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Flashcards by gurhanabdirahim, updated more than 1 year ago
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Created by gurhanabdirahim
over 12 years ago
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| Question | Answer |
| What is meant by resolution and why is this an important variable in microscopy? | Resolution- The ability to distinguish two points as being separate. This is important to microscopy because resolution is related to the wavelength of the light used and the light gathering property of the lens (numerical aperture = NA |
| What main advantage does phase contrast and/or dark field microscopy provide over bright field microscopy? | The bright field microscope forms a dark image against a brighter background. Great for staining procedures. However when viewing living un-stained organism its better to use the Dark field or phase contrast. The dark field produces detailed images of living unstained cells by simply changing the in which they are illuminated. The field surrounding a specimen appears black while the object itself is brightly illuminated. While the phase contrast microscopy the object appears dark and well defined. Phase contrast is especially useful for studying motility, shape of living cells, detecting endospores and inclusions. |
| What are the relative levels of resolution for light and electron microscopy? | Light microscopy: limit of resolution is ~0.2 Um (200 nanometers) Electron microscopy: limit of resolution is ~0.2 nm (0.2 nanometers) � |
| What are the differences between TEM, SEM, and electron cryotomography? List some advantages of each. | Tem: Transmission electron microscope. Uses elctrons instead of light rays, and a electromagnets serves as the lens. The system operates under high vacuum pressure. Electrons don't pass through cells well so the cells are sectioned into thin pieces before viewing. Advantage it has a high range of viewing you can see something as large as an alga and small like an amino acid. SEM: Scanning Electron Microscope, This method is used to examine surface features. Objects are coated with a thin film of heavy metal and the beam scans across the object. Large objects can be viewed and the depth of field is good.The Cryotomography is a method of freezing cells before viewing them this immobilizes the cell and can be viewed under electron microscope. it provides a more detailed image more features become visible. � |
| What type (shape) of lens is used in light microscopy? | Ocular lenses, or the eyepiece. |
| Define the variables in this equation: D = (0.5 λ) / (n sin θ | D= distance λ wavelength of light. n sin θ= Numerical aperture of the lens, ability of lens to gather light. |
| What are advantages and disadvantages of using a wet mount? | Advantage= it is the stage where the specimen can be viewed. it serves as the a refractive index where its goes from air through glass allowing for a higher refractive index. One disadvantage is the organism can dry out and loose functions such as motility. |
| What physical characteristic of the object is exploited in phase contrast microscopy? | In this method the difference in refractive index of cells versus their surroundings is exploited�.The unstained object appears dark and well defined. |
| What special properties of a fluorophore are exploited in fluorescence microscopy? | Fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation.This molecule is used to stain specimens to visualize the portion adhered to the specimen and when light is shined upon it, it gets excited and re-emits lights. Thus fluoresces brightly. |
| What are common approaches for labeling parts of a cell in fluorescence microscopy? | The specimen is stained with molecules called Fluorochromes that fluorescense when light is shined upon it. Bacterial pathogens can be indentified after staining with fluorochromes or specificaly tagging them with fluorescently labeled antibodies using immunofluorescence procedures. |
| Describe the basic nature of the lenses in an electron microscope. | Doughnut- shaped electromagnets called magnetic lenses are used to focus the beam. The column containing the lenses and specimen must be under high vacuum to obtain a clear image. |
| What are some common shapes of bacterial cells? | 1:Rods, sometimes called bacillus ex. Bacillus megaterium. 2: Vibrios, resemble rods howerver are comma shaped. 3: spirilla are rigid, spiral shaped cells. 4: Spirochetes, are flexible long spiral shaped. 5: Cocci or Diploccocci (many Cocci togather) |
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