Lab Exam 1 In Microbiology

Front 1

what two parts of the microscope are used to carry or support the microscope?

Back 1

arm and base

Front 2

what are the three optical parts of a microscope

Back 2

abbe condenser, ocular lenses, objective lenses

Hint 2

optic means to see

Front 3

list the four objective lenses by the name, color, and the magnification for each.

Back 3

scanning objective: red: 4x
low dry objective: yellow: 10x
high dry objective: blue: 40x
oil immersion: white: 100x

Front 4

what is the function of the abbe condenser?

Back 4

collects and condenses the light

Front 5

what is the function of the iris diaphragm?

Back 5

lever that controls the abbe condenser. It controls the amount of light going out of condenser.

Front 6

what are the four microscopic morphologies of bacteria that we talked about in lab?

Back 6

cocci, coccobacilli, bacilli, spiral

Front 7

define parfocal lenses

Back 7

once objective is in focus, you should be able to go from one objective to the next with little to no focusing needed

Front 8

what is the purpose of oil when using an oil immersion objective?

Back 8

improving resolution by preventing the scattering of light

Front 9

what are the three main steps when cleaning your microscope to be put away?

Back 9

1) clean objective lenses yellow, blue, white
2) clean oculars with alcohol swab and then polish with lens paper
3) take alcohol swap and clean the stage

Front 10

how is total magnification determined?

Back 10

ocular magnification (10x) multiplied by objective magnification (4x, 10x, 40x, 100x)

Front 11

if 5x instead of 10x oculars were used with the same objectives now on your microscope, what total magnifications would be achieved for EACH ONE?

Back 11

Red: 5x * 4x = 20x
yellow: 5x * 10x = 50x
blue: 5x * 40x = 200x
white: 5x * 100x = 500x

Front 12

explain why flaming the inoculating needle prior to and after each inoculation is essentail during culturing?

Back 12

to ensure that the needle is sterile and won't contaminate the bacteria

Front 13

explain why holding the test tube cap with you "pinky" finger with the same hand that is holding the needle is essential during culturing?

Back 13

gives your hand holding the tube more freedom to move safely without fear of damaging the test tube or the bacteria within it.

Front 14

explain why cooling the inoculating needle prior to touching the bacteria in the culture is essential during culturing?

Back 14

if it is still hot, it will burn and kill the bacteria

Front 15

explain why flaming the openings of the tubes immediately after uncapping and before recapping is essential during culturing?

Back 15

to protect the inside, the bacteria, from contamination when the needle goes in to the tube.

Front 16

define media

Back 16

nutrient rich base, used to house bacteria during incubation

Front 17

what is agar and where does it come from?

Back 17

agar is a complex polysaccharide extracted from a certain solidifying substance made from seaweed

Front 18

list the three ways to determine whether culture media given to you are sterile before you use them

Back 18

-broth should be clear before you use it
-slants or plates should have no colonies present
-run controls on newly made media

Front 19

why should you hold open culture tubes at an angle?

Back 19

to avoid the rush of air contamination

Front 20

what are two possible errors which could have occurred if you find your subcultures had no growth after incubating for 48 hours?

Back 20

-you didn't cool the needle enough before inoculating it
-you completely forgot to inoculate it

Front 21

what are two things to remember for safely using bunsen burners?

Back 21

-never reach across the flame
-light match first before turning on gas

Front 22

why is sheep blood agar used as media?

Back 22

because the bacteria will grow in the sheep blood similarly to the way it would grow in human blood, so we can get the results we need without putting ourselves at risk for contracting blood borne diseases. It also provides lots of nutrients for the bacteria to feed off of as it grows.

Front 23

what are the five characteristics of bacterial colonial morphologies?

Back 23

-texture/consistency
-density
-color/pigment
-size
-shape

Front 24

why should a Petri dish not be left open for any extended period of time?

Back 24

it could become contaminated

Front 25

what does streaking for isolation mean?

Back 25

it means that you take a small sample of whatever it is you want to examine further, streak it in a media, draw lines in media, spreading out the sample, which therefore enables individual colonies to grow, creating uncontaminated samples to be observed

Front 26

what is the purpose of inverting (keeping agar side up) plates during incubation?

Back 26

prevent condensation build up that would ruin culture

Front 27

what is normal flora?

Back 27

normal bacteria that grows on different mucosal surfaces of the body

Front 28

list four sites where normal flora occurs in the body

Back 28

mouth, skin, throat and intestinal tract

Front 29

what color is SERRATIA when grown at room temperature?

Back 29

red

Front 30

define pure culture and mixed culture. Which one should you use when performing any testing on bacteria?

Back 30

pure culture: only have on type of organism that your isolating
mixed culture: more than one organisms present in sample you're streaking from
-you should use pure culture

Front 31

what 2 things should you always do to enhance the isolation of bacteria from a colony?

Back 31

-use a firm touch on the colony: NO SCOOPING
-after primary inoculation, flame and cool your needle before streaking your bacteria

Front 32

list the four main steps in the gram stain procedure and tell the purpose of each step

Back 32

-flood slides with crystal violet for 30-60 seconds: primary stain
-flood slide with gram's iodine for 30-60 sec: mordant-keeps stain on
-decolorize with 95% Ethanol: decolorization of gram negative cells
-flood slide with safranin for 30-60 sec: counterstaining gram negative cells

Front 33

what are the chemical differences between the cell walls of the gram positive and gram negative bacteria that might explain difference in the rate of decolorization?

Back 33

Gram positive cells have a VERY thick cell wall made of peptidoglycan that can not be permeated by the alcohol, therefore the purple color from the crystal violet stain will remain on the bacteria
-whereas a gram negative's wall is much thinnger and made of lippolyssacharides, which are penetrable by the alcohol, because of this, the color can be taken away in great quantities on a gram negative cell

Front 34

if the mordant was omitted, how would the staining results be affected?

Back 34

the initial stain, crystal violet, wouldn't stick to the bacteria as well, causing the final colors of the bacteria (gram positive and negative) to be much more similar

Front 35

should the primary stain and the counterstain be of contrasting colors? why or why not?

Back 35

yes, that way the organisms the stains stick to can be easily identified and separated when examined through a microscope

Front 36

define gram variable, and then list two reasons why gram variability can occur.

Back 36

there are both gram positive and gram negative present on the slide
1) the alcohol "overdecolorizes" the organism, this happens because the slide was made too thick
2) old bacterial cells (older than 48 hours); they begin to die and disintegrate at this time

Front 37

which step in the gram stain is the most critical and why?

Back 37

3rd step (decolarization with 95% Ethanol-Ethyl Alcohol: without it, it would be practically impossible to discern, when observing the organism through a microscope, whether it is gram positive or gram negative. This would be caused by the bacteria having been stained repeatedly without any rinsing of the color.