The movement of cells, changes in cell shape including cell division, and the movement of materials within cells. Many free-living protozoa are capable of movement, as are sperm and ameboid cells of higher organisms. Coordinated movement of cells occurs during embryogenesis, wound healing, and muscle contraction in higher organisms. Cell division is observed in all organisms and is a requirement for reproduction, growth, and development. Many cells also undergo structural changes as they differentiate, such as the outgrowth of axonal and dendritic processes during nerve cell differentiation. A more subtle form of cell motility involves the active transport of membranous organelles within the cytoplasm. This form of movement is required for proper organization of the cytoplasmic contents, and the redistribution of metabolites, hormones, and other materials within the cell.