Serial Dilution Practice Problems

5 points each (-2 points if units are missing) The Online Practice must be printed off of Blackboard, and answers must be written in student’s own handwriting, with work shown when applicable, for credit. Typed or printed answers will not be accepted. 1. If you count 60 colonies after generating a dilution factor of 10^-8 and plating 100 microliters, what is the starting concentration? 6.0 × 1010 CFU/mL 2. If you count 32 colonies after making a dilution 10^-3 and plating 100 microliters, what is the starting concentration? 3.2 × 105 CFU/mL 3. If you start out with a 10^-3 pre-made dilution, and pipetted 100 microliters into a 9.9 mL saline tube then plated 100 microliters of that solution, what would be the final dilution factor? 10-6 4. The final dilution factor for your plate was 10^-4, and there were 57 colonies on your plate, what was the starting concentration? 5.7 × 105 CFU/mL 5. There are 200 colonies on a plate, you generated a dilution factor of 10^-9 and plated 100 microliters. What was the starting concentration? 2.0 × 1012 CFU/mL 6. The final dilution factor was 10^-8 and there were 120 colonies on the plate, what was the starting concentration? 1.2 × 1010 CFU/mL 7. If you counted 154 colonies after creating a dilution factor of 10^-2 and plated 100 microliters, what was the starting concentration? 1.54 × 105 CFU/mL 8. If you started with a pre-made dilution of 10^-3 and pipetted 100 microliters of that into a 9.9 mL saline tube, then pipetted 1 milliliters from that tube to a 9.0 mL saline tube and plated 100 microliters, what would be the final dilution factor? 10-7 9. If there are 35 colonies on a plate and you generated a dilution factor of 10^-7 then plated 100 microliters, what was the starting concentration? 3.5 × 109 CFU/mL 10. A pre-made dilution of 10^-2 was given to you. You pipetted 100 uL of that solution into a 9.9 mL saline tube, then plated 100 microliters, what would be your final dilution? 10-5 11. There are 45 colonies on your plate and the final dilution factor was 10^-7, what was the starting concentration? 4.5 × 108 CFU/mL 12. A pre-made dilution of 10^-2 was given to you. You pipetted 100 uL of that solution into a 9.9 mL saline tube, then pipetted 1 milliliter of that into a 9.0 mL saline tube, and plated 100 microliters of that solution. What would be your final dilution factor? 10-6 13. If you count 290 colonies on your plate that had a dilution factor of 10^-6, what would be the starting concentration? 2.9 × 108 CFU/mL 14. If you had 40 colonies on your plate that had a final dilution of 10^-4, what would be the starting concentration? 4.0 × 105 CFU/mL 15. There were 137 colonies on your plate, the final dilution factor was 10^-3, what was the starting concentration? 1.37 × 105 CFU/mL 16.There were 79 colonies on a plate after generating a dilution factor of 10^-5 and plating 100 uL, what was the starting concentration? 7.9 × 107 CFU/mL 17. If you are given a pre-made dilution of 10^-3 and you add 100 microliters 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? 10-8 18. You have a pre-made dilution of 10^-3 and a dilution factor of 10^-6, then you plate 100 microliters from that tube, what would your final dilution factor be? 10-7 19. You are given a pre-made dilution of 10^-3 and your dilution factor is 10^-7 from which 100 microliters are plated from, after incubation you see 67 colonies, what would the starting concentration be? 6.7 × 109 CFU/mL 20. You are given a pre-made dilution of 10^-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? 10-7