The growth of microorganisms follows a predictable pattern known as the growth curve. It consists of four phases: 1) a lag phase where cells adjust to their new environment, 2) an exponential or log phase where rapid reproduction occurs as resources are abundant, 3) a stationary phase where growth slows and stops due to lack of resources and buildup of waste, and 4) a death phase where cell numbers decline as cells die off until none are left alive.

1. Growth of Microorganisms The Growth Curve

2. The Growth Curve

3. The Growth Curve

4. The Growth Curve A plot of log10 (number of organisms) against time for a growing culture results in a predictable pattern. The log value is used as it is easier to plot onto a graph.

5. The Growth Curve Lag phase Short period immediately after inoculation Organisms are synthesising the enzymes needed to exploit the new medium. Cells may grow in size but not usually in number (If organisms have been transferred from an identical medium, at the same temperature, the lag phase may be very short).

6. The Growth Curve Exponential phase (log phase) Organisms have started to reproduce Abundant food, absence of competition and of inhibiting factors such as toxic waste products allows cell division to occur at a high rate. The population doubles at regular intervals.

7. The Growth Curve Plotted as arithmetic numbers of cells, the log phase would be a curve of ever increasing gradient; plotted as log10 of cell numbers, it gives a straight line .

8. The Growth Curve Stationary phase In a closed culture food soon runs out or the organisms become poisoned by their own accumulated wastes As a results growth slows down and stops. If the population is being measured by a total cell count, or by turbidity readings, there may be no apparent further change.

9. The Growth Curve Death phase A viable count will soon show a decline in cell numbers as cells die This will continue until there are no living cells left..