{"id":11208,"date":"2022-06-30T07:49:55","date_gmt":"2022-06-30T07:49:55","guid":{"rendered":"https:\/\/www.uptymes.com\/edu\/microscope-light-microscope-compound-microscope\/"},"modified":"2022-06-30T07:49:55","modified_gmt":"2022-06-30T07:49:55","slug":"microscope-light-microscope-compound-microscope","status":"publish","type":"post","link":"https:\/\/www.uptymes.com\/edu\/microscope-light-microscope-compound-microscope\/","title":{"rendered":"microscope, light microscope, compound microscope"},"content":{"rendered":"


\n<\/p>\n

\n\n\n

Preparation of samples<\/h2>\n
    \n
  • Fixation: Chemicals preserve material in a life like condition. Does not distort the specimen. <\/span><\/li>\n
  • Dehydration: Water removed from the specimen using ethanol. Particularly important for electron microscopy because water molecules deflect the electron beam which blurs the image. <\/span><\/li>\n
  • Embedding: Supports the tissue in wax or resin so that it can be cut into thin sections. <\/span>
    Sectioning Produces very thin slices for mounting. Sections are cut with a microtome or an ulramicrotome to make<\/span><\/span> them either a few micrometres (light microscopy) or nanometres
    (electron microscopy) thick. <\/span><\/li>\n
  • Staining: Most biological material is transparent and needs staining to increase the contrast between different structures. Different stains are used for different types of tissues.<\/span> Methylene blue is often used for animal cells, while iodine in KI solution is used for plant tissues.<\/span><\/li>\n
  • Mounting: Mounting on a slide protects the material so that it is suitable for viewing over a long period. <\/span><\/li>\n<\/ul>\n

    \"\"<\/p>\n

    Magnification and Resolution<\/h2>\n

    Magnification <\/span><\/b> is how much bigger a sample appears to be under the microscope than it is in real life. <\/span><\/p>\n

    Overall magnification = Objective lens x Eyepiece lens <\/span><\/p>\n

    Resolution <\/span><\/b> is the ability to distinguish between two points on an image. <\/span><\/p>\n

      \n
    • The resolution of an image is limited by the wavelength of radiation used to view the sample. <\/span><\/li>\n
    • This is because when objects in the specimen are much smaller than the wavelength of the radiation being used, they do not interrupt the waves, and so are not detected. <\/span><\/li>\n
    • The wavelength of light (min. \u2013 violet is 400nm) is much larger than the wavelength of electrons, so the resolution of the light microscope is a lot lower. <\/span><\/li>\n
    • The actual resolution is often half the size of the wavelength of radiation used. Thus, for the light microscope the maximum resolution is about 200nm. <\/span><\/li>\n
    • In other words, if two objects in the specimen are closer than 200nm in real life, then they will only show up as one object on the image. <\/span><\/li>\n
    • Using a microscope with a more powerful magnification will not<\/b> increase this resolution any further. It will increase the size of the image, but objects closer than 200nm will still only be seen as one point. <\/span><\/li>\n<\/ul>\n

      Transmission and Scanning Electron Microscopes<\/h2>\n

      \u00a0<\/p>\n

        \n
      • Transmission electron microscopes <\/span><\/b> pass a beam of electrons through the specimen. The electrons that pass through the specimen are detected on a fluorescent screen on which the image is displayed. <\/span><\/li>\n
      • Thin sections of specimen are needed for transmission electron microscopy as the electrons have to pass through the specimen for the image to be produced. <\/span><\/li>\n<\/ul>\n

        \u00a0<\/p>\n

        \u00a0<\/p>\n

          \n
        • Scanning electron microscopes <\/span><\/b> pass a beam of electrons over the surface of the specimen in the form of a \u2018scanning\u2019 beam. <\/span><\/li>\n
        • Electrons are reflected off the surface of the specimen as it has been previously coated in heavy metals. <\/span><\/li>\n
        • It is these reflected electron beams that are focussed of the fluorescent screen in order to make up the image. <\/span><\/li>\n
        • Larger, thicker structures can thus be seen under the scanning electron microscope as the electrons do not have to pass through the sample in order to form the image. <\/span><\/li>\n
        • However the resolution of the scanning electron microscope is lower than that of the transmission electron microscope. <\/span><\/li>\n<\/ul>\n

