microscopes

• Magnification = How many times larger the image is
• Resolution = The ability to see individual objects as separate entities
• light microscope -

  • Light is shone through or on a specimen
  • An objective lens and eyepiece lens combine to give a maximum magnification of x1500
• light microscope - Advantages

  • Can observe living/moving specimens
  • cheap
  • light and portable
• light microscope - disadvantages

  • Limited magnification
  • Limited resolution
  • Using stains can produce artefacts (man made images)
• electron microscope -

  • Electrons are fired at a sample in a vacuum
  • The electrons scatter as they hit the specimen and the pattern detected creates an image
  • Much higher magnification than light microscopes x10 000 000
• electron microscope - advantages

  • powerful magnification
  • fine resolution
  • Can see subcellular structures (inside cells)
• electron microscope - disadvantages

  • cannot view anything living
  • expensive and cumbersome
  • Preparation using heavy metals can produce artefacts
• transmission electron microscope -

  • Electrons are shot through a specimen.
  • 2D internal structure is revealed
  • Resolution = 0.5nm
  • Magnification = 50 000 000x
• scanning electron microscope -

  • Electrons are shot at a specimen.
  • The scattering of electrons is detected giving a 3D image of the surface
  • Resolution = 10nm
  • Magnification = 2 000 000x 
• laser scanning confocal microscopy -

  • Like a light microscope but uses laser beams
  • Very narrow focal range
  • 2D or 3D•Resolution = 300nm
  • Magnification = 3000x
• Real object: the specimen you put under the microscope

  Image: what you see when you look through the microscope; the image of the real object appears magnified

  Magnification: the number of times bigger the image looks compared to the real object

  
• Iodine – turns dark blue/black if starch is present 
• Methylene blue - turns blue with collagen
• Congo red – turns red with cell walls in plants and gram positive bacteria