Nuclei are the central parts of atoms, containing protons and neutrons. Protons are positively charged, while neutrons have no charge. The number of protons in a nucleus determines the element, such as hydrogen or carbon. In addition to atoms, the term "nuclei" can also refer to the centers of cells, known as cell nuclei. These cell nuclei house the genetic material, or DNA, which carries the instructions for the organism's growth and function. Both types of nuclei play crucial roles in their respective fields of physics and biology.