1.
Toxoplasma gondii
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Toxoplasma gondii is an obligate intracellular, parasitic alveolate that causes the disease toxoplasmosis. For example, previous estimates have shown the highest prevalence of persons infected to be in France, although mild, flu-like symptoms occasionally occur during the first few weeks following exposure, infection with T. gondii produces no readily observable symptoms in healthy human adults. This asymptomatic state of infection is referred to as a latent infection and has recently been associated with numerous subtle adverse or pathological behavioral alterations in humans, in infants, HIV/AIDS patients, and others with weakened immunity, infection can cause a serious and occasionally fatal illness, toxoplasmosis. T. gondii has been shown to alter the behavior of infected rodents in ways that increase the chances of being preyed upon by felids. Support for this hypothesis stems from studies showing T. gondii-infected rats have a decreased aversion to cat urine. The rats would not shy away from areas where cats live, widespread histone-lysine acetylation in cortical astrocytes appears to be another epigenetic mechanism employed by T. gondii. Differences in aversion to cat urine are observed between non-infected and infected humans and sex differences within these groups were apparent, as well, because T. gondii can sexually reproduce only within cats, they are defined as the definitive host of T. gondii. All other hosts – hosts in which asexual reproduction can occur – are defined as intermediate hosts. When a member of the cat family is infected with T. gondii, inside these intestinal cells, the parasites undergo sexual development and reproduction, producing millions of thick-walled, zygote-containing cysts known as oocysts. Infected epithelial cells eventually rupture and release oocysts into the intestinal lumen, oocysts can then spread to soil, water, food, or anything potentially contaminated with the feces. Highly resilient, oocysts can survive and remain infective for many months in cold, ingestion of oocysts by humans or other warm-blooded animals is one of the common routes of infection. Humans can be exposed to oocysts by, for example, consuming unwashed vegetables or contaminated water, although cats can also be infected by ingesting oocysts, they are much less sensitive to oocyst infection than are intermediate hosts. T. gondii is considered to have three stages of infection, the stage of rapid division, the bradyzoite stage of slow division within tissue cysts. Tissue cysts in tissues such as brain and muscle tissue, form approximately 7–10 days after initial infection, inside host cells, the tachyzoites replicate inside specialized vacuoles created during parasitic entry into the cell. Tachyzoites multiply inside this vacuole until the host cell dies and ruptures, releasing and spreading the tachyzoites via the bloodstream to all organs and tissues of the body, inside host cells, clusters of these bradyzoites are known as tissue cysts. The cyst wall is formed by the vacuole membrane. Although bradyzoite-containing tissue cysts can form in any organ, tissue cysts predominantly form and persist in the brain, the eyes. Cysts usually range in size between five and 50 µm in diameter, consumption of tissue cysts in meat is one of the primary means of T. gondii infection, both for humans and for meat-eating, warm-blooded animals
2.
Staining
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Staining is an auxiliary technique used in microscopy to enhance contrast in the microscopic image. Stains and dyes are used in biology and medicine to highlight structures in biological tissues for viewing. Stains may be used to define and examine bulk tissues, cell populations, in biochemistry it involves adding a class-specific dye to a substrate to qualify or quantify the presence of a specific compound. Staining and fluorescent tagging can serve similar purposes, biological staining is also used to mark cells in flow cytometry, and to flag proteins or nucleic acids in gel electrophoresis. Simple staining is staining with only one stain/dye, there are various kinds of multiple staining, many of which are examples of counterstaining, differential staining, or both, including double staining and triple staining. In vivo staining is the process of dyeing living tissues—in vivo means in life, by causing certain cells or structures to take on contrasting colour, their form or position within a cell or tissue can be readily seen and studied. In vitro staining involves colouring cells or structures that have removed from their biological context. Certain stains are often combined to reveal more details and features than a single stain alone, combined with specific protocols for fixation and sample preparation, scientists and physicians can use these standard techniques as consistent, repeatable diagnostic tools. A counterstain is stain that makes cells or structures more visible, for example, crystal violet stains only Gram-positive bacteria in Gram staining. A safranin counterstain is applied that stains all cells, allowing identification of Gram-negative bacteria, while ex vivo, many cells continue to live and metabolize until they are fixed. Some staining methods are based on this property and those stains excluded by the living cells but taken up by the already dead cells are called vital stains. Those that enter and stain living cells are called supravital stains, however, these stains are eventually toxic to the organism, some more so than others. To achieve desired effects, the stains are used in very dilute solutions ranging from 1,5000 to 1,500000, note that many stains may be used in both living and fixed cells. The preparatory steps involved depend on the type of analysis planned, fixation–which may itself consist of several steps–aims to preserve the shape of the cells or tissue involved as much as possible. Sometimes heat fixation is used to kill, adhere, and alter the specimen so it accepts stains, most chemical fixatives generate chemical bonds between proteins and other substances within the sample, increasing their rigidity. Common fixatives include formaldehyde, ethanol, methanol, and/or picric acid, pieces of tissue may be embedded in paraffin wax to increase their mechanical strength and stability and to make them easier to cut into thin slices. Permeabilization involves treatment of cells with a mild surfactant and this treatment dissolves cell membranes, and allows larger dye molecules into the cells interior. Mounting usually involves attaching the samples to a microscope slide for observation
3.
