Interphase
During the interphase of a cell's life, it is growing, and processing its food sources into adenosine triphosphate (ATP), which can then be used by the cell later as energy. All cells will also produce ribonucleic acid (RNA) during this phase. Depending on the special function of the cell, it may produce different types of proteins or even other cells in the case of unspecialized stem cells. If the cell is getting ready to divide, it will begin combining RNA into deoxyribonucleic acid (DNA) to provide enough genetic material for both cells to function correctly.
Mitosis
Cells multiply themselves through the process of mitosis, where the DNA of the cell is replicated and encapsulated into two distinct but identical cells. The process of mitosis can only occur after the cell has had sufficient time to grow and produce the necessary materials during the interphase process. Mitosis takes only a fraction of the time of the interphase process, after which the two new cells re-enter the interphase process and prepare for subsequent division.
Apoptosis
When cells die from internal processes rather than external damage, it is called apoptosis. Generally the cell will produce a protein know as P53 in order to induce apoptosis. Cells may signal apoptosis for a variety of reasons, including autoimmune cells that have completed their task of attacking a virus, cells with damaged DNA that cannot replicate correctly or cells infected with a virus that are instructed by the immune system to die so the virus will be killed too.
Lifespan
Cell life spans range from a few hours to years depending on the type and function of the cell. Human undifferentiated stem cells live as long as the person is alive and they create red and white blood cells that live, on average, for 120 days, but lack the ability to reproduce themselves. A bacterium may live only a day or so by contrast.