Electron Microscopes

• what are 2 types of electron microscopes?

  transmission electron microscopes (TEMs)

  Scanning electron microscopes (SEMs)
• how do TEMs work?

  • Use electromagnets to focus a beam of electrons which is then transmitted through the specimen
  • Denser parts of the specimen absorb more electrons which makes them look darker on the image you end up with
• pro of TEMs?

  they give high resolution images so you see the internal structure of organelles like chloroplasts
• con of TEMs?

  can only be used on thin specimens
• how do SEMs work?

  • They scan a beam of electrons across the specimen.
  • This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image
• What is the image produced from SEMs like?

  the images produced show the surface of the specimen and they can be 3D
• pro of SEMS?

  they can be used on thick specimens
• con of SEMs?

  they give lower resolution images than TEMs
• what does SEMs stand for?

  scanning electron microscopes
• what does TEMs stand for?

  Transmission electron microscopes
• transmission electron microscope image:

  
• Scanning electron microscope image:

  
• why do electrons give higher resolution?

  electrons have short wavelength
• give 3 limitations of using transmission electron microscope?

  1. artefacts present
  2. can't look at living material
  3. specimen has to be very thin