All three techniques have the same underlying purpose which is to isolate a sample, such as a cell, tissue or organ, from an organism for its subsequent growth and/or maintenance under a controlled environment. Samples are usually placed on an artificial substrate or suspended in medium that has been supplemented with essential nutrients and growth factors. These techniques also share similar applications. They can be used in drug discovery to investigate the efficacy of therapeutic or toxic compounds on the physiological function of a specific sample, or can be used to grow an entirely new organism.