microscopes

• Light microscopes


  Pass light waves through thin samples and then use glass lenses to magnify them
• Light microscopes


  • Allowed us to see inside cells which we couldn't see with the naked eye
  • The best light microscopes now allow us to magnify by 1500 times
• Magnification


  Not the only factor that's important when viewing cells
• Resolution


  The ability to determine between two points separately, rather than merged into one
• The resolution of a light microscope is around 0.2 μm, or 200 nm
• Light microscopes cannot distinguish two points closer than 200 nm, so certain objects, like ribosomes, cannot be seen
• Electron microscopes


  Use a beam of electrons instead of light rays which are focussed using electromagnets in a vacuum
• Types of electron microscope

  • Scanning electron microscope (SEM)
  • Transmission electron microscope (TEM)
• Scanning electron microscope (SEM)

  • Has a large field of view so can be used to examine the surface structure of specimens
• Transmission electron microscope (TEM)

  • Used to examine thin slices or sections of cells or tissues
• TEMs have a maximum magnification of around ×1 000 000
• The limit of resolution of the transmission electron microscope is now less than 1 nm
• The TEM has revealed structures in cells that are not visible with the light microscope