light microscopy practical

  • Created by: tia5sos
  • Created on: 17-11-20 19:21
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  • light microscopy (practical)
    • parts of a microscope
      • eyepiece lens - looked through to see the image and also magnifies the image
      • objective lens - magnifies the image, usually there are three different objective lenses (e.g. x4, x10 and x40).
      • stage - holds the slide in place
      • clip - hold the slide in place
      • handle - to carry the microscope with
      • lamp - shines light through the slide so the image can be seen more easily
      • focusing knobs - move the stage up and down to bring the image into focus
    • preparing the specimens before an investigation
      • 1. your specimens ( the sample you are looking at ) needs to let light through it for you to be able to see it clearly - if you've got quite a thick specimen, you'll need to take a thin slice of it to start with.
      • 2. next, take a clean slide (glass or plastic) and use a pipette to put one drop of water or mountant (a clear, gloopy liquid) in the middle of it - this will secure the specimen in place.
      • 3. use tweezers to place your specimen on the slide.
      • 4. add a drop of stain if needed - if your specimen is completely transparent or colourless, a drop of stain is added to make the specimen more visible.
        • different stains are used to highlight different structures or tissues. For example, eosin is used to stain cytoplasm and methylene blue stains DNA.
      • 5. place a cover slip ( a square of thin, transparent plastic or glass) at one end of the specimen, holding it at an angle with a mounted needle.
      • 6. carefully lower the cover slip onto the slide. Press it down gently with the needle so that no air bubbles are trapped under it.
    • viewing
      • 1. start by clipping the slide containing your specimens onto the stage
        • 2. select the lowest - powered objective lens (e.g. the one that produces the lowest magnification)
          • 3. use the coarse adjustment knob to move the stage up to just below the objective lens.
            • then looking down the eyepiece, move the stage downwards (so you don't crash the slide into the lens) until the specimen is just about in focus.
              • 4. then, still looking down the eyepiece, adjust the focus with the fine adjustment knob, until you get a clear image of your specimen.
                • 5. if you need to see your specimen with greater magnification, swap to a higher - powered objective lens and refocus.


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