Microbiology Lab Midterm Exam with
Complete Solutions
Compound microscope Correct Ans-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? Correct Ans-100x.
Total Magnification = Correct Ans-Magnification (Objective) x Magnification (Ocular)
Important Parts of the Microscope Correct Ans-Framework, Stage, and Lens System
Framework Correct Ans-Arm and base are the structural parts of the microscope which
support the basic frame.
Stage Correct Ans-Holds the slide. The mechanical stage clamps the slide and moves the slide
around the stage.
Lens System Correct Ans-Oculars, Objective, and Condenser
Oculars Correct Ans-Eyepiece lenses (usually 10x magnification)
,Objectives Correct Ans-Lenses attached to rotatable nosepiece, common magnification of 4x,
10x, 45x and 100x.
Parfocalized microscope focusing adjustments are not to be made when... Correct Ans-
changing the objective lenses.
The oil has approximately the same refractive index as glass to prevent... Correct Ans-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... Correct Ans-the working distance
decreases.
Working distance Correct Ans-distance between the object on slide and the objective lens,
when in focus.
Condenser Correct Ans-directs light towards the objective lens in bright field microscopy.
In dark field microscopy, the condenser... Correct Ans-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 Correct Ans-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... Correct Ans-1. The light intensity decreases
2. Contrast improves
3. Depth of field increases
4. Limit Resolution (with oil immersion lens)
Resolution Correct Ans-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... Correct Ans-lower d.
d can be decreased by... Correct Ans-lowering wavelength or increasing the NA.
Cocci Correct Ans-More or less spherical organisms.
Bacilli Correct Ans-Cylindrical organisms.
Helicoidal Correct Ans-Spiral shaped organisms.
Complete Solutions
Compound microscope Correct Ans-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? Correct Ans-100x.
Total Magnification = Correct Ans-Magnification (Objective) x Magnification (Ocular)
Important Parts of the Microscope Correct Ans-Framework, Stage, and Lens System
Framework Correct Ans-Arm and base are the structural parts of the microscope which
support the basic frame.
Stage Correct Ans-Holds the slide. The mechanical stage clamps the slide and moves the slide
around the stage.
Lens System Correct Ans-Oculars, Objective, and Condenser
Oculars Correct Ans-Eyepiece lenses (usually 10x magnification)
,Objectives Correct Ans-Lenses attached to rotatable nosepiece, common magnification of 4x,
10x, 45x and 100x.
Parfocalized microscope focusing adjustments are not to be made when... Correct Ans-
changing the objective lenses.
The oil has approximately the same refractive index as glass to prevent... Correct Ans-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... Correct Ans-the working distance
decreases.
Working distance Correct Ans-distance between the object on slide and the objective lens,
when in focus.
Condenser Correct Ans-directs light towards the objective lens in bright field microscopy.
In dark field microscopy, the condenser... Correct Ans-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 Correct Ans-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... Correct Ans-1. The light intensity decreases
2. Contrast improves
3. Depth of field increases
4. Limit Resolution (with oil immersion lens)
Resolution Correct Ans-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... Correct Ans-lower d.
d can be decreased by... Correct Ans-lowering wavelength or increasing the NA.
Cocci Correct Ans-More or less spherical organisms.
Bacilli Correct Ans-Cylindrical organisms.
Helicoidal Correct Ans-Spiral shaped organisms.
