The cell is the smallest significant unit of all living organisms; it is the basic building block of all living things. Every tissue and organ of the body is made up of cells.
Each cell contains specialised structures inside, called organelles, which carry out particular tasks that help the cell function as a whole.
All cells are either eukaryotic or prokaryotic.
In eukaryotic cells, genetic information (DNA) is enclosed within a nucleus. This is what defines them.
Eukaryotic cells vary in size. They typically have a diameter between 10 and 100 μm.
In a prokaryotic cell, the genetic material is not enclosed within a nucleus. Instead, it is a single loop of DNA in the cytoplasm. There can also be smaller rings of DNA, which are called plasmids.
Prokaryotic cells have cytoplasm, an outer cell membrane and a cell wall. However, do not confuse a bacterial cell wall with a plant cell wall.
Some prokaryotic cells may contain a flagellum, which helps them to move around. Multiple flagellum are called flagella.