The smallest and most basic unit of life is the cell. Cells serve as the fundamental building blocks of all living organisms, encompassing single-celled microorganisms like bacteria to complex multicellular organisms, such as humans. Each cell is enclosed by a membrane and contains various organelles that perform specific functions, such as energy production, growth, and waste management. Cells can be classified into two broad categories: prokaryotic (without a nucleus) and eukaryotic (with a nucleus). Understanding cell structure and function is crucial in biology, as it lays the groundwork for comprehending processes like reproduction, metabolism, and homeostasis.