a metabolism in certain parts of a cell in vacuoles, a gialoplasm, various organelles, sometimes - in a cellular wall. These substances often drop out in a deposit in an amorphous view or in the form of crystals inclusions. Inclusions have a certain form and are well visible in a light microscope.
Inclusions represent or the spare substances (which are temporarily removed from a connection metabolism), or the final products of exchange. Starched grains, lipid drops and deposits of proteins belong to the first category of inclusions; to the second crystals of some substances.
(slide 12) Starched grains are the most wide spread inclusions of plant cells. The form, the size, quantity in an amiloplasts and a structure (position of the educational center, lamination, existence or lack of cracks) of starched grains are often specific for the species of appearances plants. Usually starched grains have the spherical, ovoid or lens-shaped, however potatoes have wrong forms. The largest grains (up to 100 microns) are characteristic of cells of tubers of potatoes - from small (2-9 microns) till large (30-45 microns). Fine grains (5-30 microns) are characteristic of cells of corn seeds. Complex starched grains at rice, oats, a buckwheat.
Deposits of starch are widespread in all bodies of a plant, especially seeds, underground sprouts (tubers, bulbs and rhizomes), a parenchyma of the carrying-out tissued of roots and stalks of wood plants are especially rich with it.
Lipid drops meet practically in all plant cells. Fat oils collect at a huge number of plants and on the value are forms of spare nutrients, the second after starch. Seeds and fruits are especially rich with them. Seeds of some plants (sunflower, cotton, peanut, etc.) may contain up to 40% of oil of the mass of solid. Therefore vegetable fats receive, mainly, from seeds.
Proteinaceous inclusions in the form of various amorphous or crystal deposits are formed in various organelles of a cell. The most often proteinaceous crystals can be met in kernel, is more rare - in a gialoplazm, Strom than plastids, in expansions of tanks of endoplasmic network and mitochondrion. In the greatest number they are postponed in the reserving fabric of dry seeds in the aileron grains. They are characteristic of the reserving cells of seeds of olive plants (a flax, sunflower, pumpkin, mustard, a castor-bean tree, etc.). Less often the plain aileron grains which aren't containing crystals but only amorphous protein meet (bean, rice, corn).
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Proteins and substances of globoids are spent for growth and development of a sprout. Calcium oxalate crystals often meet in plant cells. They are postponed only in vacuoles. The form of crystals of calcium of oxalate is quite various and often specific to certain plants.
Cellular wall (cellular cover) is the characteristic sign of a plant cell distinguishing it from animal cell. The cellular wall gives to a cell a certain form. The cellular wall gives to cell durability and protects the protoplast; it counterbalances turgor pressure and interferes. The set of cellular walls forms the internal skeleton supporting a body of a plant and giving him mechanical durability.
The cellular wall is colourless and transparent, easily passes sunlight. Usually walls are impregnated with water. The cellular wall consists generally of polysaccharides which can be subdivided into skeletal substances and substances of a matrix. Skeletal substance of a cellular wall of plants is cellulose. At mushrooms skeletal substance of a cellular wall is chitin the polysaccharide constructed of the glucosamine remains. Chitin is stronger, than cellulose.
Cellular walls of plants often are exposed to chemical modifications. Ligninfication occurs in case in a matrix lignin polymeric connection of the phenolic nature is laid, insoluble in water. The lignified cellular wall loses elasticity, her hardness and durability on compression sharply increases the permeability for water decreases. Suberinization results from adjournment from the inside of a cellular wall of hydrophobic polymers a suberin and wax. The suberin film is almost impenetrable for water and for gases therefore after her education the cell usually dies off.
The cuticle protects a plant from excessive evaporation of water from a plant surface. The mineralization of a cellular wall occurs owing to adjournment in a matrix of a large amount of mineral substances, most often silicon dioxide (silicon oxide), is rarer than oxalate and a carbonate of calcium. Mineral substances give to a wall the hardness and fragility. Adjournment of silicon dioxide is characteristic of cells of an epidermis of horsetails, sedge and cereals. The rigidity of stalks and leaves acquired as a result of silicification serves as the protect against insects.
At some specialized cells the slimefication of a cellular wall is observed. At the same time instead of a cellulose secondary wall there is an adjournment of the amorphous, strongly hydrated sour polysaccharides in the form of slime and the gum close by the chemical nature to pertinacious substances. Slime is well dissolved in water with formation of mucous solutions. The slime emitted by plant cells performs various functions. So, slime of a root serves as the lubricant facilitating growth of a tip of a root in the soil. Slime pieces of iron of insectivorous plants emit sticky slime to which insects are pasted. The slime emitted by external cells of a seed peel (a flax, a quince, plantains) fixes a seed on the surface of the soil and protects a sprout from drying.
3 Cell theory.
(slide 13) Following the results of studying of a structure of vegetable and animal organisms M. Shleyden, T. Shvann and R. Virkhov to the middle of the 19th century have formulated the cellular theory. We will consider the basic and her additional provisions:
1. The cell is an elementary, functional unit of a structure of all live (except viruses which have no cellular structure).
2. The cell is uniform system; it includes a set of the elements which are naturally connected among them representing the complete education consisting of the interfaced functional units - organelles.
3. Cells of all organisms are homologous.
4. The cell occurs only by division of a maternal cell.
5. The multi-cellular organism represents difficult system from a set of the cells united and integrated into the systems of tissues and bodies connected with each other.
6. Cells of prokaryotes and eukaryotes are the systems of different level of complexity and aren't completely homologous each other.
7. At the base of cell division and reproduction of organisms copying of hereditary information lays molecules of nucleonic acids. Regulations on genetic continuity treat not only a cell in general, but also mitochondrion, plastids, genes and chromosomes.
8. Cells of multi-cellular organisms are toti-potentive, that is possess genetic potentialities of all cells of this organism, are equivalent according to genetic information, but differ from each other in a different expression (work) of various genes that results in their morphological and functional variety - to a differentiation.
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(slide 14) 4 Plant tissues and classification.
Tissues are the stable, naturally repeating complexes of cells similar by origin, to a structure and adapted for performance of one or several functions.
Tissues have arisen at plants in connection with transition of their ancestors seaweed to a land way of life.
There were groups of cells performing certain functions. In the course of evolution the structure of a body of plants became complicated: mosses have about 20 various types of cells, at the fern - about 40, at vascular plants - more than 80. The most perfect and complex fabrics on structure were created at flowering plants.
Tissues classify depending on the carried-out function. However it is necessary to remember that the same tissue can perform several functions. Distinguish the complex tissues consisting of the diverse elements performing different functions, and the plain tissues consisting of uniform elements.
Functions of tissue can change depending on her age. Classifications of tissues are quite various.
Most often allocate six types of tissues:
1) creative, or meristems;
2) the main;
3) covering;
4) secretor;
5) mechanical;
6) transport.
The last five types unite in constant tissues. They are formed of meristems by differentiation of cells.