Pathology
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Pathology is a significant component of the causal study of disease and a major field in modern medicine and diagnosis. Similarly, a condition is one caused by disease, rather than occurring physiologically. A physician practicing pathology is called a pathologist, as a field of general inquiry and research, pathology addresses four components of disease, cause, mechanisms of development, structural alterations of cells, and the consequences of changes. Further divisions in specialty exist on the basis of the involved sample types, organs, the sense of the word pathology as a synonym of disease or pathosis is very common in health care. The persistence of this usage despite attempted proscription is discussed elsewhere, the study of pathology, including the detailed examination of the body, including dissection and inquiry into specific maladies, dates back to antiquity. Notably, many advances were made in the era of Islam, during which numerous texts of complex pathologies were developed. By the 17th century, the study of microscopy was underway and examination of tissues had led British Royal Society member Robert Hooke to coin the word cell, setting the stage for later germ theory. However, pathology as an area of specialty was not fully developed until the late 19th and early 20th centuries. This realization led to the understanding that diseases are able to replicate themselves. To determine causes of diseases, medical experts used the most common and widely accepted assumptions or symptoms of their times, by the late 1920s to early 1930s pathology was deemed a medical specialty. The modern practice of pathology is divided into a number of subdisciplines within the discrete but deeply interconnected aims of biological research, anatomical pathology is itself divided into subfields, the main divisions being surgical pathology, cytopathology, and forensic pathology. Sometimes, pathologists practice both anatomical and clinical pathology, a known as general pathology. Cytopathology is a branch of pathology that studies and diagnoses diseases on the cellular level, however, cytology samples may be prepared in other ways, including cytocentrifugation. Dermatopathology is a subspecialty of pathology that focuses on the skin. It is unique, in there are two paths a physician can take to obtain the specialization. The completion of this allows one to take a subspecialty board examination. Dermatologists are able to recognize most skin diseases based on their appearances, anatomic distributions, sometimes, however, those criteria do not lead to a conclusive diagnosis, and a skin biopsy is taken to be examined under the microscope using usual histological tests. One of the greatest challenges of dermatopathology is its scope, more than 1500 different disorders of the skin exist, including cutaneous eruptions and neoplasms
4.
