1.
Meiosis
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This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants, and fungi. Errors in meiosis resulting in aneuploidy are the known cause of miscarriage. In meiosis, DNA replication is followed by two rounds of division to produce four potential daughter cells, each with half the number of chromosomes as the original parent cell. The two meiotic divisions are known as Meiosis I and Meiosis II and this S-phase can be referred to as premeiotic S-phase or meiotic S-phase. Immediately following DNA replication, meiotic cells enter a prolonged G2-like stage known as meiotic prophase, a subset of recombination events results in crossovers, which create physical links known as chiasmata between the homologous chromosomes. During Meiosis II, the cohesion between sister chromatids is released and they segregate from one another, as during mitosis, in some cases all four of the meiotic products form gametes such as sperm, spores, or pollen. In female animals, three of the four meiotic products are eliminated by extrusion into polar bodies, and only one cell develops to produce an ovum. Because the number of chromosomes is halved during meiosis, gametes can fuse to form a zygote that contains two copies of each chromosome, one from each parent. Thus, alternating cycles of meiosis and fertilization enable sexual reproduction, for example, diploid human cells contain 23 pairs of chromosomes including 1 pair of sex chromosomes, half of maternal origin and half of paternal origin. Meiosis produces haploid gametes that contain one set of 23 chromosomes, when two gametes fuse, the resulting zygote is once again diploid, with the mother and father each contributing 23 chromosomes. This same pattern, but not the number of chromosomes. First, the cell undergoes DNA replication, so each homolog now consists of two sister chromatids. Then each set of homologs pair with other and exchange DNA by homologous recombination leading to physical connections between the homologs. In the first meiotic division, the homologs are segregated to daughter cells by the spindle apparatus. The cells then proceed to a division without an intervening round of DNA replication. The sister chromatids are segregated to daughter cells to produce a total of four haploid cells. Female animals employ a variation on this pattern and produce one large ovum. Because of recombination, an individual chromatid can consist of a new combination of maternal and paternal DNA, furthermore, an individual gamete can include an assortment of maternal, paternal, and recombinant chromatids
2.
Myosotis
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Myosotis is a genus of flowering plants in the family Boraginaceae. In the northern hemisphere they are commonly called forget-me-nots or scorpion grasses, the common name forget-me-not was calqued from the German Vergissmeinnicht, and first used in English in 1398 AD via King Henry IV. Similar names and variations are found in many languages, Myosotis alpestris is the state flower of Alaska. Plants of this genus are confused with Chatham Islands forget-me-nots which belong to a related genus. Over five hundred species names have been recorded, but there are only 74 accepted species, the rest are either synonyms of currently accepted names or submissions awaiting resolution. The genus is restricted to two discrete geographic centres, western Eurasia with about 60 confirmed species and New Zealand with around 40 confirmed species. Very small numbers of species occur elsewhere including North America, South America, despite this, Mysosotis species are now common throughout temperate latitudes via the planting of cultivars and introductions of alien species. Many are popular in gardens, preferring moist habitats, in areas where they are not native, they have frequently escaped to wetlands and riverbanks. Only those native to the Northern hemisphere are commonly called Forget-me-not and it is equally possible that the genus originated in either the Northern Hemisphere or in New Zealand. One or two European species, especially the wood forget-me-not, Myosotis sylvatica have been introduced into most of the regions of Europe, Asia. Myosotis have 5-merous actinomorphic flowers with 5 sepals and petals, flowers are typically 1 cm diameter, flat, and blue, pink, white or yellow with yellow centres, growing on scorpioid cymes. They may be annual or perennial with alternate leaves and they typically flower in spring or soon after snow-melt in alpine eco-systems. Their root systems are generally diffuse and their seeds are found in small, tulip-shaped pods along the stem to the flower. The pods attach to clothing when brushed against and eventually fall off, seeds can be collected by putting a piece of paper under the stems and shaking the seed pods and some seeds will fall out. Myosotis scorpioides is also known as scorpion grass due to the curve of its inflorescence. Mysosotis are used as food plants by the larvae of some Lepidoptera species including the setaceous Hebrew character, currently 74 species are classified as accepted species at The Plant List, of which 40 are endemic to New Zealand. The full list of species includes the following, In a German legend, God named all the plants when an unnamed one cried out, Forget-me-not. God replied, That shall be your name, in another Greek legend, when the Creator thought he had finished giving the flowers their colours, he heard one whisper Forget me not
3.
Eukaryote
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A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts
4.
Chromosome
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A chromosome is a DNA molecule with part or all of the genetic material of an organism. Prokaryotes usually have one single circular chromosome, whereas most eukaryotes are diploid, chromosomes in eukaryotes are composed of chromatin fiber. Chromatin fiber is made of nucleosomes, a nucleosome is a histone octamer with part of a longer DNA strand attached to and wrapped around it. Chromatin fiber, together with associated proteins is known as chromatin, chromatin is present in most cells, with a few exceptions, for example, red blood cells. Occurring only in the nucleus of cells, chromatin contains the vast majority of DNA, except for a small amount inherited maternally. Chromosomes are normally visible under a microscope only when the cell is undergoing the metaphase of cell division. Before this happens every chromosome is copied once, and the copy is joined to the original by a centromere resulting in an X-shaped structure, the original chromosome and the copy are now called sister chromatids. During metaphase, when a chromosome is in its most condensed state, in this highly condensed form chromosomes are easiest to distinguish and study. In prokaryotic cells, chromatin occurs free-floating in cytoplasm, as these cells lack organelles, the main information-carrying macromolecule is a single piece of coiled double-helix DNA, containing many genes, regulatory elements and other noncoding DNA. The DNA-bound macromolecules are proteins that serve to package the DNA, chromosomes vary widely between different organisms. Some species such as certain bacteria also contain plasmids or other extrachromosomal DNA and these are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. Chromosomal recombination during meiosis and subsequent sexual reproduction plays a significant role in genetic diversity. In prokaryotes and viruses, the DNA is often densely packed and organized, in the case of archaea, by homologs to eukaryotic histones, small circular genomes called plasmids are often found in bacteria and also in mitochondria and chloroplasts, reflecting their bacterial origins. Some use the term chromosome in a sense, to refer to the individualized portions of chromatin in cells. However, others use the concept in a sense, to refer to the individualized portions of chromatin during cell division. The word chromosome comes from the Greek χρῶμα and σῶμα, describing their strong staining by particular dyes, schleiden, Virchow and Bütschli were among the first scientists who recognized the structures now so familiar to everyone as chromosomes. The term was coined by von Waldeyer-Hartz, referring to the term chromatin, in a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were the continuity of chromosomes and the individuality of chromosomes and it is the second of these principles that was so original
5.
Cell nucleus
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In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei. Cell nuclei contain most of the genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones. The genes within these chromosomes are the nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, because the nuclear membrane is impermeable to large molecules, nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be transported by carrier proteins while allowing free movement of small molecules. Movement of large molecules such as proteins and RNA through the pores is required for gene expression and the maintenance of chromosomes. The best-known of these is the nucleolus, which is involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA, the nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek and he observed a lumen, the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei, the nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area and he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the plays a role in generating cells. He believed that he had observed new cells assembling around cytoblasts, Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The function of the nucleus remained unclear, between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a nucleated cell, therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other groups, including amphibians. Eduard Strasburger produced the results for plants in 1884
6.
Allium
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Allium is a genus of monocotyledonous flowering plants that includes the cultivated onion, garlic, scallion, shallot and leek as well as chives and hundreds of other wild species. The generic name Allium is the Latin word for garlic, some sources refer to Greek αλεω by reason of the smell of garlic. The cooking and consumption of parts of the plants is due to the variety of flavours. The inclusion of a species to the genus Allium is taxonomically difficult, estimates of the number of species have been as low as 260, and as high as 979, but are most likely about 800–850. The type species for the genus is Allium sativum, Allium species occur in temperate climates of the Northern Hemisphere, except for a few species occurring in Chile, Brazil, and tropical Africa. They vary in height between 5 cm and 150 cm, the flowers form an umbel at the top of a leafless stalk. The bulbs vary in size between species, from small to rather large, some species develop thickened leaf-bases rather than forming bulbs as such. Plants of the Allium genus produce chemical compounds that give them a characteristic onion or garlic taste, many are used as food plants, though not all members of the genus are equally flavorous. In most cases, both bulb and leaves are edible and the taste may be strong or weak, depending on the species, in the rare occurrence of sulfur-free growth conditions, all Allium species lose their usual pungency altogether. In the APG III classification system, Allium is placed in the family Amaryllidaceae, in some of the older classification systems, Allium was placed in Liliaceae. Molecular phylogenetic studies have shown this circumscription of Liliaceae is not monophyletic, Allium is one of about fifty-seven genera of flowering plants with more than 500 species. It is by far the largest genus in the Amaryllidaceae, the genus Allium is characterised by herbaceous geophyte perennials with true bulbs, some of which are borne on rhizomes and an onion or garlic odor and flavor. A small number of species have tuberous roots, the bulbs outer coats are commonly brown or grey, with a smooth texture, and are fibrous, or with cellular reticulation. The inner coats of the bulbs are membranous, many alliums have basal leaves that commonly wither away from the tips downward before or while the plants flower, but some species have persistent foliage. Plants produce from one to 12 leaves, most species having linear, the leaf blades are straight or variously coiled, but some species have broad leaves, including A. victorialis and A. tricoccum. The leaves are sessile, and very rarely narrowed into a petiole, the flowers, which are produced on scapes are erect or in some species pendent, having six petal-like tepals produced in two whorls. The flowers have one style and six stamens, the anthers. The ovaries are superior, and three-lobed with three locules, the fruits are capsules that open longitudinally along the capsule wall between the partitions of the locule
7.
