You are given a culture of cells that are 2x106 cells per ml

You are given a culture of cells that are 2x10^6 cells per ml. Using serial dilutions describe how you would plate 3x10^5 cell in 2mls of medium.

Solution

Following steps will be followed:

1) Take 1 ml of given cell culture in a 10 ml culture tube and add 9 ml water. Shake it vigorously.

2) Further take 7.5 ml of this suspension in another culture tube and add 2.5 ml water. Again, shake this suspension vigorously.

Take 2 ml of this suspension. This will contain total of 3x 10⁵ cells.

calculations:

Given stock solution = 2x10⁶ cells/ml OR 20x10⁵ cells/ml

Desired solution = 3x10⁵ cells/2ml OR 1.5x10⁵ cells/ml

First step dilution= 20x10⁵/10 = 2x10⁵ cells/ml

Second step dilution factor: 2x10⁵/1.5x10⁵ = 1.33

Amount of cell suspension added = 10 ml/1.33 = 7.5 ml (aliquote from first dilution step)

Second step dilution = 2x10⁵/1.33 = 1.5x10⁵ cells/ml

FINAL: Taking 2 ml of the above cell culture will give you 3x10⁵ cells in 2 ml as asked in the question.