EXAM 2: MCB 2610 Exam 2 with Complete Solutions
Cultivation independent methods CORRECT ANS-DNA from unculturable bacteria can be
amplified and sequenced by PCR
Sequences can be used to produce fluorescent probes that will bind to complementary DNA
(Fluorescent In Situ Hybridization FISH)
FISH CORRECT ANS-Cells fixed in place
Fluorescently labeled probes consisting of 165 rRNA gene sequence sent to attach to RNA
View in Epifluorescence microscope
Metagenomics CORRECT ANS-DNA is isolated from an environmental sample and
sequenced
Metagenomic information must still be confirmed in cultured organisms
Microbial consortia CORRECT ANS-Microbes that can't grow on their own
Direct counts CORRECT ANS-Load known volume into gridded slide
Count under a light microscope
, EXAM 2: MCB 2610 Exam 2 with Complete Solutions
Flow Cytometry CORRECT ANS-Microbial suspension forced through small orifice with a
laser beam
Movement of microbe through orifice impacts electric current that flows through orifice
Instances of disruption of current are counted
Specific antibodies can be used to determine size and internal complexity
Spread plate technique CORRECT ANS-used to get a living (viable) cell count
Small amount of sample is pipetted onto a solid medium then spread around that medium
Measured in CFU colony forming units
Pour Plate CORRECT ANS-Original sample is diluted multiple times and the most dilute
ones are poured into a plate with liquid agar
Isolated cells grow into colonies on the surface and inside of the medium
Measured in CFU colony forming units
Calculating CFU/mL CORRECT ANS-Average cell number / (dilution X volume plated)
, EXAM 2: MCB 2610 Exam 2 with Complete Solutions
What if cells are already very diluted? CORRECT ANS-A filter apparatus can concentrate
cells
Sample is filtered through a membrane filter then the contents that don't go through are
transferred to a medium and incubated
Turbidity CORRECT ANS-Spetrophotometer sends light through a liquid culture
If the tube is cloudy, light wont reach the other side because it will hit all the bacteria in the
tube
This can give a rough estimate of cell density in the tube
Higher absorbance = higher population in culture
Indirect measurements of cell mass CORRECT ANS-Dry weight - time consuming and not
very sensitive
Quantity of particular cell constituent - DNA protein ATP
Growth CORRECT ANS-Population growth vs growth of actual cells
, EXAM 2: MCB 2610 Exam 2 with Complete Solutions
Growth Curve CORRECT ANS-Observed when microorganisms are cultivated in batch
culture (closed culture)
Usually plotted as a logarithm of cell number vs. time
Has 4 distinct fases
Lag phase CORRECT ANS-Cell synthesizing new compounds
ex. to replenish spent materials, adapt to new conditions or medium
Exponential phase CORRECT ANS-Rate of growth and division is constant and maximal
Population is most uniform
Stationary phase CORRECT ANS-Closed system
Population growth eventually ceases
Reasons - nutrient limitation, limited oxygen availability, toxic waste accumulation - can make
environment too acidic
Stationary phase and starvation response CORRECT ANS-Activate survival strategies:
Morphological changes - endospore formation, decrease in size
Cultivation independent methods CORRECT ANS-DNA from unculturable bacteria can be
amplified and sequenced by PCR
Sequences can be used to produce fluorescent probes that will bind to complementary DNA
(Fluorescent In Situ Hybridization FISH)
FISH CORRECT ANS-Cells fixed in place
Fluorescently labeled probes consisting of 165 rRNA gene sequence sent to attach to RNA
View in Epifluorescence microscope
Metagenomics CORRECT ANS-DNA is isolated from an environmental sample and
sequenced
Metagenomic information must still be confirmed in cultured organisms
Microbial consortia CORRECT ANS-Microbes that can't grow on their own
Direct counts CORRECT ANS-Load known volume into gridded slide
Count under a light microscope
, EXAM 2: MCB 2610 Exam 2 with Complete Solutions
Flow Cytometry CORRECT ANS-Microbial suspension forced through small orifice with a
laser beam
Movement of microbe through orifice impacts electric current that flows through orifice
Instances of disruption of current are counted
Specific antibodies can be used to determine size and internal complexity
Spread plate technique CORRECT ANS-used to get a living (viable) cell count
Small amount of sample is pipetted onto a solid medium then spread around that medium
Measured in CFU colony forming units
Pour Plate CORRECT ANS-Original sample is diluted multiple times and the most dilute
ones are poured into a plate with liquid agar
Isolated cells grow into colonies on the surface and inside of the medium
Measured in CFU colony forming units
Calculating CFU/mL CORRECT ANS-Average cell number / (dilution X volume plated)
, EXAM 2: MCB 2610 Exam 2 with Complete Solutions
What if cells are already very diluted? CORRECT ANS-A filter apparatus can concentrate
cells
Sample is filtered through a membrane filter then the contents that don't go through are
transferred to a medium and incubated
Turbidity CORRECT ANS-Spetrophotometer sends light through a liquid culture
If the tube is cloudy, light wont reach the other side because it will hit all the bacteria in the
tube
This can give a rough estimate of cell density in the tube
Higher absorbance = higher population in culture
Indirect measurements of cell mass CORRECT ANS-Dry weight - time consuming and not
very sensitive
Quantity of particular cell constituent - DNA protein ATP
Growth CORRECT ANS-Population growth vs growth of actual cells
, EXAM 2: MCB 2610 Exam 2 with Complete Solutions
Growth Curve CORRECT ANS-Observed when microorganisms are cultivated in batch
culture (closed culture)
Usually plotted as a logarithm of cell number vs. time
Has 4 distinct fases
Lag phase CORRECT ANS-Cell synthesizing new compounds
ex. to replenish spent materials, adapt to new conditions or medium
Exponential phase CORRECT ANS-Rate of growth and division is constant and maximal
Population is most uniform
Stationary phase CORRECT ANS-Closed system
Population growth eventually ceases
Reasons - nutrient limitation, limited oxygen availability, toxic waste accumulation - can make
environment too acidic
Stationary phase and starvation response CORRECT ANS-Activate survival strategies:
Morphological changes - endospore formation, decrease in size
