Living cells are the basic building blocks of all living organisms. They are the smallest units of life, capable of performing essential functions such as growth, reproduction, and response to stimuli. Cells can be classified into two main types: prokaryotic cells, which lack a nucleus and are generally simpler, and eukaryotic cells, which have a nucleus and more complex structures. Cells are composed of various components, including the cell membrane, cytoplasm, and organelles like mitochondria and ribosomes. Each part plays a specific role in maintaining the cell's health and functionality. Together, these components enable cells to carry out vital processes that sustain life.