Micro 303 Exam test quizzes and
answers graded A+
What is the purpose of incubating the unopened plates?
-What is an appropriate name for this plate? - ANS✅✅It acts as a negative control. Nothing grows
on these plates
-Control plate
+If growth appears on both unopened plates, what are some likely explanations?
-What if growth appears on only one plate?
*How does growth on the unopened plates affect the reliability of the other plates? -
ANS✅✅+Contamination occurred
-contamination occurred while using the plate
*You can not use the results because they can be inaccurate
A description of colony morphology provides important information about an organism. What other
colony features should you include? - ANS✅✅It's optical characteristic, incubation, shape, growth,
and temperature.
Three critical aspects of a description of bacterial growth are colony size, color and shape. At least
three other important factors typically included when describing bacterial growth. What are they
and why are they important? - ANS✅✅-Incubation: how long cells will grow
-Temp: Optimal growing capacity increase or decrease with temp
-Type of medium: different media grow different bacteria
Most colonies on streak plates grow from isolated colony-forming units. On rare occasions, however,
a colony can be a mixture of two different organisms. If a culture is started from this colony (thinking
it's pure), correct identification will be next to impossible because the extra organism could
confound the identifying test results. How could you verify the purity of a colony? If you found the
colony to be a mixture of organisms, what could you do to purify it? - ANS✅✅A gram or streak
plate can be used. You have to use a pure colony for streaking. You can also try to pick a colony off
the first plate.
,Suppose your professor handed you a test tube with 2.0 mL of E. coli broth culture in it and told you
to make a 10^-1 dilution of the entire culture. Example how you would do this. Show calculation. -
ANS✅✅V1D1=V2D2
2(1)=(X)(10^-1)
X= 20 mL - 2 mL= 18 mL
Suppose your professor handed you a test tube with 2.0 mL of E. coli broth culture in it and told you
to make a 10^-2 dilution of the entire culture. Example how you would do this. Show calculation. -
ANS✅✅V1D1=V2D2
2(1)=(X)(10^-2)
X= 200 mL - 2 mL= 198 mL
How would you produce a 10^-1 dilution of a 3 mL bacterial using the entire 3 mL volume? -
ANS✅✅C1V1=C2V2
(1)(3)=(10^-1)(X)
X= 30 mL - 3 mL= 27 mL
How would you produce a 10^-2 dilution of a 5 mL bacterial using the entire 5 mL volume? -
ANS✅✅C1V1=C2V2
(1)(5)=(10^-2)(5)
X= 500 mL - 5 mL= 495 mL
You have 0.05 mL of an undiluted culture at a density of 3.6 X 10^6 CFU/mL. You then add 4.95 mL
sterile diluent. What is the dilution and what is the final density of the cell? - ANS✅✅C1V1=C2V1
(3.6 x 10^6)(.05)=(5)(x)
X= 3.6 x 10^4 final cell density
DF= Final/Initial
3.6 x 10^4/3.6 x 10^6= 10^-2 Dilution
, You have 0.3 mL of an undiluted culture at a density of 4.2 X 10^7 CFU/mL. You then add 2.7 mL
sterile diluent. What is the dilution and what is the final density of the cell? - ANS✅✅C1V1=C2V1
(4.2 x 10^7)(.3)=(3)(x)
X= 4.2 x 10^6 final cell density
DF= Final/Initial
4.2 X 10^6/4.2 X 10^7= .1 Dilution
What is the dilution if 96 mL of dilution is added to 4 mL of bacteria suspension? -
ANS✅✅C1V1=C2V2
(1)(4)=(X)(100)
X=.04
DF:
.04/1= .04
What is the dilution if 75 mL of dilution is added to 25 mL of bacteria suspension? -
ANS✅✅C1V1=C2V2
(1)(25)=(X)(100)
X=.25
DF:
.25/1= .25
A plate with a sample volume of 10^-6 mL produced 259 colonies.
a. What is the original cell density?
b. How many colonies should be on the plate inoculated with a sample volume of 10^-5?
c. How many colonies should be on the plate inoculated with a sample volume of 10^-7? -
ANS✅✅a. 259/10^-6 = 2.59 x 10^8 cfu/mL
b. 10^-5 x (2.59 x 10^8 cfu/mL)= 25.9 cfu
answers graded A+
What is the purpose of incubating the unopened plates?
