Microbiology Lab Midterm Exam
Questions and Answers 100% Pass
Compound microscope - ✔✔1. Ocular-eyepiece lens (usually 10x)
2. Objective-nosepiece lenses (commonly 4x, 10x, 45x, and 100x)
At what magnification do you use the oil immersion technique? - ✔✔100x.
Total Magnification = - ✔✔Magnification (Objective) x Magnification (Ocular)
Important Parts of the Microscope - ✔✔Framework, Stage, and Lens System
Framework - ✔✔Arm and base are the structural parts of the microscope which support
the basic frame.
Stage - ✔✔Holds the slide. The mechanical stage clamps the slide and moves the slide
around the stage.
Lens System - ✔✔Oculars, Objective, and Condenser
Oculars - ✔✔Eyepiece lenses (usually 10x magnification)
Objectives - ✔✔Lenses attached to rotatable nosepiece, common magnification of 4x,
10x, 45x and 100x.
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,Parfocalized microscope focusing adjustments are not to be made when... - ✔✔changing
the objective lenses.
The oil has approximately the same refractive index as glass to prevent... - ✔✔light loss
due to diffraction (bending of light rays) which would occur if light traveled from one
refractive index to another (eg. glass to air)
As magnification of the objective lens increases... - ✔✔the working distance decreases.
Working distance - ✔✔distance between the object on slide and the objective lens, when
in focus.
Condenser - ✔✔directs light towards the objective lens in bright field microscopy.
In dark field microscopy, the condenser... - ✔✔directs light at oblique angles away from
the objective lens in a manner that allows only objects in the field of view to redirect or
scatter light into the objective lens. This causes objects to appear white on a dark field.
Iris Diaphragm - ✔✔lever located in the condenser that adjusts the diameter of the cone
of light so that it just fills the objective lens.
As you close down the Iris Diaphragm... - ✔✔1. The light intensity decreases
2. Contrast improves
3. Depth of field increases
4. Limit Resolution (with oil immersion lens)
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, Resolution - ✔✔Resolving Power. Expressed as d.
d = the smallest distance between two objects which can be seen as separate
d = the diameter of the smallest resolvable object
d = wavelength / 2 NA
NA = numerical aperture
To improve resolution... - ✔✔lower d.
d can be decreased by... - ✔✔lowering wavelength or increasing the NA.
Cocci - ✔✔More or less spherical organisms.
Bacilli - ✔✔Cylindrical organisms.
Helicoidal - ✔✔Spiral shaped organisms.
Incompletely separated cocci may appear in a number of different patterns depending
upon... - ✔✔the plane in which they divide and how they remain attached.
Diplococci - ✔✔pairs. Divide in one plane.
Streptococci - ✔✔chains. Divide in one plane.
Tetracocci - ✔✔tetrads. Divide in two planes.
Staphylococci - ✔✔clusters. Divide in three planes irregularly.
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Questions and Answers 100% Pass
Compound microscope - ✔✔1. Ocular-eyepiece lens (usually 10x)
2. Objective-nosepiece lenses (commonly 4x, 10x, 45x, and 100x)
At what magnification do you use the oil immersion technique? - ✔✔100x.
Total Magnification = - ✔✔Magnification (Objective) x Magnification (Ocular)
Important Parts of the Microscope - ✔✔Framework, Stage, and Lens System
Framework - ✔✔Arm and base are the structural parts of the microscope which support
the basic frame.
Stage - ✔✔Holds the slide. The mechanical stage clamps the slide and moves the slide
around the stage.
Lens System - ✔✔Oculars, Objective, and Condenser
Oculars - ✔✔Eyepiece lenses (usually 10x magnification)
Objectives - ✔✔Lenses attached to rotatable nosepiece, common magnification of 4x,
10x, 45x and 100x.
Katelyn Whitman, All Rights Reserved © 2025 1
,Parfocalized microscope focusing adjustments are not to be made when... - ✔✔changing
the objective lenses.
The oil has approximately the same refractive index as glass to prevent... - ✔✔light loss
due to diffraction (bending of light rays) which would occur if light traveled from one
refractive index to another (eg. glass to air)
As magnification of the objective lens increases... - ✔✔the working distance decreases.
Working distance - ✔✔distance between the object on slide and the objective lens, when
in focus.
Condenser - ✔✔directs light towards the objective lens in bright field microscopy.
In dark field microscopy, the condenser... - ✔✔directs light at oblique angles away from
the objective lens in a manner that allows only objects in the field of view to redirect or
scatter light into the objective lens. This causes objects to appear white on a dark field.
Iris Diaphragm - ✔✔lever located in the condenser that adjusts the diameter of the cone
of light so that it just fills the objective lens.
As you close down the Iris Diaphragm... - ✔✔1. The light intensity decreases
2. Contrast improves
3. Depth of field increases
4. Limit Resolution (with oil immersion lens)
Katelyn Whitman, All Rights Reserved © 2025 2
, Resolution - ✔✔Resolving Power. Expressed as d.
d = the smallest distance between two objects which can be seen as separate
d = the diameter of the smallest resolvable object
d = wavelength / 2 NA
NA = numerical aperture
To improve resolution... - ✔✔lower d.
d can be decreased by... - ✔✔lowering wavelength or increasing the NA.
Cocci - ✔✔More or less spherical organisms.
Bacilli - ✔✔Cylindrical organisms.
Helicoidal - ✔✔Spiral shaped organisms.
Incompletely separated cocci may appear in a number of different patterns depending
upon... - ✔✔the plane in which they divide and how they remain attached.
Diplococci - ✔✔pairs. Divide in one plane.
Streptococci - ✔✔chains. Divide in one plane.
Tetracocci - ✔✔tetrads. Divide in two planes.
Staphylococci - ✔✔clusters. Divide in three planes irregularly.
Katelyn Whitman, All Rights Reserved © 2025 3
