Microscopy F211

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  • Microscopy
    • Magnification - the degree to which the size of an image is larger than the object itself.
      • I = A/M
      • total magnification of a specimen is given by timesing the objective by the eyepiece magnification
    • Resolution -  the degree to which it is possible to distinguish between two objects that are very close together.
      • Limits - human eye 100, light microscope 200nm, electron microscope 0.2nm
    • Micrometre = µm = 0.000001m
    • nanometre = nm = 0.000000001
    • Light Microscopes
      • use a number of lenses to produce an image
        • can be viewed directly by eye
      • light passes from a bulb under the stage, through a condenser lens, through the specimen. Focused through objective lens, then through eyepiece lens
      • Have a number of different lenses to be rotated into position
        • 4 objective lenses - x4 x10 x40 x100 (x100 oil immersion lens)
      • Specimens produced by staining (chemicals that bind to chemicals on/in the specimin
        • Or by Sectioning (specimens put in was, thin sections cut, wax melted)
      • can be used to measure organelles (use graticule)
        • Value of intervals on graticule: x40 - 25µm, x100 - 10µm, x400 - 2.5µm, x1000 - 1.0µm
    • Electron Microscopes
      • Scanning Electron
        • 3D image produced
        • electron beam directed onto sample, electrons don't pass through, they bounce off
        • maximum magnification x   100,000
      • Transmission Electron
        • electron beam passes through thin sample
        • electrons pass through denser parts of the sample less easily, creating contrast
        • 2D image produced
        • maximum magnification x 500,000
      • Advantages -  resolution 0.1nm, more detailed images gained of organelles, SEM produces 3D images revealing contours and tissue arrangements.
      • Disadvantages- electron beams deflected by air molecules so must be in a vacuum, expensive, preparing samples requires a high level of training and skilll
      • electron micrographs can be put into colour
      • preparing a sample: fix specimen in glutaraldehyde to firm tissue, dehydrate it, replace water with ethanoll, embed in solid resin, cut thin (diamond knife) stain (lead salts), mount (copper grid)



This is a well organised Mind map on microscopy that summarises the key features of the different types of microscopes.There is good use of colour to separate the key themes. Research shows that images added to a Mind Map make it more memorable so perhaps adding some after download would be a useful exercise.

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