Microscopes: TEM

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Microscopes: TEM
2013-09-02 09:40:14
Cell Bio

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  1. Two types
    • a.      TEM: form images using electrons that are trasmittted through a specimen
    • b.      SEM: utilize electrons that have bounced off the surface of the specimen
  2. I.                   TEM
    a.      greater __than LM
    b.      great resolving power of EM is due to __
    • resolution 
    • wave properties of electrons
  3. limit of resolution of a microscope is what?
    directly proportional to the wavelength of the illuminating light: the longer the wavelength, the worse the resolution
  4. Wavelength of an electron varies with __, which in turn depends on the __ applied in the microscope.
    • with speed at which its traveling
    • accelerating voltage 
  5. wavelength equation
    • λ = √(150/V)
    • where λ is the wavelength in angstroms and V is the accelerating voltage in volts
  6. a.      standard TEMs have voltage from __. Their resolution is __due to serious __, which requires that the numerical aperture of the lens be made very small
                                                                  i.      practical limit of resolution is__; the actual limit is __
    • 10,000 to 100,000 V.
    • two orders less than its theoretical limit 
    • spherical aberration of electron-focusing lenses
    •  3-5 angstroms
    • 10-15
  7. Structure

     a.     __ through which the __ passes and a __containing a __ that electronically controls the operation in the column
    • tall, hollow, cylindrical column
    • electron beam
    • console 
    • panel of dials
  8.                                                               i.      top of the column contains __(a tungsten wire filament that is heated to provide a source of electrons)
    1.      electrons are __ and __ by the __ applied between the __
    • cathode 
    • drawn from the hot filament
    • accelerated as a fine beam
    • high voltage
    • cathode and anode
  9. 1.      __is pumped out of the column prior to operation, producing a __
    through which the electrons travel

    a.      if air not removed, electrons would be __
    • air 
    • vacuum 
    • prematurely scattered by collision with gas molecules
  10. a.      a beam of __ can be focused by __, which are located in the wall of the column
                                                                  i.      strength of magnets controlled by __provided them
    b.      __ placed between the __ and the specimen and the electron beam is focused on the specimen
    • negatively charged electrons
    • electromagnetic lenses
    • current 
    • condenser lenses
    • electron source
  11. a.      thin, metal grid to support specimen
    b.      One __ that provides entire range of __ delivered by the instrument
                                                                  i.      image from __ is object for additional lens system; image provided only magnified about __times
                                                                ii.      by altering __, magnifications can vary from 1000 to 250,000 times
    • objective lens
    • magnification
    • objective lens
    • 100 
    • current
  12.                                                               i.      electrons that have passed through the specimen are brought to focus on a __ situated at the bottom of the column
    1.      electrons striking the screen excite a coating of __--> the image
    • phosphorescent screen
    • fluorescent crystalsà
  13. a.      Image formation depends on __by parts of the specimen
                                                                  i.      __ by a part of the specimen is proportional to the __ of the atoms that make up the specimen
    • differential scattering of electrons 
    • scattering of electrons
    • size of the nuclei
  14. 1.      because the insoluble material of cells contains atoms with low atomic numbers, biological material cannot really __
    a.      therefore, to scatter and get better contrast, tissues are __, where they go into organelles
    • scatter electrons
    • fixed and stained with heavy metals
  15.                                                                                                                                       i.      the cell parts that bind the most metal atoms allow passage of the __
    1.      fewer electrons that are focused= __

    a.      photographs are taken by __ to produce an image
    • least number of electrons
    • the darker the spot 
    • putting photographic plate beneath screenà