Question

1. Devise a scheme to prepare a 10^-8dilution plate, using the least number of dilution tubes. [It is not practical to pipette any volume less than 0.1 ml and your equipment is similar to that in the Micro-lab, you only have 10 ml dilution tubes and supply of sterile water.]

Hint, to write 10^-110^-2 easily etc you can use the following notation 10^-1, 10^-2 etc

Please give the answer in words and not diagrams. Thank you

Answer 1

The goal is to use the least number of dilution tubes
Each dilution tube has a volume of 10 mL
Least count of pipetting is 0.1 mL
As such each tube allows us to create a dilution of 0.1 mL / 10 mL or 10^(-3) or 100 times.
Scheme:
Take 0.1 mL of culture broth or liquid in Dilution Tube #1 filled with 9.9 mL of sterile water {Total Dilution = 10^(-2)}
Take 0.1 mL of Dilution Tube #1 into Dilution Tube #2 filled with 9.9 mL of sterile water {Total Dilution = 10^(-4)}
Take 0.1 mL of Dilution Tube #2 into Dilution Tube #3 filled with 9.9 mL of sterile water {Total Dilution = 10^(-6)}
Take 0.1 mL of Dilution Tube #3 and plate onto dilution plate {Total Dilution = 10^(-8)}
As such, in total, we end up using 3 dilution tubes.