1.
Paramecium aurelia
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Paramecium aurelia are unicellular organisms belonging to the genus Paramecium of the phylum Ciliophora. They are covered in cilia which help in movement and feeding. Paramecium can reproduce sexually, asexually, Paramecium aurelia demonstrate a strong “sex reaction” whereby groups of individuals will cluster together, and emerge in conjugant pairs. This pairing can last up to 12 hours, during which the micronucleus of each organism will be exchanged, in Paramecium aurelia, a cryptic species complex was discovered by observation. Since then, some have tried to decode this complex using genetic data, the hair-like cilia that cover the outer body of the paramecium are in constant motion, helping the organism move along at a speed of four times its own length per second. As it moves forward, it rotates on its axis, which aids in pushing food into the gullet and it can move backwards by reversing the motion of the cilia. Food enters the food vacuoles, which cilia push into the gullet in a known as phagocytosis. When digestion is complete, the food content is emptied into pellicles. Osmoregulation is carried out by a pair of contractile vacuoles on either end of the cell, paramecia are attracted by acidic conditions, since they eat bacteria, which often acidify their surroundings
2.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
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.
Alveolate
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The alveolates are a group of protists, considered a major clade and superphylum within Eukarya, and are also called Alveolata. The most notable shared characteristic is the presence of alveoli, flattened vesicles packed into a continuous layer supporting the membrane. In dinoflagellates they often form armor plates, alveolates have mitochondria with tubular cristae and their flagella or cilia have a distinct structure. Almost all sequenced mitochondrial genomes of ciliates and apicomplexia are linear, the mitochondrial genome of Babesia microti is circular. This species is now known not to belong to either of the genera Babesia or Theileria. The Acavomonidia are closer to the group than the Colponemidia are. As such, the informal term colponemids, as its stands currently, the Apicomplexa and dinoflagellates may be more closely related to each other than to the ciliates. Both have plastids, and most share a bundle or cone of microtubules at the top of the cell, in apicomplexans this forms part of a complex used to enter host cells, while in some colorless dinoflagellates it forms a peduncle used to ingest prey. Various other genera are related to these two groups, mostly flagellates with a similar apical structure. These include free-living members in Oxyrrhis and Colponema, and parasites in Perkinsus, Parvilucifera, Rastrimonas, in 2001, direct amplification of the rRNA gene in marine picoplankton samples revealed the presence of two novel alveolate linages, called group I and II. Group I has no cultivated relatives, while group II is related to the dinoflagellate parasite Amoebophrya, cavalier-Smith, introduced the formal name Alveolata in 1991, although at the time he actually considered the grouping to be a paraphyletic assemblage, rather than a monophyletic group. Some studies suggested the haplosporids, mostly parasites of invertebrates, might belong here. Based on a compilation of the following works, cavalier-Smith 2014 Superclass Perkinsozoa Norén et al.1999 s. s. Class Perkinsea Levine 1978 Superclass Dinoflagellata Butschli 1885 stat. nov, Class Noctiluciphyceae Fensome et al.1993 Class Dinophyceae Pascher 1914 The development of plastids among the alveolates is intriguing. Cavalier-Smith proposed the alveolates developed from an ancestor, which also gave rise to the Chromista. Other researchers have speculated that the alveolates originally lacked plastids and possibly the dinoflagellates, a Bayesian estimate places the evolution of the alveolate group at ~850 million years ago. The Alveolata consist of Myzozoa, Ciliates, and Colponemids, in other words, The term Myzozoa meaning to siphon the contents from prey, may be applied informally to the common ancestor of the subset of alveolates that are neither ciliates nor colponemids. Predation upon algae is an important driver in alveolate evolution, as it can provide sources for endosymbiosis of novel plastids, the term Myzozoa is therefore a handy concept for tracking the history of the alveolate phylum
5.
Ciliate
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Cilia occur in all members of the group and are variously used in swimming, crawling, attachment, feeding, and sensation. All behavioral patterns are coordinated by signaling processes, ciliates are an important group of protists, common almost everywhere there is water — in lakes, ponds, oceans, rivers, and soils. About 3,500 species have been described, and the number of extant species is estimated at 30,000. Included in this number are many ectosymbiotic and endosymbiotic species, as well as some obligate, ciliate species range in size from as little as 10 µm to as much as 4 mm in length, and include some of the most morphologically complex protozoans. In most systems of taxonomy, Ciliophora is ranked as a phylum, in some systems of classification, ciliated protozoa are placed within the class Ciliata. In the taxonomic scheme proposed by the International Society of Protistologists, unlike most other eukaryotes, ciliates have two different sorts of nuclei, a tiny, diploid micronucleus, and a large, polyploid macronucleus. The latter is generated from the micronucleus by amplification of the genome, the micronucleus serves as the germ line nucleus, but does not express its genes. The macronucleus provides the nuclear RNA for vegetative growth, division of the macronucleus occurs by amitosis, and the segregation of the chromosomes occurs by a process whose mechanism is unknown. This process is not perfect, and after about 200 generations the cell shows signs of aging, periodically the macronuclei must be regenerated from the micronuclei. In most, this occurs during conjugation, here two cells line up, the micronuclei undergo meiosis, some of the haploid daughters are exchanged and then fuse to form new micronuclei and macronuclei. Anything left in the vacuole by the time it reaches the cytoproct is discharged by exocytosis. Most ciliates also have one or more prominent contractile vacuoles, which water and expel it from the cell to maintain osmotic pressure. In some genera, such as Paramecium, these have a star shape. Cilia are arranged in rows called kineties, in some forms there are also body polykinetids, for instance, among the spirotrichs where they generally form bristles called cirri. More often body cilia are arranged in mono- and dikinetids, which include one. These are arranged into rows called kineties, which run from the anterior to posterior of the cell, the infraciliature is one of the main components of the cell cortex. Others are the alveoli, small vesicles under the membrane that are packed against it to form a pellicle maintaining the cells shape. Numerous mitochondria and extrusomes are also generally present, the presence of alveoli, the structure of the cilia, the form of mitosis and various other details indicate a close relationship between the ciliates, Apicomplexa, and dinoflagellates
6.
Oligohymenophorea
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The Oligohymenophorea are a large class of ciliates. There is typically a ventral groove containing the mouth and distinct oral cilia and these include a paroral membrane to the right of the mouth and membranelles, usually three in number, to its left. The cytopharynx is inconspicuous and never forms the complex cyrtos found in similar classes, body cilia generally arise from monokinetids, with dikinetids occurring in limited distribution over part of the body. In most groups the body cilia are uniform and often dense, while the cilia are inconspicuous and sometimes reduced. Members are widely distributed, and include many free-living and symbiotic forms, most are microphagous, grazing on smaller organisms swept into the mouth by the cilia, but various other feeding habits occur. In one group, the astomes, the mouth and associated structures have been lost altogether, the Oligoohymenophorea were first proposed in 1974 as one of three classes of ciliates, together with the Polyhymenophorea or spirotrichs and the now abandoned Kinetofragmophora. Since then the apostomes have been added, but otherwise its composition has remained relatively constant, puytorac, P. de, A. Batisse, J. Bohatier, J. O. Corliss, G. Deroux, P. Didier, J. Dragesco, G. Fryd-Versavel, J. Grain, grolière, R. Hovasse, F. Iftode, M. Laval, M. Rogue, A. Savoie, and M. Tuffrau. Proposition dune classification du phylum Ciliophora Doflein,1901, comptes Rendus de lAcadémie de Sciences, Paris 278, 2799-2802
7.
Peniculid
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The peniculids are an order of ciliate protozoa, including the well-known Paramecium and related genera, such as Frontonia, Stokesia, Urocentrum and Lembadion. Most are relatively large, freshwater forms that feed by sweeping smaller organisms into the mouth and they have weird life cycles, and in many cases do not even form resting cysts. Typically the body has uniform, dense cilia, which cover a vestibule preceding the mouth. Extrusomes are characteristically in the form of spindle trichocysts, which release thread-like shafts, the oral cilia include peniculi, corresponding to the membranelles of related groups, arranged parallel to the mouth deep in the oral cavity. Nematodesmata arise from the bases of the oral or perioral cilia, two suborders are recognised, The Frontoniina typically have a shallow oral cavity, with a long paroral membrane and denser somatic kineties to the right of the mouth. These are called ophryokineties, and take part in forming the new mouth during cell division, the Parameciina typically have a deeper oral cavity, with peniculi mainly forward of the mouth, and the paroral membrane reduced, though still present throughout interphase. The peniculids were first defined by Fauré-Fremiet in 1956, originally they were one of three suborders of the hymenostomes, which are now treated as subclasses of the Oligohymenophorea. However, more recent schemes reverse this move
8.
