The smallest unit of living matter is termed a "cell." Cells are the basic building blocks of life and serve as the fundamental structural, functional, and biological units of all organisms. They can exist as single-celled organisms, such as bacteria and protozoa, or as the diverse components that make up multicellular organisms, including plants and animals. Cells perform various critical functions, including energy production, nutrient processing, and reproduction. The study of cells is essential in biology and medicine, providing insights into health, disease, and the basic principles of life.