Microbio Lab 1 Flashcards
brightfield microscope
a microscope that allows light rays to pass directly to the eye without being deflected by an intervening opaque plate in the condenser
light intensity control
varies the intensity of light
neutral density filter
needed to reduce the intensity of light below the lower limit allowed by the voltage control
ocular
eyepiece
objectives
usually three attached to rotatable nose piece
low-power objective
10X
high-dry objective
40X
oil immersion objective
100X
condenser
located under stage; collects and directs light from the lamp to the slide being studied
diaphragm
regulates the amount of light that reaches the slide
coarse/fine adjustment knobs
bring objects into focus
diopter adjustment ring
…
resolving power
the ability of the lens to completely separate two objects in a microscopic field
numerical aperture
a mathematical expression that describes how the condenser lens concentrates and focuses the light rays from the light source
parfocal/parcentral
image will remain both centered and in focus when changing from a lower-power to a higher-power objective lens
colony
a visible mass of cells
star diaphragm
allows only peripheral light rays to pass up through the condenser; requires maximum illumination
cardioid condenser
provides greater light concentration for oblique illumination that the star diaphragm
Describe the position of your hands when carrying the microscope to and from your laboratory bench.
The microscope should be carried with two hands-one under the base and the other one on the arm
Differentiate between the limit of resolution of the typical light microscope and that of the unaided human eye
The limit of resolution for a light microscope is about 0.2micrometers and 0.2mm for the unaided eye.
(a) What two adjustments can be made to the condenser?
(a) The condenser can be moved up or down using the diaphragm.
(b) Adjusting the condenser affects the amount of light that reaches the slide.
Why are condenser adjustments generally preferred over the use of the light intensity control?
Keeping the lamp on a lower voltage will increase the lamp life.
When using the oil immersion lens, what four procedures can be implemented to achieve the maximum resolution?
To achieve max resolution– (1) apply a drop of immersion oil; (2) place blue filter over light source; (3) open the diaphragm; and (4) keep condenser at the highest position.
Why is it advisable to start first with the low-power lens when viewing a slide?
It is best to start with a low power lens to get an overview of the slide and find the object you wish to study.
Why is it necessary to use oil in conjunction with the oil immersion lens and not with the other objectives?
Oil is used with oil immersion lens because the small working distance does not allow enough light to enter the lens. The oil, which has the same refractive index as glass, directs more light into the lens (limits the loss of light due to refraction)
What is the relationship between the working distance of an objective lens and its magnification power?
As magnification increases, working distance decreases
Which objective lens provides the highest magnification?
oil immersion
Which objective lens provides the second-highest magnification?
high-dry
Which objective lens provides the lowest magnification?
low-power
Which objective lens has the shortest working distance?
oil-immersion
The coarse focus knob should only be adjusted when using which objective lens?
low-power
Which lens collects and focuses light from the lamp onto the specimen on the slide?
condenser
Which lens often comes in pairs?
ocular
Diopter adjustments can be made to which lens?
ocular
A diaphragm is used to regulate light passing through which lens?
condenser
The coarse and fine focus knobs adjust the distance between….?
the stage and the objective lens
lens
ocular or eye piece (10X)
Total magnification
ocular x objective
working distance
distance between objective lens and slide; decreases with increasing magnification
field of view
area viewed through ocular; decreases with increasing magnification (center specimen before magnification)
Colonial morphology
Size: small, medium, large (relative to each other)
Color: white, cream, yellow, orange, red, etc.
Shape: round, irregular, filamentous
Edge: entire, rhizoid, lobate
Elevation: flat, convex, umbonate
In what ways do the macroscopic features of bacterial colonies differ from those of molds?
Bacterial colonies are generally small and smooth whereas fungal colonies are larger and fuzzy
Why is the level of contamination measured as number of colones rather than size of colonies?
Each colony is produced from a single cell so the number of colonies indicate the original level of colonies; colony size represents growth rate
Should one be concerned to find bacteria on the skin? How about molds?
Bacteria are a part of normal skin flora but mold are not. Molds are a contaminent picked up from the environment
How can microbial levels be controlled?
handwashing; disinfectants; filtration systems
