The continuity of life depends upon the ability of cells to reproduce. In the prokaryotes, cellular reproduction is by binary fission, an asexual division of the contents of a single cell into two new cells of approximately equal size. The process is fast and relatively simple: The circular bacterial chromosome replicates, and the two new genomes move toward opposite ends of the cell. A new plasma membrane is added between them, dividing the cytoplasm roughly in two, and the cell splits. Each of the two daughter cells formed has a complete set of genes and some materials with which to begin an independent life. During periods of active growth, the new cells acquire and metabolize nutrients, grow, replicate their bacterial chromosome, and reproduce once more. In a favorable environment—bathed in the warm rich nutrients of the small intestine, for example—the bacterial cells can divide every 20 to 30 minutes.