Cell Culture includes all relevant processes required to grow and maintain cells outside of their natural environment. A cell line is all cells derived from an original single cell. All cells within a cell line are genetically identical and represent a standard for different cell types. Many cell lines have been developed as standards for certain 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 culturing allows 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. Cells lines can be used to as an in vitro model of disease. Cell cultures are available in many different forms, including liquids and solids, which may be utilized as applications require. The dominant resource, the ATCC, stores and distributes over 3,400 cell lines from humans, animals and plants. Cost of cell lines varies but is typically in the range of $500. Some specialty cell lines or those which are more difficult to maintain may be more expensive to acquire.