Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes; some species of bacteria secrete it to form biofilms. Cellulose is the most abundant organic polymer on Earth; the cellulose content of cotton fiber is 90%, that of wood is 40–50%, that of dried hemp is 57%. Cellulose is used to produce paperboard and paper. Smaller quantities are converted into a wide variety of derivative products such as cellophane and rayon. Conversion of cellulose from energy crops into biofuels such as cellulosic ethanol is under development as a renewable fuel source. Cellulose for industrial use is obtained from wood pulp and cotton; some animals ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts, such as Trichonympha. In human nutrition, cellulose is a non-digestible constituent of insoluble dietary fiber, acting as a hydrophilic bulking agent for feces and aiding in defecation.
Cellulose was discovered in 1838 by the French chemist Anselme Payen, who isolated it from plant matter and determined its chemical formula. Cellulose was used to produce the first successful thermoplastic polymer, celluloid, by Hyatt Manufacturing Company in 1870. Production of rayon from cellulose began in the 1890s and cellophane was invented in 1912. Hermann Staudinger determined the polymer structure of cellulose in 1920; the compound was first chemically synthesized by Kobayashi and Shoda. Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30 degrees, is insoluble in water and most organic solvents, is chiral and is biodegradable, it was shown to melt at 467 °C in 2016. It can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature. Cellulose is derived from D-glucose units; this linkage motif contrasts with that for α-glycosidic bonds present in glycogen. Cellulose is a straight chain polymer. Unlike starch, no coiling or branching occurs and the molecule adopts an extended and rather stiff rod-like conformation, aided by the equatorial conformation of the glucose residues.
The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen atoms on the same or on a neighbor chain, holding the chains together side-by-side and forming microfibrils with high tensile strength. This confers tensile strength in cell walls, where cellulose microfibrils are meshed into a polysaccharide matrix. Compared to starch, cellulose is much more crystalline. Whereas starch undergoes a crystalline to amorphous transition when heated beyond 60–70 °C in water, cellulose requires a temperature of 320 °C and pressure of 25 MPa to become amorphous in water. Several different crystalline structures of cellulose are known, corresponding to the location of hydrogen bonds between and within strands. Natural cellulose is cellulose I, with structures Iα and Iβ. Cellulose produced by bacteria and algae is enriched in Iα while cellulose of higher plants consists of Iβ. Cellulose in regenerated cellulose fibers is cellulose II; the conversion of cellulose I to cellulose II is irreversible, suggesting that cellulose I is metastable and cellulose II is stable.
With various chemical treatments it is possible to produce the structures cellulose III and cellulose IV. Many properties of cellulose depend on its chain length or degree of polymerization, the number of glucose units that make up one polymer molecule. Cellulose from wood pulp has typical chain lengths between 1700 units. Molecules with small chain length resulting from the breakdown of cellulose are known as cellodextrins. Cellulose contains 44.44% carbon, 6.17% hydrogen, 49.39% oxygen. The chemical formula of cellulose is n where n is the degree of polymerization and represents the number of glucose groups. Plant-derived cellulose is found in a mixture with hemicellulose, lignin and other substances, while bacterial cellulose is quite pure, has a much higher water content and higher tensile strength due to higher chain lengths. Cellulose is soluble in Schweizer's reagent, cupriethylenediamine, cadmiumethylenediamine, N-methylmorpholine N-oxide, lithium chloride / dimethylacetamide; this is used in the production of regenerated celluloses from dissolving pulp.
