MBIO 3401 Lab Exam 2 Questions &
Answers (Grade A+)
What are the phases in bacterial growth curve? What happens in
each phase? -
correct answer ✅-lag phase: no increase in cell growth; organisms
get used to the new environment
-exponential/log phase: cell growth and cell division happen at a
fast rate and at regular time intervals; nutrients are abundant;
doubles in size
-stationary phase: the level of waste products build up to
concentrations that become toxic; bacterial cells slow down their
metabolism and do not divide anymore-- ENDOSPORES
-death phase: cells die at a rate that exceeds any cell division and
the number of cells starts to decline exponentially with time
What is generation time? -
correct answer ✅The time for one bacterium to multiply into two;
varies from organism to organism
Draw growth curve -
correct answer ✅Page 68
,MBIO 3401 Lab Exam 2 Questions &
Answers (Grade A+)
X-axis: time in units of minutes and hours
Y-axis: number of cells in log units
How do bacteria replicate? -
correct answer ✅Binary fission
What are the different methods that we can use to measure
bacterial growth? -
correct answer ✅-Standard plate counts are used to measure the
number of viable cells in a bacterial culture. This technique is done
by taking an aliquot of the bacterial culture at every time point and
the number of viable cells is determined. A serial dilution must first
be performed and then each dilution is plated.
-Light transmittance: a spectrophotometer uses light to analyze
turbidity. A spec allows you to pick out a specific wavelength of light
and then to measure absorbance or transmittance of light through
the substance. Absorbance is the amount of light that's absorbed
by the culture, and transmittance is the amount of light that's able
to reach the detector after traveling through the culture.
, MBIO 3401 Lab Exam 2 Questions &
Answers (Grade A+)
Define selective and differential media -
correct answer ✅-selective: allows the organism of interest to
grow, while inhibiting the growth of others (ex. MAC, MSA)
-differential: contains substances that allow certain groups of
bacteria to appear differently than others when grown on the same
media; differentiates between two groups of bacteria
MAC (MacConkey's agar) -
correct answer ✅**crystal violet and bile salts**
**lactose and neutral**
-growth of gram-negative bacteria
-bile salts aid in the isolation of enteric bacteria, INHIBITS GRAM
POSITIVE
Answers (Grade A+)
What are the phases in bacterial growth curve? What happens in
each phase? -
correct answer ✅-lag phase: no increase in cell growth; organisms
get used to the new environment
-exponential/log phase: cell growth and cell division happen at a
fast rate and at regular time intervals; nutrients are abundant;
doubles in size
-stationary phase: the level of waste products build up to
concentrations that become toxic; bacterial cells slow down their
metabolism and do not divide anymore-- ENDOSPORES
-death phase: cells die at a rate that exceeds any cell division and
the number of cells starts to decline exponentially with time
What is generation time? -
correct answer ✅The time for one bacterium to multiply into two;
varies from organism to organism
Draw growth curve -
correct answer ✅Page 68
,MBIO 3401 Lab Exam 2 Questions &
Answers (Grade A+)
X-axis: time in units of minutes and hours
Y-axis: number of cells in log units
How do bacteria replicate? -
correct answer ✅Binary fission
What are the different methods that we can use to measure
bacterial growth? -
correct answer ✅-Standard plate counts are used to measure the
number of viable cells in a bacterial culture. This technique is done
by taking an aliquot of the bacterial culture at every time point and
the number of viable cells is determined. A serial dilution must first
be performed and then each dilution is plated.
-Light transmittance: a spectrophotometer uses light to analyze
turbidity. A spec allows you to pick out a specific wavelength of light
and then to measure absorbance or transmittance of light through
the substance. Absorbance is the amount of light that's absorbed
by the culture, and transmittance is the amount of light that's able
to reach the detector after traveling through the culture.
, MBIO 3401 Lab Exam 2 Questions &
Answers (Grade A+)
Define selective and differential media -
correct answer ✅-selective: allows the organism of interest to
grow, while inhibiting the growth of others (ex. MAC, MSA)
-differential: contains substances that allow certain groups of
bacteria to appear differently than others when grown on the same
media; differentiates between two groups of bacteria
MAC (MacConkey's agar) -
correct answer ✅**crystal violet and bile salts**
**lactose and neutral**
-growth of gram-negative bacteria
-bile salts aid in the isolation of enteric bacteria, INHIBITS GRAM
POSITIVE