Unicellular organism
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A unicellular organism, also known as a single-celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of more than one cell. Historically, simple unicellular organisms have been referred to as monads, though this term is used more specifically to describe organisms of the genus Monas. The main groups of organisms are bacteria, archaea, protozoa, unicellular algae. Unicellular organisms fall into two categories, prokaryotic organisms and eukaryotic organisms. Unicellular organisms are thought to be the oldest form of life, prokaryotes, most Protista, and some fungi are unicellular. Although some of these live in colonies, they dont exhibit specialization. These organisms live together, and each cell in the colony is the same, however, each individual cell must carry out all life processes to survive. In contrast, even the simplest multicellular organisms have cells that depend on each other to survive, most multicellular organisms have a unicellular life-cycle stage. Gametes, for example, are reproductive unicells for multicellular organisms, additionally, multicellularity appears to have evolved independently many times in the history of life. Some organisms are partially uni- and multicellular, like Dictyostelium discoideum, additionally, unicellular organisms can be multinucleate, like Myxogastria and Plasmodium. Candidatus Magnetoglobus multicellular, related to Deltaproteobacteria, is a multicellular prokaryote and it is neither unicellular, nor a colony. Primitive cells, often referred to as protocells, are the precursors to todays unicellular organisms, the RNA world hypothesis assumes that RNA molecules could form in abiotic conditions, which would require nucleic acids and ribose to be present. Theoretical and experimental findings show that nucleic acids and sugars could have been synthesized in early prebiotic conditions, compartmentalization was necessary for chemical reactions to be more likely as well as to differentiate reactions with the external environment. For example, an early RNA replicator ribozyme may have replicated other replicator ribozymes of different RNA sequences if not kept separate, when amphiphiles like lipids are placed in water, the hydrophobic tails aggregate to form micelles and vesicles, with the hydrophilic ends facing outwards. Primitive cells likely used self-assembling fatty-acid vesicles to separate chemical reactions, because of their simplicity and ability to self-assemble in water, its likely that these simple membranes predated other forms of early biological molecules. Prokaryotes lack membrane-bound organelles, such as mitochondria or a nucleus, instead, most prokaryotes have an irregular region that contains DNA, known as the nucleoid. Most prokaryotes have a single, circular chromosome, which is in contrast to eukaryotes, nutritionally, prokaryotes have the ability to utilize a wide range of organic and inorganic material for use in metabolism, including sulfur, cellulose, ammonia, or nitrite. Prokaryotes as a whole are ubiquitous in the environment and exist in extreme environments as well, bacteria are one of the world’s oldest forms of life, and are found virtually everywhere in nature
9.
Fresh water
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Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids. The term specifically excludes seawater and brackish water although it does include mineral-rich waters such as chalybeate springs, the term sweet water has been used to describe fresh water in contrast to salt water. The term fresh water does not have the meaning as potable water. Much of the fresh water and ground water is unsuitable for drinking without some form of purification because of the presence of chemical or biological contaminants. It may also be in contact with the underlying underground water. The majority of water on Earth is in ice caps. The source of almost all water is precipitation from the atmosphere, in the form of mist, rain. Fresh water falling as mist, rain or snow contains materials dissolved from the atmosphere and material from the sea, in some cases this acid rain results in pollution of lakes and rivers. In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds. This can give rise to elevated concentrations of sodium, chloride, magnesium, significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa. Water is an issue for the survival of all living organisms. Some can use water but many organisms including the great majority of higher plants. Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Freshwater lakes contain about 87% of this surface water, including 29% in the African Great Lakes, 20% in Lake Baikal in Russia, 21% in the North American Great Lakes. Swamps have most of the balance only a small amount in rivers. In areas with no water on the ground surface, fresh water derived from precipitation may, because of its lower density. Most of the fresh water is frozen in ice sheets. Many areas suffer from lack of distribution of water, such as deserts
10.
Brackish
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Brackish water or briny water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, the word comes from the Middle Dutch root brak. Brackish water is also the primary product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment. Technically, brackish water contains between 0.5 and 30 grams of salt per litre—more often expressed as 0.5 to 30 parts per thousand, thus, brackish covers a range of salinity regimes and is not considered a precisely defined condition. It is characteristic of many brackish surface waters that their salinity can vary considerably over space and/or time, brackish water condition commonly occurs when fresh water meets seawater. In fact, the most extensive brackish water habitats worldwide are estuaries, the River Thames flowing through London is a classic river estuary. A similar pattern of replacement can be observed with the aquatic plants and this type of ecological succession from a freshwater to marine ecosystem is typical of river estuaries. Salmon are anadromous, meaning live in the sea but ascend rivers to spawn, eels are catadromous, living in rivers and streams. Besides the species migrate through estuaries, there are many other fish that use them as nursery grounds for spawning or as places young fish can feed. Herring and plaice are two commercially important species that use the Thames Estuary for this purpose, estuaries are also commonly used as fishing grounds, and as places for fish farming or ranching. Another important brackish water habitat is the swamp or mangal. Many, though not all, mangrove swamps fringe estuaries and lagoons where the salinity changes with each tide, like estuaries, mangrove swamps are extremely important breeding grounds for many fish, with species such as snappers, halfbeaks, and tarpon spawning or maturing among them. Mangroves represent important nesting site for numerous birds groups such as herons, storks, spoonbills, ibises, kingfishers, the Sundarbans and Bhitarkanika Mangroves are two of the large mangrove forests in the world, both on the coast of the Bay of Bengal. Some seas and lakes are brackish, the Baltic Sea is a brackish sea adjoining the North Sea. Because the salt water coming in from the sea is denser than freshwater, limited mixing occurs because of the lack of tides and storms, with the result that the fish fauna at the surface is freshwater in composition while that lower down is more marine. Cod are an example of a species found in deep water in the Baltic. The Caspian Sea is the worlds largest lake and contains brackish water with a salinity about one-third that of normal seawater, the Caspian is famous for its peculiar animal fauna, including one of the few non-marine seals and the great sturgeons, a major source of caviar
11.
Ocean
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An ocean is a body of saline water that composes much of a planets hydrosphere. On Earth, an ocean is one of the major divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern, the word sea is often used interchangeably with ocean in American English but, strictly speaking, a sea is a body of saline water partly or fully enclosed by land. The ocean contains 97% of Earths water, and oceanographers have stated that less than 5% of the World Ocean has been explored, the total volume is approximately 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the component of Earths hydrosphere, it is integral to all known life, forms part of the carbon cycle. The world ocean is the habitat of 230,000 known species, but because much of it is unexplored, the origin of Earths oceans remains unknown, oceans are thought to have formed in the Hadean period and may have been the impetus for the emergence of life. Extraterrestrial oceans may be composed of water or other elements and compounds, the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many planets and natural satellites, notably. The Solar Systems giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of water within a circumstellar habitable zone. Ocean planets are a type of planet with a surface completely covered with liquid. The concept of Ōkeanós has an Indo-European connection, Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases, though generally described as several separate oceans, these waters comprise one global, interconnected body of salt water sometimes referred to as the World Ocean or global ocean. This concept of a body of water with relatively free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, Oceans are fringed by smaller, adjoining bodies of water such as seas, gulfs, bays, bights, and straits. The Mid-Oceanic Ridge of the World are connected and form the Ocean Ridge, the continuous mountain range is 65,000 km long, and the total length of the oceanic ridge system is 80,000 km long
12.
Isogamy
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Isogamy is a form of sexual reproduction that involves gametes of similar morphology, differing in general only in allele expression in one or more mating-type regions. Because both gametes look alike, they cannot be classified as male or female, instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as + and − strains, although in some species there are more than two mating types. Fertilization occurs when gametes of two different mating types fuse to form a zygote and it appears that isogamy was the first stage of sexual reproduction. There is an argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. In Ascomycetes, anisogamy evolved from isogamy before mating types, there are several types of isogamy. Both gametes may be flagellated and thus motile and this type occurs for example in algae such as some but not all species of Chlamydomonas. In another type, neither of the gametes is flagellated and this is the case for example in the mating of yeast. Yeast mating types are noted as a and α instead of + and -. Another, more form, is conjugation. This occurs in some the green algae, the Zygnematophyceae, e. g. Spirogyra and these algae grow as filaments of cells. When two filaments of opposing mating types come close together, the cells form conjugation tubes between the filaments, once the tubes are formed, one cell balls up and crawls through the tube into the other cell to fuse with it, forming a zygote. In ciliates, cell fission may follow self-fertilization, or it may follow conjugation, in zygomycetes fungi, two hyphae of opposing mating types form special structures called gametangia where the hyphae touch. The gametangia then fuse into a zygosporangium, in other fungi, cells from two hyphae with opposing mating types fuse, but only cytoplasmic. The two nuclei do not fuse, leading to the formation of a cell that gives rise to a mycelium consisting of dikaryons. Karyogamy occurs in sporangia and leads to the formation of cells that immediately undergo meiosis to form spores. In many cases, isogamous fertilization is used by organisms that can reproduce asexually through binary fission, budding. The switch to sexual reproduction mode is triggered by a change from favorable to unfavorable growing conditions. Fertilization often leads to the formation of a thick-walled zygotic resting spore that can withstand harsh environments, anisogamy Evolution of sexual reproduction Gamete Mating in fungi Meiosis Oogamy Sex Hypergamy Hypogamy Sa Geng, Peter De Hoff, James G. Umen
13.
