Final answer:
Unicellular organisms proliferate by asexual reproduction, in which a preexisting cell divides to produce two new cells.
Step-by-step explanation:
Unicellular organisms proliferate by asexual reproduction, in which a preexisting cell divides to produce two new cells. This process ensures that the offspring are genetically identical to the parent. Asexual reproduction is a common method of reproduction in single-celled organisms and some multicellular organisms.