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سؤالين عن تاريخ علم الأحياء الدقيقة وعن الـ PH

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  • سؤالين عن تاريخ علم الأحياء الدقيقة وعن الـ PH

    السلام عليكم ...

    أخواني

    ياريت لو تجاوبولي على هالأسئلة ..

    الأول / تاريخ علم الأحياء الدقيقة ..

    الثاني / كيف يستطيع المحلول المنظم أن ينظم أو يحافظ على درجة الـ PH


    ياريت لو تجاوبوا عليها اليوم
    أخوكم أحمد

  • #2
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    History

    The existence of microorganisms was hypothesized during the late Middle Ages but they were not observed or proven until the invention of the microscope in the 17th century. In The Canon of Medicine (1020), Abū Alī ibn Sīnā (Avicenna) stated that bodily secretion is contaminated by foul foreign earthly bodies before being infected, but he did not view them as primary causes of disease. When the Black Death bubonic plague reached al-Andalus in the 14th century, Ibn Khatima and Ibn al-Khatib hypothesized that infectious diseases are caused by microorganisms which enter the human body.[3]

    Bacteria were first observed by Anton van Leeuwenhoek in 1676 using a single-lens microscope of his own design.[1] The name "bacterium" was introduced much later, by Ehrenberg in 1828, derived from the Greek βακτηριον meaning "small stick". While van Leeuwenhoek is often cited as the first microbiologist, the first recorded microbiological observation, that of the fruiting bodies of molds, was made earlier in 1665 by Robert Hooke.[4]

    The field of bacteriology (later a subdiscipline of microbiology) is generally considered to have been founded by Ferdinand Cohn (1828–1898), a botanist whose studies on algae and photosynthetic bacteria led him to describe several bacteria including Bacillus and Beggiatoa. Cohn was also the first to formulate a scheme for the taxonomic classification of bacteria.[5] Pasteur (1822–1895) and Robert Koch (1843–1910) were contemporaries of Cohn’s and are often considered to be the founders of medical microbiology.[6] Pasteur is most famous for his series of experiments designed to disprove the then widely held theory of spontaneous generation, thereby solidifying microbiology’s identity as a biological science.[7] Pasteur also designed methods for food preservation (pasteurization) and vaccines against several diseases such as anthrax, fowl cholera and rabies.[1] Koch is best known for his contributions to the germ theory of disease, proving that specific diseases were caused by specific pathogenic microorganisms. He developed a series of criteria that have become known as the Koch's postulates. Koch was one of the first scientists to focus on the isolation of bacteria in pure culture resulting in his description of several novel bacteria including Mycobacterium tuberculosis, the causative agent of tuberculosis.[1]

    While Pasteur and Koch are often considered the founders of microbiology, their work did not accurately reflect the true diversity of the microbial world because of their exclusive focus on microorganisms having direct medical relevance. It was not until the work of Martinus Beijerinck (1851–1931) and Sergei Winogradsky (1856–1953), the founders of general microbiology (an older term encompassing aspects of microbial physiology, diversity and ecology), that the true breadth of microbiology was revealed.[1] Beijerinck made two major contributions to microbiology: the discovery of viruses and the development of enrichment culture techniques.[8] While his work on the Tobacco Mosaic Virus established the basic principles of virology, it was his development of enrichment culturing that had the most immediate impact on microbiology by allowing for the cultivation of a wide range of microbes with wildly different physiologies. Winogradsky was the first to develop the concept of chemolithotrophy and to thereby reveal the essential role played by microorganisms in geochemical processes.[9] He was responsible for the first isolation and description of both nitrifying and nitrogen-fixing bacteria.[1

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    • #3
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      Buffer solutions are solutions which resist change in hydronium ion and the hydroxide ion concentration (and consequent pH) upon addition of small amounts of acid or base, or upon dilution. Buffer solutions consist of a weak acid and its conjugate base (more common) or a weak base and its conjugate acid (less common). The resistive action is the result of the equilibrium between the weak acid (HA) and its conjugate base (A−):

      HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq)

      Any alkali added to the solution is consumed by hydronium ions. These ions are mostly regenerated as the equilibrium moves to the right and some of the acid dissociates into hydronium ions and the conjugate base. If a strong acid is added, the conjugate base is protonated, and the pH is almost entirely restored. This is an example of Le Chatelier's principle and the common ion effect. This contrasts with solutions of strong acids or strong bases, where any additional strong acid or base can greatly change the pH.

      When writing about buffer systems they can be represented as salt of conjugate base/acid, or base/salt of conjugate acid. It should be noted that here buffer solutions are presented in terms of the Brønsted-Lowry notion of acids and bases, as opposed to the Lewis acid-base theory (see acid-base reaction theories). Omitted here are buffer solutions prepared with solvents other than water.

      Applications

      Their resistance to changes in pH makes buffer solutions very useful for chemical manufacturing and essential for many biochemical processes. The ideal buffer for a particular pH has a pKa equal to the pH desired, since a solution of this buffer would contain equal amounts of acid and base and be in the middle of the range of buffering capacity.

      Buffer solutions are necessary to keep the right pH for enzymes in many organisms to work. Many enzymes work only under very precise conditions; if the pH strays too far out of the margin, the enzymes slow or stop working and can denature, thus permanently disabling its catalytic activity. A buffer of carbonic acid (H2CO3) and bicarbonate (HCO3−) is present in blood plasma, to maintain a pH between 7.35 and 7.45.

      Industrially, buffer solutions are used in fermentation processes and in setting the correct conditions for dyes used in colouring fabrics. They are also used in chemical analysis and calibration of pH meters

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