Cell biology
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Cell biology is a branch of biology that studies the different structures and functions of the cell and focuses mainly on the idea of the cell as the basic unit of life. This is done both on a microscopic and molecular level as it encompasses prokaryotic cells and eukaryotic cells, knowing the components of cells and how cells work is fundamental to all biological sciences, it is also essential for research in bio-medical fields such as cancer, and other diseases. Research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology. The study of the cell is done on a level, however, most of the processes within the cell are made up of a mixture of small organic molecules, inorganic ions, hormones. Approximately 75-85% of the volume is due to water making it an indispensable solvent as a result of its polarity. These molecules within the cell, which operate as substrates, provide an environment for the cell to carry out metabolic reactions. The cell shape varies among the different types of organisms, and are then classified into two categories, eukaryotes and prokaryotes. Cell biology focuses more on the study of cells, and their signalling pathways. This environment of the cell is made up of hydrophilic and hydrophobic regions which allows for the exchange of the above-mentioned molecules and ions. The hydrophilic regions of the cell are mainly on the inside and outside of the cell, the cell membrane consists of lipids and proteins which accounts for its hydrophobicity as a result of being non-polar substances. Therefore, in order for these molecules to participate in reactions, within the cell and they accomplish this process of gaining access to the cell via, osmotic pressure, diffusion, concentration gradients, and membrane channels. Inside of the cell are extensive internal sub-cellular membrane-bounded compartments called organelles, cytoplasm - contents of the main fluid-filled space inside cells, chemical reactions also happen in this jelly-like substance. Nuclear Architecture is important for dictating nuclear function, vacuole - contain cell sap or other storage material. Vesicle - small membrane-bounded spheres inside cells which transport substances, the growth process of the cell does not refer to the size of the cell, but instead the density of the number of cells present in the organism at a given time. Cell growth pertains to the increase in the number of cells present in an organism as it grows and develops, Cells are the foundation of all organisms, they are the fundamental unit of life. The growth and development of the cell are essential for the maintenance of the host, for this process the cell goes through the steps of the cell cycle and development which involves cell growth, DNA replication, cell division, regeneration, specialization, and cell death. The cell cycle is divided into four phases, G1, S, G2. The G phases – which is the growth phase - makes up approximately 95% of the cycle
8.
Cell cycle
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The cell cycle or cell-division cycle is the series of events that take place in a cell leading to its division and duplication of its DNA to produce two daughter cells. In bacteria, which lack a nucleus, the cell cycle is divided into the B, C. The B period extends from the end of cell division to the beginning of DNA replication, DNA replication occurs during the C period. The D period refers to the stage between the end of DNA replication and the splitting of the cell into two daughter cells. In cells with a nucleus, as in eukaryotes, the cycle is also divided into three periods, interphase, the mitotic phase, and cytokinesis. During interphase, the cell grows, accumulating nutrients needed for mitosis, preparing it for cell division, during the mitotic phase, the chromosomes separate. During the final stage, cytokinesis, the chromosomes and cytoplasm separate into two new daughter cells, to ensure the proper division of the cell, there are control mechanisms known as cell cycle checkpoints. After cell division, each of the cells begin the interphase of a new cycle. The cell cycle consists of four phases, G1 phase, S phase, G2 phase. Activation of each phase is dependent on the progression and completion of the previous one. Cells that have temporarily or reversibly stopped dividing are said to have entered a state of quiescence called G0 phase, after cell division, each of the daughter cells begin the interphase of a new cycle. G0 is a phase where the cell has left the cycle and has stopped dividing. The cell cycle starts with this phase, the word post-mitotic is sometimes used to refer to both quiescent and senescent cells. Non proliferative cells in multicellular eukaryotes generally enter the quiescent G0 state from G1 and may remain quiescent for long periods of time and this is very common for cells that are fully differentiated. Cellular senescence occurs in response to DNA damage and external stress, some cells enter the G0 phase semi-permanently, and are considered post-mitotic e. g. some liver, kidney, stomach cells. Many cells do not enter G0 and continue to divide throughout an organisms life, before a cell can enter cell division, it needs to take in nutrients. All of the preparations are done during interphase, interphase is a series of changes that takes place in a newly formed cell and its nucleus, before it becomes capable of division again. It is also called preparatory phase or intermitosis, previously it was called resting stage because there is no apparent activity related to cell division. Typically interphase lasts for at least 90% of the total time required for the cell cycle
9.
Interphase
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Interphase is the phase of the cell cycle in which a typical cell spends most of its life. During this phase, the cell copies its DNA in preparation for mitosis, interphase is the daily living or metabolic phase of the cell, in which the cell obtains nutrients and metabolizes them, grows, reads its DNA, and conducts other normal cell functions. The majority of eukaryotic cells spend most of their time in interphase and this phase was formerly called the resting phase. However, interphase does not describe a cell that is resting, rather, the cell is actively living. A common misconception is that interphase is the first stage of mitosis, however, since mitosis is the division of the nucleus, prophase is actually the first stage. In interphase, the cell gets itself ready for mitosis or meiosis, there are three stages of cellular interphase, with each phase ending when a cellular checkpoint checks the accuracy of the stages completion before proceeding to the next. The stages of interphase are, G1, in which the cell grows, during this time, a high amount of protein synthesis occurs and the cell grows - more organelles are produced and the volume of the cytoplasm increases. If the cell is not to again, it will enter G0. Synthesis, in which the cell duplicates its DNA, G2, in which the cell resumes its growth in preparation for division. The mitochondria divide and the continues to grow until mitosis begins. In plants, chloroplasts also divide during G2, in addition, some cells that do not divide often or ever, enter a stage called G0, which is either a stage separate from interphase or an extended G1. The duration of time spent in interphase and in stage of interphase is variable. Most cells of adult mammals spend about 20 hours in interphase, interphase includes G1, S, and G2 phases. Mitosis and cytokinesis, however, are separate from interphase, when G2 is completed, the cell enters a relatively brief period of nuclear and cellular division, composed of mitosis and cytokinesis, respectively. After the successful completion of mitosis and cytokinesis, both resulting daughter cells re-enter G1 of interphase, in the cell cycle, interphase is preceded by telophase and cytokinesis of the M phase. In alternative fashion, interphase is sometimes interrupted by G0 phase, after the successful completion of the G2 checkpoint, the final checkpoint in interphase, the cell proceeds to prophase, or in plants to preprophase, which is the first stage of mitosis. G0 phase is viewed as either an extended G1 phase where the cell is neither dividing nor preparing to divide, in gamete production interphase is succeeded by meiosis. In programmed cell death, interphase is followed or preempted by apoptosis
10.
Cytokinesis
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Cytokinesis is that part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the stages of nuclear division in mitosis and meiosis. During cytokinesis the spindle apparatus partitions and transports duplicated chromatids into the cytoplasm of the daughter cells. After the completion of the telophase and cytokinesis each daughter cell enters the interphase of the cell cycle, particular functions demand various deviations from the process of symmetrical cytokinesis, for example in oogenesis in animals the ovum takes almost all the cytoplasm and organelles. This leaves very little for the polar bodies, which in most species die without function. Another form of mitosis occurs in such as liver and skeletal muscle, it omits cytokinesis. Plant cytokinesis differs from animal cytokinesis, partly because of the rigidity of plant cell walls, Cytokinesis largely resembles the prokaryotic process of binary fission, but because of differences between prokaryotic and eukaryotic cell structures and functions, the mechanisms differ. Animal cell cytokinesis begins shortly after the onset of sister chromatid separation in the anaphase of mitosis, the process can be divided to the following distinct steps, anaphase spindle reorganization, division plane specification, actin-myosin ring assembly and contraction, and abscission. Faithful partitioning of the genome to emerging daughter cells is ensured through the temporal coordination of the above individual events by molecular signaling pathways. Animal cell cytokinesis starts with the stabilization of microtubules and reorganization of the spindle to form the central spindle. Central spindle forms when non-kinetochore microtubule fibres are bundled between the spindle poles, the process of mitotic spindle reorganization and central spindle formation is caused by the decline of CDK1 activity during anaphase. The decline of CDK1 activity at the metaphase-anaphase transition leads to dephosphorylating of inhibitory sites on multiple central spindle components. First of all, the removal of a CDK1 phosphorylation from a subunit of the CPC allows its translocalization to the spindle from the centromeres. Besides being a component of the central spindle itself, CPC also plays a role in the phosphoregulation of other central spindle components, including PRC1. MKLP1, together with the Rho-family GTPase activating protein CYK-4, forms the centralspindlin complex, centralspindlin binds to the central spindle as higher-order clusters. The centralspindlin cluster formation is promoted by phosphorylation of MLKP1 by Aurora B, the second step of animal cell cytokinesis involves division plane specification and cytokinetic furrow formation. Precise positioning of the plane between the two masses of segregated chromosomes is essential to prevent chromosome loss. Meanwhile, the mechanism by which the spindle determines the division plane in animal cells is perhaps the most enduring mystery in cytokinesis, there exist three hypotheses of furrow induction
11.
