The smallest unit of life that can replicate independently is called a cell. Cells are the basic building blocks of all living organisms, capable of carrying out essential biological processes necessary for life. They come in various forms, such as prokaryotic cells (like bacteria) and eukaryotic cells (like plant and animal cells). Each cell functions autonomously and contains the necessary components, including genetic material, to sustain its own life processes, regenerate, and respond to environmental changes.