Sub-culturing cells || Cell culture basics 

Sub culturing (aka passaging), is the removal of the medium and transfer
of cells from a previous culture into fresh growth medium, a procedure that enables the further propagation of the cell line or cell strain.
The growth of cells in culture proceeds from the lag phase following seeding to the log phase, where the cells proliferate exponentially. When the cells in adherent cultures occupy all the available substrate and have no room left for expansion, or when the cells in suspension cultures exceed the capacity of the medium to support further growth, cell proliferation is greatly reduced or ceases entirely . To keep them at an optimal density for continued growth and to stimulate further proliferation, the culture has to divided and fresh medium supplied.