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Micro 1
Test 3 (Microscopy)
| Question | Answer |
|---|---|
| What is microscopy? | The passage of light or electrons at various wavelengths through lenses to magnify objects and provide resolution and contrast so that those objects can be viewed and studied. |
| Resolution/Resolving Power | ability to distinguish objects that are close together |
| Resolution distance | dependent on wavelength of the electromagnetic radiation and numerical aperture of a lens |
| Numerical Aperture | ability of a lens to gather light |
| Contrast | differences in intensity between 2 objects or between an object and its background |
| When would you need to add immersion oil to a slide? | When the working distance is so small, you add immersion oil to maximize the resolving power of the lens- refracts light rays into the lens- effectively increases the numerical aperture of the lens |
| Bright-field microscope | uses visible light; dark image on bright background |
| Dark-field microscope | uses visible light; bright image against dark background |
| Phase-contrast Microscope | uses visible light; varying intensities allow cell structures to become visible |
| Differential interference contrast | 2 separate beams result in a 3-D effect |
| Fluorescence microscope | uses UV rays; specimen is coated in fluorescing material which emits visible light rays when bombarded with UV |
| Confocal Microscope | uses UV laser to fluoresce only one plane of the coated specimen at a time |
| Transmission Electron Microscope | transmit electrons through the specimen; dense areas are dark, thin areas are light or transparent |
| Scanning Electron Microscope | produces a 3D view- electron beams bombard the surface of a metal coated specimen while scanning over it |
| What are some uses of a compound light microscope? | View the specimen live; see the size of the organisms; observe motility |
| What is the disadvantage of a wet mount? | The slide dries quickly. |
| What is the advantage of a hanging drop prep? | The motility is easier to observe |
| What is the purpose of heat fixing a smear? | Kills organisms and secures cells to slide |
| Why do you add colored dyes to heat fixed smears? | Allows us to see cells better |
| What charge does bacteria cells have? | Negative |
| What charge are basic dyes? | Positive charge |
| What charge are acidic dyes? | Negative charge |
| What is the difference between simple and differential staining? | Simple- 1 reagent; Differential-2 or more reagents (primary and counterstain) |
| Will the cell take up or reject a positive stain? | The cell will take it up and be colored. |
| Will the cell take up or reject a negative stain? | Cells will repel the stain; The background is colored. |
| What is differential staining used for? | Emphasize certain parts of cell; often used for diagnostic purposes |
| What are some examples of differential staining? | Gram stain, spore stain, acid fast stain, capsule stain, flagella stain |
| What is a gram stain? | Most basic diagnostic staining procedure; permits differentiation based on cell wall structure |
| What are the 4 steps of a gram stain? | 1) Crystal violet (primary dye) 2) Gram's Iodide (mordant) 3)Alcohol (decolorizer) 4)Safranin (red dye counterstain) |
| What colors will a gram negative and gram positive bacteria turn in a gram staining procedure? | Gram positive-purple Gram negative-red |
| What is an acid fast stain? | diagnostic stain used to stain bacteria with non-typical cell walls containing mycolic acid |
| What are the two stains used in an acid fast stain? | Primary stain- Carbol fuschin (acid fast) Counter-stain- Methylene Blue (non-acid fast) |
| What is a spore stain? | stain used to highlight endospore formation in bacterial cells |
| What two stains are used in a spore stain? | Primary stain- Malachite green (endospores) Counterstain- Safranin (vegetative cell) |
| What is a flagella stain? | This is a structural stain used to highlight flagella |
| What is a capsule stain? | This is a structural stain used to highlight the capsule of some virulent bacteria |
| What type of staining procedure does a capsule stain utilize? | Negative staining technique |
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