1. In the image above, the final dilution is 1:________________________. 2. You
ID: 64321 • Letter: 1
Question
1. In the image above, the final dilution is 1:________________________.
2. You make six 2-fold serial dilutions of a solution. Your final dilution will be 1:__________
3. You dilute 10 ?l of an unknown sample of bacteria to 1 x 10-6 and plate out 10?l onto a Petri dish. The next day you count 64 colonies. The number of viable bacteria in the original sample was
6.4 x 106 cells/?l
6.4 x 107 cells/?l
6.4 x 108 cells/?l
6.4 x 109 cells/?l
4. A 10 ?l sample of bacteria was diluted to 10-6 and 10?l was plated on the Petri dish down below What was the approximate concentration of the original sample?
5. What are two reasons serial dilution is a useful technique for counting populations of bacteria?
4. A 10 ?l sample of bacteria was diluted to 10-6 and 10?l was plated on the Petri dish down below What was the approximate concentration of the original sample?
10 ul 1011 10 ul 10 ul 10 ul 1.5 1.5 1.5 1.0 Sample 0.5 0.5 990 Dilution = 10.2 990 1 104 990 1 10-6 990 1 10-8Explanation / Answer
1.The final dilution is 1 : 100,000,000
2. In six 2-fold serial dilution the final dilution would be 1: 10-64. ( 26) In a two fold dilution the concentration of iis reduced by two and original dilution is reduced by 1/2.
3.The number of viable bacteria in the original sample is 6.4 x 107 cells/l
The number of viable bacteria in the original sample was calculated by
Number of colonies counted x 1000/ Final dilution x volume of dilution plated out
No of original viable bacteria = 64x 1000/ 1x 10-6 x 10 = 64 x 108
The number of viable bacteria in the original sample is 6.4 x 107 cells/l
4. In the petri plate 8 colonies were counted, so the concentration of original sample is 8 x 108 cells/ul
The number of viable bacteria in the original sample was calculated by
Number of colonies counted x 1000/ Final dilution x volume of dilution plated out
8x 1000/ 10-6 x 10 = 8 x 108 cells/ul
5. A.Serial dilutions is useful in counting of viable bacterial cells
B. Isolating pure colonies and single colonies
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