01 Cell Theory And Microcope
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01 Cell Theory And Microcope






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01 Cell Theory And Microcope 01 Cell Theory And Microcope Presentation Transcript

  • Early days
    • 1665 - Robert Hooke discovered and described the fundamental unit of all living things (cells) by examining thin slices of cork
    • 1674 - The first man to witness a live cell under a microscope was Anton Van Leeuwenhoek, describing the algae Spirogyra and named the moving organisms animalcules, meaning "little animals"
    View slide
    • 1838 – Matthias Schleiden suggested that all plants are made of cells
    • 1839 – Theodor Schwann suggested the same for animals
    • General cell theory emerged:
    • “ the basic unit structure and function of all living organisms is the cell”
    UNSWFYBIO/2008JK View slide
    • 1855 – Rudolph Virchow’s theory: “all cells arise from pre-existing cells by cell division”
  • Cell Theory
    • All living things are composed of cells.
    • Cells are the basic unit of structure and function in living things.
    • All cells are produced from other cells.
  • The Microscope in Cell Studies
    • 2 different types of microscopes:
    • i) light microscope – uses light as a source of radiation
    • ii) electron microscope – uses electrons
  • Electron microscope UNSWFYBIO/2008JK
    • Electrons – negatively charged particles which orbit the nucleus of an atom
    • When electrons gain high energy, they escape from their orbits. Free electrons behave like electromagnetic radiation
    • Short wavelength (greater energy, shorter wavelength)
    • Advantage of using electrons for microscopy:
      • Wavelength extremely short
      • Negatively charged (can be focused easily using electromagnets)
    • Electromagnetic spectrum – whole range of wavelengths
    • The longer the electromagnetic waves, the lower their frequency
    • The greater the energy, the shorter the wavelength
    • The limit of resolution is about ½ the wavelength of the radiation used to view the specimen (if an object is any smaller than half the wavelength of the radiation used to view it, it cannot be seen separately from nearby objects)
    • Best resolution using microscope that uses visible light is 200 nm, since shortest wavelength of visible light is 400 nm (violet light). Smaller objects can never be seen using light (ribosomes – 22 nm)
    • If an object is transparent it will allow light waves to pass through it and will still not be visible
    The electromagnetic spectrum UNSWFYBIO/2008JK
    • Beam of electrons passed through the specimen before being viewed
    • Only electrons that are transmitted (pass through the specimen) are seen
    • Allows to see thin sections of specimens (inside the cell)
    Transmission Electron Microscope UNSWFYBIO/2008JK
  • Bacterium (TEM) (Image provided by: ceiba.cc.ntu.edu.tw)
    • Electron beam is used to scan the surfaces of structures and only the reflected beam is observed
    • Surface structures can be seen
    • Great depth of field is obtained so that much of the specimen is in focus at the same time
    • Cannot achieve same resolution as a transmission electron microscope
    Scanning Electron Microscope UNSWFYBIO/2008JK
  • SEM image of a red blood cell
  • Electron microscope image of a fly foot
  • Scanning Electron Microscope (SEM) photograph of tobacco seed
  • Viewing sample with the electron microcope
    • Electron beam projected onto a fluorescent screen (areas hit by electrons shine brightly giving overall a ‘black and white’ picture)
    • Stains used to improve contrast contain heavy metal atoms which stop the passage of electrons
    • Electron beam must be in vacuum to avoid collision with air molecules
    • Specimen must be dehydrated because water boils at room temperature in vacuum (only dead material can be examined)
    • Great efforts to preserve material in life-like state when preparing specimen
  • Light microscope UNSWFYBIO/2008JK
  • Cheek cells 100X Cheek cells 400X
  • Unit of Measurements in Cell Studies
    • metre m = 1 m
    • millimetre mm = 10 -3 m
    • micrometre µm = 10 -6 m
    • nanometre nm = 10 -9 m
    • picometre pm = 10 -12 m
    • angstrom A = 10 -10 m (obsolete)
  • Magnification and Resolution
    • Magnification
    • - the number of times larger an image is compared with the real size of the object
    • - magnification = size of image
    • actual size of specimen
    • Resolution
    • - the ability to distinguish between two separate points
    • Graticule
    • Stage micrometer
  • Comparison of advantages and disadvantages of the light and electron microscope UNSWFYBIO/2008JK It is possible to investigate a greater depth of field The depth of field is restricted Has a resolving power for biological specimens of around 1 nm Can resolve objects up to 200 nm apart Magnifies objects over 500 000X Magnifies objects up to 1500X Advantages Disadvantages All images are in black and white Natural colour of material can be observed A high vacuum is required and living material cannot be observed Living as well as dead material may be viewed Preparation of material may distort it Material rarely distorted by preparation Preparation of material is lengthy and requires considerable expertise and sometimes complex equipment Preparation of material is relatively quick and simple, requiring only a little expertise Affected by magnetic fields Unaffected by magnetic fields Very large and must be operated in special rooms Small and portable Expensive to operate – requires up to 100 000 volts to produce the electric beam Cheap to operate – uses a little electricity where there is a built-in light source Expensive to purchase Cheap to purchase Disadvantages Advantages ELECTRON MICROSCOPE LIGHT MICROSCOPE