MB 303 Final OSU Exam 2025-2026
Questions with Correct Verified
Answers.
Ocular lenses (eyepieces) - Answer Lenses closest to the eye, typically magnify 10X
Ocular width adjustment - Answer Adjust for your eye span.
Revolving nosepiece - Answer Can be rotated to change from one objective to another
Objective lenses - Answer Three or four magnifications:
4X (very low power)
10X (low power)
40X (high power)
100X (oil immersion)
Immersion oil used with the 100X objective has a refractive index approximately the same as
glass - light passes through without being bent or lost.
Stage adjustment knobs - Answer Moves the slide on two horizontal planes: back and forth
and side to side.
Mechanical stage - Answer Provides movable platform for slide, to change field of view.
Iris diaphragm or aperture diaphragm - Answer Opens and closes the diaphragm to control the
amount of light striking the object. Improper illumination is a common problem as the light
must be increased as magnification increases.
Condenser - Answer Condenses light waves into a pencil shaped cone, thereby preventing the
escape of light waves. Its ideal position is just beneath the stage.
Condenser knob - Answer Raises and lowers the condenser. For this course the condenser
should normally be all the way up.
,Coarse adjustment knob - Answer Moves stage up and down rapidly for purposes of
approximate focusing. Should only be used when focusing with low power objectives.
Fine adjustment knob - Answer Moves the stage up and down very minutely for purposes of
definitive focusing.
Bright-field microscope - Answer Type of light microscope that allows an observer to see a
dark image against a brightly lit background using a light source in the base of the microscope.
Compound microscope - Answer Has two types of lenses: the oculars and the objectives.
These lenses provide a vital function for the microscope: magnification or enlargement of
objects.
Total magnification - Answer Product of the objective lens and of the ocular lens (ie
multiplication of the two quantities).
Magnification of each lens is indicated by markings on the lenses: typically 4X, 10X, 40X, or 100X
on the objectives; 10X on the oculars.
Resolution - Answer Function of microscope that enables the observer to distinguish
structures that are separated by short distances.
More important than magnification.
It is not always desirable to obtain the largest image possible, but it is necessary to obtain sharp
detail.
Resolution is dependent upon the length of the light waves used for illumination and the quality
of the lenses.
Resolution and wavelength - Answer In bright-field microscopes, visible light with a
wavelength of 400-750 nm is used.
Resolution is inversely proportional to wavelength.
Limit of resolution - Answer The smallest distance at which a microscope is capable of
distinguishing or "resolving" 2 points.
The ordinary light microscope with oil immersion objective can distinguish 2 points
approximately 0.2 microns apart.
,Limit of resolution is in the range of 0.0003 microns.
Parfocality - Answer Microscope's ability to remain in approximate focus when switching from
one objective to another.
Working distance - Answer Distance between the specimen and objective.
As you move from the 10X to the 100X objective, the working distance decreases from 8.3 mm
to 0.14 mm.
Oil immersion objective (100X) - Answer Most observations of bacteria require use of the oil
immersion objective.
To properly use this objective, one must actually place oil on the slide surface and immerse the
objective in the oil by swinging it into place.
The main effect of immersion oil is to collect aberrant (deviating) light rays and allow them to
enter the objective.
Without oil, light is diffracted as it passes through the glass slide into the air and not all light
enters the objective.
Oil has the same REFRACTIVE INDEX as glass so diffraction of the light does not occur.
Aberrant light rays - Answer Light rays that would otherwise be lost due to diffraction.
Refractive index - Answer The ratio of the speed of light in a vacuum to the speed of light in a
medium under consideration.
Phase contrast microscope - Answer A type of compound light microscope that separates light
into 2 phases that cancel each other out to form an image.
The phase contrast microscope allows one to observe details in unstained living organisms.
Advantages of phase contrast microscope - Answer Useful for:
-studying microbial motility
-determining the shape of living cells
-detecting bacterial structures such as endospores and inclusions.
They are clearly visible because they have refractive indices markedly different from that of
water.
, Semi-permanent slides - Answer Prepare by fixing and staining the preparation without gluing
on a coverslip.
Unstained wet mount - Answer Made by suspending microbes in liquid and covering the drop
with a coverslip.
Unstained wet mount CONS - Answer Typically dries after 30-60 minutes, so it cannot be used
over a long period of time.
In addition, because of the liquid between the slide and the coverslip, a wet mount can only be
observed using the 10X and 40X objectives on the microscope.
Unstained wet mount PROS - Answer However, a wet mount enables the viewer to study living
organisms and obtain information about natural pigmentation and motility.
Simple stain - Answer A stain in which one stain is used to create a contrast between the
specimen and its background.
Can be prepared quickly and give information about cell shape, size, and arrangement.
Positive simple stain - Answer If the specimen is stained and not the background.
Dye - Answer Generally a salt in which one of the ions is colored.
Salt - Answer Compound composed of a positively charged ion and a negatively charged ion.
Methylene blue dye - Answer Salt methylene blue chloride.
Dissociates as follows:
Methylene blue Cl --> methylene blue+ + chloride-
The color of the stain is in the positively charged methylene blue ion.
Charge of bacterial cells - Answer Bacterial cells have a slightly negative charge when the pH of
their surroundings is near neutrality.
The negatively charged bacterial cell combines with the positively charged methylene blue ion,
and thus the bacterial cell is stained.