          Comparison of the light and electron microscope<\/h2>\n
          \n

          \u00a0<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
          \n

          Light microscope<\/b><\/span><\/p>\n<\/td>\n

          		\n

          Electron microscope<\/b><\/span><\/p>\n<\/td>\n<\/tr>\n

          Cheap to purchase (\u00a3100 \u2013 500) <\/span><\/td>\nExpensive to buy (over \u00a3 1 000 000).<\/span><\/td>\n<\/tr>\n
          Cheap to operate. <\/span><\/td>\nExpensive to produce electron beam.<\/span><\/td>\n<\/tr>\n
          Small and portable. <\/span><\/td>\nLarge and requires special rooms.<\/span><\/td>\n<\/tr>\n
          Simple and easy sample preparation. <\/span><\/td>\nLengthy and complex sample prep.<\/span><\/td>\n<\/tr>\n
          Material rarely distorted by preparation. <\/span><\/td>\nPreparation distorts material.<\/span><\/td>\n<\/tr>\n
          Vacuum is not required. <\/span><\/td>\nVacuum is required.<\/span><\/td>\n<\/tr>\n
          Natural colour of sample maintained. <\/span><\/td>\nAll images in black and white.<\/span><\/td>\n<\/tr>\n
          Magnifies objects only up to 2000 times <\/span><\/td>\nMagnifies over 500 000 times.<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

          \u00a0<\/p>\n<\/div>\n\n

          Basic Principles of Light and Electron Microscopy<\/h2>\n

          Light Microscopy<\/u> <\/span><\/p>\n

            \n
          • Light is produced from either an internal or external light source and passes through the iris diaphragm, a hole of variable size which controls the amount of light reaching the specimen. <\/span><\/li>\n
          • The light then passes through the condenser which focuses the light onto the specimen. <\/span><\/li>\n
          • The slide is held on the stage at 90 degrees to the path of light which next travels through the specimen. <\/span><\/li>\n
          • The objective lens magnifies the image of the specimen before the light travels through the barrel of the microscope. <\/span><\/li>\n
          • The light finally passes through the eyepiece lens and into the viewer\u2019s eye which sends impulses to the brain which in turn interprets the image. <\/span><\/li>\n<\/ul>\n

            Electron Microscopy<\/u> <\/span><\/p>\n

              \n
            • A negatively charged platinum metal electrode (the cathode) emits a beam of high velocity negatively charged electrons. <\/span><\/li>\n
            • The electromagnets on the side of the barrel focus the beam of electrons on the specimen in the same way that the glass lenses on a light microscope focus the beams of light. <\/span><\/li>\n
            • The specimen is introduced via an air lock so as to maintain the internal vacuum conditions. <\/span><\/li>\n
            • The transmitted or reflected beam of electrons, depending on type of microscope are focused by the electromagnets onto a fluorescent screen to produce the image which is then viewed by the operator. <\/span><\/li>\n<\/ul>\n

              \u00a0<\/span><\/p>\n<\/td>\n<\/div>\n\n","protected":false},"excerpt":{"rendered":"

              Preparation of samples Fixation: Chemicals preserve material in a life like condition. Does not distort the specimen. Dehydration: Water removed from the specimen using ethanol. Particularly important for electron microscopy because water…<\/p>\n","protected":false},"author":1,"featured_media":16163,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-11208","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-all-posts"],"_links":{"self":[{"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/posts\/11208","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/comments?post=11208"}],"version-history":[{"count":0,"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/posts\/11208\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/media\/16163"}],"wp:attachment":[{"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/media?parent=11208"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/categories?post=11208"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.uptymes.com\/edu\/wp-json\/wp\/v2\/tags?post=11208"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}