Model organism
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Model organisms are in vivo models and are widely used to research human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the descent of all living organisms. Studying model organisms can be informative, but care must be taken when extrapolating from one organism to another, in researching human disease, model organisms allow for better understanding the disease process without the added risk of harming an actual human. The species chosen will usually meet a determined taxonomic equivalency to humans, although biological activity in a model organism does not ensure an effect in humans, many drugs, treatments and cures for human diseases are developed in part with the guidance of animal models. There are three types of disease models, homologous, isomorphic and predictive. Homologous animals have the same causes, symptoms and treatment options as would humans who have the same disease, isomorphic animals share the same symptoms and treatments. Predictive models are similar to a human disease in only a couple of aspects. The use of animals in research dates back to ancient Greece, with Aristotle, research using animal models has been central to most of the achievements of modern medicine. It has contributed most of the knowledge in fields such as human physiology and biochemistry. For example, the results have included the near-eradication of polio and the development of organ transplantation, from 1910 to 1927, Thomas Hunt Morgans work with the fruit fly Drosophila melanogaster identified chromosomes as the vector of inheritance for genes. Drosophila became one of the first, and for some time the most widely used, model organisms, D. melanogaster remains one of the most widely used eukaryotic model organisms. The mouse has since been used extensively as an organism and is associated with many important biological discoveries of the 20th. In the late 19th century, Emil von Behring isolated the diphtheria toxin and he went on to develop an antitoxin against diphtheria in animals and then in humans, which resulted in the modern methods of immunization and largely ended diphtheria as a threatening disease. The diphtheria antitoxin is famously commemorated in the Iditarod race, which is modeled after the delivery of antitoxin in the 1925 serum run to Nome. The success of animal studies in producing the diphtheria antitoxin has also attributed as a cause for the decline of the early 20th-century opposition to animal research in the United States. This led to the 1922 discovery of insulin and its use in treating diabetes, modern general anaesthetics, such as halothane and related compounds, were also developed through studies on model organisms, and are necessary for modern, complex surgical operations. In the 1940s, Jonas Salk used rhesus monkey studies to isolate the most virulent forms of the polio virus, the vaccine, which was made publicly available in 1955, reduced the incidence of polio 15-fold in the United States over the following five years. It has been estimated that developing and producing the vaccines required the use of 100,000 rhesus monkeys, models are those organisms with a wealth of biological data that make them attractive to study as examples for other species and/or natural phenomena that are more difficult to study directly
14.
Laboratory rat
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A laboratory rat is a rat of the species Rattus norvegicus which is bred and kept for scientific research. While less commonly used for research than mice, rats have served as an important animal model for research in psychology, laboratory rats share origins with their cousins in domestication, the fancy rats. In 18th century Europe, wild Brown rats ran rampant and this fueled the industry of rat-catching. Rat-catchers would not only make money by trapping the rodents, but also by selling them for food, or more commonly, rat-baiting was a popular sport which involved filling a pit with rats and timing how long it took for a terrier to kill them all. Over time, breeding the rats for these contests may have produced variations in color, notably the albino, the first time one of these albino mutants was brought into a laboratory for a study was in 1828, in an experiment on fasting. Over the next 30 years rats were used for several more experiments, the rat found early use in laboratory research in five areas, W. S. Small suggested that the rate of learning could be measured by rats in a maze, watson for his Ph. D. dissertation in 1903. The reproductive function of rats was studied at Institute for Experimental Biology at University of California, Berkeley by Herbert McLean Evans, the genetics of rats was studied by William Ernest Castle at the Bussey Institute of Harvard University until it closed in 1994. And rats have long used in cancer research, for instance at Crocker Institute for Cancer Research. The historical importance of species to scientific research is reflected by the amount of literature on it. Laboratory rats are frequently subject to dissection or microdialysis to study effects on organs. Laboratory rats not sacrificed may be euthanized or, in some cases, scientists have bred many strains or lines of rats specifically for experimentation. Most are derived from the albino Wistar rat, which is widely used. Other common strains are the Sprague Dawley, Fischer 344, Holtzman albino strains, the Long-Evans, as a result, many have been forced to study questions in mice that might be better pursued in rats. In October 2003, however, researchers succeeded in cloning two laboratory rats by nuclear transfer, so rats may begin to see more use as genetic research subjects. Much of the genome of Rattus norvegicus has been sequenced, a 1972 study compared neoplasms in “Sprague-Dawley” rats from six different commercial suppliers and found highly significant differences in the incidences of endocrine and mammary tumors. There were even significant variations in the incidences of adrenal medulla tumors among rats from the same source raised in different laboratories, all but one of the testicular tumors occurred in the rats from a single supplier. The researchers found that the incidence of tumors in Sprague-Dawley rats from different commercial sources varied as much each other as from the other strains of rats
15.
Microscopy
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Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye. There are three branches of microscopy, optical, electron, and scanning probe microscopy. This process may be carried out by irradiation of the sample or by scanning of a fine beam over the sample. Scanning probe microscopy involves the interaction of a probe with the surface of the object of interest. The development of microscopy revolutionized biology, gave rise to the field of histology and so remains an essential technique in the life and physical sciences. Optical or light microscopy involves passing visible light transmitted through or reflected from the sample through a single or multiple lenses to allow a view of the sample. The resulting image can be detected directly by the eye, imaged on a plate or captured digitally. The single lens with its attachments, or the system of lenses and imaging equipment, along with the lighting equipment, sample stage and support. The most recent development is the microscope, which uses a CCD camera to focus on the exhibit of interest. The image is shown on a screen, so eye-pieces are unnecessary. Limitations of standard optical microscopy lie in three areas, This technique can only image dark or strongly refracting objects effectively, diffraction limits resolution to approximately 0.2 micrometres. This limits the practical limit to ~1500x. Out of focus light from points outside the focal plane reduces image clarity, live cells in particular generally lack sufficient contrast to be studied successfully, since the internal structures of the cell are colourless and transparent. The most common way to increase contrast is to stain the different structures with selective dyes, staining may also introduce artifacts, apparent structural details that are caused by the processing of the specimen and are thus not legitimate features of the specimen. In general, these make use of differences in the refractive index of cell structures. It is comparable to looking through a window, you dont see the glass. There is a difference, as glass is a material. The human eye is not sensitive to this difference in phase, in order to improve specimen contrast or highlight certain structures in a sample special techniques must be used
16.
Antonie van Leeuwenhoek
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Antonie Philips van Leeuwenhoek was a Dutch businessman, scientist, and one of the notable representatives in the golden age of Dutch science and technology. A largely self-taught man in science, he is known as the Father of Microbiology. Van Leeuwenhoek is best known for his work in the field of microscopy. Raised in Delft, in the Dutch Republic, Van Leeuwenhoek worked as a draper in his youth and he made a name for himself in municipal politics, and eventually developed an interest in lensmaking. Using his handcrafted microscopes, he was the first to observe and describe microorganisms, most of the animalcules are now referred to as unicellular organisms, though he observed multicellular organisms in pond water. He was also the first to document microscopic observations of muscle fibers, bacteria, spermatozoa, Van Leeuwenhoek did not write any books, his discoveries came to light through correspondence with the Royal Society, which published his letters. Antonie van Leeuwenhoek was born in Delft, Dutch Republic, on 24 October 1632, on 4 November, he was baptized as Thonis. His father, Philips Antonisz van Leeuwenhoek, was a maker who died when Antonie was only five years old. His mother, Margaretha, came from a well-to-do brewers family, and remarried Jacob Jansz Molijn, Antonie had four older sisters, Margriet, Geertruyt, Neeltje, and Catharina. When he was ten years old his step-father died. He attended school in Warmond for a time before being sent to live in Benthuizen with his uncle. At the age of 16 he became an apprentice at a linen-drapers shop in Amsterdam owned by the Scot William Davidson. Van Leeuwenhoek left after six years, Van Leeuwenhoek married Barbara de Mey in July 1654, with whom he would have one surviving daughter, Maria. That same year he returned to Delft, where he would live and he opened a drapers shop, which he ran throughout the 1650s. His wife died in 1666, and in 1671, Van Leeuwenhoek remarried to Cornelia Swalmius with whom he had no children and his status in Delft had grown throughout the years. In 1660 he received a job as chamberlain for the Delft sheriffs assembly chamber in the City Hall. Van Leeuwenhoek was a contemporary of another famous Delft citizen, the painter Johannes Vermeer and it has been suggested that he is the man portrayed in two of Vermeers paintings of the late 1660s, The Astronomer and The Geographer. However, others argue that there appears to be little physical similarity, while running his drapers shop, Van Leeuwenhoek wanted to see the quality of the thread better than the then-current magnifying lenses available allowed
17.
