1. How would lac operon operate in E.coli growing in a culture medium where lactose is present as
   source of sugar?

Hello Student

Lactose is the substrate for β- galactosidase and it regulates the switching on and off of the lac operon. Hence it is called inducer.
In the absence of glucose, if lactose is added in the growth medium of the bacteria, the lactose is transported into the cell bypermease.