Cellulose is soluble in many kinds of ionic liquids. Cellulose consists of amorphous regions. By treating it with strong acid, the amorphous regions can be broken up, thereby producing nanocrystalline cellulose, a novel material with many desirable properties. Nanocrystalline cellulose was used as the filler phase in bio-based polymer matrices to produce nanocomposites with superior thermal and mechanical properties. Given a cellulose-containing material, the carbohydrate portion that does not dissolve in a 17.5% solution of sodium hydroxide at 20 °C is α cellulose, true cellulose. Acidification of the extract precipitates β cellulose; the portion that dissolves in base but does not precipitate with acid is γ cellulose. Cellulose can be assayed using a method described by Updegraff in 1969, where the fiber is dissolved in acetic and nitric acid to remov
The epidermis is a single layer of cells that covers the leaves, flowers and stems of plants. It forms a boundary between the external environment; the epidermis serves several functions: it protects against water loss, regulates gas exchange, secretes metabolic compounds, absorbs water and mineral nutrients. The epidermis of most leaves shows dorsoventral anatomy: the upper and lower surfaces have somewhat different construction and may serve different functions. Woody stems and some other stem structures such as potato tubers produce a secondary covering called the periderm that replaces the epidermis as the protective covering; the epidermis is the outermost cell layer of the primary plant body. In some older works the cells of the leaf epidermis have been regarded as specialised parenchyma cells, but the established modern preference has long been to classify the epidermis as dermal tissue, whereas parenchyma is classified as ground tissue; the epidermis is the main component of the dermal tissue system of leaves, stems, flowers and seeds.
Most plants have an epidermis, a single cell layer thick. Some plants like Ficus elastica and Peperomia, which have periclinal cellular division within the protoderm of the leaves, have an epidermis with multiple cell layers. Epidermal cells are linked to each other and provide mechanical strength and protection to the plant; the walls of the epidermal cells of the above ground parts of plants contain cutin, are covered with a cuticle. The cuticle reduces water loss to the atmosphere, it is sometimes covered with wax in smooth sheets, plates, tubes or filaments; the wax layers give some plants a bluish surface color. Surface wax protects the plant from intense sunlight and wind; the underside of many leaves have a thinner cuticle than the top side, leaves of plants from dry climates have thickened cuticles to conserve water by reducing transpiration. The epidermal tissue includes several differentiated cell types: epidermal cells, guard cells, subsidiary cells, epidermal hairs; the epidermal cells are the most numerous and least specialized.
These are more elongated in the leaves of monocots than in those of dicots. Trichomes or hairs grow out from the epidermis in many species. In root epidermis, epidermal hairs, termed root hairs are common and are specialized for absorption of water and mineral nutrients. In plants with secondary growth, the epidermis of roots and stems is replaced by a periderm through the action of a cork cambium; the leaf and stem epidermis is covered with pores called stomata, part of a stoma complex consisting of a pore surrounded on each side by chloroplast-containing guard cells, two to four subsidiary cells that lack chloroplasts. The stomata complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf; the stomata are more numerous over the abaxial epidermis of the leaf than the upper epidermis. An exception is floating leaves where all stomata are on the upper surface. Vertical leaves, such as those of many grasses have equal numbers of stomata on both surfaces.
The stoma is bounded by two guard cells. The guard cells differ from the epidermal cells in the following aspects: The guard cells are bean-shaped in surface view, while the epidermal cells are irregular in shape The guard cells contain chloroplasts, so they can manufacture food by photosynthesis Guard cells are the only epidermal cells that can make sugar. According to one theory, in sunlight the concentration of potassium ions increases in the guard cells. This, together with the sugars formed, lowers the water potential in the guard cells; as a result, water from other cells enter the guard cells by osmosis so they swell and become turgid. Because the guard cells have a thicker cellulose wall on one side of the cell, i.e. the side around the stomatal pore, the swollen guard cells become curved and pull the stomata open. At night, the sugar is used up and water leaves the guard cells, so they become flaccid and the stomatal pore closes. In this way, they reduce the amount of water vapour escaping from the leaf.
The plant epidermis consists of three main cell types: pavement cells, guard cells and their subsidiary cells that surround the stomata and trichomes, otherwise known as leaf hairs. The epidermis of petals form a variation of trichomes called conical cells. Trichomes develop at a distinct phase during leaf development, under the control of two major trichome specification genes: TTG and GL1; the process may be controlled by the plant hormones gibberellins, if not controlled, gibberellins have an effect on the development of the leaf hairs. GL1 causes endoreplication, the replication of DNA without subsequent cell division as well as cell expansion. GL1 turns on the expression of a second gene for trichome formation, GL2, which controls the final stages of trichome formation causing the cellular outgrowth. Arabidopsis thaliana uses the products of inhibitory genes to control the patterning of trichomes, such as TTG and TRY; the products of these genes will diffuse into the lateral cells, preventing them from forming trichomes and in the case of TRY promoting the formation of pavement cells.
