BIOL 2071: Microbial Growth assignment, Nov. 9.
Use your answers to complete the Brightspace “quiz”: Nov. 9 In-class
Growth Assignment, for up to 10 regular activity points. (This counts towards in-class assignments, not lecture quizzes.)
You have two test tubes of growth media. You inoculate one tube with 1000 cells of Bacterium X which has a
generation time of 60 minutes, and you inoculate the other tube with 10 cells of Bacterium Y, which has a generation
time of 20 minutes. (Assume log phase begins at 0 min and continues until at least 240 min after that.)
Bacterium X
Bacterium Y
Time after log
phase begins
Cells
Time after log
phase begins
Cells
Time after log
phase begins
Cells
0 min
1000
0 min
10
140 min
60 min
20 min
160 min
120 min
40 min
180 min
180 min
60 min
200 min
240 min
80 min
220 min
100 min
240 min
120 min
1.
Which tube will have more bacteria after growing in log phase for 2 hours?
2.
After 4 hours?
A researcher is making serial dilutions from a culture of bacteria in liquid medium.
3.
If 1 ml of the original culture is added to 9 ml of sterile saline, what is the dilution?
4.
If 0.1 ml of the original culture is added to 0.9 ml of sterile saline, what is the dilution?
5.
If 0.1 ml of the original culture is added to 9.9 ml of sterile saline, what is the dilution?
6.
If 1 ml of the original culture is added to 9 ml of sterile saline (in tube 1), and 1 ml from tube 1 is added to 9 ml of
sterile saline (in tube 2), what is the final dilution in tube 2?
7.
If 0.1 ml of the original culture is added to 9.9 ml of sterile saline (in tube A), and 0.1 ml from tube 1 is added to
9.9 ml of sterile saline (in tube B), what is the final dilution in tube B?
Table. Viable plate counts of dilution series made from an overnight culture of bacteria.
Dilution:
10
-1
10
-2
10
-3
10
-4
10
-5
Colony counts, Replicate 1
TNTC
TNTC
320
35
4
Colony counts, Replicate 2
TNTC
TNTC
311
37
2
TNTC = too numerous to count.
8.
A viable plate count was done, with results shown in the table above. What is the CFU/ml of the original culture?
