A cell is the basic unit of life and the smallest structure of a living organism. Cells provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. They group together to form tissues, which in turn group together to form organs, such as the heart and brain. Cells contain many functional structures called organelles, which carry out tasks such as making proteins, processing chemicals, and generating energy for the cell. The nucleus is based at the center of the cell and is the ‘control room’ for the cell. The genome is found within the nucleus.

There are two general categories of cells: prokaryotes and eukaryotes. Prokaryotes are unicellular, consisting of a single cell, and lack any of the intracellular organelles and structures that are characteristic of eukaryotic cells. Eukaryotes, on the other hand, are multicellular, or have many cells, and contain many organelles and structures.

Cell biology, or cellular biology, is the field of biology that includes the study of cells. The three basic principles of cell theory are: every organism is made up of one or more cells, the cell is the smallest (basic) unit of life, and new cells can only arise from previously existing cells. There are two types of cells: prokaryotic cells and eukaryotic cells.