Concept: Biologists use microscopes and the tools of biochemistry to study cells

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Concept Biologists use microscopes and the tools
of biochemistry to study cells

• first compound microscope Zacharias Jansen in
  1590
• three important parameters of microscopy
• Magnification the ratio of an objects image
  size to its real size
• Resolution the measure of the clarity of the
  image, or the minimum distance of two
  distinguishable points
• inversely related to the wavelength of the
  radiation a microscope uses
• Contrast visible differences in parts of the
  sample

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Studying Cells Microscopy

• in a light microscope (LM) - visible light is
  passed through a specimen and then through glass
  lenses
• the lenses refract (bend) the light - so that the
  image is magnified
• in a simple microscope - there is one lens for
  magnification
• e.g. magnifying lens
• in compound microscopes more than one lens
• ocular and objective lenses
• improves resolution and allows for more than one
  magnification
• LMs can magnify effectively to about 1,000 times
  the size of the actual specimen
• this allows for individual cells within a tissue
  to be visualized

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• various techniques enhance contrast of a LM and
  enable cell components to be stained or labeled
• BUT - most subcellular structures, including
  organelles, are too small to be resolved by an LM
• LMs cannot resolve detail finer than 0.2um -
  regardless of magnification

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• to improve resolution and magnification
  allowing for imaging of subcellular structure -
  development of two other microscopes in the 1950s
• called electron microscopes (EMs)- use a focused
  beam of electrons rather than light
• resolution increase due to the shorter
  wavelength of the electron beam
• two types
• 1. Transmission Electron Microscope (TEM)
• 2. Scanning Electron Microscope (SEM)

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Blood cells

• 1. Scanning electron microscopes (SEMs)
  electron beam is focused onto the surface of a
  subject
• providing images that look 3D
• SEM electron beam excites the electrons of the
  gold on the subjects surface
• several kinds of electrons are produced
• these electrons are detected by the scope and
  projected onto a video screen as a magnified
  image that appears 3D
• can be colorized

Pollen grains
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• 2. Transmission electron microscopes (TEMs) focus
  a beam of electrons through a specimen
• subject is sliced into a very thin layer
• so TEMs are used mainly to study the internal
  structure of cells
• subject is stained with heavy metals that adhere
  to the internal structures of the cell
• so some parts of the cell become more electron
  dense than others
• the electron beam passes through those less dense
  and scattered/reflected by the more dense regions
• the electrons that pass through hit a piece of
  film negative or hit a detector for displaying
  the image

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