Under nitrogen or glucose limitation growth rate declines in a sharp manner. E. coli was grown in M9 minimal medium with the indicated concentrations of nitrogen (in the form of NH4Cl) (a+b) or glucose (c+d). Panels a+c show OD measurements (600 nm) at a time resolutions of 3 min under nitrogen or glucose limitation respectively. Each point in the graph represents the average OD of 48 experimental replicas with standard error on the order of ~2% at each time-point. Panels b+d show the growth rate (1/hr) of each OD curve respectively (growth rate is the logarithmic derivative of the OD signal).