Blue
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Blue is the colour between violet and green on the optical spectrum of visible light. Human eyes perceive blue when observing light with a wavelength between 450 and 495 nanometres, which is between 4500 and 4950 ångströms. Blues with a frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency. Pure blue, in the middle, has a wavelength of 470 nanometers, in painting and traditional colour theory, blue is one of the three primary colours of pigments, along with red and yellow, which can be mixed to form a wide gamut of colours. Red and blue mixed together form violet, blue and yellow together form green, Blue is also a primary colour in the RGB colour model, used to create all the colours on the screen of a television or computer monitor. The clear sky and the sea appear blue because of an optical effect known as Rayleigh scattering. When sunlight passes through the atmosphere, the wavelengths are scattered more widely by the oxygen and nitrogen molecules. An optical effect called Tyndall scattering, similar to Rayleigh scattering, explains blue eyes, distant objects appear more blue because of another optical effect called atmospheric perspective. Blue has been used for art and decoration since ancient times and it is the most important color in Judaism. In the Middle Ages, cobalt blue was used to colour the stained glass windows of cathedrals, beginning in the 9th century, Chinese artists used cobalt to make fine blue and white porcelain. Blue dyes for clothing were made from woad in Europe and indigo in Asia, in 1828 a synthetic ultramarine pigment was developed, and synthetic blue dyes and pigments gradually replaced mineral pigments and vegetable dyes. Pierre-Auguste Renoir, Vincent van Gogh and other late 19th century painters used ultramarine and cobalt blue not just to depict nature, in the late 18th century and 19th century, blue became a popular colour for military uniforms and police uniforms. In the 20th century, because blue was associated with harmony, it was chosen as the colour of the flags of the United Nations. Surveys in the US and Europe show that blue is the colour most commonly associated with harmony, faithfulness, confidence, distance, infinity, the imagination, cold, and sometimes with sadness. In US and European public opinion polls it is the most popular colour, Blue is the colour of light between violet and green on the visible spectrum. Blues also vary in shade or tint, darker shades of blue contain black or grey, darker shades of blue include ultramarine, cobalt blue, navy blue, and Prussian blue, while lighter tints include sky blue, azure, and Egyptian blue. Today most blue pigments and dyes are made by a chemical process, the modern English word blue comes from Middle English bleu or blewe, from the Old French bleu, a word of Germanic origin, related to the Old High German word blao. In heraldry, the azure is used for blue
5.
Violet (color)
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Violet is the color of amethyst, lavender and beautyberries. It takes its name from the violet flower, Violet is the color at the end of the visible spectrum of light between blue and the invisible ultraviolet. Violet color has a predominant light wavelength of roughly 380-450 nanometers, light with a shorter wavelength than violet but longer than X-rays and gamma rays is called ultraviolet. In the color wheel used by painters, it is located between blue and purple. This is not true violet, since it is composed of multiple longer wavelengths rather than a wavelength shorter than that of blue light. Violet and purple look very similar, but violet is a color, with its own set of wavelengths on the spectrum of visible light, while purple is a composite color, made by combining blue. In history, violet and purple have long associated with royalty and majesty. The emperors of Rome wore purple togas, as did the Byzantine emperors, during the Middle Ages violet was worn by bishops and university professors and was often used in art as the color of the robes of the Virgin Mary. According to surveys in Europe and the United States, violet is the people most often associate with extravagance and individualism, the unconventional, the artificial. In Chinese painting, the color represents the harmony of the universe because it is a combination of red. In Hinduism and Buddhism violet is associated with the Crown Chakra, from the Middle English and old French violette, and from the Latin viola, the names of the violet flower. The first recorded use of violet as a name in English was in 1370. Violet can also refer to the first violas which were painted a similar color. In the traditional color used by painters, violet and purple are both placed between red and blue. Purple occupies the space closer to red, between crimson and violet, Violet is closer to blue, and usually less intense and bright than purple. The range of purples is created by combining blue and red light of any intensities, Violet is one of the oldest colors used by man. It has also found in the cave of Altamira and Lascaux. It was sometimes used an alternative to black charcoal, sticks of manganese, used for drawing, have been found at sites occupied by Neanderthal man in France and Israel
6.
Red
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Red is the color at the longer-wavelengths end of the spectrum of visible light next to orange, at the opposite end from violet. Red color has a predominant light wavelength of roughly 620–740 nanometers, light with a longer wavelength than red but shorter than terahertz radiation and microwave is called infrared. Red is one of the secondary colors, resulting from the combination of yellow. Traditionally, it was viewed as a primary colour, along with yellow and blue, in the RYB color space and traditional color wheel formerly used by painters. Reds can vary in shade from light pink to very dark maroon or burgundy. Red is the color of cyan. In nature, the red color of blood comes from hemoglobin, the red color of the Grand Canyon and other geological features is caused by hematite or red ochre, both forms of iron oxide. It also causes the red color of the planet Mars, the color of autumn leaves is caused by pigments called anthocyanins, which are produced towards the end of summer, when the green chlorophyll is no longer produced. One to two percent of the population has red hair, the color is produced by high levels of the reddish pigment pheomelanin. Since red is the color of blood, it has historically been associated with sacrifice, danger, modern surveys in the United States and Europe show red is also the color most commonly associated with heat, activity, passion, sexuality, anger, love and joy. In China, India and many other Asian countries it is the color of symbolizing happiness, since the 19th century, red has also been associated with socialism and communism. The word red is derived from the Old English rēad, the word can be further traced to the Proto-Germanic rauthaz and the Proto-Indo European root rewdʰ-. In Sanskrit, the word means red or blood. In the Akkadian language of Ancient Mesopotamia and in the modern Inuit language of Inuit, the words for colored in Latin and Spanish both also mean red. In Portuguese the word for red is vermelho, which comes from Latin vermiculus, in the Russian language, the word for red, Кра́сный, comes from the same old Slavic root as the words for beautiful—красивый and excellent—прекрасный. Thus Red Square in Moscow, named long before the Russian Revolution, in heraldry, the word gules is used for red. Red can vary in hue from orange-red to violet-red, and for each hue there is a variety of shades and tints. Red hematite powder was found scattered around the remains at a grave site in a Zhoukoudian cave complex near Beijing
7.