Cytoplasm
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In cell biology, the cytoplasm is the material within a living cell, excluding the cell nucleus. It comprises cytosol and the organelles – the cells internal sub-structures, all of the contents of the cells of prokaryotic organisms are contained within the cytoplasm. Within the cells of organisms the contents of the cell nucleus are separated from the cytoplasm. The cytoplasm is about 80% water and usually colorless, the submicroscopic ground cell substance or cytoplasmatic matrix which remains after exclusion the cell organelles and particles is groundplasm. It is within the cytoplasm that most cellular activities occur, such as many metabolic pathways including glycolysis, the concentrated inner area is called the endoplasm and the outer layer is called the cell cortex or the ectoplasm. Movement of calcium ions in and out of the cytoplasm is an activity for metabolic processes. In plants, movement of the cytoplasm around vacuoles is known as cytoplasmic streaming, the term was introduced by Rudolf von Kölliker in 1863, originally as a synonym for protoplasm, but later it has come to mean the cell substance and organelles outside the nucleus. There has been disagreement on the definition of cytoplasm, as some authors prefer to exclude from it some organelles. The physical properties of the cytoplasm have been contested in recent years and it remains uncertain how the varied components of the cytoplasm interact to allow movement of particles and organelles while maintaining the cell’s structure. The flow of cytoplasmic components plays an important role in cellular functions which are dependent on the permeability of the cytoplasm. An example of function is cell signalling, a process which is dependent on the manner in which signaling molecules are allowed to diffuse across the cell. While small signaling molecules like calcium ions are able to diffuse with ease, larger molecules, the irregular dynamics of such particles have given rise to various theories on the nature of the cytoplasm. There has long been evidence that the cytoplasm behaves like a sol-gel and it is thought that the component molecules and structures of the cytoplasm behave at times like a disordered colloidal solution and at other times like an integrated network, forming a solid mass. Recently it has proposed that the cytoplasm behaves like a glass-forming liquid approaching the glass transition. A cells ability to vitrify in the absence of activity, as in dormant periods. There has been examining the motion of cytoplasmic particles independent of the nature of the cytoplasm. In such an approach, the aggregate random forces within the cell caused by motor proteins explain the non-Brownian motion of cytoplasmic constituents. The three major elements of the cytoplasm are the cytosol, organelles and inclusions, the cytosol is the portion of the cytoplasm not contained within membrane-bound organelles
12.
Organelle
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In cell biology, an organelle is a specialized subunit within a cell that has a specific function. Individual organelles are usually enclosed within their own lipid bilayers. The name organelle comes from the idea that these structures are to cells what an organ is to the body, organelles are identified by microscopy, and can also be purified by cell fractionation. There are many types of organelles, particularly in eukaryotic cells, while prokaryotes do not possess organelles per se, some do contain protein-based bacterial microcompartments, which are thought to act as primitive organelles. In biology organs are defined as confined functional units within an organism, the analogy of bodily organs to microscopic cellular substructures is obvious, as from even early works, authors of respective textbooks rarely elaborate on the distinction between the two. In the 1830s, Félix Dujardin refuted Ehrenberg theory which said that microorganims have the organs of multicellular animals. Credited as the first to use a diminutive of organ for cellular structures was German zoologist Karl August Möbius, under this definition, there would only be two broad classes of organelles, mitochondria plastids. Other organelles are also suggested to have endosymbiotic origins, but do not contain their own DNA, under the more restricted definition of membrane-bound structures, some parts of the cell do not qualify as organelles. Nevertheless, the use of organelle to refer to non-membrane bound structures such as ribosomes is common and this has led some texts to delineate between membrane-bound and non-membrane bound organelles. The larger organelles, such as the nucleus and vacuoles, are visible with the light microscope. They were among the first biological discoveries made after the invention of the microscope, not all eukaryotic cells have each of the organelles listed below. Exceptional organisms have cells that do not include some organelles that might otherwise be considered universal to eukaryotes, there are also occasional exceptions to the number of membranes surrounding organelles, listed in the tables below. In addition, the number of organelles of each type found in a given cell varies depending upon the function of that cell. This idea is supported in the Endosymbiotic theory, in the past, they were often viewed as having little internal organization, but slowly, details are emerging about prokaryotic internal structures. However, more recent research has revealed that at least some prokaryotes have microcompartments such as carboxysomes and these subcellular compartments are 100–200 nm in diameter and are enclosed by a shell of proteins. The function of a protein is correlated with the organelle in which it resides. CoRR Hypothesis Ejectosome Endosymbiotic theory Organelle biogenesis Membrane vesicle trafficking Host-pathogen interface Tree of Life project, Eukaryotes
13.
Cell membrane
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The cell membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is permeable to ions and organic molecules and controls the movement of substances in. The basic function of the membrane is to protect the cell from its surroundings. It consists of the bilayer with embedded proteins. Cell membranes can be artificially reassembled, Some authors that did not believe that there was a functional permeable boundary at the surface of the cell preferred to use the term plasmalemma to the extern region of the cell. The cell membrane surrounds the cytoplasm of living cells, physically separating the components from the extracellular environment. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, fungi, bacteria, most archaea, and plants also have a cell wall, which provides a mechanical support to the cell and precludes the passage of larger molecules. The cell membrane is permeable and able to regulate what enters and exits the cell. The movement of substances across the membrane can be passive, occurring without the input of cellular energy, or active. The membrane also maintains the cell potential, the cell membrane thus works as a selective filter that allows only certain things to come inside or go outside the cell. The cell employs a number of mechanisms that involve biological membranes,1. Passive osmosis and diffusion, Some substances such as carbon dioxide and oxygen, can move across the membrane by diffusion. Because the membrane acts as a barrier for certain molecules and ions, such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water. Transmembrane protein channels and transporters, Nutrients, such as sugars or amino acids, must enter the cell, such molecules diffuse passively through protein channels such as aquaporins in facilitated diffusion or are pumped across the membrane by transmembrane transporters. Protein channel proteins, also called permeases, are quite specific, recognizing and transporting only a limited food group of chemical substances. Endocytosis, Endocytosis is the process in which cells absorb molecules by engulfing them, the plasma membrane creates a small deformation inward, called an invagination, in which the substance to be transported is captured. The deformation then pinches off from the membrane on the inside of the cell, Endocytosis is a pathway for internalizing solid particles, small molecules and ions, and macromolecules. Endocytosis requires energy and is thus a form of active transport and this is the process of exocytosis
14.
Cell (biology)
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The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, the study of cells is called cell biology. Cells consist of cytoplasm enclosed within a membrane, which contains many such as proteins. Organisms can be classified as unicellular or multicellular, while the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion cells. Most plant and animal cells are only under a microscope. The cell was discovered by Robert Hooke in 1665, who named the unit for its resemblance to cells inhabited by Christian monks in a monastery. Cells emerged on Earth at least 3.5 billion years ago, Cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular, prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling and being self-sustaining. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus, prokaryotes include two of the domains of life, bacteria and archaea. The DNA of a prokaryotic cell consists of a chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid, most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter. Though most prokaryotes have both a cell membrane and a wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, the cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment, some eukaryotic cells also have a cell wall. Inside the cell is the region that contains the genome, ribosomes. The genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular, linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. Though not forming a nucleus, the DNA is condensed in a nucleoid, plasmids encode additional genes, such as antibiotic resistance genes
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Cell division
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Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a cell cycle. Meiosis results in four daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, and 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 equally into two daughter cells. All cell divisions, regardless of organism, are preceded by a round of DNA replication. For simple unicellular organisms 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, after growth, cell division by mitosis allows for continual construction and 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 cells genome. Before division can occur, the information that is stored in chromosomes must be replicated. A great deal of infrastructure is involved in keeping genomic information consistent between generations. Interphase is the process a cell must go through mitosis, meiosis. Interphase consists of four stages, G1, S, G2. If the cell does not progress through G1, the cell enters a stage called G0. In G0, cells are living but they are put on hold. The cells may later be called back into interphase if needed at a later time, 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 content to be maintained. During G2, the cell undergoes the final stages of growth before it enters the M phase, the M phase, can be either mitosis or meiosis depending on the type of cell
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Prophase
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Prophase, is a stage of Mitosis. This is when the chromatin condenses into two rod-shaped structures called chromosomes in which the chromatin becomes visible and this process, known as chromatin condensation, is involved with the condensin complex. Since the genetic material has been replicated in the interphase of the cell cycle. Those copies are called sister chromatids and they are attached to each other at a DNA element present on every chromosome called the centromere, also during prophase, giemsa staining can be applied to elicit G-banding in chromosomes. An important organelle in mitosis is the centrosome, the organizing center in metazoans. During prophase, the two centrosomes, which replicate independently of mitosis, have their microtubule-activity increased due to the recruitment of γ-tubulin, the centrosomes will be pushed apart to opposite ends of the cell nucleus by the action of molecular motors acting on the microtubules. At the end of prophase, the tiny nucleolus within the nucleus dissolves, the nucleolus starts moving towards the nuclear membrane at the beginning of prophase, and its disintegration occurs near the nuclear envelope. Its contents are dispersed in masses, basically, the chromatin in the nucleus coils into chromosomes. The centrosomes move to opposite poles of the cell, forming a bridge of spindle fibers, at the end of prophase, the nucleolus disperses. In prometaphase, the step of mitosis, the nuclear membrane breaks apart. Interphase Metaphase Anaphase Telophase Farhan Phase Media related to Prophase at Wikimedia Commons
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Prometaphase
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Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryotic somatic cells. Prometaphase is sometimes included as part of the end of prophase. In prometaphase, the nuclear membrane breaks apart into numerous membrane vesicles, kinetochore microtubules emerging from the centrosomes at the poles of the spindle reach the chromosomes and attach to the kinetochores, throwing the chromosomes into agitated motion. Other spindle microtubules make contact with microtubules coming from the opposite pole, forces exerted by protein motors associated with spindle microtubules move the chromosomes toward the center of the cell. The microtubules are composed of two types, kinetochore microtubules and non-kinetochore microtubules, kinetochore microtubules begin searching for kinetochores to attach to. A number of microtubules or polar microtubules find and interact with corresponding nonkinetochore microtubules from the opposite centrosome to form the mitotic spindle. The role of prometaphase is completed all of the kinetochore microtubules have attached to their kinetochores. An unattached kinetochore, and thus a non-aligned chromosome, even when most of the chromosomes have lined up. This prevents premature progression into anaphase by inhibiting the complex until all kinetochores are attached. Media related to Prometaphase at Wikimedia Commons
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Metaphase
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Metaphase is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage. These chromosomes, carrying information, align in the equator of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycles duration, preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase. In metaphase, the centromeres of the chromosomes convene themselves on the metaphase plate, in certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the middleline. One of the cell cycle checkpoints occurs during prometaphase and metaphase, only after all chromosomes have become aligned at the metaphase plate, when every kinetochore is properly attached to a bundle of microtubules, does the cell enter anaphase. Such a signal creates the mitotic spindle checkpoint and this would be accomplished by regulation of the anaphase-promoting complex, securin, and separase. The analysis of chromosomes is one of the main tools of classical cytogenetics. Chromosomes are condensed and highly coiled in metaphase, which makes them most suitable for visual analysis, Metaphase chromosomes make the classical picture of chromosomes. For classical cytogenetic analyses, cells are grown in short term culture, further they are used for slide preparation and banding of chromosomes to be visualised under microscope to study structure and number of chromosomes. Staining of the slides, often with Giemsa or Quinacrine, produces a pattern of in total up to several hundred bands, normal metaphase spreads are used in methods like FISH and as a hybridization matrix for comparative genomic hybridization experiments. Malignant cells from solid tumors or leukemia samples can also be used for analysis to generate metaphase preparations. Interphase Prophase Anaphase Telophase Media related to Metaphase at Wikimedia Commons
19.
