Assignment B: Math of Microbiology
(10 pts.)
This assignment is intended to help you review some basic math involved in science and to specifically challenge you
to think about and calculate some microbiologically related problems. Many of these problems come from real

world
situations in biotechnol
ogy industry, research, and medicine. You should feel free to work with classmates or seek
any help you need to become comfortable with these types of calculations. This assignment will be graded worth 10
pts…
but
ultimately you will have a 30 pt quiz ad
ministered during the final exam time in order to prove you
r
mastery
of these mathematical skills.
Some of these we have
already
worked on in class, some we have not.
1.
An object is 17.2
cm long. How many micrometers is the object?
How many nanometers?
How
many
kilometers?
Write your response
s
in scientific notation
.
(for assistance
,
review the final Appendix in your lab
manual, pg 214)
2.
You need to make 400ml of a 12.5
% sodium chloride solution (this is very salty, by the way). How many
grams of NaCl (f
.w.=58.44) will you need? What is the molarity
(M)
of this solution?
3.
The ant
ibiotic Streptomycin is available
as a stock solution at 760 milli
grams per ml.
You need 400 ml of a
220
microgram
per
ml
Streptomycin
working
solution. How will you prepare
this
working
solution from your
stock?
4.
You p
erform 7
steps of a 1:10 (10 fold) serial dilution on a 24 hr growth of
liquid
bacteria culture. You plate
100 microliters of the last two dilution tubes and find that the plate made from t
he most dilute tube
gives
you 172
colonies. What is the concentration of the bacteria (cells/ml) in the original liquid growth tube?
5.
You grow
12
,000 liters of a
bacillus
bacteria suspension to a density of
4.8
X 10
8
cells per ml
. If all the cells
line up in a streptobaci
llus arrangement, w
ith each cell having a size of 1
micrometer by
4
micrometers, how
many times will
it reach
from the earth to
the moon? (average distance from earth to moon is 384,400 km)
6.
You grow a liquid culture
initially containing
16
,000 bacteria, which have a doubling time of
52
minutes, in log
growth phase for 16 hours. How many cells do you have?
7.
You have 3.57 X 10
7
bacteria on a surface
measuring 25cm X 50cm
. You disinfec
t w
ith a chemical and destroy
99
.63
% of the cells
. If
the sanitization requ
irement reads
“
an average of no more than 1 X 10
2
cfu per square
cm”, have you achieved sufficient decontamination
?
8.
You count o
ut 15 soybean seeds, suspend them in 20
0 ml buffer in a bottle, shake the bottle to release the
bact
eria
from the seed surface
, and perform serial dilutions and platings. You find that a
200
microliter
plated sample from the 10

5
dilution tube gives you
73
live bacterial colonies. How many average bacteria
are
on the surface of each seed
?
9.
You have produc
ed a 4
,000 liter tank of fungal spores at a density of
8.6
X 10
5
cfu/ml
. You must package
these spores in 1.5 liter containers at a final concentration of
1.5
X 10
4
cfu/ml
. How much volume of your
spore suspension and how much water must be added to each
packaging container? How many containers
will you
be able to
produce?
10.
Soybean seeds coated with 1 X 10
5
Bacillus amyloliquefaciens
bacteria germinate more rapidly and grow
taller than uncoated seeds. Soybeans weigh 650 seeds per kg. If
B.
amyloliquefaciens
is supplied at a
concentration of 5 X 10
9
cfu/ml, how much volume of bacterial suspension must be used to appropriately
coat 600 kg of seeds needed for planting?
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