Unit 5 Lab Exam Flashcards
The pour plate technique is a common laboratory method used when counting ________ microorganisms
living
What type of plate uses the beads to mix
spread plate
The beads used in the spread technique are ________; pour about ___-_______ beads
sterile; 5-10
how is dilution factor calculated
1/ dilution
What is the dilution and dilution factor of the following: you take 1 mL of your sample and mix it with 99 mL of diluent
dilution total: 100mL
dilution factor: 1/100mL
What is a straight forward way to count the number of living bacteria in a sample
spread a small sample on a petri dish and count the number of colonies through serial dilutions
What is the statistically significant countable number of colonies on a plate
30-300 colonies
What is serial dilutions
a way of making very large dilutions accurately using small volumes
In microliters what is the range of measurement for the following pipette:
P20 (yellow dot)
2 ul - 20ul
In microliters what is the range of measurement for the following pipette:
P200 (yellow dot)
20 ul - 200 ul
In microliters what is the range of measurement for the following pipette:
P1000 (blue dot)
200ul - 1000 ul
Explain the two stop system
Hit resistance to suck up the intended amount and when you push it out do it fully past the resistance
Where do you want to submerge the tip of pipettes
just below the meniscus of the liquid to be transferred and slowly aspirate the solution
DO NOT GET ANY LIQUID IN THE _____ OF THE MICROPIPETTE
BORE
What two ways can you get liquid into the bore of the pipette
- tipping it up
- having bubbles of the solution that can shoot up into the bore
Spectrophotometer is a machine that has a light source and a detector to measure _________
transmittance
When one is measuring a cell sample in the spectrophotometer, one is measuring
the light scattering or transmission
Turbidity is a measurement with the _____________-
spectrophotometer
What are the two ways we will do viable cell count by plating
spread plates with glass beads
pour plates with melted medium
(T) aka % transmittance =
percent of light that reaches the detector
What is optical density (1/T)
measure of amount of light scattering
_______ OD = more light scattering = ______ cells
higher; more
What is viable count measuring
cell’s ability to form a colony
To accurately take an absorbance reading, a _______ wavelength of light must be used since samples may scatter or absorb different wavelengths of light differently
single
What is the single wavelength selected by
monochromator
What do monochromators do
they break white light into its component wavelengths
What is our way of direct counting
petroff-hausser or hemacytometer
What is an advantage of viable cell count
it helps us observe the dynamic changes in bacterial growth–live cells
Does direct cell counting count both live and dead cells
yes
There are _________ cells in a liquid sample than a solid sample
fewer
What is the log phase
actively growing phase; this is the period when the microbes are growing and dividing at a steady rate
When is the lag phase
right away as the microbes adjust to their environment
What is the stationary phase
growth of microbes slows down because nutrients have been exhausted
bacteria replicate via
binary fission
How do we plot the rate of growth:
X axis
Y axis
time unit
cell number
What is growth rate
the number of generations (doubling) per hour
What is generation time
time it takes for the population to double
