This figure is a simple graph in which the horizontal axis is labelled time and the vertical axis is labelled number of cells. The four phases of the growth curve are distinguished using background shading of different colours. In the lag phase (yellow), cell number increases very slowly with time; cell number increases progressively rapidly during the exponential phase (red), levels off to a constant value in the stationary phase (blue), then falls during the death phase (grey).

 1.1 Bacterial growth