Both prokaryotic and eukaryotic cells go through a set of processes known as the cell cycle in order to reproduce. DNA replication, mitosis, and cell division, on the other hand, can be thought of as having their own, in principle independent cycles that are bound together by mechanisms external to the cell cycle—checkpoints—that keep the events in order. Cell division is the means of reproduction in unicellular organisms and the means of tissue growth and maintenance in multicellular creatures. A cell's growth rate must match its rate of division to maintain a consistent size throughout cellular proliferation. Proliferation factors must therefore coordinate two separate processes: cellular biosynthesis, which promotes mass accumulation, and progression through the cell division cycle. The cell cycle is a complicated, multi-faceted process that involves a series of biochemically independent activities that occur in sequence.