Final answer:
Programmed cell death, or apoptosis, only occurs in multicellular eukaryotes. It is a mechanism for cells to die in a controlled manner when they are damaged or no longer necessary.
Step-by-step explanation:
Programmed cell death, or apoptosis, only occurs in multicellular eukaryotes. When a cell is damaged, superfluous, or potentially dangerous to an organism, it can trigger programmed cell death as a mechanism to prevent the release of potentially damaging molecules from inside the cell. This process allows the cell to die in a controlled manner. For example, in normal development, apoptosis plays a crucial role during embryonic development and metamorphosis, where cells are temporarily required for maturation processes.