Anaphase
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Anaphase, is the stage of mitosis after the metaphase when replicated chromosomes are split and the daughter chromatids are moved to opposite poles of the cell. Chromosomes also reach their overall maximum condensation in late anaphase, to chromosome segregation. Anaphase starts when the anaphase promoting complex marks an inhibitory chaperone called securin with ubiquitin for destruction, securin is a protein which inhibits a protease known as separase. The destruction of securin unleashes separase which then breaks down cohesin, the centromeres are split, and the new daughter chromosomes are pulled toward the poles. They take on a V-shape or Y-shape as they are pulled back, while the chromosomes are drawn to each side of the cell, the non-kinetochore spindle fibers push against each other, in a ratcheting action, that stretches the cell into an oval. Once anaphase is complete, the moves into telophase. Anaphase accounts for approximately 1% of the cell cycles duration and it begins with the regulated triggering of the metaphase-to-anaphase transition. Metaphase ends with the destruction of B cyclin, B cyclin is marked with ubiquitin which flags it for destruction by proteasomes, which is required for the function of metaphase cyclin-dependent kinases. Interphase Prophase Metaphase Telophase Anaphase I Anaphase II Cdc20 Media related to Anaphase at Wikimedia Commons
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Telophase
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Telophase is the final stage in both meiosis and mitosis in a eukaryotic cell. During telophase, the effects of prophase and prometaphase are reversed, the chromosomes reach the poles as the nuclear membranes re-form around each set of chromatids, the nucleoli also reappear. The remaining spindle microtubules begin to depolymerize, the chromosomes also unwind back into the expanded chromatin that is present during interphase. Telophase accounts for approximately 2% of the cell cycles duration, cytokinesis typically begins before late telophase. In land plant cells, vesicles derived from the Golgi apparatus move to the middle of the cell along a microtubule scaffold called the phragmoplast and this structure directs packets of cell wall materials which coalesce into a disk-shaped structure called a cell plate. The cell plate grows out centrifugally and eventually develops into a cell wall. Interphase Prophase Metaphase Anaphase Media related to Telophase at Wikimedia Commons
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Spindle apparatus
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In cell biology, the spindle apparatus refers to the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. Besides chromosomes, the apparatus is composed of hundreds of proteins. Microtubules comprise the most abundant components of the machinery, attachment of microtubules to chromosomes is mediated by kinetochores, which actively monitor spindle formation and prevent premature anaphase onset. Microtubule polymerization and depolymerization dynamics drive chromosome congression, once every chromosome is bi-oriented, anaphase commences and cohesin, which couples sister chromatids, is severed, permitting the transit of the sister chromatids to opposite poles. The spindle apparatus is vaguely ellipsoid in cross section and tapers at the ends, in the wide middle portion, known as the spindle midzone, antiparallel microtubules are bundled by kinesins. At the pointed ends, known as spindle poles, microtubules are nucleated by the centrosomes in most animal cells, acentrosomal or anastral spindles lack centrosomes or asters at the spindle poles, respectively, and occur for example during female meiosis in most animals. In this instance, a Ran GTP gradient is the regulator of spindle microtubule organization. In fungi, spindles form between spindle pole bodies embedded in the envelope, which does not break down during mitosis. Microtubule-associated proteins associate with microtubules at the midzone and the poles to regulate their dynamics. γ-tubulin is a specialized tubulin variant that assembles into a complex called γ-TuRC which nucleates polymerization of α/β tubulin heterodimers into microtubules. The growing ends of microtubules are protected against catastrophe by the action of plus-end microtubule tracking proteins to promote their association with kinetochores at the midzone, cLIP170 was shown to localize near microtubule plus-ends in HeLa cells and to accumulate in kinetochores during prometaphase. CLIP-associated proteins like CLASP1 in humans have also shown to localize to plus-ends. Plus-end polymerization may be moderated by the EB1 protein, which directly binds the growing ends of microtubules and coordinates the binding of other +TIPs. MCAK localizes to the tips of microtubules at kinetochores where it can trigger catastrophe in direct competition with stabilizing +TIP activity. These proteins harness the energy of ATP hydrolysis to induce destabilizing conformational changes in protofilament structure that cause kinesin release, loss of their activity results in numerous mitotic defects. Additional microtubule destabilizing proteins include Op18/stathmin and katanin which have roles in remodeling the mitotic spindle as well as promoting chromosome segregation during anaphase. The activities of these MAPs are carefully regulated to maintain proper microtubule dynamics during spindle assembly, with many of these serving as Aurora. The precise orientation of this complex is required to ensure accurate chromosome segregation, however, it remains unclear how the spindle becomes organized
22.
Apoptosis
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Apoptosis is a process of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes and death and these changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, chromosomal DNA fragmentation, and global mRNA decay. Between 50 and 70 billion cells die each day due to apoptosis in the human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day, for example, the separation of fingers and toes in a developing human embryo occurs because cells between the digits undergo apoptosis. Because apoptosis cannot stop once it has begun, it is a regulated process. Apoptosis can be initiated through one of two pathways, in the intrinsic pathway the cell kills itself because it senses cell stress, while in the extrinsic pathway the cell kills itself because of signals from other cells. Both pathways induce cell death by activating caspases, which are proteases, the two pathways both activate initiator caspases, which then activate executioner caspases, which then kill the cell by degrading proteins indiscriminately. Research on apoptosis has increased substantially since the early 1990s, in addition to its importance as a biological phenomenon, defective apoptotic processes have been implicated in a wide variety of diseases. Excessive apoptosis causes atrophy, whereas an insufficient amount results in uncontrolled cell proliferation, some factors like Fas receptors and caspases promote apoptosis, while some members of the Bcl-2 family of proteins inhibit apoptosis. German scientist Karl Vogt was first to describe the principle of apoptosis in 1842, in 1885, anatomist Walther Flemming delivered a more precise description of the process of programmed cell death. However, it was not until 1965 that the topic was resurrected, while studying tissues using electron microscopy, John Foxton Ross Kerr at University of Queensland was able to distinguish apoptosis from traumatic cell death. Following the publication of a paper describing the phenomenon, Kerr was invited to join Alastair R Currie, as well as Andrew Wyllie, in 1972, the trio published a seminal article in the British Journal of Cancer. Kerr had initially used the term programmed cell necrosis, but in the article, Kerr, Wyllie and Currie credited James Cormack, a professor of Greek language at University of Aberdeen, with suggesting the term apoptosis. Kerr received the Paul Ehrlich and Ludwig Darmstaedter Prize on March 14,2000 and he shared the prize with Boston biologist H. Robert Horvitz. For many years, the apoptosis and programmed cell death were not highly cited. The 2002 Nobel Prize in Medicine was awarded to Sydney Brenner, Horvitz, the genes were identified by studies in the nematode C. elegans and homologues of these genes function in humans to regulate apoptosis. In Greek, apoptosis translates to the falling off of leaves from a tree, Cormack, professor of Greek language, reintroduced the term for medical use as it had a medical meaning for the Greeks over two thousand years before. Hippocrates used the term to mean the falling off of the bones, galen extended its meaning to the dropping of the scabs
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Mutation
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In biology, a mutation is the permanent alteration of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA or other genetic elements. Mutations may also result from insertion or deletion of segments of DNA due to mobile genetic elements, mutations may or may not produce discernible changes in the observable characteristics of an organism. Mutations play a part in normal and abnormal biological processes including, evolution, cancer, and the development of the immune system. The genomes of RNA viruses are based on RNA rather than DNA, the RNA viral genome can be double stranded or single stranded. In some of these viruses replication occurs quickly and there are no mechanisms to check the genome for accuracy and this error-prone process often results in mutations. Mutation can result in different types of change in sequences. Mutations in genes can either have no effect, alter the product of a gene, mutations can also occur in nongenic regions. Mutations can involve the duplication of large sections of DNA, usually through genetic recombination and these duplications are a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years. Most genes belong to larger families of shared ancestry, known as homology. Here, protein domains act as modules, each with a particular and independent function, that can be mixed together to produce genes encoding new proteins with novel properties. For example, the eye uses four genes to make structures that sense light. Another advantage of duplicating a gene is that this increases engineering redundancy, other types of mutation occasionally create new genes from previously noncoding DNA. Changes in chromosome number may involve even larger mutations, where segments of the DNA within chromosomes break and then rearrange. For example, in the Homininae, two fused to produce human chromosome 2, this fusion did not occur in the lineage of the other apes. Sequences of DNA that can move about the genome, such as transposons, make up a fraction of the genetic material of plants and animals. For example, more than a million copies of the Alu sequence are present in the genome. Another effect of these mobile DNA sequences is that when they move within a genome, they can mutate or delete existing genes, nonlethal mutations accumulate within the gene pool and increase the amount of genetic variation. The abundance of some changes within the gene pool can be reduced by natural selection, while other more favorable mutations may accumulate
24.
