🔬Electron microscopy 🔬

• In electron microscopy, a beam of electrons with a wavelength of less than 1 nm is used to illuminate the specimen

  The smaller wavelength allows for more detail of the cell ultrastructure to be seen

  They can produce images with magnifications up to x500,000 and still have clear resolution
• Disadvantages of electron microscopes:

  • very expensive
  • can only be used inside a carfully controlled environment e.g. vacuum
  • specimens can be damaged by the electron beam
• The two types of electron microscope are the transmission electron microscope (TEM) and the scanning electron microscope (SEM).
• Transmission electron microscope (TEM) - the beam of electrons is transmitted through the specimen and focused to produced image. It is similar to light microscopy. TEM has the best resolution with resolving power of 0.5nm
• Scanning electron microscope (SEM) - a beam of electrons is sent across the surface of the specimen and the reflected electrons are collected. This has a resolving power from 3-10nm so the resolution isn't as good as with TEM. However, it produces 3D images of surfaces are produced giving valuable information about the appearance of different organisms.
• SAMPLE PREP FOR ELECTRON MICROSCOPES

  • inside an electron microscope is a vacuum to ensure electron beams travel in straight lines. This means the samples need to be processed in a special way
  • this involves fixation using chemicals or freezing
  • staining with heavy metals
  • dehydration with solvents
  • samples for a TEM will them be set in resin and may be stained again
  • samples for a SEM may be fractured to expose the inside ans will then need to be coated with heavy metals
• An artefact is a visible structural detail caused by processing the specimen and not a feature of the specimen itself

  Artefacts appear in both light and electron microscopy

  An example of an artefact is an air bubble that gets trapped under the coverslip as you prepare the slide
• Changes in the ultrastructure of cells are inevitable during processing They are seen as the loss of continuity in membranes, distortion of organelles and empty spaces in the cytoplasm of cells