The primary functional unit of life is the cell. Cells are the basic building blocks of all living organisms, whether unicellular or multicellular. They perform essential functions necessary for life, such as metabolism, energy production, and reproduction. Cells come in two main types: prokaryotic cells, which lack a nucleus and are typically simpler in structure (e.g., bacteria), and eukaryotic cells, which have a nucleus and more complex internal structures (e.g., plant and animal cells). Each cell contains various organelles that carry out specific tasks. Understanding cell biology is crucial for advancements in medicine, genetics, and biotechnology.