One might say that the cells kill themselves for the greater good. Also, positive and negative selection occur among the cells of the immune system. Finally, cells that are infected by a virus can sometimes recognize the infection and kill themselves before the virus has time to replicate and spread to other cells. Cell death is common among plants, especially among the higher plants. The xylem in trees, through which water rises to the leaves, consists of spaces left by dead cells.
Cell death occurs very visibly when deciduous trees drop their leaves in the fall.
The answer gets caught up in a question of semantics between a cell choosing to die and being forced to die. But some forms of programmed death are found in unicellular organisms, including bacteria. The death of the mother cell during sporulation, the process in which spores are created, could be considered a kind of programmed cell death. Another parallel example occurs among slime molds , such as Dictyostelium discoideum , a species at the interface between unicellular and multicellular organisms. These animals spend most of their lives as unicellular amoebae.