Christiaan Huygens
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Christiaan Huygens, FRS was a prominent Dutch mathematician and scientist. He is known particularly as an astronomer, physicist, probabilist and horologist, Huygens was a leading scientist of his time. His work included early telescopic studies of the rings of Saturn and the discovery of its moon Titan and he published major studies of mechanics and optics, and pioneered work on games of chance. Christiaan Huygens was born on 14 April 1629 in The Hague, into a rich and influential Dutch family, Christiaan was named after his paternal grandfather. His mother was Suzanna van Baerle and she died in 1637, shortly after the birth of Huygens sister. The couple had five children, Constantijn, Christiaan, Lodewijk, Philips, Constantijn Huygens was a diplomat and advisor to the House of Orange, and also a poet and musician. His friends included Galileo Galilei, Marin Mersenne and René Descartes, Huygens was educated at home until turning sixteen years old. He liked to play with miniatures of mills and other machines and his father gave him a liberal education, he studied languages and music, history and geography, mathematics, logic and rhetoric, but also dancing, fencing and horse riding. In 1644 Huygens had as his mathematical tutor Jan Jansz de Jonge Stampioen, Descartes was impressed by his skills in geometry. His father sent Huygens to study law and mathematics at the University of Leiden, Frans van Schooten was an academic at Leiden from 1646, and also a private tutor to Huygens and his elder brother, replacing Stampioen on the advice of Descartes. Van Schooten brought his mathematical education up to date, in introducing him to the work of Fermat on differential geometry. Constantijn Huygens was closely involved in the new College, which lasted only to 1669, Christiaan Huygens lived at the home of the jurist Johann Henryk Dauber, and had mathematics classes with the English lecturer John Pell. He completed his studies in August 1649 and he then had a stint as a diplomat on a mission with Henry, Duke of Nassau. It took him to Bentheim, then Flensburg and he took off for Denmark, visited Copenhagen and Helsingør, and hoped to cross the Øresund to visit Descartes in Stockholm. While his father Constantijn had wished his son Christiaan to be a diplomat, in political terms, the First Stadtholderless Period that began in 1650 meant that the House of Orange was not in power, removing Constantijns influence. Further, he realised that his son had no interest in such a career, Huygens generally wrote in French or Latin. While still a student at Leiden he began a correspondence with the intelligencer Mersenne. Mersenne wrote to Constantijn on his sons talent for mathematics, the letters show the early interests of Huygens in mathematics
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Infusion
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An infusion is also the name for the resultant liquid. The process of infusion is distinct from decoction, which involves boiling the plant material, or percolation, the first recorded use of essential oils was in the 10th or 11th century by the Persian polymath Avicenna, possibly in The Canon of Medicine. Tea is far older than this, dating back to the 10th century BC as the earliest recorded reference, an infusion is a very simple chemical process used with botanicals that are volatile and dissolve readily, or release their active ingredients easily, in water, oil or alcohol. The botanicals are typically dried herbs, flowers or berries, the liquid is typically boiled and then poured over the herb, which is then allowed to steep in the liquid for a period of time. The liquid may then be strained or the herbs otherwise removed from the liquid, unless the infusion is to be consumed immediately, it may then be bottled and refrigerated for future use. The amount of time the herbs are left in the liquid depends on the purpose for which the infusion is being prepared, usually steeping for not more than 15 to 30 minutes, or until the mix cools, will create a beverage with optimal flavor. Steeping for a longer time typically results in a somewhat bitter-tasting infusion, four hours, however, is a more appropriate length of time for achieving herbal potency if health benefits are the priority. Quantities of the herb and liquid used will vary according to the herb or how strong the infusion is required to be, a common proportion used is 28 g of herb to 0.5 L of liquid. There have been several accessories and techniques for removing the steeped or left over products that were used to infuse liquids such as water, oil, the use of a metal steeper, which looks like a metal clamp. Tea infusers work as strainers and assist in removal of used herbs, leaves, french presses are commonly used to infuse water with various teas and coffee. Lastly, and most commonly used, the tea bag, tea bags today are made with filter paper and filled with various tea flavors. A common example of an infusion is tea, most varieties of tea call for steeping the leaves in hot water, although some variants call for decoction instead. Many herbal teas are prepared by infusion, as well, lemon, chamomile, senna, apple, ginger, rooibos, herbal infusions in water and oil are both commonly used as herbal remedies. Coffee can also be made through infusion, but is often made through percolation. Plants with desirable flavors may be steeped in an oil or vinegar for an extended period, the infused oil or vinegar is often sold still containing the plant. Chiles, lemon, garlic, and many plants may be used. There can be ambiguity in the labeling of oils, for example, what is described as sesame oil may be oil extracted from sesame seeds
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John Hill (botanist)
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John Hill, called because of his Swedish honours, Sir John Hill, was an English author and botanist. He contributed to periodicals and was awarded the title of Sir in recognition of his illustrated botanical compendium The Vegetable System. He was the son of the Rev. Theophilus Hill and is said to have born in Peterborough. He was apprenticed to an apothecary and on the completion of his apprenticeship he set up in a shop in St Martins Lane. He also travelled over the country in search of herbs, with a view to publishing a hortus siccus. He had a degree from Edinburgh, and he practised as a quack doctor. His first publication was a translation of Theophrastuss History of Stones, from this time forward he was an indefatigable writer. He edited the British Magazine, and for two years he wrote a letter, The Inspector, for the London Advertiser and Literary Gazette. He also produced novels, plays and scientific works, and was a contributor to the supplement of Ephraim Chamberss Cyclopaedia. From 1759 to 1775 he was engaged on a huge botanical work--The Vegetable System --adorned by 1600 copper-plate engravings, Hills botanical labours were undertaken at the request of his patron, Lord Bute, and he was rewarded by the Order of Vasa from the King of Sweden in 1774. Of the seventy-six separate works with which he is credited in the Dictionary of National Biography, Samuel Johnson said of him that he was an ingenious man, but had no veracity. See a Short Account of the Life, Writings and Character of the late Sir John Hill, John Hills often provocative and scurrilous writings involved him in many quarrels, both in the field of science and that of literature. His works On the manner of seeding mosses and On Windsor loam appeared in the Royal Societys journal, on the basis of these contributions, Hill apparently hoped to be elected Fellow of the Royal Society. Furthermore, he had the backing of members of the Royal Society, the botanist Peter Collinson, the physician and scientist William Watson. Despite Hills merits as a scientist and his relations, his election to the title of Fellow failed to materialise, disappointed by the Royal Societys lack, in his opinion, of scientific standards, Hill started to criticise the Society. In December 1749, he started writing anonymous, critical reviews of articles published in the Philosophical Transactions. Moreover, in January 1750, Hill began a campaign of criticism and derision against the Royal Society by publishing, under an alias, a treatise entitled Lucina sine concubitu. Under the false name of Abraham Johnson, a physician and man-midwife and he had other literary passages-at-arms with John Rich, who accused him of plagiarising his Orpheus, also with Samuel Foote and Henry Woodward
20.
