Dilution Worksheet.
A dilution is the mixing of a small accurately measured sample with a large
volume of diluent (usually sterile water or saline solution)
1. What is the dilution factor if you add 0.1 mL aliquot of a specimen to 9.9 mL of
diluent?
2. a 1/8 dilution of the stock solution is made followed by a 1/6 dilution what is the
final dilution.
3. You have a microtube containing 1 mL of a solution with 4.3 x 104 cells/mL
and you are to produce a solution that contains 43 cells/mL. What dilutions must
you perform?
A serial dilution is any dilution where the concentration decreases by the
same quantity in each successive step. Serial dilutions are mutiplicative.
4. You have decided to determine how many microbes are living on the lettuce
in the salad bar at your favorite restaurant. You place 1 gram of lettuce and 99
mls of water in a blender and blend the mixture. This is sample A. You then
transfer 1 ml of this dilution into to another that contains 9 mls of water. This
becomes sample B. You next transfer 1 ml of sample B into a separate container
that contains 9 mls of water. This is sample C. Next you transfer 1 ml each from
samples B & C onto separate nutrient rich agar plates, swirl, let harden and
incubate at 37C. When you examine the plates after 48 hours you find 110
colonies growing on plate C. (For your information 1 gram lettuce = 1 ml).
a)
-what was the bacterial count in SAMPLE A? b)-would you expect to find more colonies growing on the plate that was
inoculated from sample B or sample C? c)-how many microbes were living on that 1 gram of lettuce.
5. During examination of Chinese Hamster Ovary (CHO) cells kept in culture, the
technician discovers that the flask of cells has signs of contamination. Given that
the CHO cell line is relatively hardy, she decides to use antibiotics to try and
salvage the cells. The stock solution of the antibiotic is 0.1 g/mL, and it needs to
be used at a working concentration of 10 μg/mL.
(a) How many 10-fold serial dilutions will need to be performed to reach the
working concentration of the antibiotic in the cell culture medium? A 10-fold
dilution is 1/10th the concentration of the previous dilution. Each subsequent
dilution is made from a previous dilution, so a 10-fold serial dilution is a series of
10-fold dilutions.
(b) The working concentration of the antibiotic is how many orders of magnitude
less than the stock concentration?