Prokaryote
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A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle. The word prokaryote comes from the Greek πρό before and καρυόν nut or kernel, prokaryotes can be divided into two domains, Archaea and bacteria. In contrast, species with nuclei and organelles are placed in the domain Eukaryota, in the prokaryotes, all the intracellular water-soluble components are located together in the cytoplasm enclosed by the cell membrane, rather than in separate cellular compartments. Bacteria, however, do possess protein-based bacterial microcompartments, which are thought to act as primitive organelles enclosed in protein shells, some prokaryotes, such as cyanobacteria may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles, molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species. Eukaryotes are organisms, including humans, whose cells have a well defined membrane-bound nucleus, the division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization. Distinctive types of prokaryotes include extremophiles and methanogens, these are common in extreme environments. Prokaryotes have a cytoskeleton, albeit more primitive than that of the eukaryotes. At least some also contain intracellular structures that can be seen as primitive organelles. Membranous organelles are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, in addition, some species also contain carbohydrate-enclosed microcompartments, which have distinct physiological roles. Most prokaryotes are between 1 µm and 10 µm, but they can vary in size from 0.2 µm to 750 µm, Bacteria and archaea reproduce through asexual reproduction, usually by binary fission. DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has mainly studied in bacteria. In bacteria, gene transfer occurs by three processes and these are bacterial virus -mediated transduction, plasmid-mediated conjugation, and natural transformation. Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of virus particles, the transfer of bacterial DNA is under the control of the bacteriophage’s genes rather than bacterial genes. Conjugation in the well-studied E. coli system is controlled by plasmid genes, infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of the host bacterial DNA to another bacterium. Plasmid mediated transfer of host bacterial DNA also appears to be a process rather than a bacterial adaptation. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the intervening medium, for a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state called competence. About 40 genes are required in Bacillus subtilis for the development of competence, the length of DNA transferred during B. subtilis transformation can be as much as a third to the whole chromosome
25.
Fission (biology)
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In biology, fission is the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original. The object experiencing fission is usually a cell, but the term may refer to how organisms, bodies, populations. The fission may be binary fission, in which a single entity produces two parts, or multiple fission, in which a single entity produces multiple parts, organisms in the domains of Archaea and Bacteria reproduce with binary fission. This form of reproduction and cell division is also used by some organelles within eukaryotic organisms. Binary fission results in the reproduction of a prokaryotic cell by dividing the cell into two parts, each with the potential to grow to the size of the original. Unlike the process of mitosis used by cells, binary fission takes place without the formation of a spindle apparatus in the cell. The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane, when the cell begins to pull apart, the replicated and original chromosomes are separated. The consequence of this method of reproduction is that all the cells are genetically identical. The process of fission in bacteria involves the following steps. First, the cells DNA is replicated, the replicated DNA copies then move to opposite poles of the cell in an energy-dependent process. Then, the plate of the cell constricts and separates the plasma membrane such that each new cell has exactly the same genetic material. More specifically, the following occur, The bacterium before binary fission is when the DNA is tightly coiled. The DNA of the bacterium has uncoiled and duplicated, the DNA is pulled to the separate poles of the bacterium as it increases size to prepare for splitting. The growth of a new cell wall begins to separate the bacterium, the new cell wall fully develops, resulting in the complete split of the bacterium. The new daughter cells have tightly coiled DNA rods, ribosomes, and plasmids, binary fission is generally rapid though its speed varies between species. For E. coli, cells typically divide about every 20 minutes at 37 °C and this time period can therefore be referred to as the doubling time. Some species other than E. coli may have faster or slower doubling times, some organelles in eukaryotic cells reproduce using binary fission. Mitochondrial fission occurs frequently within the cell, even when the cell is not actively undergoing mitosis, binary fission in organisms can occur in four ways, irregular, longitudinal, transverse, oblique
26.
Animal
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Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, arthropods, annelids, nematodes, flatworms, cnidarians, ctenophores, the study of animals is called zoology. The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms, Metazoa and Protozoa. The protozoa were later moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
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Nuclear membrane
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A nuclear membrane, also known as the nucleolemma or karyotheca, is the phospho lipid bilayer membrane which surrounds the genetic material and nucleolus in eukaryotic cells. The nuclear membrane consists of two lipid bilayers—the inner nuclear membrane, and the nuclear membrane. The space between the membranes is called the space, a region contiguous with the lumen of the endoplasmic reticulum. It is usually about 20–40 nm wide, the nuclear membrane also has many small holes called nuclear pores that allow material to move in and out of the nucleus. The outer nuclear membrane also shares a border with the endoplasmic reticulum. While it is linked, the outer nuclear membrane contains proteins found in far higher concentrations than the endoplasmic reticulum. All 4 Nesprin proteins present in mammals are expressed in the nuclear membrane. Nesprin proteins connect cytoskeletal filaments to the nucleoskeleton, nesprin-mediated connections to the cytoskeleton contribute to nuclear positioning and to the cell’s mechanosensory function. Nesprin-3 and-4 may play a role in unloading cargo, Nesprin-3 proteins bind plectin. Nesprin-4 proteins bind the end directed motor kinesin-1. The outer nuclear membrane is also involved in development, as it fuses with the nuclear membrane to form nuclear pores. It is connected to the membrane by nuclear pores which penetrate the membranes. While the two membranes and the reticulum are linked, proteins embedded in the membranes tend to stay put rather than dispersing across the continuum. The nuclear membrane is punctured by thousands of nuclear pore complexes—large hollow proteins about 100 nm across and they link the inner and outer nuclear membranes. During the G2 phase of interphase, the membrane increases its surface area. In lower eukaryotes, such as yeast, which undergo closed mitosis, the spindle fibers either form within the membrane, or penetrate it without tearing it apart. In higher eukaryotes, the membrane must break down during the prometaphase state of mitosis to allow the mitotic spindle fibers to access the chromosomes inside. The breakdown and reformation processes are not well understood, in mammals, the nuclear membrane can break down within minutes, following a set of steps during the early stages of Mitosis
28.
Fungus
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A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from the other eukaryotic life kingdoms of plants, a characteristic that places fungi in a different kingdom from plants, bacteria and some protists, is chitin in their cell walls. Similar to animals, fungi are heterotrophs, they acquire their food by absorbing dissolved molecules, growth is their means of mobility, except for spores, which may travel through the air or water. Fungi are the principal decomposers in ecological systems and this fungal group is distinct from the structurally similar myxomycetes and oomycetes. The discipline of biology devoted to the study of fungi is known as mycology, in the past, mycology was regarded as a branch of botany, although it is now known fungi are genetically more closely related to animals than to plants. Abundant worldwide, most fungi are inconspicuous because of the size of their structures. Fungi include symbionts of plants, animals, or other fungi and they may become noticeable when fruiting, either as mushrooms or as molds. Fungi perform a role in the decomposition of organic matter and have fundamental roles in nutrient cycling. Since the 1940s, fungi have been used for the production of antibiotics, Fungi are also used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, the fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans, losses of crops due to fungal diseases or food spoilage can have a large impact on human food supplies and local economies. The fungus kingdom encompasses a diversity of taxa with varied ecologies, life cycle strategies. However, little is known of the biodiversity of Kingdom Fungi. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, phylogenetic studies published in the last decade have helped reshape the classification within Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten subphyla. The English word fungus is directly adopted from the Latin fungus, used in the writings of Horace, a group of all the fungi present in a particular area or geographic region is known as mycobiota, e. g. the mycobiota of Ireland. Like plants, fungi grow in soil and, in the case of mushrooms, form conspicuous fruit bodies. The fungi are now considered a kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago. Fungi have membrane-bound cytoplasmic organelles such as mitochondria, sterol-containing membranes and they have a characteristic range of soluble carbohydrates and storage compounds, including sugar alcohols, disaccharides, and polysaccharides
29.
