Question

Bacterial growth curve why log number of cell are taken

Answer 1

Ex. if you want to isolate a protein that it is only produced when cultures are in stationary phase like most secondary metabolites you should wait until the culture has reached this stage. On the other hand if you are looking for proteins for house keeping it will be a better idea to use in log-phase for example. DNA you can have it at any point of cultivation but RNA depends on the stage of growing to asure it will be present.