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For Little People

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