-What is an appropriate name for this plate? - ANS✅✅It acts as a negative control. Nothing grows
on these plates
-Control plate
+If growth appears on both unopened plates, what are some likely explanations?
-What if growth appears on only one plate?
*How does growth on the unopened plates affect the reliability of the other plates? -
ANS✅✅+Contamination occurred
-contamination occurred while using the plate
*You can not use the results because they can be inaccurate
A description of colony morphology provides important information about an organism. What other
colony features should you include? - ANS✅✅It's optical characteristic, incubation, shape, growth,
and temperature.
Three critical aspects of a description of bacterial growth are colony size, color and shape. At least
three other important factors typically included when describing bacterial growth. What are they
and why are they important? - ANS✅✅-Incubation: how long cells will grow
-Temp: Optimal growing capacity increase or decrease with temp
-Type of medium: different media grow different bacteria
Most colonies on streak plates grow from isolated colony-forming units. On rare occasions, however,
a colony can be a mixture of two different organisms. If a culture is started from this colony (thinking
it's pure), correct identification will be next to impossible because the extra organism could
confound the identifying test results. How could you verify the purity of a colony? If you found the
colony to be a mixture of organisms, what could you do to purify it? - ANS✅✅A gram or streak
plate can be used. You have to use a pure colony for streaking. You can also try to pick a colony off
the first plate.
,Suppose your professor handed you a test tube with 2.0 mL of E. coli broth culture in it and told you
to make a 10^-1 dilution of the entire culture. Example how you would do this. Show calculation. -
ANS✅✅V1D1=V2D2
2(1)=(X)(10^-1)
X= 20 mL - 2 mL= 18 mL
Suppose your professor handed you a test tube with 2.0 mL of E. coli broth culture in it and told you
to make a 10^-2 dilution of the entire culture. Example how you would do this. Show calculation. -
ANS✅✅V1D1=V2D2
2(1)=(X)(10^-2)
X= 200 mL - 2 mL= 198 mL
How would you produce a 10^-1 dilution of a 3 mL bacterial using the entire 3 mL volume? -
ANS✅✅C1V1=C2V2
(1)(3)=(10^-1)(X)
X= 30 mL - 3 mL= 27 mL
How would you produce a 10^-2 dilution of a 5 mL bacterial using the entire 5 mL volume? -
ANS✅✅C1V1=C2V2
(1)(5)=(10^-2)(5)
X= 500 mL - 5 mL= 495 mL
You have 0.05 mL of an undiluted culture at a density of 3.6 X 10^6 CFU/mL. You then add 4.95 mL
sterile diluent. What is the dilution and what is the final density of the cell? - ANS✅✅C1V1=C2V1
(3.6 x 10^6)(.05)=(5)(x)
X= 3.6 x 10^4 final cell density
DF= Final/Initial
3.6 x 10^4/3.6 x 10^6= 10^-2 Dilution
, You have 0.3 mL of an undiluted culture at a density of 4.2 X 10^7 CFU/mL. You then add 2.7 mL
sterile diluent. What is the dilution and what is the final density of the cell? - ANS✅✅C1V1=C2V1
(4.2 x 10^7)(.3)=(3)(x)
X= 4.2 x 10^6 final cell density
DF= Final/Initial
4.2 X 10^6/4.2 X 10^7= .1 Dilution
What is the dilution if 96 mL of dilution is added to 4 mL of bacteria suspension? -
ANS✅✅C1V1=C2V2
(1)(4)=(X)(100)
X=.04
DF:
.04/1= .04
What is the dilution if 75 mL of dilution is added to 25 mL of bacteria suspension? -
ANS✅✅C1V1=C2V2
(1)(25)=(X)(100)
X=.25
DF:
.25/1= .25
A plate with a sample volume of 10^-6 mL produced 259 colonies.
a. What is the original cell density?
b. How many colonies should be on the plate inoculated with a sample volume of 10^-5?
c. How many colonies should be on the plate inoculated with a sample volume of 10^-7? -
ANS✅✅a. 259/10^-6 = 2.59 x 10^8 cfu/mL
b. 10^-5 x (2.59 x 10^8 cfu/mL)= 25.9 cfu
