Nucleated cells are cells that contain a nucleus, which is a membrane-bound structure that houses the cell's genetic material, or DNA. This nucleus plays a crucial role in regulating cell activities, including growth, metabolism, and reproduction. Nucleated cells are found in many organisms, including animals, plants, and fungi. In contrast, red blood cells in mammals are an example of non-nucleated cells, as they lose their nucleus during maturation to maximize space for hemoglobin, the protein that carries oxygen. Nucleated cells can be classified into various types, such as muscle cells, nerve cells, and epithelial cells, each serving specific functions in the body.