Expression of the gene MIXTA, or its analogue in other species in the process of cel
In geometry, a polyhedron is a solid in three dimensions with flat polygonal faces, straight edges and sharp corners or vertices. The word polyhedron comes from as poly - + - hedron. A convex polyhedron is the convex hull of finitely many points on the same plane. Cubes and pyramids are examples of convex polyhedra. A polyhedron is a 3-dimensional example of the more general polytope in any number of dimensions. Convex polyhedra are well-defined, with several equivalent standard definitions. However, the formal mathematical definition of polyhedra that are not required to be convex has been problematic. Many definitions of "polyhedron" have been given within particular contexts, some more rigorous than others, there is not universal agreement over which of these to choose; some of these definitions exclude shapes that have been counted as polyhedra or include shapes that are not considered as valid polyhedra. As Branko Grünbaum observed, "The Original Sin in the theory of polyhedra goes back to Euclid, through Kepler, Poinsot and many others... at each stage... the writers failed to define what are the polyhedra".
There is general agreement that a polyhedron is a solid or surface that can be described by its vertices, edges and sometimes by its three-dimensional interior volume. One can distinguish among these different definitions according to whether they describe the polyhedron as a solid, whether they describe it as a surface, or whether they describe it more abstractly based on its incidence geometry. A common and somewhat naive definition of a polyhedron is that it is a solid whose boundary can be covered by finitely many planes or that it is a solid formed as the union of finitely many convex polyhedra. Natural refinements of this definition require the solid to be bounded, to have a connected interior, also to have a connected boundary; the faces of such a polyhedron can be defined as the connected components of the parts of the boundary within each of the planes that cover it, the edges and vertices as the line segments and points where the faces meet. However, the polyhedra defined in this way do not include the self-crossing star polyhedra, their faces may not form simple polygons, some edges may belong to more than two faces.
Definitions based on the idea of a bounding surface rather than a solid are common. For instance, O'Rourke defines a polyhedron as a union of convex polygons, arranged in space so that the intersection of any two polygons is a shared vertex or edge or the empty set and so that their union is a manifold. If a planar part of such a surface is not itself a convex polygon, O'Rourke requires it to be subdivided into smaller convex polygons, with flat dihedral angles between them. Somewhat more Grünbaum defines an acoptic polyhedron to be a collection of simple polygons that form an embedded manifold, with each vertex incident to at least three edges and each two faces intersecting only in shared vertices and edges of each. Cromwell gives a similar definition but without the restriction of three edges per vertex. Again, this type of definition does not encompass the self-crossing polyhedra. Similar notions form the basis of topological definitions of polyhedra, as subdivisions of a topological manifold into topological disks whose pairwise intersections are required to be points, topological arcs, or the empty set.
However, there exist topological polyhedra. One modern approach is based on the theory of abstract polyhedra; these can be defined as ordered sets whose elements are the vertices and faces of a polyhedron. A vertex or edge element is less than an edge or face element when the vertex or edge is part of the edge or face. Additionally, one may include a special bottom element of this partial order and a top element representing the whole polyhedron. If the sections of the partial order between elements three levels apart have the same structure as the abstract representation of a polygon these ordered sets carry the same information as a topological polyhedron. However, these requirements are relaxed, to instead require only that sections between elements two levels apart have the same structure as the abstract representation of a line segment. Geometric polyhedra, defined in other ways, can be described abstractly in this way, but it is possible to use abstract polyhedra as the basis of a definition of geometric polyhedra.
A realization of an abstract polyhedron is taken to be a mapping from the vertices of the abstract polyhedron to geometric points, such that the points of each face are coplanar. A geometric polyhedron can be defined as a realization of an abstract polyhedron. Realizations that forgo the requirement of planarity, that impose additional requirements of symmetry, or that map the vertices to higher dimensional spaces have been considered. Unlike the solid-based and surface-based definitions, this works well for star polyhedra. However, without additional restrictions, this definition allows degenerate or unfaithful polyhedra (for instance, by mapp
A stem is one of two main structural axes of a vascular plant, the other being the root. The stem is divided into nodes and internodes: The nodes hold one or more leaves, as well as buds which can grow into branches. Adventitious roots may be produced from the nodes; the internodes distance one node from another. The term "shoots" is confused with "stems". In most plants stems are located above the soil surface but some plants have underground stems. Stems have four main functions which are: Support for and the elevation of leaves and fruits; the stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits. Transport of fluids between the roots and the shoots in the xylem and phloem Storage of nutrients Production of new living tissue; the normal lifespan of plant cells is one to three years. Stems have cells called meristems. Stems are specialized for storage, asexual reproduction, protection or photosynthesis, including the following: Acaulescent – used to describe stems in plants that appear to be stemless.