Mitotic cell rounding
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Mitotic cell rounding is a shape change that occurs in most animal cells that undergo mitosis. Cells abandon the spread or elongated shape characteristic of interphase and contract into a spherical morphology during mitosis, the phenomena is seen both in artificial cultures in vitro and naturally forming tissue in vivo. In 1935, one of the first published accounts of mitotic rounding in live tissue described cell rounding in the epithelium of the mammalian neural tube. Sauer noticed that cells in mitosis rounded up to the apical, or luminal, for a long time it was not clear why cells became round in mitosis. Recent studies in the epithelia and epidermis of various organisms, however, failure to achieve this may result in mislocalization of one daughter cell to the basal region on the tissue layer and clearance via apoptotic cell death. Secondly, mitotic rounding has been proposed to be a driver for morphological events during tissue development, examples include epithelial invagination of the Drosophila melanogaster tracheal placode and the anisotropic shape and growth of the inner ear lumen in Zebrafish. Thus mitotic cell rounding is involved in organization and homeostasis. To understand the mechanisms of how cells round up in mitosis researchers have conducted mechanical measurements with cultured cells in vitro. More than 90% of the forces are generated by the activity of myosin II molecular motors in the actin cortex. As a result, the tension and effective stiffness of the actin cortex increase as has been consistently observed in mitotic cells. In HeLa cells in vitro, the force generated by a mitotic cell is on the order of 50 to 100 nanonewtons. Internal hydrostatic pressure has been measured to increase from below 100 pascals in interphase to 3 to 10 fold that in mitosis, in similar in vitro experiments, it was found that the threshold forces required to prevent mitosis are in excess of 100 nN. At threshold forces the cell suffers a loss of cortical F-actin uniformity and these effects potentiate distortion of cell dimensions and subsequent perturbation of mitotic progression via spindle defects. Release of stable focal adhesions is another important aspect of mitotic rounding, overall, the biochemical events governing the morphological and mechanical changes in mitotic cells are orchestrated by the mitotic master regulator Cdk1. Qucosa, The Mechanics of Mitotic Cell Rounding, ETH ETH E-Collection, The Mechanism of Mitotic Rounding, Role of the Actomyosin Cortex — ETH E-Collection. Two Minute Talk, Mitotic Cell Rounding — YouTube
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Sperm
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Sperm is the male reproductive cell and is derived from the Greek word sperma. In the types of reproduction known as anisogamy and its subtype oogamy. A uniflagellar sperm cell that is motile is referred to as a spermatozoon, Sperm cells cannot divide and have a limited life span, but after fusion with egg cells during fertilization, a new organism begins developing, starting as a totipotent zygote. The human sperm cell is haploid, so that its 23 chromosomes can join the 23 chromosomes of the egg to form a diploid cell. In mammals, sperm develops in the testicles and is released from the penis, the mammalian sperm cell consists of a head, neck, a midpiece and a tail. The head contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, the neck contains the sperm centriole. The midpiece has a central core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix, uterus. The tail or flagellum executes the lashing movements that propel the spermatocyte, although semen contains millions of sperm, the egg will admit only one. The other ones will die and be absorbed. The spermatozoa of animals are produced through spermatogenesis inside the gonads via meiotic division. The initial spermatozoon process takes around 70 days to complete, the spermatid stage is where the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when it is called a spermatozoan, Sperm cells are carried out of the male body in a fluid known as semen. Human sperm cells can survive within the reproductive tract for more than 5 days post coitus. Semen is produced in the vesicles, prostate gland and urethral glands. In 2016 scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids artificially from stem cells and they injected these spermatids into mouse eggs and produced pups. Sperm quantity and quality are the parameters in semen quality. Thus, in humans, it is a measure of fertility in a man, the genetic quality of sperm, as well as its volume and motility, all typically decrease with age. Human sperm cells are vulnerable to free radical attack and the generation of oxidative DNA damage
31.
Egg cell
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The egg cell, or ovum, is the female reproductive cell in oogamous organisms. The egg cell is not capable of active movement. When egg and sperm fuse, a cell is formed. Karl Ernst von Baer discovered the mammalian ovum in 1827, the fusion of spermatozoa with ova was observed by Oskar Hertwig in 1876. In animals, egg cells are known as ova. The term ovule is used for the young ovum of an animal, in vertebrates, ova are produced by female gonads called ovaries a number of ova are present at birth in mammals and mature via oogenesis. White et al. disproved the longstanding dogma that all of the ova are produced before birth, the team from the Vincent Center for Reproductive Biology, Massachusetts, Boston could prove that oocyte fromation takes place in ovaries of reproductive-age women. This report challenged a fundamental belief, held since the 1950s, in all mammals the ovum is fertilized inside the female body. The human ova grow from primitive germ cells that are embedded in the substance of the ovaries, each of them divides repeatedly to give secretions of the uterine glands, ultimately forming a blastocyst. The ovum is one of the largest cells in the human body, the human ovum measures approximately 0.12 mm in diameter. Ooplasm is the yolk of the ovum, a substance at its center, which contains its nucleus, named the germinal vesicle. Mammalian ova contain only an amount of the nutritive yolk. In contrast, bird eggs contain enough to supply the chick with nutriment throughout the period of incubation. In the oviparous animals the ova develop protective layers and pass through the oviduct to the outside of the body and they are fertilized by male sperm either inside the female body, or outside. After fertilization, an embryo develops, nourished by nutrients contained in the egg and it then hatches from the egg, outside the mothers body. See egg for a discussion of eggs of oviparous animals, the egg cells cytoplasm and mitochondria are the sole means the egg is able to reproduce by mitosis and eventually form a blastocyst after fertilization. Some fish, reptiles and many use this technique. Nearly all land plants have alternating diploid and haploid generations, gametes are produced by the gametophyte, which is the haploid generation
32.
Hugo von Mohl
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Hugo von Mohl was a German botanist from Stuttgart. He was a son of the Württemberg statesman Benjamin Ferdinand von Mohl, while a pupil at the gymnasium he pursued botany and mineralogy in his leisure time, till in 1823 he entered the University of Tübingen. After graduating with distinction in medicine he went to Munich, where he met a circle of botanists. This seems to have determined his career as a botanist, in 1832 he was appointed professor of botany in Tübingen, a post which he never left. Unmarried, his pleasures were in his laboratory and library, and in perfecting optical apparatus and microscopic preparations and he was largely a self-taught botanist from boyhood, and, little influenced in his opinions even by his teachers, preserved always his independence of view on scientific questions. He received many honours during his lifetime, and was elected fellow of the Royal Society in 1868. He recognized under the name of primordial utricle the protoplasmic lining of the vacuolated cell and these and other observations led to the overthrow of Schleidens theory of origin of cells by free-cell-formation. His contributions to knowledge of the cell-wall were no less remarkable and he first explained the true nature of pits, and showed the cellular origin of vessels and of fibrous cells, he was, in fact, the true founder of the cell theory. Mohls early investigations on the structure of palms, of cycads, following on his early demonstration of the origin of stomata, he wrote a classical paper on their opening and closing. In 1843 he started the weekly Botanische Zeitung in conjunction with Schlechtendal, in 1850, he was elected a foreign member of the Royal Swedish Academy of Sciences. In his latter years his productive activity fell off, doubtless through failing health, translated by Henry E. F. Garnsey, revised by Isaac Bayley Balfour. Oxford, Clarendon Press and Biodiversity Heritage Library and this article incorporates text from a publication now in the public domain, Chisholm, Hugh, ed. article name needed
33.
Green algae
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The green algae are a large, informal grouping of algae consisting of the Chlorophyte and Charophyte algae, which are now placed in separate divisions. The land plants, or Embryophytes, are thought to have emerged from the Charophytes, therefore, cladistically, Embryophytes belong to green algae as well. However, as the Embryophytes are traditionally classified as neither algae nor green algae, the clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, in the Charales, the closest relatives of higher plants, full cellular differentiation of tissues occurs. There are about 8,000 species of green algae, many species live most of their lives as single cells, while other species form coenobia, long filaments, or highly differentiated macroscopic seaweeds. A few other organisms rely on green algae to conduct photosynthesis for them, the chloroplasts in euglenids and chlorarachniophytes were acquired from ingested green algae, and in the latter retain a nucleomorph. Green algae are also found symbiotically in the ciliate Paramecium, and in Hydra viridissima, some species of green algae, particularly of genera Trebouxia of the class Trebouxiophyceae and Trentepohlia, can be found in symbiotic associations with fungi to form lichens. In general the species that partner in lichens cannot live on their own. Trentepohlia is a green alga that can live independently on humid soil. Green algae have chloroplasts that contain chlorophyll a and b, giving them a green color, as well as the accessory pigments beta carotene and xanthophylls. The cell walls of green algae usually contain cellulose, and they store carbohydrate in the form of starch, all green algae have mitochondria with flat cristae. When present, paired flagella are used to move the cell and they are anchored by a cross-shaped system of microtubules and fibrous strands. Flagella are only present in the male gametes of charophytes and are absent from the gametes of Pinophyta. Members of the class Chlorophyceae undergo closed mitosis in the most common form of division among the green algae. By contrast, charophyte green algae and land plants undergo open mitosis without centrioles, instead, a raft of microtubules, the phragmoplast, is formed from the mitotic spindle and cell division involves the use of this phragmoplast in the production of a cell plate. This primary endosymbiosis event gave rise to three autotrophic clades with primary plastids, the plants, the red algae and the glaucophytes. Green algae are classified with their embryophyte descendants in the green plant clade Viridiplantae. Viridiplantae, together with red algae and glaucophyte algae, form the supergroup Primoplantae, the Viridiplantae diverged into two clades
34.
