Card Set Information
Laboratory Exercises Microbiology
microlab practical 1
Reading & Questions
Where does initial magnification occur in a bright-field microscope?
There are multiple objective lens and must be aligned with the ____, in which the final magnification occurs
T or F: Focal length is about equal or greater than the working distance between specimens.
This piece of the microscope focuses the light on a small area above the stage.
What does the Iris diaphragm do?
Controls the amount of light that enters the condenser
What does the condenser and Iris diaphragm do?
: focuses the light on a small area above the stage
: controls the amount of light that enters the condenser
T or F: one must decrease the light as one increases the magnification
What does the ocular do?
Magnifies the image formed by the objective lens
What is meant by the term parfocal?
Focus on a lower power to start a focus and go up from thhere
Resolving power vs. Magnifying power
: refers to making an image bigger
Resolving power:refers to resolution, or being able to see the image
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)
What is meant by the limit of resolution?
s the shortest distance between 2 parts on a specimen that can be distinguished by the observer
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
What is the most commonly used obj?
What kind of motion do spirochetes move in?
Corckscrew and bending type
Why are unstained bacteria more difficult to observe than stained bacteria?
Unstained bacteria have same color or contrast as background
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
Define flagellar motion and gliding motion
: bacteria moving in a purposeful motion
: bacteria that appears to move due to the movement of liquid
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
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
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.
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
When do you use darkfield microscopy besides unstained bacteria?
For looking at internal structures
What is the function of the Abbe condenser?
Directs light away to make a dark field
What does Phase microscopy allow?
Permits the observation of otherwise indistinct, living, unstained bacteria and their associated structures.
: condenser alignment screw
: collector lens
: Aperture Diaphragm control
: Fine course knob
: Focus condenser knob
: rheostat control knob
: Mechanical stage
: Stage adjustment knobs
: Objective lenses
: Coarse adjustment knobs
: reversed nosepiece
: stage finger assembly
: Binocular body
T or F: Phase-contrast permits the observation of otherwise invisible living, unstained microorganisms
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
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.