These stems are just short, the leaves appearing to rise directly out of the ground, e.g. some Viola species. Arborescent – tree like with woody stems with a single trunk. Axillary bud – a bud which grows at the point of attachment of an older leaf with the stem, it gives rise to a shoot. Branched – aerial stems are described as being branched or unbranched Bud – an embryonic shoot with immature stem tip. Bulb – a short vertical underground stem with fleshy storage leaves attached, e.g. onion, tulip. Bulbs function in reproduction by splitting to form new bulbs or producing small new bulbs termed bulblets. Bulbs are a combination of stem and leaves so may better be considered as leaves because the leaves make up the greater part. Caespitose – when stems grow in a tangled mass or clump or in low growing mats. Cladode – a flattened stem that appears more-or-less leaf like and is specialized for photosynthesis, e.g. cactus pads. Climbing -- stems that wrap around other plants or structures. Corm – a short enlarged underground, storage stem, e.g. taro, gladiolus.
Decumbent -- stems that lie flat on the turn upwards at the ends. Fruticose -- stems. Herbaceous – non woody, they die at the end of the growing season. Internode – an interval between two successive nodes, it possesses the ability to elongate, either from its base or from its extremity depending on the species. Node – a point of attachment of a leaf or a twig on the stem in seed plants. A node is a small growth zone. Pedicel – stems that serve as the stalk of an individual flower in an inflorescence or infrutescence. Peduncle – a stem that supports an inflorescence Prickle – a sharpened extension of the stem's outer layers, e.g. roses. Pseudostem – a false stem made of the rolled bases of leaves, which may be 2 or 3 m tall as in banana Rhizome – a horizontal underground stem that functions in reproduction but in storage, e.g. most ferns, iris Runner – a type of stolon, horizontally growing on top of the ground and rooting at the nodes, aids in reproduction. E.g. garden strawberry, Chlorophytum comosum.
Scape – a stem that holds flowers that comes out of the ground and has no normal leaves. Hosta, Iris, Garlic. Stolon – a horizontal stem that produces rooted plantlets at its nodes and ends, forming near the surface of the ground. Thorn – a modified stem with a sharpened point. Tuber – a swollen, underground storage stem adapted for storage and reproduction, e.g. potato. Woody – hard textured stems with secondary xylem. Stem consist of three tissues, dermal tissue, ground tissue and vascular tissue; the dermal tissue covers the outer surface of the stem and functions to waterproof and control gas exchange. The ground tissue consists of parenchyma cells and fills in around the vascular tissue, it sometimes functions in photosynthesis. Vascular tissue provides structural support. Most or all ground tissue may be lost in woody stems; the dermal tissue of aquatic plants stems. The arrangement of the vascular tissues varies among plant species. Dicot stems with primary growth have pith in the center, with vascular bundles forming a distinct ring visible when the stem is viewed in cross section.
The outside of the stem is covered with an epidermis, covered by a waterproof cuticle. The epidermis may contain stomata for gas exchange and multicellular stem hairs called trichomes. A cortex consisting of hypodermis and endodermis is present above the pericycle and vascular bundles. Woody dicots and many nonwoody dicots have secondary growth originating from their lateral or secondary meristems: the vascular cambium and the cork cambium or phellogen; the vascular cambium forms between the xylem and phloem in the vascular bundles and connects to form a continuous cylinder. The vascular cambium cells divide to produce secondary xylem to the inside and secondary phloem to the outside; as the stem increases in diameter due to production of secondary xylem and secondary phloem, the cortex and epidermis are destroyed. Before the cortex is destroyed, a cork cambium develops there; the cork cambium divides to produce waterproof cork cells externally and sometimes phelloderm cells internally. Those three tissues form the periderm.
