| Method for studying the behavior and nature of eukaryotic cells.
In the body, our cells are reasonably well taken care of. Nutrients and oxygen diffuse or are transported in from the surrounding environment
and waste is disposed of. However, for the biologist interested in studying cellular processes, the body is far too complicated and impractical to
study single cells in. Thus, the body of techniques and protocols referred to as 'tissue culture' allows the biologist to grow a monoculture of a
specific cell type in a petri dish or other in vitro setting.
Immortality
One sought after characteristic of a cell line that is used in tissue culture is immortality. Most cells in our body are programmed to divide only a
certain number of times and then stop. For the biologist who wants to keep studying the same cells for years under different conditions, this is
unsatisfactory. Immortal cell lines have lost this limitation and can be passed on as many times as desired. Tumor cells are particularly good
sources of immortal cell lines, as tumors themselves grow out of control, having lost the checks that limit growth. Cells can come from any
number of sources including humans, goats, dogs, horses, chickens ... even insects. They also can come from different tissues such as heart, skin,
liver, etc.
Nourishment
Another challenge is to maintain the cells so that they will grow. Cells extracted from tissues are not used to surviving on their own, and must
be provided with all necessary nutrients. Its important the the media used to grow the cells have the right salts and ions, right nutrients, right pH
and all kinds of parameters. The media is a very rich broth, usually consisting of chemical buffers and blood serum (the nutrient source). Cells
must be grown at body temperature, and are usually maintained in an incubator.
Applications
Having a stable, maintainable cell line, one can then start to experiment with conditions that affect growth and development. Maybe one can try
using growth factors or morphogens that cause a cell to assume a specific fate (i.e. force a generic cell to decide what kind of tissue it is a part
of). One can express desired proteins in the cell to see their effect on cell processes. One can test the effects of drug and chemical therapies on
individual cells before testing animals and patients. | 
