How much of your stock solution should you take to make the 1000 cells/mL mixture? [closed]

Question

You need a solution containing 1000 buccal cells/mL. You count that you have 125 buccal cells in 50uL, from a total solution of 8 mL. How much of your stock solution should you take to make the 1000 cells/mL mixture? How much solvent if you would like a total volume of 5mL?

I don't even know how to approach this!!! Help??

Answer 1

welcome to cell culture & dimensional analysis

125/50µl or 2.5 cells/µl is your concentration (better way of expressing it)

2.5 * 8000µl = 20,000 total cells you have. 1000µl in 1ml that's why the 8000µl

20,000 cells / 1000 cells/ml = 20mls final culture volume to reach desired concentration

20mls - 8mls = 12mls so you need to add 12mls of medium / saline / whatever to your 8mls to dilute it to the correct concentration.

when you ask about solvent to ADD to make 5mls. Prob with this question is you don't state the desired concentration. So assuming its still 1000 cells/ml kinda go backwards, 1000 cells/ml * 5mls = 5000 cells is what you want to get

to get it:

5000 / 2.5 cells/µl = 2000µl or 2mls of your culture.

So take 2mls of your culture and mix it with 3mls of solvent / medium (5mls - 2mls).

I'm quite certain chris below is not correct.

Answer 2

Oh, come on, thats simple math. First calculate how many cells you have per ml: 50$\mu$l are $\frac{1}{20}$ of 1 ml. So multiply 125 with 20 to get the concentration per ml: $125 \times 20 = 2500 \frac{cells}{ml}$

If you want to know how many cells you have in total, multiply by 8 (for the 8ml you have) and you come to 20.000 cells in your 8ml solution.

When you want to know, how much of your solution you need, you calculate: $\frac{2500 \frac{cells}{ml}}{1000 cells} = \frac{1 ml}{x}$.

This can be transformed into $x = \frac{1}{2,5} ml = 400 \mu l$.

So you need 400 $\mu$l for each ml of your final cell solution. So if you want to have 5ml with 1000 cells/ml you need $5 \times 400 \mu l = 2000 \mu l = 2 ml$ of your cell solution. To reach 5 ml add 3 ml of your solvent/media.