Questions with Correct Verified
Answers.
Ocular lenses (eyepieces) - Answer Lenses closest to the eye, typically magnify 10X
Ocular width adjustment - Answer Adjust for your eye span.
Revolving nosepiece - Answer Can be rotated to change from one objective to another
Objective lenses - Answer Three or four magnifications:
4X (very low power)
10X (low power)
40X (high power)
100X (oil immersion)
Immersion oil used with the 100X objective has a refractive index approximately the same as
glass - light passes through without being bent or lost.
Stage adjustment knobs - Answer Moves the slide on two horizontal planes: back and forth
and side to side.
Mechanical stage - Answer Provides movable platform for slide, to change field of view.
Iris diaphragm or aperture diaphragm - Answer Opens and closes the diaphragm to control the
amount of light striking the object. Improper illumination is a common problem as the light
must be increased as magnification increases.
Condenser - Answer Condenses light waves into a pencil shaped cone, thereby preventing the
escape of light waves. Its ideal position is just beneath the stage.
Condenser knob - Answer Raises and lowers the condenser. For this course the condenser
should normally be all the way up.
,Coarse adjustment knob - Answer Moves stage up and down rapidly for purposes of
approximate focusing. Should only be used when focusing with low power objectives.
Fine adjustment knob - Answer Moves the stage up and down very minutely for purposes of
definitive focusing.
Bright-field microscope - Answer Type of light microscope that allows an observer to see a
dark image against a brightly lit background using a light source in the base of the microscope.
Compound microscope - Answer Has two types of lenses: the oculars and the objectives.
These lenses provide a vital function for the microscope: magnification or enlargement of
objects.
Total magnification - Answer Product of the objective lens and of the ocular lens (ie
multiplication of the two quantities).
Magnification of each lens is indicated by markings on the lenses: typically 4X, 10X, 40X, or 100X
on the objectives; 10X on the oculars.
Resolution - Answer Function of microscope that enables the observer to distinguish
structures that are separated by short distances.
More important than magnification.
It is not always desirable to obtain the largest image possible, but it is necessary to obtain sharp
detail.
Resolution is dependent upon the length of the light waves used for illumination and the quality
of the lenses.
Resolution and wavelength - Answer In bright-field microscopes, visible light with a
wavelength of 400-750 nm is used.
Resolution is inversely proportional to wavelength.
Limit of resolution - Answer The smallest distance at which a microscope is capable of
distinguishing or "resolving" 2 points.
The ordinary light microscope with oil immersion objective can distinguish 2 points
approximately 0.2 microns apart.
,Limit of resolution is in the range of 0.0003 microns.
Parfocality - Answer Microscope's ability to remain in approximate focus when switching from
one objective to another.
Working distance - Answer Distance between the specimen and objective.
As you move from the 10X to the 100X objective, the working distance decreases from 8.3 mm
to 0.14 mm.
Oil immersion objective (100X) - Answer Most observations of bacteria require use of the oil
immersion objective.
To properly use this objective, one must actually place oil on the slide surface and immerse the
objective in the oil by swinging it into place.
The main effect of immersion oil is to collect aberrant (deviating) light rays and allow them to
enter the objective.
Without oil, light is diffracted as it passes through the glass slide into the air and not all light
enters the objective.
Oil has the same REFRACTIVE INDEX as glass so diffraction of the light does not occur.
Aberrant light rays - Answer Light rays that would otherwise be lost due to diffraction.
Refractive index - Answer The ratio of the speed of light in a vacuum to the speed of light in a
medium under consideration.
Phase contrast microscope - Answer A type of compound light microscope that separates light
into 2 phases that cancel each other out to form an image.
The phase contrast microscope allows one to observe details in unstained living organisms.
Advantages of phase contrast microscope - Answer Useful for:
-studying microbial motility
-determining the shape of living cells
-detecting bacterial structures such as endospores and inclusions.
They are clearly visible because they have refractive indices markedly different from that of
water.
, Semi-permanent slides - Answer Prepare by fixing and staining the preparation without gluing
on a coverslip.
Unstained wet mount - Answer Made by suspending microbes in liquid and covering the drop
with a coverslip.
Unstained wet mount CONS - Answer Typically dries after 30-60 minutes, so it cannot be used
over a long period of time.
In addition, because of the liquid between the slide and the coverslip, a wet mount can only be
observed using the 10X and 40X objectives on the microscope.
Unstained wet mount PROS - Answer However, a wet mount enables the viewer to study living
organisms and obtain information about natural pigmentation and motility.
Simple stain - Answer A stain in which one stain is used to create a contrast between the
specimen and its background.
Can be prepared quickly and give information about cell shape, size, and arrangement.
Positive simple stain - Answer If the specimen is stained and not the background.
Dye - Answer Generally a salt in which one of the ions is colored.
Salt - Answer Compound composed of a positively charged ion and a negatively charged ion.
Methylene blue dye - Answer Salt methylene blue chloride.
Dissociates as follows:
Methylene blue Cl --> methylene blue+ + chloride-
The color of the stain is in the positively charged methylene blue ion.
Charge of bacterial cells - Answer Bacterial cells have a slightly negative charge when the pH of
their surroundings is near neutrality.
The negatively charged bacterial cell combines with the positively charged methylene blue ion,
and thus the bacterial cell is stained.
