Suppose you have a 500mL flask containing 425E12 cells an un

Suppose you have a 500mL flask containing 4.25E+12 cells, an unlimited volume of dilution medium broth, and a container full of sterile 1.0mL microcentrifuge tubes. What is the concentration (cells/mL) of the 500mL solution? What total dilution would have to be made to yield 850 total cells in a 1mL solution? (e.g. diluting 1.0E+10 cells/mL to a total of 10 cells requires a 10^-9 dilution.

Solution

Ans. A. Concentration = Number of cells / Volume (in mL) of solution

                                    = 4.25 x 10¹² cells / 500 mL

                                    = 8.5 x 10⁹ cells/ mL

Ansa. B. Required total dilution = Final concentration / Initial concentration

                                                = 850 cells mL^-1 / (8.5 x 10⁹ cells mL^-1)

                                                = 850 / (8.5 x 10⁹)

                                                = 1.0 x 10^-7

That is, diluting 1.0 mL of original solution (8.5 x 10⁹ cells mL^-1) to 10⁷ mL gives the solution with concentration 850 cells per mL.