MICROSCOPES
-
One of
the most widely used tools in Biology
-
An
instrument that produces an enlarged image of an object
-
Magnification – the increase in an object’s apparent size
-
Resolution – the power of a microscope to clearly show
detail
TYPES OF
MICROSCOPES
Compound Light Microscope
- LM
- With this
type of microscope the thin sliced (enough to be transparent) and
sometimes stained specimen is mounted on a glass slide to be viewed
- The slide
is placed on the stage and a light source (a light bulb or mirror
in the base) directs the light upward
- Light
passes through the specimen and through the objective lens, which
is positioned directly above the specimen
- A set of
objective lenses is located on the rotating nosepiece enlarges the image
of the specimen with different powers of magnification
- The most
powerful objective lens produces an image 40 times (40X) the actual size of the specimen
- From the
objective lens, the magnified image is projected up through the body tube to
the ocular lens in the eyepiece where it is magnified further (10X)
- To
compute the total magnification of a microscope, multiply the power of
magnification of the lens being used (40X, 100X) by the power of magnification
of the ocular or eyepiece lens (10X) example: 40 X 10 = 400X total power of
magnification
- The
Resolution power of LM's is limited by the physical characteristics of
light (At powers of magnification beyond about 2000X, the image of the specimen
becomes blurry.)
LIGHT MICROSCOPE
Electron Microscopes
- Used to
view extremely small objects
- Beam of Electrons, rather than light, produces an enlarged image
- Electron
microscopes are more powerful than LM's
- There are
several types of electron microscopes
Transmission
Electron Microscope
- Can
magnify objects up to 200,000 times
- Projects
image onto a screen or photographic plate
- Used to
produce greatly magnified images of internal details of a specimen
- Can not
be used to view living specimens
TEM MICROSCOPE
Scanning
Electron Microscope (SEM)
- Produces
a 3 dimensional image
- Specimens
aren’t sliced but are sprayed with a fine metal coating
- A beam of
electrons is passed over the surface of the metal coating to emit a shower of
electrons
- Showered
electrons are projected onto a fluorescent screen or photographic plate
- SEM's
produce greatly magnified image of surface details of specimens
- Can
magnify up to 100,000 times
-
Can not
be used to view living specimens
SEM MICROSCOPE
