Lab 1-4

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Author:
edeleon
ID:
308826
Filename:
Lab 1-4
Updated:
2015-10-04 00:38:09
Tags:
Laboratory Exercises Microbiology
Folders:
microlab practical 1
Description:
Reading & Questions
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  1. Where does initial magnification occur in a bright-field microscope?
    Objective Lens
  2. There are multiple objective lens and must be aligned with the ____, in which the final magnification occurs
    Ocular lens
  3. T or F: Focal length is about equal or greater than the working distance between specimens.
    True
  4. This piece of the microscope focuses the light on a small area above the stage.
    The condenser
  5. What does the Iris diaphragm do?
    Controls the amount of light that enters the condenser
  6. What does the condenser and Iris diaphragm do?
    • Condenser: focuses the light on a small area above the stage
    • Iris: controls the amount of light that enters the condenser
  7. T or F: one must decrease the light as one increases the magnification
    False
  8. What does the ocular do?
    Magnifies the image formed by the objective lens
  9. What is meant by the term parfocal?
    Focus on a lower power to start a focus and go up from thhere
  10. Resolving power vs. Magnifying power
    • Magnifying power: refers to making an image bigger
    • Resolving power:refers to resolution, or being able to see the image
  11. Why is oil necessary when using the 90x to 100x obj?
    Oil has the same optical qualities of glass so it permits continuous stream of light. Oil increases the numerical aperature (aka keeps the light from scattering)
  12. What is meant by the limit of resolution?
    Is the shortest distance between 2 parts on a specimen that can be distinguished by the observer
  13. How can you increase the bulb life of your microscope if the bulb's voltage is regulated by a rheostat?
    Turn it on lowest possible setting until you see
  14. What is the most commonly used obj?
    100x
  15. What kind of motion do spirochetes move in?
    Corckscrew and bending type
  16. Why are unstained bacteria more difficult to observe than stained bacteria?
    Unstained bacteria have same color or contrast as background
  17. What are some reasons for making a hanging drop slide?
    It allows the observation of motility in bacteria for a longer duration by not drying out
  18. Define flagellar motion and gliding motion
    • Flagellar: bacteria moving in a purposeful motion
    • Gliding: bacteria that appears to move due to the movement of liquid
  19. Why do you have to reduce the amount of light with the diaphragm in order to see the bacteria in a hanging drop slide?
    With low light, you can see more optical density by using the iris diaphragm
  20. What happens to the light passing through in a dark-field microscope? What does it result in?
    • Light passing through the speciment is diffracted and enters the obj lens, whereas undiffracted light does not.
    • This results in a bright image against a dark background
  21. What is dark-field useful for?
    Since light objects against a dark background is easier to see, it is useful in observing unstained living microorganisms, or ones that are hard to stain.
  22. What is the principal behind dark-field microscopy?
    The only light that enters the objective lens is from the deflection off objects, resulting in a dark background and bright objects
  23. When do you use darkfield microscopy besides unstained bacteria?
    For looking at internal structures
  24. What is the function of the Abbe condenser?
    Directs light away to make a dark field
  25. What does Phase microscopy allow?
    Permits the observation of otherwise indistinct, living, unstained bacteria and their associated structures.
    • A: condenser alignment screw
    • B: collector lens
    • C: Aperture Diaphragm control
    • d: Base
    • A: Fine course knob
    • b: Focus condenser knob
    • c: rheostat control knob
    • D: Mechanical stage
    • e: Stage adjustment knobs
    • f: condenser
    • a: Objective lenses
    • b: Coarse adjustment knobs
    • c: reversed nosepiece
    • d: stage finger assembly
    • a: Diopter
    • b: Ocular/Eyepieces
    • C: Binocular body
    • D: arm
  26. T or F: Phase-contrast permits the observation of otherwise invisible living, unstained microorganisms
    True
  27. What 3 things is particularly useful with the phase-contrast micriscopy?
    • 1. Studying motility
    • 2. Determining shape of living cells
    • 3. Detecting bacterial structures such as endospores and inclusion bodies
  28. In the phase-contrast microscope, what does the annular diaphragm do?
    Takes the light and produces a hollow cone. It knocks half of the light away resulting in our eye seeing an optical density or exagerrated speciment.

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