Question

1. If you had a 1 ml liquid culture, how would you make a 1:10 dilution? A 1:50 dilution? A 1:100 dilution?

2. If you make a 1:100 dilution with a final volume of 1 ml, then use 100 ul or 0.1 ml into 900 ul of H2O. What would be your final dilution?

Answer 1

Answer 1 :

To make 1:10 dilution of 1 ml liquid culture, we have to add (10–1) = 9 ml of H2O into that liquid culture.

To make 1:50 dilution of 1 ml of liquid culture, we have to add (50–1) = 49 ml of H2O into that liquid culture.

To make 1:100 dilution of 1 ml of liquid culture, we have to add (100–1) = 99 ml of H2O into that liquid culture.

**** In the above cases, the final volume or diluted volume is increased in accordance to the volume of water added. But, we can dilute the sample liquid culture by maintaining to final volume to 1 ml. The process is as following...

1ml = 1000 ul

To make 1:10 dilution we have to add 1/10×1000 = 100 ul of liquid culture in (1000–100) = 900 ul of H2O.

To make 1:50 dilution we have to add 1/50×1000 = 20 ul of liquid culture in (1000–20) = 980 ul of H2O.

To make 1:100 dilution we have to add 1/100×1000 = 10 ul of liquid culture in (1000–10) = 990 ul of H2O.

Answer 2 :

If we make a 1:100 dilution with a final volume of 1 ml, then the part of stock liquid culture in the final solution is 1/100×1 = 0.01 ml = 0.01×1000 ul = 10 ul.

If we take 100 ul of that 1000 ul of diluted culture then the part of stock liquid culture taken is 100/1000×10 = 1 ul.

If we add that 100 ul diluted culture (comprised of 1 ul stock culture) into 900 ul then in the final solution would be 100+900 = 1000 ul where the stock liquid culture is 1 ul.

So, the final dilution ie 1:1000.

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