Cladophora
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Cladophora is a genus of reticulated filamentous Ulvophyceae. Unlike Spirogyra the filaments of Cladophora branch and it doesnt undergo conjugation, there are two multicellular stages in its life cycle - a haploid gametophyte and a diploid sporophyte - which look highly similar. The only way to tell the two apart is to either count their chromosomes, or examine their offspring. The haploid gametophyte produces gametes by mitosis and the diploid sporophyte produces haploid spores by meiosis. The only visible difference between the gametes and spores of Cladophora is that the gametes have two flagella and the spores have four, the Cladophora species can be a major nuisance causing major alteration to benthic conditions linked particularly with increased phosphorus loading. Cladophora balls are formed from the filaments of the alga which are photosynthetic, large numbers of these balls were thrown ashore in Devon, England. They had an diameter of 2.5 cm and several million balls were found forming a layer. In Laos, Cladophora spp. are commonly eaten as a delicacy, the algae grow on underwater rocks and thrive in clear spots of water in the Mekong river basin. They are harvested 1 to 5 months a year and most often eaten in dry sheets, much like Japanese nori, luang Prabangs speciality is dry khai with sesame, while Vang Vieng is famous for its roasted kháy sheets. They can be eaten in strips as an appetizer or with a meal, luang Prabang kháy sheets are the most readily available form of Mekong weed and are famous throughout the country and in the neighbouring Isaan, though difficult to find beyond Vientiane. Mekong weed can also be eaten raw, in soups, or cooked as in a Lao amok preparation called ຫມົກໄຄ, Cladophora is accused of damaging the fishing industry and shoreline property values along the Great Lakes in the United States. Quagga mussel populations have increased tremendously in the same time frame. It is also a matter for Indian Sambha lake Species include, Cladophora aegagropila - not anymore, J. Entwisle & M. D. Guiry. Monterey Bay Aquarium Marsin, P. and J. Tomasz, introductory studies on the morphology of the genus Cladophora from the Gulf of Gdańsk. Studies,34, 187-193 Images of Cladophora at Algaebase
35.
Matthias Jakob Schleiden
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Matthias Jakob Schleiden was a German botanist and co-founder of cell theory, along with Theodor Schwann and Rudolf Virchow. Born in Hamburg, Schleiden was educated at University of Jena, then practiced law in Heidelberg, Schleiden preferred to study plant structure under the microscope. While a professor of botany at the University of Jena, he wrote Contributions to our knowledge of phytogenesis, thus, Schleiden and Schwann became the first to formulate what was then an informal belief as a principle of biology equal in importance to the atomic theory of chemistry. He also recognized the importance of the nucleus, discovered in 1831 by the Scottish botanist Robert Brown. Schleiden was one of the first German biologists to accept Charles Darwins theory of evolution and he became professor of botany at the University of Dorpat in 1863. He concluded that all plant parts are made of cells and that an embryonic plant organism arises from the one cell and he died in Frankfurt am Main on 23 June 1881. London, Printed for the Sydenham Society,1847, chisholm, Hugh, ed. Schleiden, Matthias Jakob
36.
Robert Remak
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As well as several other key discoveries. According to historian Paul Weindling, Rudolf Virchow, one of the founders of cell theory. Remak had reached the conclusion after observing red blood cells from embryos in various stages of division. Dr. Remak obtained his degree from Friedrich Wilhelm University in Berlin in 1838 specializing in neurology. He is best known for reducing Karl Ernst von Baers four germ layers to three, the ectoderm, mesoderm, and endoderm and he also discovered unmyelinated nerve fibers and the nerve cells in the heart sometimes called Remaks ganglia. He studied under Johannes Muller at the University of Berlin, even then he was never fully recognized for his discoveries. His son Ernst Julius Remak was also a neurologist and his grandson was the mathematician Robert Remak who died in Auschwitz in 1942, bulletin of the history of medicine,60, pp. 523–43, PMID3545332 Seeliger, H P, The discovery of Achorion schoenleinii
37.
Histology
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Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is commonly performed by examining cells and tissues under a microscope or electron microscope, the specimen having been sectioned, stained. Histological studies may be conducted using tissue culture, where human or animal cells are isolated and maintained in an artificial environment for various research projects. The ability to visualize or differentially identify microscopic structures is frequently enhanced through the use of histological stains, histology is an essential tool of biology and medicine. Trained physicians, frequently licensed pathologists, are the personnel who perform histopathological examination and their field of study is called histotechnology. In the 17th century, Italian Marcello Malpighi invented one of the first microscopes for studying tiny biological entities, Malpighi analysed several parts of the organs of bats, frogs and other animals under the microscope. Malpighi, while studying the structure of the lung, noticed its membranous alveoli and his discovery established how the oxygen we breathe enters the blood stream and serves the body. In the 19th century, histology was a discipline in its own right. The French anatomist Bichat introduced the concept of tissue in anatomy in 1801, the 1906 Nobel Prize in Physiology or Medicine was awarded to histologists Camillo Golgi and Santiago Ramon y Cajal. They had dueling interpretations of the structure of the brain based in differing interpretations of the same images. Cajal won the prize for his theory and Golgi for the staining technique he invented to make it possible. There are four types of animal tissues, muscle tissue, nervous tissue, connective tissue. All tissue types are subtypes of these four basic tissue types and their structure is very different from animal tissues. The most common fixative for light microscopy is 10% neutral buffered formalin, for electron microscopy, the most commonly used fixative is glutaraldehyde, usually as a 2. 5% solution in phosphate buffered saline. These fixatives preserve tissues or cells mainly by irreversibly cross-linking proteins and this can be detrimental to certain histological techniques. Further fixatives are often used for electron microscopy such as osmium tetroxide or uranyl acetate Formalin fixation leads to degradation of mRNA, miRNA and DNA in tissues, however, extraction, amplification and analysis of these nucleic acids from formalin-fixed, paraffin-embedded tissues is possible using appropriate protocols. Frozen section procedure is a way to fix and mount histology sections using a refrigeration device called a cryostat. It is often used after surgical removal of tumors to allow determination of margin
38.
Nematode
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The nematodes or roundworms constitute the phylum Nematoda. They are an animal phylum inhabiting a broad range of environments. Nematodes are classified along with insects and other moulting animals in the clade Ecdysozoa, Nematodes have successfully adapted to nearly every ecosystem from marine to fresh water, to soils, and from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are found in part of the earths lithosphere, even at great depths below the surface of the Earth in gold mines in South Africa. They represent 90% of all animals on the ocean floor, the many parasitic forms include pathogens in most plants and animals. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes, trees would still stand in ghostly rows representing our streets and highways. In 1758, Linnaeus described some nematode genera, then included in Vermes, the name of the group Nematoda, informally called nematodes, came from Nematoidea, originally defined by Karl Rudolphi, from Ancient Greek νῆμα and -eiδἠς. It was treated as family Nematodes by Burmeister, at its origin, the Nematoidea erroneously included Nematodes and Nematomorpha, attributed by von Siebold. Along with Acanthocephala, Trematoda and Cestoidea, it formed the obsolete group Entozoa and they were also classed along with Acanthocephala in the obsolete phylum Nemathelminthes by Gegenbaur. In 1861, K. M. Diesing treated the group as order Nematoda, in 1877, the taxon Nematoidea, including the family Gordiidae, was promoted to the rank of phylum by Ray Lankester. In 1919, Nathan Cobb proposed that nematodes should be recognized alone as a phylum and he argued they should be called nema in English rather than nematodes and defined the taxon Nemates, listing Nematoidea sensu restricto as a synonym. Since Cobb was the first to all but nematodes from the group, some sources consider the valid taxon name to be Nemates or Nemata. The phylogenetic relationships of the nematodes and their close relatives among the protostomian Metazoa are unresolved, traditionally, they were held to be a lineage of their own but in the 1990s, they were proposed to form the group Ecdysozoa together with moulting animals, such as arthropods. The identity of the closest living relatives of the Nematoda has always considered to be well resolved. Morphological characters and molecular phylogenies agree with placement of the roundworms as a taxon to the parasitic Nematomorpha. Together with the Scalidophora, the Nematoida form the clade Cycloneuralia, the Cycloneuralia or the Introverta—depending on the validity of the former—are often ranked as a superphylum. Due to the lack of knowledge regarding many nematodes, their systematics is contentious, an earliest and influential classification was proposed by Chitwood and Chitwood—later revised by Chitwood—who divided the phylum into two—the Aphasmidia and the Phasmidia. These were later renamed Adenophorea and Secernentea, respectively, the Secernentea share several characteristics, including the presence of phasmids, a pair of sensory organs located in the lateral posterior region, and this was used as the basis for this division
39.
