Subculturing keeps cells and microorganisms alive by transferring them from a previous growth culture to a fresh growth medium. It also helps the cells to grow and multiply.
There are three reasons why microorganisms and cell lines cannot be kept in a culture indefinitely. The cells increase in number due to growth, there is gradual rise in toxic metabolites and the demand for nutrients increases over time. Scientists use the subculturing process to create a new culture that has a lower density of cells than the original culture, has no toxic metabolites and has fresh nutrients to allow continued cell growth and avoid cell death.
It is important to subculture from a culture that has a specific volume into a new growth medium with the same volume to allow long-term maintenance of the cell line. However, subculturing into a larger growth medium volume works when the desired end result is an increased number of cells. This is common in scientific experiments or industrial processes.
When subculturing, scientists record the number of divisions a cell makes by counting the number of subcultures or passages. This ensures continued growth and multiplication of the cells. For instance, plant tissue cells' somaclonal variation is likely to increase over long periods spent in culture. The protocol followed in subculturing depends on whether the cells involved are adherent cells or non-adherent cells.