Microscopy (2)

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AS Level F211: Biology ( Microscopes) Mind Map on Microscopy (2), created by anndjan21 on 09/19/2014.
anndjan21
Mind Map by anndjan21, updated more than 1 year ago
anndjan21
Created by anndjan21 over 10 years ago
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Resource summary

Microscopy (2)
  1. Use Of Electrons
    1. Light microscopes - low resolution. If magnification is above x1500 - unclear image. Visible light wavelength = 400 - 750nm so strucutres closer than 200nm appear as 1 object.
      1. Achieve higher resolution with electron microscopes.
      2. Electron microscopes (EM) generate electron beam with wavelength of 0.004nm - 100 000x shorter than light wavelength.
        1. EM can distinguish between objects 0.2nm apart. Use electromagnets to focus electron beam onto prepared specimen.
          1. Electrons not visible to human eye - image produced from electron beam projected onto photgraphic paper to make greyscale image = micrograph.
            1. Electron micrographs sometimes in colour. Final image produced from EM always black, white + grey; colours added after using specialised software.
              1. Such images labelled 'false colour' electron micrographs.
            2. Resolution of EM is 500 000x greater than the human eye.
          2. 2 types of EM:
            1. Transmission Electron Microscope (TEM)
              1. 1. Electron beam passes through v. thin prepared sample.
                1. 2. Electrons pass through denser parts of sample less easily - giving more contrast.
                  1. 3. Final image produced is 2D.
                    1. Magnification possible - x500 000.
                    2. Scanning Electron Microscope (SEM)
                      1. 1. Electron beam directed onto sample. Electrons don't pass through specimen.
                        1. 2. They're bounced off the sample.
                          1. 3. Final image produced is 3D view of surface of the sample.
                            1. Magnification possible - x100 000.
                          2. Advantages and DIsadvantages of EM
                            1. Advantages
                              1. Resolution - 0.1nm (2000x more than light microscope) - means EM can be used to prooduce detailed images of organelles inside cells.
                                1. SEM produces 3D images - can reveal detail of contours + cellular/tissue arrangements - not possible with light microscopes.
                                2. Disadvantages
                                  1. Electron beams deflected by molecules in air, so samples have to be placed in vacuum.
                                    1. EM are extremely expensive.
                                      1. Preparing samples + using EM both require high degree of skill + training.
                                    2. Use of EM
                                      1. When EM first developed, many scientists thought complicated preparation of specimens produced artefacts (structures that result from preparation process).
                                        1. Not true representations of specimen's original structure.
                                        2. 1980s, scientists arguing about true value of EM but tech + quality has improved in recent years. Scientists also used X-ray crystallography to investigate cell structure.
                                          1. Confirmed that EM do give true insight into internal workings of cells.
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