Walther Flemming
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Walther Flemming was a German biologist and a founder of cytogenetics. He was born in Sachsenberg as the child and only son of the psychiatrist Carl Friedrich Flemming and his second wife. He graduated from the Gymnasium der Residenzstadt, where one of his colleagues, Flemming trained in medicine at University of Rostock, graduating in 1868. Afterwards, he served in 1870–71 as a physician in the Franco-Prussian War. From 1873 to 1876 he worked as a teacher at the University of Prague, in 1876 he accepted a post as a professor of anatomy at the University of Kiel. He became the director of the Anatomical Institute and stayed there until his death, with the use of aniline dyes he was able to find a structure which strongly absorbed basophilic dyes, which he named chromatin. He identified that chromatin was correlated to threadlike structures in the cell nucleus – the chromosomes, the Belgian scientist Edouard Van Beneden had also observed them, independently. Flemming investigated the process of division and the distribution of chromosomes to the daughter nuclei. However, he did not see the splitting into identical halves and he studied mitosis both in vivo and in stained preparations, using as the source of biological material the fins and gills of salamanders. These results were published first in 1878 and in 1882 in the seminal book Zellsubstanz, on the basis of his discoveries, Flemming surmised for the first time that all cell nuclei came from another predecessor nucleus. Flemming is famously known for the work outside of his work that he did and he weekly feed those who were homeless, donating every year, 20% of his salary to homeless shelters. He taught especially young children who were too poor to attend school about mathematics, Flemming was unaware of the work of Gregor Mendel on heredity, so he did not make the connection between his observations and genetic inheritance. Two decades would pass before the significance of Flemmings work was realized with the rediscovery of Mendels rules. Flemmings name is honoured by a medal awarded by the German Society for Cell Biology, walter Flemming, discoverer of chromatin and mitotic cell division. Walther Flemming, pioneer of mitosis research, beitrage zur Kenntniss der Zelle und ihrer Lebenserscheinungen. Beiträge zur Kenntniss der Zelle und Ihrer Lebenserscheinungen, Flemming, W. Zur Kenntniss der Zelle und ihrer Theilungs-Erscheinungen. In, Schriften des Naturwissenschaftlichen Vereins für Schleswig-Holstein 3, 23–27, the Analysis of Mitosis Shifts Attention to the Chromosomes. Lasker Labs Zellsubstanz, Kern und Zelltheilung, original text of the book, as PDF
40.
Greek language
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Greek is an independent branch of the Indo-European family of languages, native to Greece and other parts of the Eastern Mediterranean. It has the longest documented history of any living language, spanning 34 centuries of written records and its writing system has been the Greek alphabet for the major part of its history, other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic and many other writing systems. Together with the Latin texts and traditions of the Roman world, during antiquity, Greek was a widely spoken lingua franca in the Mediterranean world and many places beyond. It would eventually become the official parlance of the Byzantine Empire, the language is spoken by at least 13.2 million people today in Greece, Cyprus, Italy, Albania, Turkey, and the Greek diaspora. Greek roots are used to coin new words for other languages, Greek. Greek has been spoken in the Balkan peninsula since around the 3rd millennium BC, the earliest written evidence is a Linear B clay tablet found in Messenia that dates to between 1450 and 1350 BC, making Greek the worlds oldest recorded living language. Among the Indo-European languages, its date of earliest written attestation is matched only by the now extinct Anatolian languages, the Greek language is conventionally divided into the following periods, Proto-Greek, the unrecorded but assumed last ancestor of all known varieties of Greek. The unity of Proto-Greek would have ended as Hellenic migrants entered the Greek peninsula sometime in the Neolithic era or the Bronze Age, Mycenaean Greek, the language of the Mycenaean civilisation. It is recorded in the Linear B script on tablets dating from the 15th century BC onwards, Ancient Greek, in its various dialects, the language of the Archaic and Classical periods of the ancient Greek civilisation. It was widely known throughout the Roman Empire, after the Roman conquest of Greece, an unofficial bilingualism of Greek and Latin was established in the city of Rome and Koine Greek became a first or second language in the Roman Empire. The origin of Christianity can also be traced through Koine Greek, Medieval Greek, also known as Byzantine Greek, the continuation of Koine Greek in Byzantine Greece, up to the demise of the Byzantine Empire in the 15th century. Much of the written Greek that was used as the language of the Byzantine Empire was an eclectic middle-ground variety based on the tradition of written Koine. Modern Greek, Stemming from Medieval Greek, Modern Greek usages can be traced in the Byzantine period and it is the language used by the modern Greeks, and, apart from Standard Modern Greek, there are several dialects of it. In the modern era, the Greek language entered a state of diglossia, the historical unity and continuing identity between the various stages of the Greek language is often emphasised. Greek speakers today still tend to regard literary works of ancient Greek as part of their own rather than a foreign language and it is also often stated that the historical changes have been relatively slight compared with some other languages. According to one estimation, Homeric Greek is probably closer to demotic than 12-century Middle English is to modern spoken English, Greek is spoken by about 13 million people, mainly in Greece, Albania and Cyprus, but also worldwide by the large Greek diaspora. Greek is the language of Greece, where it is spoken by almost the entire population
41.
August Weismann
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For the 19th-century New York politician, see Augustus Weismann. August Friedrich Leopold Weismann was a German evolutionary biologist, ernst Mayr ranked him as the second most notable evolutionary theorist of the 19th century, after Charles Darwin. Weismann became the Director of the Zoological Institute and the first Professor of Zoology at Freiburg, other cells of the body—somatic cells—do not function as agents of heredity. The effect is one-way, germ cells produce somatic cells and are not affected by anything the somatic cells learn or therefore any ability an individual acquires during its life, genetic information cannot pass from soma to germ plasm and on to the next generation. Biologists refer to this concept as the Weismann barrier and this idea, if true, rules out the inheritance of acquired characteristics as proposed by Jean-Baptiste Lamarck. The idea of the Weismann barrier is central to the evolutionary synthesis. In Weismanns opinion the largely random process of mutation, which must occur in the gametes is the source of change for natural selection to work on. Weismann became one of the first biologists to deny soft inheritance entirely, Weismanns ideas preceded the rediscovery of Gregor Mendels work, and though Weismann was cagey about accepting Mendelism, younger workers soon made the connection. Ernst Mayr judged him to be the most important evolutionary thinker between Darwin and the evolutionary synthesis around 1930–1940, and one of the biologists of all time. His piano teacher was a butterfly collector and introduced him to the collecting of imagos. But studying natural sciences was out of the due to the cost involved and limited job prospects. A friend of the family, Friedrich Wöhler, recommended studying medicine, a foundation from the inheritance of Weismanns mother allowed him to take up studies in Göttingen. Following his graduation in 1856, he wrote his dissertation on the synthesis of hippuric acid in the human body, immediately after university, Weismann took on a post as assistant at the Städtische Klinik in Rostock. Weismann successfully submitted two manuscripts, one about hippuric acid in herbivores, and one about the content of the Baltic Sea. The paper about the salt content dissuaded him from becoming a chemist, after a study visit to see Viennas museums and clinics, he graduated as a physician and settled in Frankfurt with a medical practice in 1868. During the war between Austria, France and Italy in 1859, he became Chief Medical Officer in the military, during a leave from duty, he walked through Northern Italy and the County of Tyrol. After a sabbatical in Paris, he worked with Rudolf Leuckart at the University of Gießen and he returned to Frankfurt as personal physician to the banished Archduke Stephen of Austria at Schaumburg Castle from 1861 to 1863. His son Julius Weismann was a composer, at the beginning of Weismanns preoccupation with evolutionary theory was his grappling with Christian creationism as a possible alternative
42.
Drosophila melanogaster
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Drosophila melanogaster is a species of fly in the family Drosophilidae. The species is generally as the common fruit fly or vinegar fly. It is typically used because it is a species that is easy to care for, has four pairs of chromosomes, breeds quickly. D. melanogaster is a common pest in homes, restaurants, flies belonging to the family Tephritidae are also called fruit flies. This can cause confusion, especially in Australia and South Africa, the D. melanogaster lifespan is about 30 days at 29 °C. The developmental period for D. melanogaster varies with temperature, as with many ectothermic species, the shortest development time,7 days, is achieved at 28 °C. Development times increase at higher temperatures due to heat stress, under ideal conditions, the development time at 25 °C is 8.5 days, at 18 °C it takes 19 days and at 12 °C it takes over 50 days. Under crowded conditions, development time increases, while the emerging flies are smaller, females lay some 400 eggs, about five at a time, into rotting fruit or other suitable material such as decaying mushrooms and sap fluxes. The eggs, which are about 0.5 mm long, the resulting larvae grow for about 4 days while molting twice, at about 24 and 48 h after hatching. During this time, they feed on the microorganisms that decompose the fruit, the mother puts feces on the egg sacs to establish the same microbial composition in the larvaes guts which has worked positively for herself. Then the larvae encapsulate in the puparium and undergo a four-day-long metamorphosis, the female fruit fly prefers a shorter duration when it comes to sex. Males, on the hand, prefer it to last longer. Males perform a sequence of five behavioral patterns to court females, first, males orient themselves while playing a courtship song by horizontally extending and vibrating their wings. Soon after, the positions itself at the rear of the females abdomen in a low posture to tap. Finally, the male curls its abdomen and attempts copulation, females can reject males by moving away, kicking, and extruding their ovipositor. Copulation lasts around 15–20 minutes, during which males transfer a few hundred, females store the sperm in a tubular receptacle and in two mushroom-shaped spermathecae, sperm from multiple matings compete for fertilization. A last male precedence is believed to exist in which the last male to mate with a female sires about 80% of her offspring and this precedence was found to occur through both displacement and incapacitation. The displacement is attributed to sperm handling by the fly as multiple matings are conducted and is most significant during the first 1–2 days after copulation
. PMID 17660363.
