Methods of studying cells

• What are the two main types of microscopes used for studying cells?


  Light microscopes and electron microscopes
• What is the resolution limit of light microscopes?


  0.2 µm
• Why is the resolution of light microscopes limited to 0.2 µm?


  Because it is the wavelength of light
• What is the resolution limit of electron microscopes?


  0.1 nm
• How is magnification calculated in microscopy?


  Magnification = size of image / size of real object
• What does resolution refer to in microscopy?


  It is the minimum distance apart that two objects can be distinguished as separate
• What is the function of a transmission electron microscope (TEM)?


  A beam of electrons passes through a thin section of a specimen
• How does a scanning electron microscope (SEM) work?


  A beam of electrons passes across the surface and scatters to build a 3D image
• What are the limitations of using electron microscopes?


  • Must be in a vacuum, so living specimens cannot be observed
  • Requires complex staining, which may introduce artefacts
  • Specimens must be very thin, especially for TEM
  • SEM has lower resolving power than TEM
• What is cell fractionation?

  It is the process of separating different parts and organelles of a cell
• What is the most common method of cell fractionation?

  Differential centrifugation
• What is homogenization in cell fractionation?


  Blending cells to form a fluid called homogenate
• What happens to the heaviest organelles during centrifugation?


  They are forced to the bottom of the tube forming a pellet
• Why is the homogenate placed in a cold, buffered solution?


  To prevent organelles from bursting and to maintain pH