Linnaean taxonomy
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Linnaean taxonomy can mean either of two related concepts, the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturae and subsequent works. In the taxonomy of Linnaeus there are three kingdoms, divided into classes, and they, in turn, into orders, families, genera, a term for rank-based classification of organisms, in general. That is, taxonomy in the sense of the word. This term is used as opposed to cladistic systematics, which groups organisms into clades. It is attributed to Linnaeus, although he neither invented the concept of ranked classification nor gave it its present form, in his Imperium Naturae, Linnaeus established three kingdoms, namely Regnum Animale, Regnum Vegetabile and Regnum Lapideum. This approach, the Animal, Vegetable and Mineral Kingdoms, survives today in the mind, notably in the form of the parlour game question, Is it animal. The work of Linnaeus had a impact on science, it was indispensable as a foundation for biological nomenclature. However, the impact he had on science was not because of the value of his taxonomy and his classes and orders of plants, according to his Systema Sexuale, were never intended to represent natural groups but only for use in identification. They were used for that purpose well into the nineteenth century, within each class were several orders. The Linnaean classes for plants, in the Sexual System, were, monandria, flowers with 1 stamen Classis 2. Diandria, flowers with 2 stamens Classis 3, triandria, flowers with 3 stamens Classis 4. Tetrandria, flowers with 4 stamens Classis 5, pentandria, flowers with 5 stamens Classis 6. Hexandria, flowers with 6 stamens Hexandria monogynia pp. 285–352 Hexandria polygynia pp. 342–343 Classis 7, heptandria, flowers with 7 stamens Classis 8. Octandria, flowers with 8 stamens Classis 9, enneandria, flowers with 9 stamens Classis 10. Decandria, flowers with 10 stamens Classis 11, dodecandria, flowers with 12 stamens Classis 12. Icosandria, flowers with 20 stamens, perigynous Classis 13, polyandria, flowers with many stamens, inserted on the receptacle Classis 14. Didynamia, flowers with 4 stamens,2 long and 2 short Classis 15, tetradynamia, flowers with 6 stamens,4 long and 2 short Classis 16. Monadelphia, flowers with the separate, but the filaments united
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Christian Gottfried Ehrenberg
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Christian Gottfried Ehrenberg, German naturalist, zoologist, comparative anatomist, geologist, and microscopist, was one of the most famous and productive scientists of his time. The son of a judge, Christian Gottfried Ehrenberg was born in Delitzsch and he first studied theology at the University of Leipzig, then medicine and natural sciences in Berlin and became a friend of the famous explorer Alexander von Humboldt. In 1818, he completed his dissertation on fungi, Sylvae mycologicae Berolinenses. In 1820–1825, on an expedition to the Middle East with his friend Wilhelm Hemprich, he collected thousands of specimens of plants. He investigated parts of Egypt, the Libyan Desert, the Nile valley and the coasts of the Red Sea. Subsequently parts of Syria, Arabia and Abyssinia were examined, some results of these travels and of the important collections that had been made were reported on by Humboldt in 1826. While in Sudan he designed the mansion of the governor of Dongola. After his return, Ehrenberg published several papers on insects and corals and two volumes Symbolae physicae, in many particulars of the mammals, birds, insects. Other observations were communicated to scientific societies, Ehrenberg was appointed professor of medicine at Berlin University in 1827. In 1829 he accompanied Humboldt through eastern Russia to the Chinese frontier, after his return he began to concentrate his studies on microscopic organisms, which until then had not been systematically studied. He was particularly interested in a group of protists called diatoms, but he also studied. Until Ehrenberg took up the study it was not known that considerable masses of rock were composed of forms of animals or plants. He also demonstrated that the phosphorescence of the sea was due to organisms and he was a member of the Royal Swedish Academy of Sciences from 1836 and a foreign member of the Royal Society of London from 1837. In 1839, he won the Wollaston Medal, the highest award granted by the Geological Society of London, Ehrenberg was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1849. He continued until late in life to investigate the microscopic organisms of the deep sea and he died in Berlin on 27 June 1876. After his death in 1876, his collections of organisms were deposited in the Museum für Naturkunde at the University of Berlin. The Ehrenberg Collection includes 40,000 microscope preparations,5,000 raw samples,3,000 pencil and ink drawings and his collection of scorpions, and other arachnids from the Middle East, is also held in the Berlin Museum. He was also the first winner of the Leeuwenhoek Medal in 1877, in his hometown, Delitzsch, the highest A-Level school, the Ehrenberg-Gymnasium is named after him
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Protozoa
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In 21st-century systems of biological classification, the Protozoa are defined as a diverse group of unicellular eukaryotic organisms. Historically, protozoa were defined as single-celled animals or organisms with animal-like behaviors, such as motility, the group was regarded as the zoological counterpart to the protophyta, which were considered to be plant-like, as they are capable of photosynthesis. The terms protozoa and protozoans are now mostly used informally to designate single-celled, non-photosynthetic protists, such as the ciliates, amoebae and flagellates. The term Protozoa was introduced in 1818 for a taxonomic class, in several classification systems proposed by Thomas Cavalier-Smith and his collaborators since 1981, Protozoa is ranked as a kingdom. The seven-kingdom scheme proposed by Ruggiero et al. in 2015, places eight phyla under Protozoa, Euglenozoa, Amoebozoa, Metamonada, Choanozoa, Loukozoa, Percolozoa, Microsporidia and Sulcozoa. This kingdom does not form a clade, but an evolutionary grade or paraphyletic group, from which the fungi, for this reason, the terms protists, Protista or Protoctista are sometimes preferred for the high-level classification of eukaryotic microbes. In 2005, members of the Society of Protozoologists voted to change the name of organization to the International Society of Protistologists. The word protozoa was coined in 1818 by zoologist Georg August Goldfuss, as the Greek equivalent of the German Urthiere, meaning primitive, Goldfuss erected Protozoa as a class containing what he believed to be the simplest animals. Originally, the group included not only microbes, but also some lower animals, such as rotifers, corals, sponges, jellyfish, bryozoa. In 1848, in light of advancements in cell theory pioneered by Theodore Schwann and Matthias Schleiden, von Siebold redefined Protozoa to include only such unicellular forms, to the exclusion of all metazoa. At the same time, he raised the group to the level of a phylum containing two broad classes of microbes, Infusoria, and Rhizopoda. As a phylum under Animalia, the Protozoa were firmly rooted in the old two-kingdom classification of life, criticism of this system began in the latter half of the 19th century, with the realization that many organisms met the criteria for inclusion among both plants and animals. For example, the algae Euglena and Dinobryon have chloroplasts for photosynthesis, as an alternative, he proposed a new kingdom called Primigenum, consisting of both the protozoa and unicellular algae, which he combined together under the name Protoctista. In Hoggss conception, the animal and plant kingdoms were likened to two great pyramids blending at their bases in the Kingdom Primigenum, six years later, Ernst Haeckel also proposed a third kingdom of life, which he named Protista. Despite these proposals, Protozoa emerged as the taxonomic placement for heterotrophic microbes such as amoebae and ciliates. A variety of systems were proposed, and Kingdoms Protista and Protoctista became well established in biology texts. While many taxonomists have abandoned Protozoa as a group, Thomas Cavalier-Smith has retained it as a kingdom in the various classifications he has proposed. As of 2015, Cavalier-Smiths Protozoa excludes several major groups of organisms traditionally placed among the protozoa, including the ciliates, dinoflagellates, Protozoa, as traditionally defined, are mainly microscopic organisms, ranging in size from 10 to 52 micrometers
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Cilium
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A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the larger cell body. There are two types of cilia, motile cilia and nonmotile, or primary cilia, which serve as sensory organelles. In eukaryotes, motile cilia and flagella together make up a group of known as undulipodia. Eukaryotic cilia are structurally identical to eukaryotic flagella, although distinctions are made according to function and/or length. Biologists have various ideas about how the various flagella may have evolved, cilia can be divided into primary and motile forms. In animals, primary cilia are found on nearly every cell, in comparison to motile cilia, non-motile cilia usually occur one per cell, nearly all mammalian cells have a single non-motile primary cilium. The dendritic knob of the neuron, where the odorant receptors are located. Although the primary cilium was discovered in 1898, it was ignored for a century. Only recently has great progress made in understanding the function of the primary cilium. Until the 1990s, the view of the primary cilium was that it was merely a vestigial organelle without important function. The primary cilium is now known to play an important role in the function of human organs. Larger eukaryotes, such as mammals, have motile cilia as well, motile cilia are usually present on a cells surface in large numbers and beat in coordinated waves. In humans, for example, motile cilia are found in the lining of the trachea, in female mammals, the beating of cilia in the Fallopian tubes moves the ovum from the ovary to the uterus. The functioning of cilia is strongly dependent on the maintenance of optimal levels of fluid bathing the cilia. Epithelial sodium channels ENaC that are expressed along the entire length of cilia apparently serve as sensors that regulate fluid level surrounding the cilia. Ciliates are microscopic organisms that possess motile cilia exclusively and use them for either locomotion or to move liquid over their surface. Inside cilia and flagella is a microtubule-based cytoskeleton called the axoneme, the axoneme of primary cilia typically has a ring of nine outer microtubule doublets, and the axoneme of a motile cilium has two central microtubule singlets in addition to the nine outer doublets
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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
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Cell cortex
