MCB 3020 lab practical Exam Questions
With Correct Answers
Always label petri dishes where? - answer✔✔on the bottom of the plate with your name, date,
and organism
Always store inoculated petri dishes ____ - answer✔✔inverted
Most petri dishes are incubated at _____ degrees celcius - answer✔✔37, not yeast
What are the 3 types of media - answer✔✔general purpose, selective, and differential
Aseptic technique does what - answer✔✔limits the presence and spread of harmful organisms,
prevents exposure of yourself and others to harmful bacteria, and reduces possibility of
contaminating samples.
What can you sterilze with? (loops, test tubes, forceps) - answer✔✔microicinerator or bunsen
burner
Loop sterilization - answer✔✔inset loop into incinerator up to the handle (3/4) until it turns red
and allow loop to cool
never grab test tubes by the ____ and always hold tubes in _____ hand. - answer✔✔cap, non-
dominant
Seven step 2 tube transfer - answer✔✔1. sterilize loop
2. uncap tubes
3. sterilize tubes
4. transfer culture into fresh medium
5. sterilize tubes
6. recap tubes
7. sterilize loop
How do you sample a slant inoculation? - answer✔✔zig zag, fishtail
Staining is useful for determining - answer✔✔morphology, size, and arrangement of bacterial
sample
What are the 3 types of stains - answer✔✔simple, differential, structural
Cationic dyes - answer✔✔basic dyes that are positively charged chromophores and a positive
ion exhibits blue/purple
(Methylene blue or crystal violet)
Anionic dyes - answer✔✔acidic dyes, negatively charged chromophores and a negative ion
exhibits a red color (Acid fuchsin, congo red, nigrosin)
Negative stains do not penetrate _____ - answer✔✔the cell, they color the background
A bacterial cell with a net negative charge is used and negative dye will be repelled and stain
____ - answer✔✔the background
Negative stain is special because it does not use ____ - answer✔✔heat
Negative stain is good for determining morphology and size of bacteria with no ____ ___ -
answer✔✔heat fixing
What is an example of a negative stain? - answer✔✔nigrosin
Nigrosin - answer✔✔negative stain, black anionic dye repelled by bacterial surface
Simple stain distinguishes between _____, ____, and _____ - answer✔✔morphology,
arrangement, and size
Simple stain uses ____ resulting in some cells becoming distorted - answer✔✔heat
The positive charge of the cationic dye interacts with the negative charge of the bacterial cell
wall and colors the surface purple using _____ ______ - answer✔✔crystal violet
Smear preparation from broth - answer✔✔transfer 1 loopful of bacteria onto clean slide and
spread, heat fix, for 10 seconds
Smear prep from slant or plate (solid - needs WATER) - answer✔✔add 1 loop of WATER to the
slide, collect bacteria from slant, heat fix for 10 seconds
What objective does the microscope start at - answer✔✔4x
microscope condensor - answer✔✔directs light towards the objective
iris diaphragm - answer✔✔adjusts the diameter of the cone of light so it fills the objective lens
What magnification is the ocular lens? - answer✔✔always 10x
What magnification is the objective (4) - answer✔✔4x, 10x, 40x, and 100x
Microscopes resolving power is ____ and the average microbe is ____ - answer✔✔0.2um,
1.0um
______x = oil immersion - answer✔✔100
You must use oil with the ___ objective lens - answer✔✔100x
What does oil do for a microscope - answer✔✔oil has the same refractive index as glass and
stops the refraction of light between specimen and lens
What do you clean the oil off the lens with? - answer✔✔lens paper cleaner
d(resolution) = wavelength/(2NA) - answer✔✔RESOLUTION/ RESOLVING POWER
d= resolution
wavelength = light (nm)
n = numerical aperature (light gathering capacity in the lens)
wavelength / 2NA which needs to be smaller for the resolution to be greater? -
answer✔✔wavelength needs to be smaller
Cocci - answer✔✔spherical bacteria
Streptococcus - answer✔✔chain of cocci
sarcinae - answer✔✔a cube like packet of eight spherical bacteria (sarcina is Latin for bundle)
Staphylococci - answer✔✔grape-like clusters
Bacilli - answer✔✔Rod shaped bacteria
Streptobacilli - answer✔✔chains of bacilli
vibrio cholerae - answer✔✔comma shaped
Spirillum volutans - answer✔✔rigid and spiral
pleomorphic - answer✔✔composed of a variety of types of cells
simple stain - answer✔✔one dye is used to color the bacteria
differential stain - answer✔✔detects differences between organisms with the use of many dyes
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