Light and electron microscopes

• object - what’s under microscope

  image - appearance of object when viewed under microscope

  magnification - number of times larger an image is compared to real size of object
• Resolution is the minimum distance between two objects where they appear to be different objects

  With a high resolution you will see more details even at a higher magnification
• Electron microscopes are better than light microscopes because even at higher magnification they have a higher resolution. This means that small objects that are very close together can still be seen as separate objects instead of being merged together
• Light microscope

  • magnifies by using two lenses
  • focuses beams of light
  • for an object to be seen it must interfere with the light wave . wavelength of light determines smallest object which can be resolved
• Limitations of light microscope

  • very high magnification isn’t possible
  • limited resolution
  • separate objects will be seen as one object if close together
• • if an organelle interferes with light wave it is seen
  • limit of resolution is about half of the wavelength
• electron microscope

  • magnifies images by using negatively charged electrons and electromagnets
  • electrons passed through thin specimen then focused by electromagnets onto a fluorescent screen where the image is projected
  • electrons have a short wavelength than light meaning it can resolve smaller objects than light microscope
• Transmission electron microscope

  • beam of electrons passed through specimen
  • see structures inside cell

  Scanning electron microscope

  • electron beam used to scan surface of structure
  • only reflected beam is observed
  • surface
• Limitations of electron microscope

  • can’t use live specimens as slide preparation process would kill them (need a vacuum meaning no O2)
  • expensive
  • not portable