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The cell cortex, also known as the actin cortex or actomyosin cortex, is a specialized layer of cytoplasmic protein on the inner face of the plasma membrane of the cell periphery. It functions as a modulator of plasma membrane behavior and cell surface properties, in most eukaryotic cells lacking a cell wall, the cortex is an actin-rich network consisting of F-actin filaments, myosin motors, and actin-binding proteins. The actomyosin cortex is attached to the membrane via membrane-anchoring proteins called ERM proteins. The protein constituents of the cortex undergo rapid turnover, making the cortex both mechanically rigid and highly plastic, two properties essential to its function, in most cases, the cortex is in the range of 100 to 1000 nanometers thick. In some animal cells, the protein spectrin may be present in the cortex, spectrin helps to create a network by cross-linked actin filaments. The proportions of spectrin and actin vary with cell type, spectrin proteins and actin microfilaments are attached to transmembrane proteins by attachment proteins between them and the transmembrane proteins. In plant cells, the cortex is reinforced by cortical microtubules underlying the plasma membrane. The direction of these cortical microtubules determines which way the cell elongates when it grows, in mitosis, F-actin and myosin II form a highly contractile and uniform cortex to drive mitotic cell rounding. The surface tension produced by the actomyosin cortex activity generates intracellular hydrostatic pressure capable of displacing surrounding objects to facilitate rounding, in cytokinesis the cell cortex plays a central role by producing a myosin-rich contractile ring to constrict the dividing cell into two daughter cells. Cell cortex contractility is key for amoeboidal type cell migration characteristic of cancer cell metastasis events. Chapter 6 – Actin and Membranes
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Anatomical terms of location
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Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. All vertebrates have the basic body plan – they are strictly bilaterally symmetrical in early embryonic stages. That is, they have left and right halves if divided down the centre. For these reasons, the directional terms can be considered to be those used in vertebrates. By extension, the terms are used for many other organisms as well. While these terms are standardized within specific fields of biology, there are unavoidable, sometimes dramatic, for example, differences in terminology remain a problem that, to some extent, still separates the terminology of human anatomy from that used in the study of various other zoological categories. The vertebrates and Craniata share a heritage and common structure. To avoid ambiguities this terminology is based on the anatomy of each animal in a standard way, for humans, one type of vertebrate, anatomical terms may differ from other forms of vertebrates. Thus what is on top of a human is the head, whereas the top of a dog may be its back, for example, many species are not even bilaterally symmetrical. In these species, terminology depends on their type of symmetry, all descriptions are with respect to the organism in its standard anatomical position, even when the organism in question has appendages in another position. This helps avoid confusion in terminology when referring to the organism in different postures. In humans, this refers to the body in a position with arms at the side. While the universal vertebrate terminology used in medicine would work in human medicine. Many anatomical terms can be combined, either to indicate a position in two axes simultaneously or to indicate the direction of a movement relative to the body, for example, anterolateral indicates a position that is both anterior and lateral to the body axis. There is no limit to the contexts in which terms may be modified to qualify each other in such combinations. Generally the modifier term is truncated and an o or an i is added in prefixing it to the qualified term, where desirable three or more terms may be agglutinated or concatenated, as in anteriodorsolateral. Such terms sometimes used to be hyphenated, but the tendency is to omit the hyphen. There is however little basis for any rule to interfere with choice of convenience in such usage
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Heterotroph
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A heterotroph is an organism that cannot fix carbon from inorganic sources but uses organic carbon for growth. These reduced carbon compounds can be used as a source by the autotroph. Ninety-five percent or more of all types of living organisms are heterotrophic, including all animals and fungi and most bacteria, organotrophs exploit reduced carbon compounds as energy sources, like carbohydrates, fats, and proteins from plants and animals. They use organic compounds to build structures and they do not fix carbon dioxide and apparently do not have the Calvin cycle. Chemolithoheterotrophs can be distinguished from mixotrophs, which can utilize either carbon dioxide or organic carbon as the carbon source and this applies not only to animals and fungi but also to bacteria. The term heterotroph very often refers to chemoorganoheterotrophs, heterotrophs function as consumers in food chains, they obtain organic carbon by eating autotrophs or other heterotrophs. They break down organic compounds produced by autotrophs into simpler compounds. They release energy by oxidizing carbon and hydrogen present in carbohydrates, lipids. Most opisthokonts and prokaryotes are heterotrophic, in particular, all animals, some animals, such as corals, form symbiotic relationships with autotrophs and obtain organic carbon in this way. Furthermore, some plants have also turned fully or partially heterotrophic. Animals are heterotrophs by ingestion, fungi are heterotrophs by absorption
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Bacteria
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Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods, Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology, There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants, Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of bodies and bacteria are responsible for the putrefaction stage in this process. In March 2013, data reported by researchers in October 2012, was published and it was suggested that bacteria thrive in the Mariana Trench, which with a depth of up to 11 kilometres is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, You can find microbes everywhere—theyre extremely adaptable to conditions, the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial particularly in the gut flora. However several species of bacteria are pathogenic and cause diseases, including cholera, syphilis, anthrax, leprosy. The most common fatal diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year. In developed countries, antibiotics are used to treat infections and are also used in farming, making antibiotic resistance a growing problem. Once regarded as constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and these evolutionary domains are called Bacteria and Archaea. The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, for about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. In 2008, fossils of macroorganisms were discovered and named as the Francevillian biota, however, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea, here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea
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Mixotroph
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Possible combinations are photo- and chemotrophy, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic and they can take advantage of different environmental conditions. If a trophic mode is obligate, then it is necessary for sustaining growth and maintenance, if facultative. Some organisms have incomplete Calvin cycles, so they are incapable of fixing carbon dioxide, organisms may employ mixotrophy obligately or facultatively. Obligate mixotrophy, in order to support growth and maintenance, an organism must utilize both heterotrophic and autotrophic means. Facultative autotrophy with obligate heterotrophy, Heterotrophy is sufficient for growth and maintenance, but autotrophy may be used to supplement, for example, facultative mixotrophy, Maintenance and growth may be obtained by heterotrophic or autotrophic means alone, and mixotrophy is used only when necessary. In order to characterize the sub-domains within mixotrophy, several very similar categorization schemes have been suggested, a, Heterotrophy is the norm, and phototrophy is only used when prey concentrations are limiting. B, Phototrophy is the dominant strategy, and phagotrophy is employed as a supplement when light is limiting, C, Phototrophy results in substances for both growth and ingestion, phagotrophy is employed when light is limiting. D, Phototrophy is most common type, phagotrophy only used during prolonged dark periods. This scheme characterizes mixotrophs by their efficiency, paracoccus pantotrophus is a bacterium that can live chemoorganoheterotrophically, whereby a large variety of organic compounds can be metabolized. The sulfur compounds serve as electron donors and are consumed to produce ATP, the carbon source for these organisms can be carbon dioxide or organic carbon. Organoheterotrophy can occur under aerobic or under conditions, lithoautotrophy takes place aerobically. Zooxanthellate soft corals Many examples of the genus Euglena, oriental hornet Vespa orientalis Venus Flytrap Dionaea muscipula Amongst plants, mixotrophy classically applies to carnivorous, hemi-parasitic and partially hetero-mycotrophic species. Primary nutritional groups Photosynthesis Troost TA, Kooi BW, Kooijman SA, adaptive dynamics theory applied to a dynamic energy budget model. Sanders, Robert W. Mixotrophic Nutrition of Phytoplankton, Venus Fly Traps of the microbial world
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Endosymbiont
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An endosymbiont or endobiont is any organism that lives within the body or cells of another organism, i. e. forming an endosymbiosis. The most common examples of obligate endosymbioses are mitochondria and chloroplasts, some human parasites, e. g. Wuchereria bancrofti and Mansonella perstans, thrive in their intermediate insect hosts because of an obligate endosymbiosis with Wolbachia spp. They can both be eliminated from said hosts by treatments that target this bacterium, however, not all endosymbioses are obligate. Also, some endosymbioses can be harmful to either of the organisms involved, two major types of organelle in eukaryotic cells, mitochondria and plastids such as chloroplasts, originated as bacterial endosymbionts. Such symbiogenesis was first suggested in 1905, and articulated by the Russian botanist Konstantin Mereschkowski in 1910 and it was reintroduced by Lynn Margulis in the 1960s. Symbiogenesis explains the origins of such as mitochondria and chloroplasts in eukaryotic cells. The theory proposes that chloroplasts and mitochondria evolved from certain types of bacteria that eukaryotic cells engulfed through endophagocytosis and these cells and the bacteria trapped inside them entered a symbiotic relationship, a close association between different types of organisms over an extended time. However, to be specific, the relationship was endosymbiotic, meaning one of the organisms lived within the other. The theory suggests that an anaerobic cell probably ingested an aerobic bacterium, the aerobic bacterium flourished within the cell because the cells cytoplasm was abundant in half-digested food molecules. The bacterium digested these molecules with oxygen and gained great amounts of energy, because the bacterium had so much energy, it probably leaked some of it as adenosine triphosphate into the cells cytoplasm. This benefited the anaerobic cell because it was now able to breathe aerobically, eventually, the aerobic bacterium could no longer live independently from the cell, and it, therefore, became a mitochondrion. The origin of the chloroplast is very similar to that of the mitochondrion, a cell must have captured a photosynthetic cyanobacterium and failed to digest it. The cyanobacterium thrived in the cell and eventually evolved into the first chloroplast, there are several lines of evidence that support endosymbiosis theory. Mitochondria and chloroplasts contain their own supply of DNA, which may be remnants of the genome the organelles had when they were independent aerobic bacteria. The single most convincing evidence of the descent of organelles from bacteria is the position of mitochondria, mitochondria have sequences that clearly indicate origin from a group of bacteria called the alphaproteobacteria. Plastids have DNA sequences that indicate origin from the cyanobacteria, in addition, there are organisms alive today, called living intermediates, that are in a similar endosymbiotic condition to the prokaryotic cells and the aerobic bacteria. Living intermediates show that the proposed by the endosymbiont theory is possible. For example, the giant amoeba Pelomyxa lacks mitochondria but has aerobic bacteria that carry out a similar role, a variety of corals, clams, snails, and one species of Paramecium permanently host algae in their cells