Mallory body
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In histopathology, a Mallory body, Mallory-Denk body, and Mallorys hyaline, is an inclusion found in the cytoplasm of liver cells. Mallory bodies are damaged intermediate filaments within the hepatocytes, Mallory bodies are classically found in the livers of people suffering from alcoholic liver disease and were once thought to be specific for that. They are most common in hepatitis and alcoholic cirrhosis. They are a feature of Wilsons disease, primary biliary cirrhosis, non-alcoholic cirrhosis, hepatocellular carcinoma and morbid obesity. However, it has also reported in certain other unrelated conditions. Mallory bodies are highly eosinophilic and thus appear pink on H&E stain, the bodies themselves are made up of intermediate cytokeratin 8/18 filament proteins that have been ubiquinated, or bound by other proteins such as heat shock proteins, or p62. It is named for the American pathologist Frank Burr Mallory, who first described the structures in 1911 and they were renamed as Mallory-Denk bodies in 2007 to honor the contribution of Austrian pathologist Helmut Denk for the molecular analysis of the pathogenesis of MDBs. Ballooning degeneration - another histopathologic finding of steatohepatitis
8.
Red blood cell
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RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the bodys capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, a biomolecule that can bind oxygen and is responsible for the red color of the cells. In humans, mature red cells are flexible and oval biconcave disks. They lack a nucleus and most organelles, in order to accommodate maximum space for hemoglobin, they can be viewed as sacks of hemoglobin. Approximately 2.4 million new erythrocytes are produced per second in human adults, the cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Each circulation takes about 60 seconds, approximately a quarter of the cells in the human body are red blood cells. Nearly half of the volume is red blood cells. Red blood cells are known as RBCs, red cells, red blood corpuscles, haematids. Packed red blood cells are red blood cells that have donated, processed. Almost all vertebrates, including all mammals and humans, have red blood cells, red blood cells are cells present in blood in order to transport oxygen. The only known vertebrates without red blood cells are the crocodile icefish, they live in very cold water. While they no longer use hemoglobin, remnants of hemoglobin genes can be found in their genome, oxygen can easily diffuse through the red blood cells cell membrane. Myoglobin, a related to hemoglobin, acts to store oxygen in muscle cells. The color of red cells is due to the heme group of hemoglobin. However, blood can appear bluish when seen through the vessel wall, pulse oximetry takes advantage of the hemoglobin color change to directly measure the arterial blood oxygen saturation using colorimetric techniques. Hemoglobin also has a high affinity for carbon monoxide, forming carboxyhemoglobin which is a very bright red in color. Flushed, confused patients with a reading of 100% on pulse oximetry are sometimes found to be suffering from carbon monoxide poisoning. The red blood cells of mammals are typically shaped as disks, flattened and depressed in the center, with a dumbbell-shaped cross section
9.
