Cell Culture includes all relevant processes required to grow and maintain cells outside of their natural environment. Many cell lines have been developed as standards for certain cell types.  A cell line is all cells derived from an original single cell. This is important because all cells within a cell line are genetically identical and represent a standard for different cell types. For example, the cell line MCF-7 is a standard for cancerous mammary cells and U87 is a standard for glioblastoma cells. Cell culture practices allow these cell lines to be tested and observed in order to better understand how they behave in response to changes such as the insertion or deletion of genes, varying solutes in their media, varying external conditions, and more.