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Algae
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Algae is an informal term for a large, diverse group of photosynthetic organisms which are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular genera, such as Chlorella and the diatoms, to forms, such as the giant kelp. Most are aquatic and autotrophic and lack many of the cell and tissue types, such as stomata, xylem, and phloem. No definition of algae is generally accepted, one definition is that algae have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells. Some authors exclude all prokaryotes thus do not consider cyanobacteria as algae, Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria, diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, and the roots, leaves, and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago, the singular alga is the Latin word for seaweed and retains that meaning in English. Although some speculate that it is related to Latin algēre, be cold, a more likely source is alliga, binding, entwining. The Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it, the Latinization, fūcus, meant primarily the cosmetic rouge. It could be any color, black, red, green, accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name Fucus appears in a number of taxa, most algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and presumably represent reduced endosymbiotic cyanobacteria, however, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three groups of algae. Their lineage relationships are shown in the figure in the upper right, many of these groups contain some members that are no longer photosynthetic
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Chlorella
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Chlorella is a genus of single-cell green algae belonging to the phylum Chlorophyta. It is spherical in shape, about 2 to 10 μm in diameter, Chlorella contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplast. Through photosynthesis, it rapidly, requiring only carbon dioxide, water, sunlight. The name Chlorella is taken from the Greek χλώρος, chloros, meaning green, in 1961, Melvin Calvin of the University of California received the Nobel Prize in Chemistry for his research on the pathways of carbon dioxide assimilation in plants using Chlorella. Mass-production methods are now being used to cultivate it in large artificial circular ponds and it is also abundant in calories and vitamins. When first harvested, Chlorella suggested as a protein supplement to the human diet. Advocates sometimes focus on other supposed health benefits of the algae, such as claims of control, cancer prevention. According to the American Cancer Society, available scientific studies do not support its effectiveness for preventing or treating cancer or any disease in humans. Under certain growing conditions, Chlorella yields oils that are high in polyunsaturated fats—Chlorella minutissima has yielded EPA at 39. 9% of total lipids. Many people during this time thought hunger would be an overwhelming problem, many institutions began to research the algae, including the Carnegie Institution, the Rockefeller Foundation, the NIH, UC Berkeley, the Atomic Energy Commission, and Stanford University. Because meat was costly and energy-intensive to produce, protein shortages were also an issue, increasing cultivated area alone would go only so far in providing adequate nutrition to the population. The USDA calculated that, to feed the U. S. population by 1975, it would have to add 200 million acres of land, hopes rested solely on new agricultural techniques and technologies. Because of these circumstances, a solution was needed. To cope with the upcoming post-war population boom in the United States and elsewhere, initial testing by the Stanford Research Institute showed Chlorella could convert 20% of solar energy into a plant that, when dried, contains 50% protein. In addition, Chlorella contains fat and vitamins, the pilot research performed at Stanford and elsewhere led to immense press from journalists and newspapers, yet did not lead to large-scale algae production. Chlorella seemed like an option because of the technological advances in agriculture at the time. Algae researchers had even hoped to add a neutralized Chlorella powder to conventional products, as a way to fortify them with vitamins. When the preliminary results were published, the scientific community at first backed the possibilities of Chlorella
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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
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Osmoregulation
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Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the pressure of a solution, the more water tends to move into it. Pressure must be exerted on the side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water. Two major types of osmoregulation are osmoconformers and osmoregulators, osmoconformers match their body osmolarity to their environment actively or passively. Most marine invertebrates are osmoconformers, although their ionic composition may be different from that of seawater, osmoregulators tightly regulate their body osmolarity, maintaining constant internal conditions. They are more common in the animal kingdom, osmoregulators actively control salt concentrations despite the salt concentrations in the environment. The gills actively uptake salt from the environment by the use of mitochondria-rich cells, water will diffuse into the fish, so it excretes a very hypotonic urine to expel all the excess water. A marine fish has an internal osmotic concentration lower than that of the seawater, so it tends to lose water. It actively excretes salt out from the gills, most fish are stenohaline, which means they are restricted to either salt or fresh water and cannot survive in water with a different salt concentration than they are adapted to. However, some show a tremendous ability to effectively osmoregulate across a broad range of salinities, fish with this ability are known as euryhaline species. Flounder have been observed to inhabit two utterly disparate environments — marine and fresh water — and it is inherent to adapt to both by bringing in behavioral and physiological modifications. Some marine fish, like sharks, have adopted a different, efficient mechanism to conserve water and they retain urea in their blood in relatively higher concentration. Urea damages living tissues so, to cope with this problem and this provides a better solution to ureas toxicity. Sharks, having slightly higher concentration, do not drink water like fresh water fish. Strong winds, low humidity and high temperatures all increase evapotranspiration from leaves, abscisic acid is an important hormone in helping plants to conserve water — it causes stomata to close and stimulates root growth so that more water can be absorbed. Plants share with animals the problems of obtaining water but, unlike in animals, certain plants have evolved methods of water conservation. Xerophytes are plants that can survive in dry habitats, such as deserts, succulent plants such as the cacti store water in the vacuoles of large parenchyma tissues. Other plants have modifications to reduce water loss, such as needle-shaped leaves, sunken stomata
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Contractile vacuole
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A contractile vacuole is a sub-cellular structure involved in osmoregulation. It is found predominantly in protists and in unicellular algae and it was previously known as pulsatile or pulsating vacuole. The contractile vacuole acts to regulate the quantity of water inside of a cell, in freshwater environments, the concentration of solutes inside the cell is of a higher concentration than outside the cell. Under these conditions, water flows from the environment into the cell by osmosis, the contractile vacuole acts as part of a protective mechanism that prevents the cell from absorbing too much water and possibly lysing through excessive internal pressure. The contractile vacuole is a type of vacuole, vacuoles are found in most cells. The contractile vacuole, as its name suggests, expels water out of the cell by contracting, the growth and contraction of the contractile vacuole are periodical. One cycle takes several seconds, depending on the species and the environments osmolarity, the stage in which water flows into the CV is called diastole. The contraction of the contractile vacuole and the expulsion of water out of the cell is called systole, water always flows first from outside the cell into the cytoplasm, and is only then moved from the cytoplasm into the contractile vacuole for expulsion. The amount of water expelled from the cell and the rate of contraction are related to the osmolarity of the environment, in hyperosmotic environments, less water will be expelled and the contraction cycle will be longer. The most well understood contractile vacuole belong to the protists Paramecium, Amoeba, Dictyostelium and Trypanosoma, not all species that possess a contractile vacuole are freshwater organisms, some marine, soil microorganisms and parasites also have a contractile vacuole. The contractile vacuole is predominant in species that do not have a cell wall, the number of contractile vacuoles per cell varies, depending on the species. Amoeba have one, Dictyostelium discoideum, Paramecium aurelia and Chlamydomonas reinhardtii have two, and giant amoeba, such as Chaos carolinensis, have many, the number of contractile vacuoles in each species is mostly constant and is therefore used for species characterization in systematics. The contractile vacuole has several structures attached to it in most cells, such as membrane folds, tubules, water tracts and these structures have been termed the spongiome, the contractile vacuole together with the spongiome is sometimes called the contractile vacuole complex. The spongiome serves several functions in water transport into the contractile vacuole and in localization, Paramecium and Amoeba possess large contractile vacuoles, which are relatively comfortable to isolate, manipulate and assay. The smallest known contractile vacuoles belong to Chlamydomonas, with a diameter of 1.5 µm, in Paramecium, which has one of the most complex contractile vacuoles, the vacuole is surrounded by several canals, which absorb water by osmosis from the cytoplasm. After the canals fill with water, the water is pumped into the vacuole, when the vacuole is full, it expels the water through a pore in the cytoplasm which can be opened and closed. Other protists, such as Amoeba, have CVs that move to the surface of the cell when full, in Amoeba contractile vacuoles collect excretory waste, such as ammonia, from the intracellular fluid by both diffusion and active transport. The way in which water enters the CV had been a mystery for many years, water could theoretically cross the CV membrane by osmosis, but only if the inside of the CV is hyperosmotic to the cytoplasm
