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Origin of Cells and the Cell Theory

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					Cells and the
Origin of Cell
Theory
History of the Cell Theory
 • Before microscopes, belief in
   supernatural causes of
   diseases
 • Could not see
   microorganisms
 • What branch of biology?
 • Cells = basic units of living
   organisms
Microscopes

 • Originally a hand lens to view
   quality of cloth
 • Anton van Leeuwenhoek
   (mid-1600s) first to examine
   water under microscope
 • Credited with development of
   light microscope
Anton von Leeuwenhoek’s
Microscope
   Improvements
• Compound light
  microscope- series of lens
  to magnify objects (1500x)
• Robert Hooke used one to
  observe cork magnified
  30x
• Observed small geometric
  shapes
• Dubbed these cells
  (resembled monk rooms)
Hooke’s Microscope
     Cell Theory
• 1830’s German scientist
  Matthias Schleiden
  realized that plants made
  up of cells
• Theodore Schwann
  made same
  determination of animals
• = Cell Theory
• Many resources
  (including your book)
  give only credit to
  Scleiden and Schwann
• Original third tenet was
  spontaneous generation
• Rudolph Virchow -
  "Omnis cellula e cellula”
     Cell Theory
• All organisms are
  composed of one or
  more cells
• The cell is the basic unit
  of organization of
  organisms
• All cells come from
  preexisting cells
Recent Developments
 • 1940’s were able to use
   beam of electrons
   instead of light
 • 500 000x
 • Electron microscope
 • Scanning Electron
   Microscope
 • Transmission Electron
   Microscope
   Scanning Electron
      Microscope
• SEM
• Electrons
  are
  reflected off
  the surface
  of the
  specimen
• 3D shape
• http://micro.magnet.fsu.edu/
  primer/virtual/virtual.html
• http://www.mos.org/sln/SEM
  /gallery.html
Transmission Electron
Microscope
 • TEM                • http://nobelpriz
                        e.org/physics/e
 • Allows to see        ducational/micr
   inside of cell       oscopes/tem/
 • Electrons pass
   through
   instead of light
Size Comparison
Prokaryote vs. Eukaryote
  • With the invention of
    microscopes, scientists
    could see two groups of
    cells
  • Prokaryotes

  • Eukaryotes
   Prokaryote
• 1-10 m in diameter
• NO membrane-bound
  organelles
• 1 circular DNA molecule
  located in nucleoid
  region
• Plasma membrane,
  cytoplasm & ribosomes
• Most have a cell wall
  (peptidoglycan)
• May have a
  polysaccharide capsule
   –Ex. bacteria &
    cyanobacteria
Prokaryotic Cell
   Eukaryote
• 10-100 m in diameter
• Nucleus & other membrane-
  bound organelles
• 2 or more linear DNA
  molecules located in
  nucleus
• Plasma membrane,
  cytoplasm & ribosomes
  some have a cell wall
  (cellulose or chitin)
Ex. plants, animals, fungi,
  protista
         Animal Cell




Anima
l Cell
Plant Cell
QUESTIONS?????

				
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posted:3/23/2012
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