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
• Allows to see inside of cell
• Electrons pass through instead of light
• http://nobelprize.org/physics/educational/microscopes/tem/
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
Animal Cell
Plant Cell
QUESTIONS?????