Need help mastering dilutions practice worksheet Courtesy of

Need help mastering dilutions practice worksheet.

Courtesy of Fong Hue Biology 151L NAME: DILUTIONS: Practice 1 Why are dilutions important? Under good growing conditions, bacteria such as E. coli will divide many times, reaching a very high cell concentration. Often, it is necessary to dilute bacterial cultures to isolate single colonies or to obtain estimates of their numbers. What does it mean to dilute a culture? Dilution of a culture requires mixing a small, accurately measured sample with a large volume of sterile water, TSB, or saline called the diluent. What are serial dilutions? Experience has shown that better accuracy is obtained by making a series of smaller dilutions rather than one large dilution. This series of smaller dilutions is called a serial dilution, and the total dilution factor (TDF) is the product of the Practice Exercise 1 1ml of sample into 3ml of diluent is a dilution 0.2ml of sample into 9.8ml of diluent is a dilution 2ml of sample into 4ml of diluent is a dilution 0.5ml of sample into 3.5ml of diluent is a dilution Exercise 2 Diagram two different ways (using different volumes) to make a 1:8 dilution, so that your final volume is no larger than 10ml. (do not diagram a serial dilution) Diagram two different ways (using different volumes) to make a 1:10 dilution, so that your final volume is no larger than 10ml. (do not diagram a serial dilution)

Solution

Exercise 1

1 ml of sample into 3ml of diluent is a 1:4 dilution. 1ml of sample into 3 ml makes the total volume to 4 ml. So it is ¼ dilution

0.2 ml of sample into a 9.8 ml of diluents is a 1:50 dilution

2 ml of sample into 4ml of diluent is 1:4 dilution

0.5 ml of sample into 3.5ml of diluents is a 1:8 dilution.

Exercise 2 -

To make 1:8 dilution, so that the final volume is not more than 10ml?

Take 1 ml of sample and add 7 ml of diluents. The dilution is 1:8.

Or

Take 0.5 ml of sample and add 3.5 ml of diluent. The dilution is 1:8

Exercise 3-

To make 1:10dilution, so that the final volume is not more than 10ml?

Take 1 ml of sample and add 9 ml of diluents. The dilution is 1:10.

Or

Take 0.5 ml of sample and add 4.5 ml of diluent. The dilution is 1:10