Exam 1 Objectives Flashcards
what is a simple microscope
it is used to produce an enlarged image of an object placed within its focal length; single lens; no condenser
what is a compound microscope
3 to 5 lenses; better magnifying power; has condenser lens; illuminator is the source of light; used for detail and studying structure
what is the power of the objective and ocular lenses
ocular=10x oil immersion=100x scanning=4x objective=10x objective=40x
explain the use of immersion oil and how it allows the microscopist to obtain greater resolution
placing a drop of oil with some refractive index as glass between the cover slip and objective lens eliminates two refractive surfaces, can achieve greater magnification while preserving resolution
describe resolving power
the actual measurement f how far apart two points must be for microscope to view them as separate
describe numerical aperture
measure of a lens ability to capture light coming in from specimen and used to make an image
what does the blue light equal
shorter wavelength
explain why a blue filter is used beneath the condenser of our microscopes
it increases contrast between a specimen and its background, also has better higher resolution
describe the change in working distance as magnification increases
as magnification increases, working distance decreases
what does parfocal mean
having corresponding focal points in all the same plane
what is the advantage to the microscopist parfocally
the advantage is it allows more accurate focusing at maximum focal length and then zooming back to a shorter focal length to compose the image
describe the change in the size of the field of view as magnification increases
as magnification increases, size of field decreases
what is the field of view
how much of your subject you see through the lens
how does the orientation of the image change under the microscope compared to the orientation of slide
the optics of the microscope inverts the image(turns it upside)
compare the size of human blood cells with yeast cells and typical bacilli and cocci
human blood cells= 12um
yeast= 3-4 um
bacilli= .2-2 um
cocci= 1-2 um
what is meant by depth of field
distance through which you can move the specimen and still have it remain in focus
what is a pure culture
lab culture with one species of organism
what is a mixed culture
lab culture with two species of organism
what is aseptic
without contamination of culture, the sterile medium or the surroundings
what is sterile
killing all forms of microbe life
what is contamination
the unintended introduction of microbes in areas or on surfaces they should not be
what is broth
used to grow stock culture
what is a slant
a growth medium in a test tube; this provides the medium with more surface area for microbial growth
what is meniscus
when a liquid is in a cylinder the liquid will be higher than in the middle creating a concave
identify the times when a microbiologist must use a pure culture
1-look for a particular pathogen that caused a disease
2-to look for antibiotic susceptibilities on that pathogen
3-to inhibit evolutionary change
describe characteristics of a properly a adjusted bunsen burner flame
bunsen burner produces a flame with two cones, an outer cone that is relatively colorless and an inner cone that is blue in color and should be about one inch in height
describe the instruments microbiologists most often use to transfer microorganisms
inoculating loop
inoculating needle
nutrient agar slants
what is a mohr pipette
they have markings that always end before the tip
what is a serological pipette
have marks that continue all the way down the tip
what is the meaning of the markings on the top end of a serological pipette
they indicate whether the pipette is a blow out pipette and the size and the measurement graduations of the pipette
identify aseptic technique procedures that are performed when working with microorganisms
inoculating loop is placed at the tip of the inner cone until it is bright orange and then it is dragged through the flame before and after transferring a microorganism. The test tube containing the microbe is also run through the flame before and after the transfer
explain how to protect yourself from laboratory acquired infection
lab coat and goggles and closed toed shoes; keep personal things away from the desk
why is a new stock culture always made as the first incoculation from a stock culture tube
we make a stock culture as a duplicate cuz the stock culture that we used for transfer is no longer sterile
what is a serial dilution
series of controlled transfers down a line of blank dilution, reduces the concentration of a culture(produce between 30-300 colonies when plated
provides a way to calculate the original concentration
what is a tube with solidified agar in an upright position, as opposed to a slant
agar pour (deep)
what does TNTC mean
too numerous to count, >300
what does TFTC mean
too few to count, <30
this is bacterial colony shaped like a double convex lens
lenticulate
this means no growth
NG
what does CFU mean
colony forming units from a single, pair or chains of bacterial cells
this is a count viable bacteria (meat)
heterotrophic plate count
this is a plate count agar, medium used to assess total number of viable growth, not a selective medium
standard method agar
what is a colony forming unit
1 cell or a group of 2 or more cells which when plated give rise to a colony
why are plates labeled on the bottom of the dish and inverted for incubation/storage
in case of lid loss, the label will still be on bacterial culture and to avoid condensation disturbance of growth as well as rehydrate bacterial colonies
how to calculate the dilution factor for each dilution made
D2=V1D1/V2
what is countable plate
between 30-300
why plates with fewer or greater number of colonies are unreliable
<30= not true representation of original concentration >300= overlapping colonies can cause human error in the counting process
what is the basic assumption made concerning the number of bacteria in the inoculum and the number of colonies on a plate
the number of colonies is equal to the number of bacteria transferred
what is the formula used to determine the concentration of bacteria in the original sample after making plate counts from a dilution series
original cell density=colony forming units/(dilution written on tube)x(volume transferred to the plate)
reasons a microbiolgist might wish to ascertain the number of bacteria per milliliter in a sample of meat
to understand the likelihood that a specific pathogen capable of causing disease will be present in the food and that the food will spoil
maximum number of bacteria per gram of meat for the meat to be sellable
10^6
what are the limitations of the procedures used to estimate bacterial numbers
only bacteria capable of growing in the culture medium under the environmental conditions provided will be accounted for
