Learning Module - Experiment 2A

Bacterial growth is logarithmic:

Logaarithmic growth example

Optical Density is a measure of transmitted light:

Beer's law, cuvette

Absorbance (O.D.) is proportional to cell number over a limited range.

There are four phases in bacterial growth:

  • LAG phase - cells recover from stationary phase
  • EXPONENTIAL (LOG) phase - cells are dividing by binary fission
  • STATIONARY phase - nutrients have been consumed and cells stop growing
  • DEATH phase - cells die (and subsequently lyse) from lack of food and accumulation of toxic waste products

Growth phase graph

Doubling time is the time it takes for the O.D. to double.

DILUTIONS

Serial dilution:

Serial dilution example

Overall dilution is the product of the individual dilutions.

A 1:10 or ten-fold dilution:

10-fold dilution example

If there are 100 cells / mL in the first tube, then there are 10 cells / mL in the second tube.