Serial dilution homework

When you need to cover several factors of ten (several "orders of magnitude") with a series of dilutions, it usually makes the most sense to plot the dilutions (relative concentrations) on a logarithmic scale. This avoids bunching most of the points up at one end and having just the last point way far down the scale.

He was instructed to use the dilution scheme shown in the diagram. The stock solution was turbid, as shown below. He delivered 1 ml from each tube into a separate sterile Petri dish and poured melted agar into each dish. When he examined the plates after 48 hour incubation at 37oC, he found no growth in any of the seven plates.

In serial dilution, the density of cells is reduced in each step so that it is easier to calculate the concentration of the cells in the original solution by calculating the total dilution over the entire series. Serial dilutions are commonly performed to avoid having to pipette very small volumes (1-10 µl) to make a dilution of a solution.

Inoculum from one dilution is transferred to a sequence of plates. Each tube in a set of tubes is a dilution of the previous tube. Identical volumes of a bacterial sample are transferred to several Petri dishes. Melted agar is poured into a series of sterile Petri plates.