3 - Microscopy Flashcards
The ability of the lenses to distinguish fine detail and structures is called
a. illumination
b. magnification
c. refractive index
d. resolution
d. resolution
Which microscope would you choose to view the cellular contents of a microbe in its natural state?
a. compound light microscope
b. phase-contrast microscope
c. darkfield microscope
d. electron microscope
b. phase-contrast microscope
Which microscope uses an ultraviolet light source?
fluorescence microscope
How does a compound light work?
uses lenses and visible light to magnify
What is another name for the compound light microscope?
Brightfield microscopy
What is the total magnification of a compound light microscope?
2000x max magnification
How is magnification calculated on compound light microscope?
objective lens x magnification of ocular lens
What is resolution?
ability to distinguish between two points
What is the path of light of a light microscope?
- illuminator
- condenser lenses
- specimen
- objective lenses
- body tube (prism)
- ocular lens
- line of vision
Ocular lens
eyepiece: remagnifies the image formed by the objective lens
Body tube
transmits the image from the objective lens to the ocular lens
Objective lens
primary lenses that magnify the specimen
Stage
holds the microscope slide in position
Condenser
focuses light through the specimen
Iris diaphragm
controls the amount of light entering the condenser (like a door)
Illuminator
the light source
Darkfield microscope
visualizes microbes that are invisible in normal light or can’t be stained/ it blocks light so that the specimen is light and the background is dark
Phase-contrast microscope
details of internal structures in microbes; light wave phases:peaks and valley - inside cell clearer
Fluorescence microscope
uses UV light, specimen may naturally fluoresce or is stained with fluorescent dyes
Confocal microscope
constructs 3D images using a computer - it takes scan slices of an image that a computer puts together
What is electron microscopy?
objects smaller than 0.2um - uses beams of electrons instead of light and electromagnets instead of glass lenses
Transmission electron microscope
- beams pass through specimen
- 10,000-100,000x mag.
- INTERNAL structure
- distortion
Scanning electron microscope
- gives 3D views
- 1,000-10,000x mag.
- bema is directed to SURFACE of specimen
What is a smear?
microbe attached to slide
Why do we fix bacteria?
keeps microbe from being washed off slide with stain
Why are basic dyes used?
cell surface has a slightly negative charge and positive ion of dye adheres to surface
Simple stain
single basic dye
Differential stain
distinguish between bacteria - multiple dyes that react differently with different bacteria
Gram stain steps (4):
- crystal violet
- iodine (mordant)
- alcohol (decolorize)
- safranin (counterstain)
Why would we do an acid-fast stain?
mycobacterium (TB/leprosy) - binds to bacteria with waxy material (mycolic acid) in cell walls
List the steps of the acid-fast stain:
- stained with red dye carbolfuchsin (simple stain)
- washed and covered with alcohol (removes red from non acid-fast bacteria)
- stained with methylene blue
What color will acid fast vs. non-acid fast bacteria be?
- acid-fast= red (carbolfuchsin is soluble in lipids of cell wall)
- non-acid-fast= blue
Negative stain
for microbes with capsules - microbe is mixed with color particles - contrast b/w microbe and colored background
Endospore stain
malachite green stains endospores within pink stained cells
Flagella stain
structures of cell movement/carbolfuchsin
Primary stain
color to all cells
