of that to a 9.9 ml saline tube, pipette 1000 microliters from that to a 9.0 mL
ID: 255891 • Letter: O
Question
of that to a 9.9 ml saline tube, pipette 1000 microliters from that to a 9.0 mL saline tube, then pipette 1000 microliters from that tube to another 9.0mL tube, then plate 100 microliters from there, what would your final dilution be? 17. If you are given a pre-made dilution of 104-3 and you add 100 microliters 18. You have a pre-made dilution of 10-3 and a dilution factor of 10A-6, then you plate 100 microliters from that tube, what would your final dilution factor be? 19. You are given a pre-made dilution of 10A-3 and your dilution factor is 10A-7 from which 100 microliters are plated from, after incubation you see 67 colonies, what would the starting concentration be? 20. You are given a pre-made dilution of 10A-4 and add 100 microliters of that to a 9.9 mL saline tube and plate 100 microliters from that tube, what is your final dilution factor?Explanation / Answer
17. Let the initial concentration is x.
Given concentration (10-3) = 1/1000 x.
Adding 0.1 mL to 9.9 mL will give 1/100 dilution and hence a total concentration = 1/100,000 x.
Adding 1 mL of this to 9 mL will give final concentration = 1/100,000,0 x.
Further, adding 1 mL of this to 9 mL will give final concentration = 1/100,000,00 x.
The final dilution will be 10-7.
18. Final dilution factor will be 10-9.
19. Final dilution factor will be 10-10. Since there are 67 colonies in 0.1 mL of final dilution, 1 mL will contain 670 colonies. Hence, initial culture will have a total of 670 x 1010 or 6.7 x 1012 colonies.
20. 0.1 mL is added to 9.9 mL will lead to 100 fold dilution so the final dilution factor will be 10-6.
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