I need to understand how to do the math. please be sure that the information you
ID: 199924 • Letter: I
Question
I need to understand how to do the math. please be sure that the information you give is correct.
Question V. You are hired as a microbiologist after graduating fro m CSU, Chico. On the first day of real work ( shows you the incubator where he is growing a new strain of bacteria a break down plastic bags and tells vou this is the company's next big thi g he is in the process of harvesting the key enzymes for the process after you have dealt with Human Resources) your boss excitedly ten that his Shortly thereafter at 10:45 am he receives a call from kindergar ut the door, daughter fell out of a tree and he will needs to pick her up. As he is running o he mentions it is very important that the cells be transferred into centrifuge bottles and trifuge for an 12 hour spin exactly when the cells reach a density of 1.28 x 9 109 cells mL-1. Furthermore, he tells you his notes are on his desk about culture grows. You look on his desk and you see that he inoculated the cultures at am, the cells were at an initial AGoo of 0.05. The cells had no lag phase. You measure t cells at 11 am and the A6oo is now 0.115. It is Valentines Day and you were looking forward to a movie date that night and planned on seeing the 9:55 pm showing of The Shape of Water. Are you going to make it to the movie AND get the cells into the centrifuge? How many minutes will you miss the movie by or how many minutes will you have to spare? (FYI, the transfer to centrifuge bottles takes 20 minutes). Hint you may have to use some of the values you determined in lab.Explanation / Answer
This problem is based on the growth curve of bacteria.
As per the given information. the initial OD of the culture was 0.05 at 9 Am and at 11 am it was found to be 0.115.
The problem does not mention anything about the number of cells present in OD 0.05.
So, let us assume that the bacteria at 0.05 OD has 4.0 x 107 cells (Note: this is the number of cells commonly observed in E. coli. The problem requires initial concentration of cells at 0.05 OD.)
At 0.115 OD we have
[(0.115) (4.0 x 107 cells)] / 0.05 = 9.2 x 107 cells
In order to obtain 1.28 x 109 cells, we have to calculate the equivalent OD
0.115 = 9.2 x 107 cells
? (x) = 1.28 x 109cells
By cross-multiplication
x = [(1.28 x 109) (0.115)] / (9.2 x 107)
x = 1.6
So, at OD 1.6 we can expect 1.28 x 109 cells.
Now let us find out the time required to reach this OD
The time required to reach 1.6 OD from 0.115 OD can be calculated as follows:
Initial OD x time = final OD x time (here initial OD is the one which is recorded at 11 am)
0.155 x 120 minutes = 1.6 x time (T)
T = (0.155 x 120 minutes) / 1.6
T = 11.625 minutes.
To reach 1.6 OD, the culture has to be incubated again for 12 minutes (by rounding off).
Now let us find out the final answer
1. After checking the OD, the microbiologist will keep the culture again for incubation.
2. Every five minutes he will check the OD
3. As per the above calculation, he has to stop the incubation at 1.6 OD
4. Exactly at 11.12 am the culture reached 1.6 OD
5. The transfer of cultures to centrifuge bottles takes 20 minutes. So, after this process, the time will be 11.32 am.
6. Immediately the microbiologist will keep the culture for centrifugation.
7. After 12 hours the time will be 11.32.
8. The microbiologist has to attend a movie "The shape of water" which is a 2 hour 3 minutes movie.
9. The movie will start by 9.55 PM and it will end by 11.58 PM. But, the microbiologist has to come to the lab to recover the cells from the centrifuge.
10. The movie will end by 11.58 PM. But he has to recover the cells by 11.32 PM. So he will miss 26 minutes of the movie.
Note: The above explanation depends on the initial concentration of cells at 0.05 OD. Values may change depending on the initial concentration. But the maths behind this problem is same.