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In this microscope the image from the objective lens is magnified again by the ocular lens.
Total magnification =objective lens x ocular lens
the ability of the lenses to distinguish two points.
Limit of Resolution for the light microscope is 0.2 mm.
A microscope with a resolving power of 0.2 mm can distinguish between two points ≥ 0.2 mm.
Dark objects are visible against a bright background.
Light reflected off the specimen does not enter the objective lens.
Light objects are visible against a dark background.
Light reflected off the specimen enters the objective lens
differential interference contrast microscopy
Accentuates diffraction of the light that passes through a specimen; uses two beams of light.
Uses UV light. Fluorescent substances absorb UV light and emit visible light. Cells may be stained with fluorescent dyes (fluorochromes).
Uses fluorochromes and a laser light. The laser illuminates each plane in a specimen to produce a 3-D image.
Uses electrons instead of light. The shorter wavelength of electrons gives greater resolution.
Transmission Electron Microscopy (TEM)
Ultrathin sections of specimens. Light passes through specimen, then an electromagnetic lens, to a screen or film.
Specimens may be stained with heavy metal salts. 10,000-100,000x; resolution 2.5 nm
scanning electron microscopy (SEM)
An electron gun produces a beam of electrons that scans the surface of a whole specimen. Secondary electrons emitted from the specimen produce the image.1000-10,000x; resolution 20 nm
consist of salts with a positive and negative ion.
Bacteria have slight negative charge at pH=7. Therefore, Basic dyes commonly used to stain bacteria.
Some basic dyes: Crystal Violet, Methylene blue, Malachite Green, Safranin.
In a ---, the chromophore is a cation. Bacteria have slight negative charge at pH=7. Therefore, this type of dye is commonly used to stain bacteria. ex: Crystal Violet, Methylene blue, Malachite Green, Safranin.
React differently with different species of bacteria, therefore can be used for identification. (ex. Gram stain, Acid-Fast stain)
binds strongly to bacteria with waxy lipids in cell wall.
Mycobacterium tuberculosis and Mycobacterium leprae are two important pathogens identified.
Primary stain - Carbolfuchsin (Red)
Acid-fast microbes retain red primary stain.
Counterstain - Methylene Blue
Non Acid-Fast cells are blue
are used to color and isolate specific parts of microbes.
1. Capsule - Gelatinous covering of microbe.
2. Endospore - A special dormant structure that survives adverse environmental conditions.
Primary stain - malachite green.
Counterstain - safranin.
Endospores appear green within red/pink cells.
3. Flagella - Structure of locomotion.
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