Fig. (5) Phenotypic Properties for Pre-induced Lac Operon on 5 mM of Lactose. (a) & (b) Growth rate for cells exposed to different concentrations of IPTG in pre-culture on lactose medium in entry into Early exponential Phase and Late Exponential Phase. (c) & (d) β-galactosidase activity for cells exposed to different concentrations of IPTG in pre-culture on lactose medium in EEP and LEP. Concentrations of IPTG on X-axis represent the concentration of IPTG to which cells are exposed in pre-culture. Glycerol (1g/L) was used in pre-culture.