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Osmosis
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It may also be used to describe a physical process in which any solvent moves across a semipermeable membrane separating two solutions of different concentrations. Osmosis can be made to do work, osmotic pressure is defined as the external pressure required to be applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a property, meaning that the osmotic pressure depends on the molar concentration of the solute. Osmosis is a process in biological systems, as biological membranes are semipermeable. Permeability depends on solubility, charge, or chemistry, as well as solute size, water molecules travel through the plasma membrane, tonoplast membrane or protoplast by diffusing across the phospholipid bilayer via aquaporins. Osmosis provides the means by which water is transported into. The turgor pressure of a cell is maintained by osmosis across the cell membrane between the cell interior and its relatively hypotonic environment. Jean-Antoine Nollet first documented observation of osmosis in 1748, the word osmosis descends from the words endosmose and exosmose, which were coined by French physician René Joachim Henri Dutrochet from the Greek words ἔνδον, ἔξω, and ὠσμός. Osmosis is the movement of a solvent across a membrane toward a higher concentration of solute. In biological systems, the solvent is water, but osmosis can occur in other liquids, supercritical liquids. When a cell is submerged in water, the water pass through the cell membrane from an area of low solute concentration to high solute concentration. For example, if the cell is submerged in saltwater, water molecules out of the cell. If a cell is submerged in freshwater, water molecules move into the cell, when the membrane has a volume of pure water on both sides, water molecules pass in and out in each direction at exactly the same rate. There is no net flow of water through the membrane, the mechanism responsible for driving osmosis has commonly been represented in biology and chemistry texts as either the dilution of water by solute or by a solutes attraction to water. Both of these notions have been conclusively refuted, the diffusion model of osmosis is rendered untenable by the fact that osmosis can drive water across a membrane toward a higher concentration of water. The bound water model is refuted by the fact that osmosis is independent of the size of the solute molecules—a colligative property—or how hydrophilic they are, one fact to take note of is that heat from the surroundings is able to be converted into mechanical energy. Osmotic pressure is the cause of support in many plants. The osmotic entry of water raises the pressure exerted against the cell wall, until it equals the osmotic pressure
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Vacuole
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A vacuole is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these, the organelle has no basic shape or size, its structure varies according to the needs of the cell. In seeds, stored proteins needed for germination are kept in protein bodies, vacuoles also play a major role in autophagy, maintaining a balance between biogenesis and degradation, of many substances and cell structures in certain organisms. They also aid in the lysis and recycling of misfolded proteins that have begun to build up within the cell, thomas Boller and others proposed that the vacuole participates in the destruction of invading bacteria and Robert B Mellor proposed organ-specific forms have a role in housing symbiotic bacteria. In protists, vacuoles have the function of storing food which has been absorbed by the organism and assisting in the digestive. The vacuole probably evolved several times independently, even within the Viridiplantae, contractile vacuoles were first observed by Spallanzani in protozoa, although mistaken for respiratory organs. Dujardin named these stars as vacuoles, in 1842, Schleiden applied the term for plant cells, to distinguish the structure with cell sap from the rest of the protoplasm. In 1885, de Vries named the vacuoule membrane as tonoplast, large vacuoles are found in three genera of filamentous sulfur bacteria, the Thioploca, Beggiatoa and Thiomargarita. The cytosol is extremely reduced in these genera and the vacuole can occupy between 40–98% of the cell, the vacuole contains high concentrations of nitrate ions and is therefore thought to be a storage organelle. Gas vacuoles, which are freely permeable to gas, are present in species of Cyanobacteria. They allow the bacteria to control their buoyancy, most mature plant cells have one large vacuole that typically occupies more than 30% of the cells volume, and that can occupy as much as 80% of the volume for certain cell types and conditions. Strands of cytoplasm often run through the vacuole, a vacuole is surrounded by a membrane called the tonoplast and filled with cell sap. Also called the membrane, the tonoplast is the cytoplasmic membrane surrounding a vacuole. As a membrane, it is involved in regulating the movements of ions around the cell. The low pH of the vacuole also allows degradative enzymes to act, although single large vacuoles are most common, the size and number of vacuoles may vary in different tissues and stages of development. For example, developing cells in the meristems contain small provacuoles and cells of the vascular cambium have many small vacuoles in the winter, aside from storage, the main role of the central vacuole is to maintain turgor pressure against the cell wall. Proteins found in the tonoplast control the flow of water into and out of the vacuole through active transport, pumping potassium ions into, due to osmosis, water will diffuse into the vacuole, placing pressure on the cell wall. If water loss leads to a significant decline in turgor pressure, turgor pressure exerted by the vacuole is also essential in supporting plants in an upright position
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Mutualism (biology)
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Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits from the activity of the other. Similar interactions within a species are known as co-operation, symbiosis involves two species living in close proximity and includes relationships that are mutualistic, parasitic, and commensal. Symbiotic relationships are sometimes, but not always, mutualistic, a well-known example of mutualism is the relationship between ungulates and bacteria within their intestines. The ungulates benefit from the produced by the bacteria, which facilitates digestion. This can also be found in many different symbiotic relationships. Mutualism plays a key part in ecology, in addition, mutualism is thought to have driven the evolution of much of the biological diversity we see, such as flower forms and co-evolution between groups of species. However mutualism has historically received less attention than other such as predation. It is therefore common to categorise mutualisms according to the closeness of the association, using such as obligate. Defining closeness, however, is also problematic and it can refer to mutual dependency or the biological intimacy of the relationship in relation to physical closeness. The term mutualism was introduced by Pierre-Joseph van Beneden in 1876, other examples include rhizobia bacteria that fix nitrogen for leguminous plants in return for energy-containing carbohydrates. Pollination in which nectar or pollen are traded for pollen dispersal or ant protection of aphids, phagophiles feed on ectoparasites, thereby providing anti-pest service, as in cleaning symbiosis. Elacatinus and Gobiosoma, genus of gobies, also feed on ectoparasites of their clients while cleaning them, zoochory is the dispersal of the seeds of plants by animals. This is similar to pollination in that the plant produces food resources for animals that disperse the seeds, strict service-service interactions are very rare, for reasons that are far from clear. Therefore, what appears to be a service-service mutualism in fact has a service-resource component, a second example is that of the relationship between some ants in the genus Pseudomyrmex and trees in the genus Acacia, such as the whistling thorn and bullhorn acacia. The ants nest inside the plants thorns, in exchange for shelter, the ants protect acacias from attack by herbivores and competition from other plants by trimming back vegetation that would shade the acacia. In addition, another component is present, as the ants regularly feed on lipid-rich food-bodies called Beltian bodies that are on the Acacia plant. In the neotropics, the ant, Myrmelachista schumanni makes its nest in cavities in Duroia hirsute. Plants in the vicinity that belong to other species are killed with formic acid and this selective gardening can be so aggressive that small areas of the rainforest are dominated by Duroia hirsute
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Didinium
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Didinium is a genus of unicellular ciliates with at least ten accepted species. Most are found in fresh and brackish water, but three species are known. Their diet consists largely of Paramecium, although they also attack. Some species, such as D. gargantua, also feed on non-ciliate protists, including dinoflagellates, cryptomonads, Didinia are rounded, oval or barrel-shaped and range in length from 50 to 150 micrometres. The cell body is encircled by two bands, or pectinelles. This distinguishes them from the related genus Monodinium, which have only a single band, the pectinelles are used to move Didinium through water by rotating the cell around its axis. At the anterior end, a cone-shaped structure protrudes, supported by a palisade of stiff microtubular rods and this cone encloses the cytostome or mouth opening, as in other haptorian ciliates. The dimensions of this vary among the different species. The macronucleus is long, and may be curved, horseshoe-shaped or twisted into a shape resembling a figure eight, a contractile vacuole and anal aperture are in the posterior of the cell. Like all ciliates, Didinia reproduce asexually via binary fission, or sexually through conjugation, much of what has been published about this genus is based on numerous studies of a single species, Didinium nasutum. A voracious predator, D. nasutum uses specialized structures called toxicysts to ensnare, once captured, the prey is engulfed through Didiniums expandible cytostome. While D. Moreover, strains of Didinium raised on a Colpidium campylum will actually show a preference for a made up of that species, as well as a diminished ability to kill. In the absence of food, D. nasutum will encyst, in the laboratory, other environmental stimuli, such as the age of the growth medium or the accumulation of certain metabolic waste products, can also trigger encystment. When the encysted form of D. nasutum is exposed to a culture of Paramecium, it will excyst, reverting to its active. Didinium cysts have been shown to remain viable for at least 10 years, Didinium was discovered by the eighteenth-century naturalist O. F. Müller and described in his Animalcula Infusoria under the name Vorticella nasuta, later in the century, under the taxonomical scheme created by Otto Bütschli, Didinium was removed from among the Peritrichs, and placed in the order Holotricha. O. Corliss created the order Haptorida, within the subclass Haptoria, for rapacious carnivorous forms such as Didinium, Dileptus and this group has since been placed in the class Litostomatea Small & Lynn,1981. Genetic analysis of Haptorian ciliates has shown that they do not form a monophyletic group
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