Certain parts of the brain govern specific functions. For example, the cerebellum is involved with coordination; the hippocampus with memory. Nerve cells (neurons) are the basic unit of communication in the brain.
Eukaryotic organisms use mitosis to reproduce sexually. In mitosis, the parent cell is divided into two daughter cells which be identical to the parent cell. Edit
Most unicellular organisms, and a few multicellular organisms, use cell division to reproduce, in a process called asexual reproduction. In asexual reproduction, one organism produces one or more new organisms that are identical to itself and that live independently of it.