Golgi apparatus
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The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. It was identified in 1897 by the Italian scientist Camillo Golgi, part of the cellular endomembrane system, the Golgi apparatus packages proteins into membrane-bound vesicles inside the cell before the vesicles are sent to their destination. The Golgi apparatus resides at the intersection of the secretory, lysosomal, owing to its large size and distinctive structure, the Golgi apparatus was one of the first organelles to be discovered and observed in detail. It was discovered in 1898 by Italian physician Camillo Golgi during an investigation of the nervous system, after first observing it under his microscope, he termed the structure the internal reticular apparatus. Some doubted the discovery at first, arguing that the appearance of the structure was merely an illusion created by the observation technique used by Golgi. With the development of modern microscopes in the 20th century, the discovery was confirmed, early references to the Golgi referred to it by various names including the Golgi–Holmgren apparatus, Golgi–Holmgren ducts, and Golgi–Kopsch apparatus. The term Golgi apparatus was used in 1910 and first appeared in the literature in 1913. Among eukaryotes, the localization of the Golgi apparatus differs. In mammals, a single Golgi apparatus complex is located near the cell nucleus. Tubular connections are responsible for linking the stacks together, localization and tubular connections of the Golgi apparatus are dependent on microtubules. If microtubules are experimentally depolymerized, then the Golgi apparatus loses connections, in yeast, multiple Golgi apparatuses are scattered throughout the cytoplasm. In plants, Golgi stacks are not concentrated at the centrosomal region, organization of the plant Golgi depends on actin cables and not microtubules. The common feature among Golgi is that they are adjacent to endoplasmic reticulum exit sites, in most eukaryotes, the Golgi apparatus is made up of a series of compartments consisting of two main networks, the cis Golgi network and the trans Golgi network. The CGN is a collection of fused, flattened membrane-enclosed disks known as cisternae, a mammalian cell typically contains 40 to 100 stacks. Between four and eight cisternae are usually present in a stack, however and this collection of cisternae is broken down into cis, medial, and trans compartments. The TGN is the final structure, from which proteins are packaged into vesicles destined to lysosomes, secretory vesicles. The TGN is usually positioned adjacent to the stacks of the Golgi apparatus, the TGN may act as an early endosome in yeast and plants. There are structural and organizational differences in the Golgi apparatus among eukaryotes, in some yeasts, Golgi stacking is not observed
10.
Iron
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Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
11.
Prussian blue
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Prussian blue is a dark blue pigment with the idealized chemical formula Fe 718. To better understand the situation in this complex compound the formula can also be written as Fe 43 · xH 2O. Another name for the color is Berlin blue or, in painting, Turnbulls blue is the same substance, but is made from different reagents, and its slightly different color stems from different impurities. Prussian blue was the first modern synthetic pigment and it is employed as a very fine colloidal dispersion, as the compound itself is not soluble in water. It is famously complex, owing to the presence of variable amounts of other ions, the pigment is used in paints, and it is the traditional blue in blueprints. In medicine, Prussian blue is used as an antidote for certain kinds of metal poisoning, e. g. by thallium. In particular it was used to absorb 137Cs+ from those poisoned in the Goiânia accident, the therapy exploits Prussian blues ion exchange properties and high affinity for certain soft metal cations. It is on the World Health Organizations List of Essential Medicines, Prussian blue lent its name to prussic acid, which was derived from it. In Germany, hydrogen cyanide is called Blausäure, and Joseph Louis Gay-Lussac gave cyanide its name, from the Greek word κυανός, because it is easily made, cheap, nontoxic, and intensely colored, Prussian blue has attracted many applications. It was adopted as a pigment very soon after its invention and was almost immediately used in oil, watercolor. The dominant uses are for pigments, about 12,000 tonnes of Prussian blue are produced annually for use in black, a variety of other pigments also contain the material. Engineers blue and the pigment formed on cyanotypes—giving them their common name blueprints, certain crayons were once colored with Prussian blue. It is also a popular pigment in paints, similarly, Prussian blue is the basis for laundry bluing. Prussian blues ability to incorporate monocations makes it useful as a agent for certain heavy metal poisons. Pharmaceutical-grade Prussian blue in particular is used for people who have ingested thallium or radioactive caesium, according to the International Atomic Energy Agency, an adult male can eat at least 10 g of Prussian blue per day without serious harm. The U. S. Prussian blue is a common stain used by pathologists to detect the presence of iron in biopsy specimens. The original stain formula, known historically as Perls Prussian blue after its inventor, German pathologist Max Perls, used separate solutions of potassium ferrocyanide, iron deposits in tissue then form the purple Prussian blue dye in place, and are visualized as blue or purple deposits. The formula is known as Perls Prussian blue and as Perls Prussian blue
12.
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