Areas of loosely pack
Bast fibre is plant fibre collected from the phloem or bast surrounding the stem of certain dicotyledonous plants. It provides strength to the stem; some of the economically important bast fibres are obtained from herbs cultivated in agriculture, as for instance flax, hemp, or ramie, but bast fibres from wild plants, as stinging nettle, trees such as lime or linden and mulberry have been used in the past. Bast fibres are classified as soft fibres, are flexible. Fibres from monocotyledonous plants, called "leaf fibre", are classified as hard fibres and are stiff. Since the valuable fibres are located in the phloem, they must be separated from the xylem material, sometimes from the epidermis; the process for this is called retting, can be performed by micro-organisms either on land or in water, or by chemicals or by pectinolytic enzymes. In the phloem, bast fibres occur in bundles that are glued together by calcium ions. More intense retting separates the fibre bundles into elementary fibres, that can be several centimetres long.
Bast fibres have higher tensile strength than other kinds, are used in high-quality textiles, yarn, composite materials and burlap. An important property of bast fibres is that they contain a special structure, the fibre node, that represents a weak point, gives flexibility. Seed hairs, such as cotton, do not have nodes. Plants that have been used for bast fibre include flax, jute, kudzu, milkweed, okra, paper mulberry and roselle hemp. Bast fibres are processed for use in carpet, rope, traditional carpets, hessian or burlap, sacks, etc. Bast fibres are used in the non-woven and composite technology industries for the manufacturing of non-woven mats and carpets, composite boards as furniture materials, automobile door panels and headliners, etc. From prehistoric times through at least the early 20th century, bast shoes were woven from bast strips in the forest areas of Eastern Europe. Where no other source of tanbark was available, bast has been used for tanning leather. International Jute Study Group Bast Fibre cords in Viking ships Bast fibre production with hemp
Water is a transparent, tasteless and nearly colorless chemical substance, the main constituent of Earth's streams and oceans, the fluids of most living organisms. It is vital for all known forms of life though it provides no calories or organic nutrients, its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient pressure, it forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of its solid state; when finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is water vapor. Water moves continually through the water cycle of evaporation, condensation and runoff reaching the sea. Water covers 71% of the Earth's surface in seas and oceans. Small portions of water occur as groundwater, in the glaciers and the ice caps of Antarctica and Greenland, in the air as vapor and precipitation.
Water plays an important role in the world economy. 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a major source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers and canals. Large quantities of water and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a wide variety of chemical substances. Water is central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, sport fishing, diving; the word water comes from Old English wæter, from Proto-Germanic *watar, from Proto-Indo-European *wod-or, suffixed form of root *wed-. Cognate, through the Indo-European root, with Greek ύδωρ, Russian вода́, Irish uisce, Albanian ujë; the identification of water as a substance Water is a polar inorganic compound, at room temperature a tasteless and odorless liquid, nearly colorless with a hint of blue.
This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances. This allows it to be the "solvent of life", it is the only common substance to exist as a solid and gas in normal terrestrial conditions. Water is a liquid at the pressures that are most adequate for life. At a standard pressure of 1 atm, water is a liquid between 0 and 100 °C. Increasing the pressure lowers the melting point, about −5 °C at 600 atm and −22 °C at 2100 atm; this effect is relevant, for example, to ice skating, to the buried lakes of Antarctica, to the movement of glaciers. Increasing the pressure has a more dramatic effect on the boiling point, about 374 °C at 220 atm; this effect is important in, among other things, deep-sea hydrothermal vents and geysers, pressure cooking, steam engine design. At the top of Mount Everest, where the atmospheric pressure is about 0.34 atm, water boils at 68 °C. At low pressures, water cannot exist in the liquid state and passes directly from solid to gas by sublimation—a phenomenon exploited in the freeze drying of food.
At high pressures, the liquid and gas states are no longer distinguishable, a state called supercritical steam. Water differs from most liquids in that it becomes less dense as it freezes; the maximum density of water in its liquid form is 1,000 kg/m3. The density of ice is 917 kg/m3. Thus, water expands 9% in volume as it freezes, which accounts for the fact that ice floats on liquid water; the details of the exact chemical nature of liquid water are not well understood. Pure water is described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths, frogs are known to be able to smell it. However, water from ordinary sources has many dissolved substances, that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water by avoiding water, too salty or putrid; the apparent color of natural bodies of water is determined more by dissolved and suspended solids, or by reflection of the sky, than by water itself.
