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Serial Dilution

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Submitted By faizulisl1
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A serial dilution is a series of sequential dilutions used to reduce a dense culture of cells to a more usable concentration. Each dilution will reduce the concentration of bacteria/yeast by a specific amount. So, by calculating the total dilution over the entire series, it is possible to know how many bacteria/yeast it was started with.
Procedure: test tube A is filled with 10 milliliters (mL) of a solution. The second test tube B is filled with 9 mL of a buffer. This buffer will serve to dilute the original solution. The buffer is frequently distilled water, but this actually depends on the composition of the solution in test tube A. The solution is then diluted. 1 mL of solution from test tube A is drawn out with a pipette and transferred to test tube B and mix thoroughly. The solution that originally had a volume of 10 ml now has a volume of 1 mL in test tube B. The solution, therefore, has been diluted by a factor of 10. 1 mL of the solution in test tube B is moved to test tube C using the technique described previously and thoroughly mix the contents of test tube C. The solution in test tube C has been diluted by a factor of 100. The solution in test tube B has 1/10 the concentration of the solution in test tube A and the solution in test tube C has 1/10 the concentration of the solution in test tube B. The solution in test tube C, therefore, has 1/100 (1/10 x 1/10 = 1/100) the concentration of the solution in test tube A. This process may be repeated as many times as necessary to achieve the desired solution. In an experiment involving concentration curves, use serial dilution to create a series of solutions with dilutions of 1, 1/10, 1/100, 1/1,000. Then perform an experiment on each dilution to measure how the behavior of a particular solution changes with concentration.
The reason this technique is used is when we have a very high count of yeast, it is very difficult to count the neat (undiluted) colonies as it can be hundreds of colonies once plated on an agar plate. This makes the counting tedious, not to mention the possibility of counting error, hence the reason why serial dilution is used and the colonies are counted twice with different people and the average number of colonies is reported as the number of yeast present in the sample after multiplying the dilution factor.

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