BIO 126L
EXAM 1, Sample 1
Dr. Pratibha Saxena
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TA’S NAME
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NAME OF YOUR MIC 226/228 INSTRUCTOR
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INSTRUCTIONS:
MIC 129 K EXAM I has 8 pages, and 18 questions.
There are a total of 200 points, accounting for 20% of your final grade.
Place your name at the top of each page and check that your exam is complete.
ANSWER ALL QUESTIONS.
Be brief and precise in your answers. DO NOT RAMBLE!
You must show your calculations where asked.
Copying and all other forms of cheating will be met with the appropriate disciplinary action.
In case you dispute the answer that is deemed correct, you MUST first submit
to your TA your question and the reason that you think your answer is the best (not just right, but the
best of the answer choices) along with references that support your
viewpoint. This must be done within 1 week after the exams are returned.
YOU MUST HAND OVER YOUR COMPLETED EXAM TO YOUR TA WHEN LEAVING THE ROOM AND
MAKE SURE THAT YOUR NAME HAS BEEN
WRITTEN DOWN
1. (18 points) Fill in the blank:
a. 0.25 micrometers is the same as ______________ nanometers.
b. 200 microliter is the same as _______________ milliliters.
c. To examine the colony morphology of a microbe on a blood agar plate you will use
oblique ____________________ light microscopy.
d. In Gram staining, iodine acts as a _____________.
e. Kovac’s reagent reacts with ________________ (name the chemical), to produce a
water insoluble compound. The appearance of this red colored compound indicates the
presence of
____________________ (name the enzyme complex) in the organism.
For Questions 2-5, circle the best answer.
2. (4 points) What is the resolution of a lens with the following parameters:
400 nm light source, 10x ocular lens, 100x objective lens and a numerical aperture of 1?
6. (20 points) Define the following terms in less than 30 words:
a. Siderophore
b. Parfocal lenses
c. Aerotolerant anaerobe
d. Zone of inhibition
7. (9 points) Most bacterial cells have a distinctive cellular morphology. Based on the
cell’s morphology, these can be divided into three groups. Name these shapes:
___________________,
___________________,
___________________
8. (5 points) What is the importance of using chemically defined media for growing
bacterial cultures?
9. (12 points) Fill in the MacConkey agar chart below with the expected colony color
(Write N.G. when no growth is expected):
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Complete Mac
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Mac w/o CV
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Mac w/o lactose
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Gram - ve lactose fermenter |
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Gram - ve lactose non-fermenter |
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Gram + ve lactose fermenter |
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Gram + ve lactose non-fermenter |
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10. (6 points) Why is it VERY important to do a GOOD streak plate when you need to
identify a mixture of unknowns from a broth?
11. (8 points)
a. What does a blue color in the THIOGLYCOLATE PLUS 0.5% GLUCOSE medium indicate?
b. What is the purpose of cystine and thioglycolate in this medium?
12. (12 points) The following sketches shows the growth/inhibition of a lawn of
Arthrobacter flavescens JG-9 under different associations. Classify the relationship
between Arthrobacter flavescens JG-9 and the microorganisms shown in the sketches.
Microorganism Relationship
A ____________
B ____________
C ____________
D ____________
13. (12 points) Carbohydrate fermentation broth is used to identify the occurrence of
certain biochemical reactions carried out by an organism. A positive result is indicated
when the inoculated broth turns yellow (initially it is red) in about 24 hours.
a. What is the main chemical characteristic of the component(s) that turns the broth yellow?
b. Why does the color revert to red if the incubation is continued for an additional 12 hours or more?
c. What is the purpose of the Durham tube?
14. (3 points) You used the Spectrophotometer in the lab to measure the absorbance of
a microbial culture. Following are some of the important steps you took to measure the
absorbance of the bacterial culture. Arrange these steps IN THE CORRECT ORDER.
STEPS : ________________
a. Calibrate to 100% transmittance using the uninoculated culture medium.
b. Adjust to 0% transmittance (100% absorbance) using the wooden block.
c. Read absorbance of the sample.
15. (6 points) Microorganisms growing under aerobic conditions need to degrade
hydrogen peroxide, a bactericidal chemical, in order to continue their growth before toxic levels of
H2O2 accumulate in the cell. Name the enzyme used by the aerobically growing microbe
to degrade H2O2. This enzyme can be assayed rapidly using bacterial cultures growing on
a plate. You are given a culture of organism “X” on a blood agar plate.
Mention the steps (BE brief, DO NOT ELABORATE) you’ll take to assay for the presence of this enzyme in “X”. (You can discard the plate after you have assayed for the enzyme).
Name of the enzyme: ___________________________________
Steps:
16. (18 points) Use the dilution scheme shown below to fill in the blank spaces in the
table: (SHOW YOUR CALCULATIONS)
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Stock
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A |
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B |
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C |
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D |
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E |
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Vol. in the tubes
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5 ml
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1.8 ml
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4.5 ml
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9.9 ml
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1 ml
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0.9 ml
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Vol. transferred
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0.2 ml
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0.5 ml
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0.1 ml
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1 ml
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0.1 ml
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You plated 100 microliters of the diluted culture from tube E and obtained 19 and 21
colonies. You also plated 100 microliters from tube D and got 240 and 260 colonies.
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Stock |
A |
B |
C |
D |
E |
Step dil |
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______
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______
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______
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Cum dil |
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______
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______
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Titer(cfu/ml)
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______
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______
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17. (35 points)
A. Use the growth curve below to answer the following questions:
a. On the graph, indicate the different phases of the growth pattern, showing
the approximate points at which the phases start and end.
b. Calculate the approximate generation time. (Show your calculations).
__________________
B. Using the information from question 17A, draw the graphs:
OD vs time _________ (solid line) and
titer vs. time ------- (dashed line)
for the following conditions in the space provided.
In each case the drug is added at 40 min. Make sure you label the axis!
a. Bactericidal (not bacteriolytic)