Light in the visible electromagnetic spectrum can traverse a couple meters of pure water without significant absorption, so that it looks transparent and colorless. Thus aquatic plants and other photosynthetic organisms can live in water up to hundreds of meters deep, because sunlight can reach them. Water vapour is invisible as a gas. Through a thickness of 10 meters or more, the intrinsic color of water is visibly turquoise, as its absorption spectrum has
Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell, a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes. Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, sister chromatids are separated in the second division. Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor. Prokaryotes undergo a vegetative cell division known as binary fission, where their genetic material is segregated into two daughter cells. All cell divisions, regardless of organism, are preceded by a single round of DNA replication.
For simple unicellular microorganisms such as the amoeba, one cell division is equivalent to reproduction – an entire new organism is created. On a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Mitotic cell division enables sexually reproducing organisms to develop from the one-celled zygote, which itself was produced by meiotic cell division from gametes. After growth, cell division by mitosis allows for continual repair of the organism; the human body experiences about 10 quadrillion cell divisions in a lifetime. The primary concern of cell division is the maintenance of the original cell's genome. Before division can occur, the genomic information, stored in chromosomes must be replicated, the duplicated genome must be separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between generations. Interphase is the process a cell must go through before mitosis and cytokinesis.
Interphase consists of three main stages: G1, S, G2. G1 is a time of growth for the cell where specialized cellular functions occur in order to prepare the cell for DNA Replication. There are checkpoints during interphase that allow the cell to be either progressed or denied further development. In S phase, the chromosomes are replicated in order for the genetic content to be maintained. During G2, the cell undergoes the final stages of growth before it enters the M phase, where spindles are synthesized; the M phase, can be either meiosis depending on the type of cell. Germ cells, or gametes, undergo meiosis. After the cell proceeds through the M phase, it may undergo cell division through cytokinesis; the control of each checkpoint is controlled by cyclin and cyclin dependent kinases. The progression of interphase is the result of the increased amount of cyclin; as the amount of cyclin increases and more cyclin dependent kinases attach to cyclin signaling the cell further into interphase. The peak of the cyclin attached to the cyclin dependent kinases this system pushes the cell out of interphase and into the M phase, where mitosis and cytokinesis occur.
There are three transition checkpoints. The most important being the G1-S transition checkpoint. If the cell does not pass this phase the cell will most not go through the rest of the cell division cycle. Prophase is the first stage of division; the nuclear envelope is broken down, long strands of chromatin condense to form shorter more visible strands called chromosomes, the nucleolus disappears, microtubules attach to the chromosomes at the kinetochores present in the centromere. Microtubules associated with the alignment and separation of chromosomes are referred to as the spindle and spindle fibers. Chromosomes will be visible under a microscope and will be connected at the centromere. During this condensation and alignment period, homologous over. In metaphase, the centromeres of the chromosomes convene themselves on the metaphase plate, an imaginary line, equidistant from the two centrosome poles. Chromosomes line up in the middle of the cell by MTOCs by pushing and pulling on centromeres of both chromatids which causes the chromosome to move to the center.
The chromosomes are still condensing and are at one step away from being the most coiled and condensed they will be. Spindle fibres have connected to the kinetochores. At this point, the chromosomes are ready to split into opposite poles of the cell towards the spindle to which they are connected. Anaphase is a short stage of the cell cycle and occurs after the chromosomes align at the mitotic plate. After the chromosomes line up in the middle of the cell, the spindle fibers will pull them apart; the chromosomes are split apart as the sister chromatids move to opposite sides of the cell. While the sister chromatids are being pulled apart and plasma gets elongated from non-kinetochore microtubules Telophase is the last stage of the cell cycle. A cleavage furrow splits the cell in two; these two cells form around the chromatin at the two poles of the cell. Two nuclear membranes begin to reform and the chromatin begin to unwind. Cells are broadly classified into two main categories: simple, non-nucleated prokaryotic cells, complex, nucleated eukaryotic cells.
Owing to their structural differences and prokaryotic cells do not divide in the same way. The pattern of cell division that tr