Electron microscope

• Why is the resolution of a light microscope limited?

  Because the long wavelength of light limits the resolution
• What is the main advantage of electron microscopes over light microscopes?

  They use a beam of electrons, which has a shorter wavelength
• What can electron microscopes be used to observe?

  Much smaller structures and details inside cells
• What are the two types of electron microscopes?

  • Transmission Electron Microscope (TEM)
  • Scanning Electron Microscope (SEM)

  
• How does a Transmission Electron Microscope (TEM) work?

  A beam of electrons is fired at the specimen and focused by electromagnets

  
• What happens to denser parts of the specimen in a TEM?

  They absorb electrons and prevent them from passing through

  
• What type of image does a TEM produce?

  A 2D black and white image
• What is the maximum magnification of a TEM?

  Greater than 1,000,000X
• What is the maximum resolution of a TEM?

  0.5 nm
• Why must specimens be sliced very thinly for a TEM?

  To allow electrons to pass through

  
• Why is a vacuum required inside a TEM?

  To prevent air molecules from deflecting the electron beam
• Why is a copper grid used instead of a glass slide in a TEM?

  A glass slide would stop the flow of electrons
• What is a limitation of preparing specimens for a TEM?

  The preparation is complicated and time-consuming
• How does a Scanning Electron Microscope (SEM) work?

  It scans a beam of electrons across the surface and collects reflected electrons

  
• What is the maximum magnification of a SEM?

  500,000X
• What is the maximum resolution of a SEM?

  1. 10 nm
• What is an advantage of SEM compared to TEM?

  Specimens do not need to be cut as thin

  
• What is a disadvantage of SEM compared to TEM?

  SEM images have lower magnification and resolution

  
• What is the purpose of staining in electron microscopy?

  To provide contrast between structures
• What type of solutions are used for staining in electron microscopy?

  Solutions of heavy metal salts
• What is the result of using heavy metal salts in staining?

  They scatter electrons, giving contrast
• What type of images are produced in electron microscopy?

  Always black and white images
• What are the main differences between light and electron microscopes?

  • Light microscopes are inexpensive, portable, and can view living samples.
  • Electron microscopes are expensive, large, and can only view dead samples.
  • Light microscopes have a maximum magnification of X2000 and resolution of 200 nm.
  • Electron microscopes have a maximum magnification of X1,000,000 (TEM) and X500,000 (SEM) with resolutions of 0.5 nm (TEM) and 3-10 nm (SEM).
• What are artefacts in microscopy?

  Visible structures on the image that are not part of the specimen
• Why are artefacts more likely with electron microscopes?

  Because the sample preparation is more complicated
• What must scientists learn to do regarding artefacts in microscopy?

  Determine between real structures and artefacts in an image
• What is an example of an artefact in microscopy?

  An air bubble in a light microscope slide